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UNDER THE SUPEVILON OF
OnFICE OF EXPEBInR.N T STATIONS,
U. 8. D.PA.RTEMT OF AGRICULTURE
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GOV.BLM.lNT PRINTING OrrICE.
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E:.:..; E::m"mE::E:.. :.ME
HAWAII AGRICULTURAL EXPERIMENT STATION, HONOLU il...|
[Under the supervision of A. C. TRUE, Director of the Office of Experiment Sta iI
United States Department of Agriculture.]
WALTER H. EVANS, Chief of Division of Insular Stations, Office of Experiment Statinii
E. V. WILCOX, Special Agent in Charge. i
J. EDGAR HIGGINS, Horticulturist. *
W. P. KELLEY, Chemist.
C. K. MCCLELLAND, Agronomist.
D. T. FULLAWAY, Entomologist.
W. T. McGEORGE, Assistant Chemist.
ALICE R. THOMPSON, Assistant Chemist.
C. J. HUNN, Assistant Horticulturist.
V. S. HOLT, Assistant in Horticulture.
C. A. SAHR, Assistant in Agronomy.
F. A. CLOWES, Superintendent Hawaii Substations.
W. A. ANDERSON, Superintendent Rubber Substation.
J. DE C. JERVES, Superintendent Homestead Substation.
JOSEPH K. CLARK, Superintendent Waipio Substation.
GEORGE COPP, Superintendent Kula Substation.
ADDITIONAL COPIES of this publication :
A may be procured from the SUPERINTEND-
ENT OF DOCUMENTS, Government Printing
Office, Washington, D. C., at 10 cents per copy
F E: flWnn SSA4eU.LE SA5 AJT1 fT9SlAAY.DA U.S U S EA SLu *t UL J. ITU tLLUA I U SLI U LJ' J ^LLI J
h^^Pauip to the growth of all kinds of plants. The careful study
Sthe various chemical and mechanical changes produced in soils
*thse application of heat, as set forth in this bulletin, throws con-
Sjabe light upon the reasons for this beneficial effect. Studies
Sthe effects of heat on soils. have usually been confined to a few
" platcfood elements, whereas in this bulletin a large number of the
b organic and organic substances are considered. The bulletin is,
I: tore, considered a distinct contribution to the literature of this
I iteas ting phase of soil work.
Respectfully, E. V. WILcox,
Special Agent in Charge.
D ;r. A C. TRUE,
Director Office of Experiment Stations,
U. 8. Department of Agriculture, Washington, D. 0.
A. C. Taur, Director.
SD. F. HOUSTON,
Secretary of Agriculture.
Introduction............e----------....-.. ..-.. ................. S
The effects of heat on the solubility of inorganic constituents--.......-....
Preliminary work.--- --- --- --- --- ---
Preliminary work.............................................. ."
Method of preparing extracts.......... ......;................ ... .
Soil types--- .-.-.-------------------------..,- ..
Silica. -..--..........-- ..-....-.-.------,-..-..----.,. .......--- -- ---- --.----- 1
S ilica................................. ........... ....... ... ,
Iron.. .................................... .. ............ ........... .
Lime and magnesia ....--............. ..................
Potash. -......... ........ ............ ... .............,...........
hosphoric acid .... ................ ........ ... ........, ,.;- -. .i:it..
Effect of heat upon rice and taro soils........... .......................
Discussion..... .--.- -... ....... ........... ....... .... ...:...;.. :l
The effects of heat on soil nitrogen, ................................... ,,
Introduction-..............-- .. ..........................-... -,-..
Effects of heat on nitrates...................... ........... ....... ;
Effects of heat on the ammonia content ......................-.... ...
Effects of brush burning in the field........... -.......... ......... ..
Effects of heat on the organic nitrogen.................................
.1 : lll
iiiiuaeeumaL nIuslue urn ns iA utI ivteiy. t muonuecUion1 WiH certiam
.sogns demanding early forcing, however, soil burning is practiced
S -ngh universally. The seed of tobacco, cabbage in some locali-
...:,and some other crops that are grown from transplanted seedlings
I m stiil sown in soil which has been previously burned. In prepar-
ig seed beds for tobacco the'soil is frequently burned heavily, usually
a strong wood1 fire being maintained on the bed for several hours.
It is a matter of common observation that the growth of seedlings
on the burned soil is usually .superior to that on the surrounding
unbmned land. The effects of burning are by no means confined to
the germination and growth of seedlings. In newly cleared lands
a~rop of various kinds usually grow more rapidly and produce
i~areased harvests on the spots where brush or log heaps have been
bramed, and often the effects persist through two or more years.
,, Hawaii the growth of certain crops is enormously influenced by
mere burning of small accumulations of brush and undergrowths
Sguava and lantana. The effect on cotton on the uplands of Oahu
ou. eed by these small fires may represent the difference between
sce.e. and failure. The color and vigor of the crop on these small
areass dotted here and there over a field attract attention. Other
S opesare affected similarly.
S' 11si ges asm milam used far this purpae
aeration and encourages deeper root development. By means
the hydrous compounds become dehydrated, plasticity and:ii
siveness are overcome, the movement of soil moistuae fa
a more congenial environment for root development is pr
If sufficiently great heat be employed, the clay may be baked i
hard lumps, which yield to cultural and weathering influence
difficulty, and, therefore, injury may result. In any event:
dehydrated silicates and oxids return very slowly to their
state and the crumb structure induced by the heat persists'fomr
The physical effects of heat on clays are so pronounced that'
admixing of a few tons per acre of the burnt with the natura'i
was formerly employed in Europe as a means of ameliorating 'lfl2i
clay lands. .v 1
Regarding the chemical effects of burning it is also well knowitt3 i
clay soils undergo chemical changes. In general the solubil ity
aluminum and potassium in acids is greatly increased up to a eirtfa
temperature, beyond which a decrease sets in. It is generally h
that under the influence of high temperatures, especially with thela;
of oxidizing conditions, a wasteful destruction of soil organic miatti
and consequent loss of nitrogen takes place.
In addition to the above-named physical and chemical effeiitthi
killing of weed seeds, parasitic fungi, disease-producing organisms,
and insects are generally looked upon as being among the bendcia
effects of soil burning. K
While the old system of burning the soil has gradually fallen oti of -
use, the closely related partial sterilization by means of heat and volb
tile antiseptics is of great interest at the present time. In greenhoubt
work steam sterilization finds extensive application and has been th.
subject of interesting investigations during the past few years.
Likewise the action of dry heat in its relation to partial sterilizatida
and in comparison with the effects of volatile antiseptics on subsi',
quent biological activities has received considerable study. T1'JI
old idea of considering the subject in a restricted physical and limited
chemical sense is, therefore, giving way to a broader view of' th~
question. The more specific chemical effects involved, including esdl
tain physico-chemical effects dealt with more in detail in this papei
and the biological results are now being studied.
It has been found that moderate temperatures bring abou-t "
increase in the solubility not only of the mineral constituents of
but also in the organic matter. Furthermore, a number of invedi
gators have found that steam sterilization, particularly when uindeW'
oght about by aeration. The application of fertilizers produces
: ou. ch effects.
Iun connection.with a general study of soil aeration the authors
I, i e, therefore, been led to a study of the effects of heat on these
s ls. The present paper deals with one phase of this question, the
Sphysio-chemical changes produced. In the first part are presented
te data obtained-with reference to the solubility of the inorganic
S constituents and in the second part are some data of a more or less
empirical nature on the grosser effects of heat on soil nitrogen.
TEE EFFECTS OF HEAT. ON THE SOLUBILITY OF INORGANIC
While a considerable number of investigators have studied the
question of the effect of heat upon the solubility of phosphoric acid,
using various solvents, apparently few have gone beyond this and
determined its effect upon the solubility of the remaining mineral
Constituents commonly occurring in soils. In fact, with few excep-
tions, the entire stress has been laid upon the three elements generally
i considered to be of greatest plant-food value, namely, nitrogen, phos-
i phonic acid, and potash.
In most instances the results of these earlier investigations have
:. shown an increase in solubility of phosphoric acid, with increase in the
i| temperature to which the soils have been heated. M. Nagaoka,' on
Bul. CoL Ar., Tokyo Imp. Univ., 8 (19Ot), No. p. 263.
in 12 per cent hydrochloric.acid before and after igni tio, ..
indication of the phosphoric acid combined with organic:
Fraps,2 while finding an increase in the solubility' of phospho
on ignition, considers that this increase is not wholly due to
phosphorus, but that mineral phosphates in soils are alo .
more soluble by ignition, thereby rendering the ignition met
unsuitable one for determining organically combined ph6
On the other hand, Lipman found whileworking on a series ci
fornia soils, that heating decreased the solubility of phosphorif
in strong nitric acid. Peterson' found that the solubilityine~ ii
rapidly with increase in temperature from 1300 up to 2000 0,
that the solubility of the mineral phosphates in soils was not iircS r
by heating below 2400 C.
Valuable work on the solubility of the mineral constitue nW '
soils is to be found among the publications of the Bureau of Boils9'U1J
work being confined largely to the use of water as solventt. '" : .:ti
bulletin of that bureau,5 King gives comparative results of work ui8~ i
fresh and oven-dried soils which show the effect of heating to 1100I':i,
to be striking. On the average more nitrates, phosphoric acid 1u :
phates, bicarbonates, and silica were recovered from the oven-dtiN-lM
soils than from the fresh samples, while the average of the chiM~~lfi
determinations showed a decrease. No determination of the ba ~iki
constituents are tabulated, but King states that upon later invAe.:Vr
gations he found an increase in potash, lime, and magnesia in i2i ;|
dried soils. He makes several suggestions as to the cause of this-uai '.
crease, both from a physical and chemical standpoint, but it is evident
from his discussions that he considered the cause to be priiihailyi..;
physical. A number of other investigators have noted an incra "ie
in total inorganic matter soluble in water* as a result of heatiti6
but no separation of the elements was made.
The special phase to which this paper is devoted is that of the effect&
of heat upon the solubility of the mineral constituents, distilled wdts'I|
and fifth-normal nitric acid being used as solvents.
1 Illinois Sta. Bul. 145.
2 Texas Sta. Bul. 136.
Jour. Indus. and Engin. Chem., 4 (1912), No. 9, p. 663. :
Wisconsin Sta. Research Bul. 19.
*U. S. Dept. Agr., Bur. Soils Bul. 26, p. 55. .
*New York Cornell Sta. Bul. 275.
.. ..... K 'i
..... .v'vr. W Man aI............ ...OI..... IR. n 14.5 Z.UD -...... 8 .U iid. 11 5 1.U I15.U
Wii;S ..-...... 7.days... 157.0 23.2 2.05 12.8 71.9 70. 4 137.1 227.0
i: driid ....-......... ..do..... 688.0 6.4 2.14 17.2 47.2 76.1 83.8 158.2
-)::: ..l. ;:1,:,dried...............do..... 180.0 17.0 2.76 ........ 8 109.0 151.0 68.0
18. Noio. 6319:
rsiiih ... .............. I hour... 140.0 3.04 .76 1.52 127.6 60. 2 137.1 142.2
Akr dried.............. ...do..... 975.0 20.2 1.80 15.70 224.0 120.0 105.5 278.0
S:i wne dried.............do..... 558.0 11.2 7.05 ........ 194.1 119.5 136.0 135.0
sh..................24hours. 200.0 4.6 1.37 4.6 197.6 105.1 133.7 170.8
S : r dried.................do.....1,300.0 40.5 1.80 15.7 103.2 81.5 67.2 274.0
i Oven dried...............do..... 270.0 15.4 3.31 ........ 123.5 103.5 133.0 70.5
Frsh............. ...... 7 days... 99.0 10.3 1.06 7.6 206.7 55.0 155.6 155.0
Air dried.......... r. ..o..... 1,280.0 9.0 2.02 29.2 162.0 102.0 C3.1 234.0
,Ovndried......... ...do..... 485.0 ............... ....... 212.0 124.0 159.0 147.0
The soils chosen were from the Koolaupoko district, on Oahu,
No. 313 being a sample of brown ferruginous clay soil which occurs
widely distributed in this district. It was very dry at the time of sam-
pling and was covered with a heavy growth of guava. No. 314 is the
subsoil to No. 313, and No. 319 is a sample of a similar type which
had been plowed and planted to pineapples.
The extracts were made by treating the soils with distilled water
S i the proportion of 5 parts of the latter to 1 of the former in glass-
stoppered bottles, shaking occasionally during the period noted in
the table, each being shaken an equal number of times. The values
are figured to parts per million of the oven-dry soil. Sample No. 313
S contained, originally, 18.65 per cent moisture, No. 314 19.65 per cent,
aud No. 319 30.3 per cent.
'It will be seen that in every case the air-dried soil contained the
largest~ amount of soluble HCO,, the oven-dried sample next, and the
freshsoil the least, regardless of the time of extraction.
iiiiii ii i ...... ....
are discordant, but indicate the air-dried form to be the most also Tl
Phosphoric acid.-This series is remarkably concordant and .i* I
cates an increase in solubility of this constituenit upon drying i i
oven and at the same time, without exception, shows an increase 1f :
solubility with increase in time of extraction. '
Manganese.-These results indicate an increase in solubility of ) :
manganese with increase in time of extraction and also an increasiea i:ii~.
solubility upon drying. Unfortunately the whole series of mangaslNiiii
determinations on the oven-dried samples was lost through accidentti":,
Lime.-While the results from the lime determinations are vi::i
inconsistent, the general average tends to show an increase in solw' :i
ability upon heating in the oven and a maximum solubility in the e-
hour period of extraction. This latter may be due, however, to sulb.
sequent precipitation in the longer extractions.
Magnesia.-The table shows a marked consistency, especially with .
reference to the rate of increase in solubility of magnesia, due to
drying. The concentration of the extracts from the fresh soils was
least, with only one exception, while that from the oven-dried soils
was greatest in most instances. While there is considerable varia-
tion, the data indicate the most complete extraction in that of seven
Sulphuric acid.-The relative amounts of this constituent extracted
show it to be slightly more soluble in the fresh soil, judging from the
average of the series, although only slightly more so than in the
oven-dried soil, and that the concentration is practically the same
for the several periods of extraction.
Potash.-The potash series shows this element to be much more
soluble in the air-dry and fresh soils than in the oven-dried soils, i
while there is scarcely any difference in the solubility as induced by
increasing the time of extraction from 24 hours to 7 days.
The above results tended to establish the advisability of an arpi-
trary extraction of not over 24.hours, and partly for this reason it Wa s
decided that the method at present in general use, namely, shaking :;
for a period of 1 hour and allowing to settle for 24 hours would be"
suitable to our conditions. Owing to the mechanical texture of
Hawaiian soils, caused by the presence in them of highly ferruginous
clays, which assume a colloidal form if worked when too wet, it was
found necessary to allow the extracts to settle and in every instance, .
except when heated to 250 C. or ignited, it was necessary to add a |
nuq irTLOMhoUL LUWf.w au \Sb v., wtLLt. W LLLW LSLU AS OVA.Cf WbO uLUS lltOU.
ra Bunsen burner, at first carefully on a wire gauze for 2 hours to
Iat dusting and then over the direct flame for 2 hours, thus
| styiPng practically all the organic matter.
l ia er zextract.-This extraction was made by treating 200 gram
ns of the soils with 1 liter distilled water, shaking occasionally
4i'! :1 hour, as previously mentioned, and then allowing to settle 24
A'1 MIours, adding small amounts of ammonium chlorid as a coagulant
hi|i: wa necessary. Particular attention was given to these extrac-
Slions in order that all the samples in each series of the same soil
i should receive similar treatment as regards the number of times of
taking, thus making the results more directly comparable. Like-
ise, all distilled water for a series was taken from the same lot in
order to eliminate any slight influence which varying amounts of car-
bon dioxid in the distilled water would have upon the solubility of
the minerals. After settling 24 hours the solution wab filtered
S through double filter papers and from this solution 500 cubic centi-
meters was evaporated to a small volume and used for analysis.
All determinations were made gravimetrically except phosphoric
add, iron, and bicarbonate. The former was made colorimetrically
ia 50 cubic centimeters of the original solution.' Iron was deter-
mined colorimetrically2 in a solution of the ammonia precipitate
from the 500 cubic centimeters portion, and bicarbonate was de-
.trmined by titrating 50 cubic centimeters of the original solution
with twenieth-normal acid potassium sulphate, using methyl orange
S as indicator.
Ni rilc aid extrac.-The soils for this phase of the work were pre-
pared in the same manner as above described as regards tempera-
-- ---- .- --- ,:-f- -
I'V. Dep. Ag., Bar. Begs BU. S1, p. 4
IsU. LDepa., Bar. seas laBa l4p. a.
"'" +~i:!! .+:+++ ..... .
SOIL TYPES. : .- i
The types of soil selected for. this work were of the widest
ble range, and represented, in a general way, the normal ,
normal types, both physical and chemical, to be found 'in the is.
The following table gives the chemical analyses of samples at,!(
mined with hydrochloric acid of specific gravity 1.115: '
Chemical analyses of soil used.
Soil So oil Soi so sil Boil Boil Soil. Soil -Soti i.""1
No. No. No. No. No. No. No. No. No. No. No
74. 164. 9. 292. 290. 405. 416. 417. 406. 428i.
P.ct. P. t. P.ct. P.ct. P.ct. P.. c t. Pt. P. ct. P. etP .. P t.J. .l
Moisture (HsO)............. 25.46 1.22 5.36 7.65 8.44 8.02 6.17 16.26 10.34 14.94 10.4 1iWi
Volatile matter........... 13.08 3.56 16.78 8.42 15.80 12.50 17.73 17.53 17.73 22.24 18its I.
Insoluble matter........... 32.69 48.17 31.67 38.49 40.02 39.12 36.09 30.92 37.31 34.99 24 i.
Iron oxid (Fe0Oa).......... 10.13 30.58 18.60 16.63 16.41 15.24 13.20 11.24 10.92 8.24 22!.
Alumina (AlOa)....-...... -12.59 3.05 14.67 12.85 14.11 20.54 20.39 19.38 20.20 10.T 13.1 S
Titanium oxid (TiOs)............1.72 .68 2.00 1.50 2.40 1.60 1.40 1.80 3.29 3 lli
Manganese oxid (Mn30I)... .13 .10 9.21 .24 .30 .15 3.84 2.85 .06 .20
Lime(CaO) .................. 2.63 .12 1.32 1.84 .77 .86 .33 .21 .48 1.91 i.
Magnesia (MgO)........... 1.09 1.22 .52 8.71 1.30 .99 .44 .36 .67 2.24
Potash (K20).............. .14 .48 .79 .39 .17 .20 .39 .45 .2 .24 .
Soda (NasO)............. .34 1.46 .38 1.36 .42 .48 .59 .36 .48 1.40
Sulphuric acid (SO).......-- 22 .44 .15 .08 .10 .33 .35 .43 .30 .45 .
Phosphoric acid (P20s)... 1.02 .08 .20 .57 .27 .44 .20 .24 .48 .22 1 ,. ..
No. 74 is a yellowish-brown soil from Waimea, Hawaii, of 'a ';
silt texture, with an abnormally low clay content, and maintaitii"ia ,
very loose, open structure. :. I1
No. 164 represents a peculiar type of soil more or less scaftt:er
over the islands, which upon absolute analysis shows about 20 p'i
cent of titanium oxid. It is high in iron and aluminum, and' a:b
contains a larger percentage of ferrous iron than any of the sis :;
examined heretofore. It has a high specific gravity, bluish-~i y 7
color, packs quite closely, has a clayeyy silt" texture, and containAf
an abnormally low content of moisture and organic matter. i' 'i
No. 9 is a sample of the highly manganiferous type found in ti:ih
Wahiawa district on Oahu. It has a chocolate-brown color, a sandy
silt texture, and maintains an excellent mechanical condition, itUeii
permitting good aeration.
No. 292 represents the type of soil occurring in the lowlands tjiln
and about Honolulu now being used for bananas, rice, and lrtm*
farming. It has a sandy texture, grayish-brown color, and abnp l
mally high magnesia content. iA
4. 90isa pcuia tpe ofsilocurring Mn the: valley the
et s~tatin grounds, and is undoubtedly of sedimentary
,it" nature being largely determined by, washngs fro the
tin.- It is a bluea clay soill, exceedingl plastic when wet, but
-ding forms hard compact lumps, and is somewhat similar to
'or gumbo so.Ila. This soil also h~as a soapy feel, and during
%htyseason aeration' and drainage axe almost impossible.
e.40'5 an(' 46 are samples' Of & silty soil, to be found in: the
ditrctof Honolulu, which is being used for aquatic agricul-
;--A the former for rice the latter for taro culture.
"INos 416 and 417 represent: the type of red clay soil which is so
hadat On all the islands. These samples were taken only a short
*6ce apart with the- view in mind of deteiig the effect of
altiatio, 41 being a cultivated soil, while 417 is practically the
Oame soil from the unbroken sod,
Wo. 428 is a sample of highly organic7 dark-colored soil from Glen-
*d, Olsa. district, Hawaiai. It has a yery sandy' texture and is
Oected to heavy rain l and good drainage, but for some reason,
-ob y c t ipr tive.
No. 426 Is a sample from Kealia, Kauai, and represents at brown
Ofsoil which has partly undergone a recementation of the par-
64Mintoa yeow sft rock, hence:the sample contains considerable
No r of Yellow clay scattered throughout
tieilns in certain districts, this sample having been taken from
SThe relative. 2alubility of the various constituents is shown sepa-
ftteY 'ordr i- bing out moire clearly the effects of heat, one table
beig evoted to each element.
Theollwin table shows the. results obtained in the study. of the
effctofheain o the soluability- of the sillica:*
S Nkbiity f Oiji*ca inuat andmifa-norina nikic acid.
[Calculated on boats of dry 0.1L
Ai dy.Dried at Dried at UtaAidr.Dried at Dried at
IM'- C. 250- C. IoV C. 2509 C. sn.
%...........M. 30 L 3 O 7 8& 7 0. 196 0.187 0.113 0. =5
b)$,......... 10&0 210 3.0 4.0 W07 .006 .027.0
---- L,........ 25 9.5 & 5 7.4 .115 .091 .084.19
M............. C2. & 3 7.2 10.3 .102 .5W0 .616 .9
-- ww ww wa L2 2.1 17.2 &6 .1li0 .148 .264 .59
W............. 23 9b.7 A8 I 1W0 .219 240 267
S 4M................... 1L.5 7.9 7.8 10.-M .065065 .077 .192
48,.......... 2.4 AS. M. 22L3 M07 .076 .097 .206
---------- .... A 4L5 31.2 83.5 ."65 .173 .301 .292
(M............ ILO MO 1LO I L 9 0.2U1 .3202 329
M.......... LIS L38 7.9 1.13 .024 .000 .062 -1 IM
as LO & 0 2U -Z .07i.32
show the greatest solubility of silica indilute nitric acid, an ..
tion in this particular is found in sample No. 164, a soil almost d: i
of organic matter and containing a very high titanium, irn, q4
silica content. A further discussion of these results will be ta.ke
following the table of alumina determinations in consideration U .
relation of these two elements in the soil. .
The following table shows the results obtained in the determninao 'i
of alumina in heated and unheated soils:
Solubility of alumina in water and fifth-normal nitric acid.
[Calculate# on basis of dry soil.]
Soluble in fifth normal. ntls OW t
Soluble in water (parts per million). olble in fifth n al ntri
..._ ------------------------------------------------------------------"..--"-----_".,. i .a- .
Soil No. -
Dried at Dried at Dried at Dried at
Air dry. 100" C. 250" C. Ignited. Air dry. 1000 C. 250 C.
74.................... 11.1 3.2 10.3 22.3 0.291 0.292 0.818 :';
164................... 7.5 9.5 9.5 5.0 .060 .048 .139 .,288
9..................... 4.8 1.1 9.5 3.7 .583 .675 .676 .O4
292................... 16.6 17.6 14.5 17.1 .874 .598 .584 1. o t
290................... 19.1 12.7 12.8 17.7 .266 .292 .691
405................... 7.6 13.8 17.6 12.2 .169 .133 444
416................... 17.6 12.8 16.1 20.9 .420 .509 1.057 LiAi
417.................. 15.3 9.0 4.8 28.9 .679 .661 1.413 1,495
406................. 10.3 19.6 28.5 38.0 .295 .314 .882 1.42 C
428 ................. 4.4 6.3 11.9 8.8 2.261 2.031 2.208 24 14
426.................. 2.9 6.6 1.7 2.1 .308 .347 1.192 L 71
448................... 4.9 .7 5.8 2.6 .979 1.757 1.6 7
It will be observed from this table that the alumina is affected in.:.''
very much the same way as the silica. The results, while somewhat
inconsistent, show an increase in water-soluble alumina in the heated.
soils, the number showing increase of alumina by heating from 100 to i;
2500 C., being about the same as in passing to ignition. The effect of
heat upon the solubility of this element in dilute nitric acid is very
marked and increases regularly with increase in temperature. There. .:
is scarcely any correlation between the solubility of the alumina and
the total amount of silica present. However, it is worthy of note
that there seems to be a relation between the solubility of the alumin; :.
in dilute nitric acid and the volatile matter (organic matter andi.
combined water) existing in the soil, as will be readily seen from the'.
r ,!. Ii
S, [Calculated on basis of dry soil.]
Soluble in fifth-normal nitric acid (per
BI? Soluble in water (parts per million). ble in fth- nitric acid (per
S o il N o --------------------
I Dried at Dried at Dried at Dried at
Si Ajiry. 100 C. 250" C. Ignited. Air dry. 100 C. 250 C. Ited.
74.................... 17.6 9.7 9.2 12.5 0.003 0.002 0.006 0.055
I--................... 3.5 3.5 3.5 5.1 .005 .007 .083 .047
.................... 3.7 5.3 3.9 4.5 .007 .016 .006 .006
2i ................... 2.9 5.3 3.1 3.5 .194 .037 .037 .013
S 20................... 4.8 3.2 4.4 1.8 .069 .069 .142 .046
................. 6.4 9.2 5.4 5.1 .324 .302 .290 .157
.................. 2.8 2.8 2.8 8 2.5 .032 .032 .027 .015
417................... 5.2 2.7 3.3 3.8 .026 .029 .029 .033
40 ................... 4.6 2.7 4.0 2.1 .515 .487 .333 .158
...--.....--..-... 1.9 2.7 3.2 1.6 .024 .033 .039 .107
4 ................... 3 1.3 1.6 1.3 .037 .061 .014 .082
44-............... 2.1 3.2 2.3 2.1 .051 .038 .077 .024
Again, there is considerable inconsistency in the results, but an
ii average shows the solubility of iron in water to be greatest in the
air-dried soil. The solubility in dilute nitric acid is much less con-
sistent than that in water, thereby making it impossible to advance
any conclusions except to call attention to the fact that the alumina
in Hawaiian soils is very much more soluble, both in water and in
dilute nitric acid, than is the iron. But if the results from samples
Nes. 292, 405, and 406 be disregarded, and this is plainly permissible
amce these soils are used in aquatic agriculture and the major part
S ofthe soluble iron is in the ferrous condition and would be oxidized
... .. .[;: ::m.. ..
tion of ferrous iron from the wet and air-dry samples. In'se
the samples in the series there is a close correlation between the
of the heat on iron and alumina, but it is by no means gener
Iron, alumina, and silica are apparently the constituents least
ble in water. The greater solubility of iron in the air-dried-soil
be explained by the fact that the normal mechanical conditiZ"
Hawaiian soils is conducive to reducing conditions which rwesULi
the formation of small quantities of ferrous compounds. Hawaaiiu '
soils, although characteristically basic, normally give an acid'l*ao 1
tion, due indirectly to the high clay content and its accompa yi i
poor aeration. Magnification of this condition is to be found intt i.'I
rice and taro soils, as will be shown in a later table (p. 24), in whit..i
soluble iron is found in comparatively large amounts. In such ape
.. .., ... ...
it is to be expected that the direct effect of heat would be to oxid ::
the iron and thus render it less soluble. Further confirmation :
this theory is found in the cultivated and uncultivated soils (Nos.
416 and 417, respectively), in which the iron content of the latter i i
shown to be the more soluble. After heating at 1000 the solubility.
in many instances is greater than in the air-dry samples and is prob- .
ably due to physico-chemical effects upon the soil films and hydrated A
silicates. These latter effects are also responsible for the increased .i
solubility of iron in dilute nitric acid as a result of heat.
The results obtained from the manganese (MnO,) determination. 31
are shown in the following table:
Solubility of manganese in water and fifth-normal nitric acid.
(Calculated on basis of dry soil.]
Soluble in fifth-normal nitric acid (per
Soluble in water (parts per million). cent).
Soil No. *i
Dried at Dried at Dried at Dried at 'm. :mE
Air dry. Dried at Dredat Ignited. Air dry. D at Dd I :
Air dry 100. C. 250 C. 100 C. 25 00 C.
74.................... 26.5 30.4 30.4 30.4 0.063 0.041 0.217 0. |
164 ................. 9.0 11.0 10.0 9.0 .003 .008 .013 .A00
...... ............ 23.5 26.5 25.5 20.1 .494 .669 1.692 1 T:
292. ................. 5.2 4.1 41.4 14.5 .070 .098 .106 .067
290................... 29.4 20.4 40.8 45.1 .049 .076 .115 .1 a
405.................. 5.9 10.3 14.9 18.4 .062 .062 .047 .0,41?
416.................. 2.2 4.5 14.4 14.8 .349 .529 1.314 .
417................... 15.7 8.7 180.5 219.2 .385 .580 1.052 t -
406................. 9.1 4.4 6.0 9.6 .035 .030 .048: ,
428.................. 15.9 161.1 32.8 6.3 .094 -.102 .225 ,.
426.................. 6.9 9.0 90.3 33.8 .004 .012 040 02 :
448................. 2.8 13.4 108.7 119.6 .028 .032 .126:. .;
WAS:Ur j .wI5.U =y&ts A J I .A UDAU.Y. .LL ALA-J -utLc L 510O ILA--O 3.O1 JM-.--5. j Jl LLOcj-u uM
: least partially, as manganese dioxide. But in the normal types con-
on ..: abentrand-here- the- g se pt Iy eistrar
a s c^ plfiblflye exis-t-s-largelyx
:i; m a lowe state of oxdAlion and' hnce in a more soluble form. In
any- case-man mite-. 4 d-4ats myy-occur to a limited extent. As
already noted e Wd4ls heated to 2(o C. and ignition gave the more
S. Gono t wed -.ater extract, an average indicating the maximum con--
l qi[Dtratl& fro -r e ignited soils. The effect of heat upon the physk:
i 4, icl properties is probably the prime factor which influences the sol-
utility in -waer.' lth one exception the oxids of manganese are
I' quite insolubl in nittic acid, this oxid being manganous oxid (MnO),
Sserefore the higher oxids, such as manganomanganic oxid (MnOQ
af. ad manganid oxid (Mn03 ), which are both essentially: combinations
I, i. maraese oid and .manganous oxidare.soilein .nibru id,
ti5 tite extent of their MnO content, while their MnO, content remains
oConsequently the solubility of manganese oxids increases
ncrease'iit heat owing to the above-mentioned decrease i state
oxidation as hiigh temperatures convert 'M ; into. Mn,O, and
i, a of' which is partially soluble in c acid. Therefore
Smio hirs. .-I aid. e
S.wo .t .nd to i pre the ,solubility c d portion' l "
B:V i i nin:j ih known that the action fat upon organic com-
Sae and also certain oE t converts them.int
M:us- O+Mno Hosw:ipou tstO oa
:, ,I 1400-Bu. 3-1----8 a-
l- 1 ... ... ............ .. .. .
Solubility of lime in water Undfift--nornial itie acid.
[Calculated on baits ofatdr saodL
| i '" .. *!! 1-a
Soluble in water (parts pr nJmiion)..
olube in ifth-tpr nit
I I I- -i~ -. .- -
74.................. 176.8 330.6 2,801.1 1,l 9.6 2.812 P.332 Mia .s
164................... 28.1 44.2 64.3. 38.1 .026 .030 .024
9.................... 224.9 302.9 910.9 766.8 .448 ..W9 .. 1
292................. 112.6 86.9 242.3 207.1 .147 .856 .986
290........ ......... 183.0 232.1 195.6 206.3 .29 .406 .318
405.................. 296.9 133.3 363.0 261.9 .344 .362 .330
416................. 82.2 107.3 270.6 232.6 .16 .115 .14
417................... 26.5 98.5 330.5 332.9 .174 .174 .167
406................... 57.1 93.9 697.5 547.7 .388 .409 .320
428................. 184.4 1,455.6 1,509.3 220.6 .466 .479 .39g .
426.............. ... 16.1 33.8 225.8 106.1 .056 .083 .ui OS
448.................... 59.2 67.1 763.6 708.6 .248 .252 .226 .162
Solubility of magnesia in water and fifth-normal nitric acid.
(Calculated on basis of dry .oil.] ..
S .."I .I
Soluble in water partp per miliop).
Soluble in fifth-nornj nitric
I ~ I .' i
I I N' .1
Ig it .
I I N'
The series of lime determinatipns shows that this constitp~mt p
most soluble in water in the soils which were heated to 2,50 p,'
and least soluble in the air-dried soils. This ip true of every qmp1~
except Qoe (Wo. 290), this litter being a ppeoliar do.e tye 4 d
soil from thp experiment station grounis. I diltp ipitrip aji4 ji
will be observed that lime is most soluble in those soils heated to
1000 C., and, unlike thp water extr4ciqns, the Jeast conwt4ration
is obtained from the ignites poils. Thus it is shown that the action
of nitric acid in no way correlates with that of distilled water. How.
ever, the results show the more highly organic soil to contain. HIg
Sto be found in sample No. 290, which represents a soil having a
S A racteristic soapy property indicating the presence of hydrous
:. magnesium silicate.
..... The effect of heat on the solubility of lime and magnesia is more
S striking than in case of the other elements. It is highly probable that
S the increased concentration of the water extract of the soil heated to
100 C. over thieair-dried sample is produced through physical causes,
i uiely, destruction of the soil film and dehydration accompanied by
. a ilig.ht decomposition of organic matter. On the other hand, the soil
S wihen heated to 2500 C. undergoes more completely all'the above trans-
formations as well as decomposition of organic matter. Since calcium
i a~ magnesium are two of the elements universally combined with
iQgamnii matter, there necessarily follows an increase in solubility as
Si.* .result of the more complete decomposition. The soils showing the
i latest solubility of these elements in water were those containing
!: highest organic matter.
iil ] The decrease in solubillty of lime and magnesia in water and in
nitric acid at 2500 0. and ignition is hard to explain. It is utdoubt-
Sedy partly due to chemical changes in the soluble forms resulting
f a the decomposition of the organic matter and is also influenced
by the decrease in exposed surfaces as a result of an aggregation of the
soil particles and probably other physical factors. It is suggested
i that one of th chwnical changes taking pleae so a result of heat is
that of a replacement of the potash and soda in the silicates by
,...... ......... .. .
-1 .i JiiJ
'Calculated on basis of dry sol.
. .: ,*'* fl ll
Soluble In water (parts per million). Eoluble. in ifh-normal ri
Soil No. l..
SAir r Dried at Dried at Dried at Driedat
1 i Air 100" C. 250" C. e d 100 2A500. ~C S :r
-. 7 ..= .. ::.. .il l
74..-....-.. ........------- 128.2 117.4 339. 3 217. 5 0,05 0.066 0.050 4
164.................. 64.3 82.3 40.1 132.5 '.032 A.0"
9..... .......--.-... 117.8 192.7 301.9 260.6 .073 .081 ..
...-.. ..... .... 77.2 76.3 118.0 83.8l
.... ;. .. 87.1 92.4 91..6 77.4 .177 .054
.....96.6 55.1 ; 45.9 % 43.6 q y *f t4 N 0s8 .10
..........98.2 96.2 78.3 147.6 .055 .056
17 .- ... ; 0.3 100i8. 77:4 1 .061 05
4016........ ... .. 36.5 49.2 19.4 78.2 .014 .013 .032
428..,.. .. ...... 44.8 202.8 353.5 220.7 :038 .051 .02-
426... ... ....... 43.8 58.7 56.4 182.9 .025 .024 .030
448................. 119.8 107.4 64.4 59.0 .032 .032 .033 .5" 4
. .. .... ^
. The fig~ires -show that the effect .of heat. upon potash is slight
different fibomthe:effects onr lime and magnesia. The ignited s oib
appear to contain this element in the most soluble formi,- while th i
samples dried in air and at 1000 C. contain it in the'-least soluble
form. In the air-dried samples potash is also more sohible in thI '
cultivated than'in the uncultivated soil, and the greatest solubility'
of this element is also found in the highly organic soils;
SSoils in general possess fixing power for potash and for phos :
phoric acid in particular. The fixing of potash isgenzerally believed
to. be due to hydrated silicates and organic-matter. 'Cameron and:
Bell on. continuously extracting a soil with: water until no more: !
potash dissolved, then grinding the sample and rbextracting, found'
ani Additiona'aniaffnt of.potash to be removedL This they attributed
to'a colloidalE alumiinum .silicate upon the surface' of the particles
thus protecting them from the action of the water as well as absorb 0
iag the pbtash.r Dehydration and deconiposition would therefore !
materially overcome the fixing power, and the potash replaced "i
lime or magnesia would not be refixed during a short pe.iodi. i ;
.'. U.S. Dept. Agr., Bur. Soils Bu,3, .3, .
i more.ajuole 1in he uncultivatead an tle cultivated sou8, wte former,
however decreasing with increase in heat. In the extractions made
ith dilute nitric acid the average indicates a greater solubility in
t: he ignited soils, the solubility tending to increase with increase in
iI;I. ..perature. : .
Phosphoric acid e aists in soils in major part combined with iron,
luminumI, ImgnesiuR, and calcium, and is also found combined with
S.r.ganic matter, being always present in the so-called humus of soils.
Stmay be in the for of basic'phosphates, hydrogen phosphates, or as
I" plex phosphates in combination with more than one element.
-Iis probably comnbiled mostly with iron and aluminum and titanium
S;Hawaian sois. Considerable work has been done upon the effect
I :t-:heat upon th6 solubility of this constituent and several attempts
Siihave been made to draw conclusions-from these results as to its state
l of comiinaftion; that is, whether organically or inorganically com-
b bined. Peterson t using fifth-normal nitric acid found that after
Soxidizing thi organic matter with hydrogen peroxid there was no
Sincrese i i -n ;solubility of phosphoric acid when the soil was headed
~- 240a 0.,iHe concluded, therefore that the solubility of mine
phosphates ii soils is not increased u t 2400 C. The author's ies
S ad to indicate decrease in solubi of phosphoric acid at high t
WbsoemwaI St. Beumph Bul. SL
li *P. f. J
effect of heat would directly increase the solubility of these a
stituents in dilute nitric acid gradually up to the point of i
at which point the decomposition of the hydrates would be 5
maximum. Changes due to the destruction of organic matteiri..
cause an increase in the solubility of this element. Anothe-r ii '
of some importance in this connection is that of precipitation sub"
quent to solution. The increased solubility of aluminum and :mia
ganese would probably produce some precipitation of phosphor
acid, particularly in the water extract.
:" : EE) i
:. i: i a,
S.. ," .... ....
"."* i :: i :i
The following table shows the solubility of sulphates (S OJ.4(m
affected by heat:" l
Solubility of suphuric acid in water and fifth-noral nitric acid.
[Calculated on basis of dry soil.1
.. i; .....L ;
Soluble in water (parts per million). Soluble in fifth-normal nitrie cM
Air dry. Dried at Dried at Ignited. Air dry. Dried at Dried at' *'
A dr 1000 C. 2500 C. ignited. 1000 c. 2500 C. C. iOU,
74.................... 172.4 130.5 1.961.6 1,30. 2 0.027 0.019 6.16 '
164................... 72.3 66.2 206.7 168.6 .037 .031 .027
9..................... 111.4 146.2 1.339.7 1,294.4 .017 .019 .053
292................... 164.7 159.5 722.5 532.3 .067 .018 .019
290.................. 100.2 176.2 1.128.3 799.5 .022 .026 .062
405................. 129.6 149.3 942.0 583.6 .018 .016 .067
416................... 59.4 100.6 702.3 664.3 .028. .035 .038
417................... 98.9 103.1 872.1 926.0 .032 .032 .037 Ii
406.................... 2U0.3 326.4 1,555.9 1,479.9 .061 .086 .163
428. ................. 494.8 2,123.7 2,598.0 680.1 .08o .073 .10
426.................. 46.2 54.2 119.7 241.6 .018 .034 .010 *
448................... 110.0 107.4 1,621.3 1,575.7 .028 .029 .044
It will be seen from this table that the effect of heat upon the s mi- l
ability of the sulphates is quite marked, more so in the water extracts
In this series the air-dried soil is the least soluble, that dried at 1000 .q-:
next, while the maximum solubility is reached at about 2500 C., d m IE
creasing upon ignition. On the other hand, the solubility in dihlII'
nitric acid is slightly different in that the average shows the maim i
solubility to be obtained from the ignited samples, the least soluble
being in the oven-dried (1000 C.) soil. The surprising feature of thesi
results is the markedly greater solubility of sulphates in water than in
i: : J I
a.L w"IEIf WIIa u no a_-aLALU au. v nag WrT vu SL.L16 .Iu Ui.uK'JU UUL vJL wr JL~UJU.L EJ
Smore soluble than the other. Sulphur also exists in soils as sulphids
': e a erally combined with iron, or as sulphates in combination with iron,
bi f:ie, or magnesia, also combined with organic matter in many essential
( frii s. The effect of heat would be most marked upon the latter in
that it would undergo considerable decomposition at 2500, the sulphur
Being oxidized to ulphlr dioxide or trioxid, which upon treatment
with water as a solvent would tend to form sulphuric acid or sulphates
Sto the extent of the bases in solution. On the other hand, it is evident
t: large amounts of sulphur will be lost through volatilization upon
ignition. Soil No. 428, a highly organic soil, illustrates this effect
best in that the increase from air dried to oven dried (1000 C.) is
@0 p~ts per million, while the decrease from the sample heated
from 250 C. to ignition is 1,900 parts per million. It is evident
from these data that upon igniting the soils the sulphur set free from
tW: destruction of the organic matter is oxidized and volatilized so
tui it is lost before combination with the bases takes place.
e folowi~g table shows the bicarbonate content of the water
Soaubily ofbicarbonotes in ahter.
rspw ,nWia pof1 dry a.l
i soi Beal al B oi ol so Bol So Boal S eft
tM n t of sol. Np. No. No. No. No. No.No No. No. No. No.
74. a & 45. dA 417. BL. 42B. 42.
Stl"c........ I I Ht. 1: Wt I A t:11A Is
atl ..:::::,: as %* m I:O S )? q. *
.r.Is. .VPt. .4,^s.., s4. 25 f1A P.
Me Saolubility of the bases with which car onic acid combine .l.2
reason suggested in the above tao~e for a decrease in wiaerkr l
nstituents upon ignition is that ignition would cause a tr fd
ton of the bicarbonates into norinal carbonates, therefore teip
reducing their solubility in water. .
.At the beginning of this work. some determinations of tfit
were made,' but, these .were not carriedd through the seri.
element was riot present in the water extract'in large enough q4ji. ;
to be determined. In the dilute.nitric acid extracts it was'p i
very small amounts in the samples driedib air and at 1000C"'
much larger quap ities in the extracts from samples heated to'2
and ignition, 'the maximum solubility'being obtained tpon the
.. r "... :::. :........:i: :l
samples. ". ,
EFFECT OF HEAT UPON RICE AND TARO SOILS. .
In the following, table is shown the effect of heat upon the soils.sed
ipi aquatic agriculture, comparingi this with the solubility of ai
elements in the wet and soggy condition: i
SEffect of heat upon soiliW'sed in aquatic agriculture.
S[Parts per millionof dry soil water extract.]
S. .. -. .. J
S Condition of Silica mu Iron n Lime Potash phonic 1
mi a oid oe Lim e s t. phoee Ji d t
sample. (bO). (Al0). Os). xid (Ca). (MgO). (IK(O). a (
SA120 ..,e0 ,.n3hi
Rice soil, No. 405: .
Wet......... 6.9 5.6 12.2 64.7 664.8 4 82' 111.9 43.7 13.9' '
Airdry....... 2.3 7.6 6.4 5.9 296.9 209.7 96.6 27.1, 129.6 16-4
SDried at 1000 !
0 -........- .6.9 13.8 9.2 10.3 133.3 130.9 55.1 31.0 149,8 .
Dried at 250 '
C.......... 5.7 17,6 5.4 .14.9 363.0 141.6 45.9 33.0 942.0 157J
Ignited...... 16.1 12.2 5.1 18.4 261.9 147.0 43-6 25.3 .583.6 1-
Taro soil,No. 406:
Wet........ 36.6 62.'4 86.1 34.4 318.6 310.0 '31.8 -3827 *13718 : &
Air dry...... 4.6 10.3 4.6 9.1 57.1 82.2 36.5 28.4 260.3 4,5
Dried at 100* .
C.......... 4.5 19.6 2.7 4.4 93.9 87.2 49.2 35.7 326.4 136.4
Dried at 250
C.......... 31.2 28.5 4.0 6:0 697.5 234.7 19.4 .21.2 1,~5. 9 '~8.
Ignited...... 33.5 38.0 2.1 9.6 547.7 245.9 78.2 23.4 1,479.9 11 5
"* n ]
When the types of soil were chosen for use in this series, two were
selected with a view to. obtaining some information. upon the sdils
in use for Hice and taro culture. It would be expected' that heat and 1
its accompanying oxidapin vould have. a marked effect upon 'hIs:
type of soil for the reason-that-for the most.part it existsn-in a-redo4- -- i
., '. i -, .'
ing environment. The 'bbvp table shows solubility in-water onl I., ,
The samples were taken fromp the field.in wt'condition-and extra. -.
tions -were made upoOn- weighed samples ."iimecatelyg ..nAi
in the laboratory, the moisture content in this state being about ,
ei.' not necessarily indicate that the mineral constituents, with the
S ecnuption of iron, are actually more soluble than those of dry-land
agib Neither should we conclude that the abnormal concentra-
M tiM is wholly due to more complete diffusion coupled with greater
ii.aiolbility induced by the environment to which these soils are sub-
..ii: ted. The amount of water always present in these soils is far in
wIeens of that occurring in dry-land soils, and since there necessarily
; musiat be a tendency toward constancy in concentration regardless
of the amount of solvent present, in time the absolute amounts of
: slids going into solution would be considerably greater in submerged
soils. The moisture content of these two soils when received at the
laboratory was about 50 per cent, whereas the dry-land soils contain
w!i iy much less moisture. The water extracts obtained by the
Methods employed, therefore, would necessarily contain greater
absolute amounts of substances already in solution in the soil water.
Hence the concentration of the nutrient solution occurring in sub-
S merged soils need not necessarily be greater than that of dry-land
The foregoing results show that an increase in solubility of the
S mineral constituents of various types of Hawaiian soils is effected
by heating. The samples represent most of the normal and abnormal
I pes of the islands. That there are both chemical and physical
i fa: tors concerned in the phenomena at hand must be admitted at
outset. It is believed, however, that the most important set
1i Aittors "affecting the solubility of inorganic soil constituents are
ff *ftphysiaical nature.
a ndoubtedly the means by which the physical factors act is through
the soil moisture in its relation to the physical properties of the soil.
The nSdit ions conducive to the formation of a colloidal state and the
suboeqtt relation of heat to the destruction of this colloid are two
of the most important of these factors.
. ."I;' lII.
tides. The moisture therefore occurs as thin films which, aoseet
to certain physical conceptions, must be held around the partial.
an enormous pressure. From purely physical considerations
pressure has been estimated at several thousand atmospheres. Uud u
such pressure the concentration of film water with reference to ": ..
mineral matter should be much greater than that. of the fre e
capillary water in the soil.
Then the air-dried soil, the particles of which are still surrounded
by a film of moisture, when shaken with water, should theoreticaly l
show the least solubility. The results reported in this bulletin -i
most instances are in harmony with this assumption. But if the doil .
be allowed to remain in the condition and environment prevailing in
submerged cultures, that is, in the presence of a large excess of water,
then in time diffusion would bring about a more or less equal distribu-
tion of dissolved materials throughout the entire water present and
the pressure of soil films would be decreased to a minimum or entirely
eliminated. Hence the amount of materials going into solution iM
the free water in such soils would be expected to be abnormally high.
Upon air drying such soils the normal films would again appear with
a resulting decrease in solubility. Subsequent heating ought then,
to affect these soils in a way similar to that produced on dry-land
soils. The data presented in the previous tables are again in harmony
with this view.
Water, however, not only exercises a solvent action on minerals
but forms various hydrates, the solubility and physical character of
which in some instances are greatly altered; organic as well as inor-
ganic matter goes into solution with the result that the moisture fils
around the particles became solution films, holding in suspension and
more or less intermingled with colloids, both organic and inorganic.
The films then may be looked upon as being of a colloidal nature.1
Upon heating to 1000 C. alterations in the films would take place
through evaporation and by partial dehydration of colloids, thus de-
stroying the pressure by which the film was previously held around
the particles. At the temperature of 1000 C. the concentration of the
soil moisture would also be temporarily increased, due to increase in
solubility with heat. During the course of the evaporation the con-
centration of the soil moisture would increase to the saturation point,
after which the mineral matter would be deposited on the surface of
the film as evaporation went on.2 Also the materials held in solution
in the interior of the permeable particles would be partially deposited
I No claim is made for originality in this view. The idea of soil films, colloidal films, etc., has been made
use of by various writers on soils.
King (loc. cit.) in discussing the relative solubilities of fresh and dried soils advanced this idea.
aII: i ai period addition to coming mto immediate contact with
ji dsi deposited on the surface of the particles.
W hy several of the mineral constituents of the soil should be so
i;. akedly more soluble when heated to 250 C. than at the other
temperaatures is a question not easily answered. The difference in
physical effects were quite noticeable in that there was a greater
aggregation of particles. Again, there was a more complete destruc-
Stioniof organic matter effected at this temperature, and also it is not
entirely impossible that drying at 1000 C. for eight hours does not
effect a complete elimination of the soil moisture and especially the
water of chemical combination. It seems reasonable, then, that the
effects of heating to 1000 C. are simply magnified when heated to
2500 C. Added to this there is a more complete destruction of organic
m 'atter, the effect, both physical and chemical, being of the same
General nature bii more complete at the higher temperature. The
destruction of organic constituents being more complete would neces-
Ssarilyincrease the solubility of the mineral matter held in combination,
S as it is generally conceded that the organic constituents of the soil
in its natural state are quite insoluble in water and acids, more
especially in the former. There is also evidence of the existence of
fatty or resinous organic matter which would materially affect the
properties of the soil film. For the decomposition of such bodies it
Should be necessary to heat the soils considerably above 1000 C.
I In addition to the above-mentioned effects of heat the relation
between solid and solvent would naturally be affected by other factors.
Among these is the absorption or "fixing power" of the soil.1 It is
-reasonable to expect soils with widely varying physical and chemical
properties, such as those used in this series, to differ greatly in
absorptive power. Hence it is not at all unlikely that the lack of
Consistency in some of the results in the foregoing tables is due
primarily to this factor. Not only is there lack of uniformity in
a Blehter (Landw. Vers. Stat., 47 (186), p. 260) found that heating increased the absorptive power o0
the rso for water.
specific rather than general nature, as has been already :
Among these effects are the volatilization of certain sulphur
pounds, conversion of bicarbonates into normal' carbonat a
hydration of silicates, etc., replacing of potash by line, an
chemical transformations. In addition there is produced a -
aggregation of the soil particles, resulting in a. decrease in
area exposed to the solvent and an accompanying change ii :
fixing and absorbing powers of the soil. It is possible, by apr
of these conceptions, to explain the majority of changes, both in:ij
and decrease in.solubility, resulting from ignition.
THE EFFECTS OF HEAT ON SOIL NITROGEN.
The data presented in the preceding pages indicate the existence
of colloidal films surrounding the soil particles. These films "t i
probably both organic and inorganic in nature and undergo altdeit:~
tion under the influence of heat. By such alteration new surlifa il
become exposed to the action of solvents, thereby making p lsj b "Ii i
the solution of materials otherwise effectively protected from';F t6 |
solvents used. There is considerable evidence in the data, howe .i : ::,''
that other changes were also produced by the heating. Some oxfl& i ;
tionis must have taken place, and probably decompositions of o&e.
types. Changes in the organic matter were produced at the h-big
temperatures, as shown by the color of the water extracts.
The effect of heat on soil organic matter has been the subject of some
previous investigation. It has been observed, for example, that
water extracts from heated soils are usually darker in color and oSAn
tain greater amounts of organic matter than similar extracts fro 1
unheated soils. : '
Darbishire and Russell1 found that plants absorb more nitrogfen1':i.l
from soils that have been previously heated to 950 and 1200 C. than .
from unheated soils. They concluded that the heating brought about..|
some decompositions in the organic matter and also caused a modb:i:1
fiction in the bacterial flora.
1Jour. Agr. Sci., 2 (1907), p. 305.
iiiiiii~glO o no smaIl amounts oI ammomia, Dut no subsequent ammonm-
oii Mn set in. The nitrates were little affected although nitrification
Iiein!iii t'irely *inhibited by the treatment. From the fact that volatile
i'ptics bring about similar effects, these authors believe that
*! sW i alll sterilization kills certain biological agents which, in the
n iarteaid soil, effectively hold in check the multiplication and activ-
i,. of the ammonifying organisms. After these inhibiting agents
&e destroyed the ammonifying efficiency of the soil rises rapidly,
i: us making available greatly increased amounts of nitrogen.
ILodge and Smith4 found that decoctions from soils show an
iarease in ammonia after steam sterilization at 15 pounds pressure,
i ut a decreasegi ammonia took place from the sterilization of the
rI: :ilathrop and Brown5 found that the amounts of ammonia and
total nitrogen soluble in water increased with an increase in the
-pressure under which the soil was heated. At 10 atmospheres
appro ximately 40 per cent of the total nitrogen was rendered soluble,
whj, Ole the ammonia thus split off was found to vary from 7.83 per
I ni t to 15.64 per cent.
Recently Schreiner and Lathrop' published a comprehensive
i iies tigation of the effects of steam heat on soil organic matter. In
ibis work they isolated from heated soils a number of compounds
Iot found in the unheated soil. Among the compounds isolated a
S Jour. Agr. Sl., 2 (1908), p. 411.
S *New Yrk Cod Sta. Bul. 275 (1910).
S Jour. Ag. Sd, 3 (1900), pp. 111-144
ramae. ahaet Sta. B Rpt. 1p11, pt. 1, pp. 12-134.
r *Jour. Indus and Engin. Chem., 3 (1911), p. 657.
*U. S. Dept. Au., Bar. Sols BuL 890 Jour. Ame. Chbm. Soc, 34 (1912), pp. 12S42-I.
nature, but it remained for Schreiner and Lathrbp to detM
definitely what is at least one of the toxic bodies thus pro:
On the one hand, these authors have shown that definite nitoqil
compounds of a character beneficial to plant growth are fo l
the action of heat, while on the other, a toxic compound, alsoI ~'a '
and definite in character, may be generated at the same time, o -i iiW l
significance of these discoveries is at once apparent; the vm:i.i;i
such definite and fundamental data can not fail to be important. ,.i,:1 '
A knowledge of the effects of steam heat on soil organic matt er. :
special bearing on greenhouse practices, but may it not well be. askid ':.
what are the effects of dry heat without pressure ? This phase of the!
question has not been exhaustively studied. It is unsafe to co:nle'
a priori that the same types of cleavage and hydrolysis take placsr .
the absence as under the influence of pressure. There is evidence i
the growth and appearance of crops on burned soil that nitrogen J
made available by the heat. The deep green color of the crop. i
sometimes very striking. It is important, therefore, that this phase
of the question be investigated in a general study of soil heating on
account of the importance of nitrogen in the nutrition of plants.
In an altogether different connection our attention was drawn to
the very large increase in the ammonia of some Hawaiian soils brought
about by the action of heat. It was observed that the ammonia co-
tent of certain soils increased from a few parts to over 400 parts per
million. At the same time the nitrates were decomposed. -From
these observations and its general bearing on soil heating, an investi-
gation of the nitrogen transformations seemed of interest and impor-
tance. Whence the ammonia thus set free and from what class of
compound does it arise ?
The nitrogen of soils having been at one time bound up in organized
tissue, plant and animal, and, therefore, largely of proteid nature,
undergoes hydrolysis under the action of enzyms, bacteria, etc., with
the resulting formation or splitting off of simpler compounds., In
soils there must occur every stage of these changes.from the protid
complex, on the one hand, to inorganic compounds, on the other. The'.
larger part of soil nitrogen exists, however, in complex organic corn-
binations. Nevertheless, the simple inorganic nitrogen compounds,
SU. S. Dept. Agr., Bur. Soils Bul. 80 (1911).
stillation with magnesium oxid is known ,to liberate ammonia
e I amuuids. In a few instances the modified method of Schloesing,'
Swich consists in leaching the soil with dilute hydrochloric acid and
im distilling the ammonia from the filtrate with the use of mag-
i...is oxid, nwa employed. The results were very similar to those
iassinsed by direct distillation. The following table shows the effects
o:f heat on the nitrate content:
00I. .. ,- .
The effects of heat on soil nitrates.
[Nitrate nitrogen expressed in parts per million of air-dried soil.]
Soil oil Bon Soil Son Son Soil Son
Temptr- No. 9. No. 290. No. 292. No. 329. No. 335. No. 407. No. 411. No. 428.
........... 108.0 18.0 17.6 197.0 3.3 0.7 560 70.0
SIP -. ...... ....2 96.0 18. 6 13.0 158. 0 2.0 .7 60. 0 70.0
C. -.. 57.0 12.5 23.5 615 3.0 .6 L7 40.5
C.....L.... .0 6.5 3.5 13 .6 .5 L5 .8
5. .....- ......- 4 .5 1 4 35 LO .4 .5 .5
i..- 94.0 10.5 125 148.0 LO .6 48L0 4.0
*; These data are of interest as showing the destructive effect of heat
I.p soil nitrates. In most instances the nitrates underwent considera-
!i dreBaad to by lodidi, Mlgan Sta. Tee. Bal. 4, p. 11
EaFZj.lUjb AC r L i fiaA& a flf aaati~ j .m UOUFOJAOBOENT.
In the next table will be found the data showing the effects of
on the ammonia content.
Efects of heat on the ammonia content of soils.
[Ammonia nitrogen expressed in parts per million of air-dried sof .)
TemBolpl sol so soa Soa Soil S Bo
temperature. No. 9. No. 290. No. 292. No. 329. No. 335. No. 407. No. 411.
Unheated ............ 28.0 18.1 11.2 56.0 12.6 9.1 19.6
00 C............... 23.8 19.6 10.5 64.4 1.2 13.5 28.0
150 C............... 67.2 45.2 32.2 81.6 17.5 28.7 77.7
200C.............. 187.6 464.8 174.3 218.4 32.2 368.2 170.8 '
250' C-.............. 40.6 206.5 336.0 28.0 19.6 114.8 98.0 :jSI i
Steam pressure, 2 at-
mospheres..-...... 83.3 51.1 16.8 77.7 16.1 46.2 69.2 04$
__________ .. .- .I- -
The ammonia content of soils Nos. 329 and 428 before heating ha |
here shown to be abnormally high. Generally soils contain ammoni :i
to the extent of a few parts per million only, whereas the nitrate con '.
tent may rise to considerable concentration.1
Under the influence of heat the ammonia content of all the so-ils -
studied was greatly increased, practically reaching a maximum iat
about 200 C. Above this temperature a falling off took place which
was probably due to a loss of ammonia through volatilization. We
here have, therefore, some interesting and, as seems probable, very
important facts. As pointed out above, heat considerably increases
the solubility of the inorganic matter. Here it is shown that the
ammonia content is enormously increased also.
Formerly little attention was given to the ammonia content of soils ;
except in its relation to nitrification. During the past few years,
however, the idea that ammonia may serve as a direct source of nitro-
gen to higher plants has steadily gained ground. It is now known N
that certain aquatic plants, rice in particular, not only can utilize
ammonium nitrogen but that this form of nitrogen is better adapted
to assimilation by rice 2 than is nitrate. Other crops 3 have also
been found to be able to transform ammonia into proteids *ith
1 Ammonia in soils, produced by biological agents, has for some time been looked upon as being merely:
a transitional state, its formation being essential to nitrification. The nitrifying organisms seize on thi :
ammonia and convert it into nitrites and then into nitrates, thus effectively preventing an accumulation
of ammonia in the soil at any one time. One of the essentials of vigorous nitrification, however, is free
oxygen, while ammonification may take the place under anaerobic conditions. In many Hawaiian agq :
aeration is very low, and for this reason (perhaps others), nitrification frequently does not keep pace wi-th&
SSee Hawaiian Sta. Bul. 24.
a Kriiger, Landw. Jahrb., 34 (1905). No. 5, p. 761.
iIIi me Hawaiian soils the effect of partial sterilization on subse-
.....j..t : ammoniication has recently been found to be exceptionally
I g !t If the accumulation of ammonia as a result of partial sterili-
!i;i'n,. n re.ts beneficially on plants, we certainly have a right to con-
-ade ti: : .t its direct production by means of heat would also prove
i. an!r::. ln active to crops.
? EFFECTS OF BRUSH BURNING IN THE FIELD.
|i.:,rWith the view to determining the effects produced by burning
r .use, brush, etc., in the field, a few samples of soil from spots where
brush had been burned were examined' at two different times. The
i u..ah was -burnme about September 1 and the samples were taken
::;, September 10, and November 7, respectively. Care was taken to
..rem~ove the ashes so as to secure portions of the uncontaminated
oil. Samples of unburned soil near by were taken at the same
tme., Ammonia and nitrates were determined in the samples as
Efects of burning brush on soil nitrogen.
[Parts per million of nitrogen in air-dried soil.]
As nitrates. As ammonia.
Laboratory No. Two Two
After 10 After 10
dAtr months 0 months
-'-*,,,;" days. later S. later.
)................................................... 6.5 5.5 50.4 100.
burned)............... ............ ..- .............. 20.0 18.0 89.2 70.0
)............... ........................ 6.0 8.0 161.0 106.4
b red) ............. ......................... 6.0 8.0 21.0 32.2
S b)...................... ......... ... 16.0 22.0 77.0 114.8
b ned).....- .. ..............-............. ....-..... 2.0 62.0 8.4 30.8
prevented the development of the nitrifying .bacteria. ThmeV@i.
had not been cultivated for two years previously asnd receivmii44
tillage during the time of observation. It is not possible to st
temperature' to which the soil was heated in these instances. A
proximate test applied in another locality, however, indicate
the burning of small brush heaps similar to those burned on th
above discussed created a temperature of about 2000 C .. i ..n.
below the surface. The temperature would naturally vary :.g1a ,
from place to place. ....
EFFECTS OF HEAT ON THE ORGANIC NITROGEN.
Having found that large amounts of ammonia are formed from. th
action of heat, a study of the organic nitrogen as affected by he a
seemed of interest. It is well known that ammonia is one of the' ;i
cleavage products of protein hydrolysis. It is also known that in
the destructive distillation of organic nitrogenous substances ammo- .
nia is one of the decomposition products. It was observed that the .
amounts of ammonia recovered from heated soils by means of di- "
tillation were not proportional to the total nitrogen present, but
seemed to depend largely on the type of the soil. The amount o E
ammonia obtained, for example, from soil No. 335 was very md.id .
less than that from the other samples studied (page 32). Ammonaia;
therefore, was probably volatilized and driven out of the soil to a:
greater extent in some instances than in others. Soil 335 is a sandy -;
soil composed very largely of coral sand (CaCO,). In the foregoing
work total nitrogen determinations were not made. Hence it is im- -
possible to correlate the rise and fall of ammonia with losses of
In order to throw further light on these questions total nitrogen
and the several groups of nitrogen compounds rendered soluble in
boiling hydrochloric acid were studied. For this purpose the
method of Hausmann' as modified by Osborne and Harrisz was ap"
plied. This method was devised for a study of protein chemistry,
but has been previously used by Jodidi and others in studying t he
organic nitrogen of soils.3
Ztachr. Physiol. Chem., 27 (1899), p. 95. Jour. Amer. Chem. Soc., 25 (1903), p. 323.
Michigan Sta. Tech. BuL, 4 (1909); Iowa Sta. Research Bu., 1 (1911). -
a ;l ge products m me same ratio m wmcn mntrogen occurs m
I', tu or;:er whether certain of these groups yield inorganic or elementary
i Arogn more readily than others.
Samples of both heated and unheated soil were studied in this
S en eoation. The former were subjected to a temperature of 2000
a.,for a period of two hours, after which the same treatment and
dewrminations were made as in the unheated portions. The results
ate recorded in the following table:
Nitrogen compounds in heated and unheated soils.
Soluble in hydrochloric acid. Composition of hydM
chloric acid soluble.
din bmmbwm 2 u 1
Uiatad:I P. ac P. P. c. P. ctP.. P. P P. ct. P. .. ct P. ct. ct.
379.................... 0.5460.001 0.001 0.096 0.030 0.298 0.426 78.02 0.23 22.53 7.04 69.95
gL.................... .179 .0001 .005 .042 .018 .100 .165 92.18 3.03 25.45 10.91 66.66
4d6................ .504.0015 .006 .079 .055 .240 .381 75.59 1.57 20.74 14.43 62.97
43....... .......... .779 .0045 .022 .129 .029 .363 .558 71.63 3.94 23.12 5.9 65.05
447..................... .396 .0062 .001 .074 .033 .125 .239 60.35 .41 30.69 13.80 52.30
37t..................... .417 .0 .069 .098 .034 .168 .369 88.49 18.9 26.56 9.20 45.53
4....................... .178 .0 .0 .055 .017 .044 .152 85.39 23.68 36.18 11.18 28.95
40...................... 419 .0 .067 .103 .019 .092 .281 67.05 23.84 36.65 6.76 32.74
48.....................808 .0 .031 .077 023 .079 .210 34.54 14.76 386.6 10.95 37.82
447....................207 .0 .020 .039 .022 .028. .109 52.65 18.35 35.78 20.18 25.89
Considering first the unheated soils, the nitrates and ammonia
j e shown to constitute a relatively small percentage of the total
nitrogen and to vary greatly in the different soils examined. Soil
-447 was found to contain the highest amount of nitrates, while in
SNo. 405 nitrates were present to the extent of only one part per
i itliMon. No. 428 contained an abnormally high ammonia content,
devoted to aquatic agriculture (rice and taro) for many yf'
soils 379, 428, and 447 have been subjected to dry-land eul rt
The chemical decompositions and hydrolyses that take
naturally in the organic matter of soils being brought about -l
by biological agents, it is probable that the range and types of i
reactions in submerged soils are somewhat different from:abl::::i
taking place in well-aerated soils. There are several lines of relk :l^
ing not necessary to mention here that lead to this conc..ltikit .
From this point of view, then, the biological effects on soil nitro'r
may reasonably be expected to be different in the two inst~Pantti:
The nature of the organic matter originally incorporated with .r..lti...
soil probably has some bearing on this question also. I: ;
Among the several groups of nitrogen compounds brought iant. W i
solution by hydrochloric acid it is noteworthy that the amidsw an'd
monamino acids constitute the main portion. The latter comprins
approximately two-thirds of the total nitrogen dissolved. It should ;,!
be borne in mind, however, that the monamino nitrogen was deter-
mined by difference; that is, by subtracting the sum of the other
groups from the total nitrogen in solution. It is known, however,
that this difference is. not made up entirely of monamino acids.
Jodidi1 found, for example, that the monamino nitrogen group .
in Iowa soils was made up of from 40.12 to 92.11 per cent of actual,
monamino acids, the variation in this respect being dependent
in part on the treatment to which the soil had been previously
subjected. It is of interest that the relative amounts of amids, *'
monamino, and diamino nitrogen in Hawaiian soils were found
similar to those of soils elsewhere.
Turning now to the question of heat as affecting soil nitrogen, it.
was found that with the exception of No. 405 the average loss of .
nitrogen was about 25 per cent, but in certain soils the loss was 1
much greater than in others. Soil No. 447 suffered a loss of prac-
tically 50 per cent while No. 405 sustained almost no loss of nitrogen.
It is also of interest that the reduction in the amounts of nitrog4- a : :
extracted by hydrochloric acid was greater in two instances and less |Ja
in three than the absolute loss of nitrogen occasioned by heat. hi ;
every instance enormous increases in ammonia and a total decomp&- '1
sition of nitrates took place. On the whole, the absolute amounts o .-
neither the amids nor the diamino acids were greatly affected y biy
SIowa Sta. Research Bul. 1 (1911). !
md it was noticed that a pronounced charrmg in this soil took
P- p: e under the action of the heat. It seems probable that such
1 charring of the organic matter would tend to protect the nitrogen
E bodies in the interior of the particles from the action of the solvent,
S this apparently increasing the percentage of insoluble nitrogen.
S, .,.. SUBKMAY.
I: '"(1) Twelve different soils representing a wide range of types and
agricultural conditions were studied with reference to the effects of
heating to 1000 C., to 2500 C., and to ignition. The solubility of
E l the mineral constituents except sodium was determined, using
S water and fifth-normal nitric acid as solvents. The effects on the
I nitrogen compounds were also investigated.
i (2) The results showed considerable variation. .Neither the abso-
: toe nor the relative solubility of the inorganic constituents were
effected similarly in all the samples studied.
.. (3) -On the average, drying at 1000 C. was found to bring about
S an increase in the water soluble manganese, lime, magnesia, phos-
phoric acid, sulphates, and bicarbonates. At this temperature an
iaerease in the solubility of potash, silica, and alumina was pro-
S duced in about 50 per cent of the soils examined, but a decrease
wIas observed in the solubility of these elements in some instances.
i. The solubility of iron was decreased in most instances.
(4) Heating to 2500 C. or ignition produced effects on the solu-
bility in water similar to those brought about at 1000 C., but vary-
ing in degree, these being sometimes greater, sometimes less in
intensity than those produced at 1000 C.
(5) The solubility in fifth-normal nitric acid was not greatly
affected by heating to 1000 C., but in some instances heating to
::P ...... .. ... .
r~ii;;ji;iii~ iiiiiL .. :.:: ii;i:i: .........
-9 -"- W"- M J MS piSifillSt q i B
the solubility of silica, alumina, potash, phosphoric add, ani dr'~t
phates was increased, while the solubility of lime and maiai
underwent a corresponding decrease. .
(6) The solubility of soils used in aquatic agriculture is,:aba "m A ~
mally high, but upon drying out these become much less soluble
and approach a state similar to that existing in aerated soils. Whe "
such soils are heated after drying they seem to undergo changes of
the same order as are produced in dry-land soils.
(7) No single factor is sufficient to cover the solubility effeWt
resulting from heating Hawaiian soil. On the other hand, the .i.
subject is very complex and involves many factors. Among..the
more important of these may be mentioned flocculation, deo&idae
tion of manganese dioxid, oxidation, particularly of iron, double
decomposition, dehydration, and the attending physical alterations
of soil films. Such alteration would destroy film pressure, thus
allowing the solvent to come into more intimate contact with the
soil constituents. At the higher temperatures bicarbonates become
converted into normal carbonates, thus effectively lowering the solu-
bility of lime and magnesia.
(8) Nitrates undergo decomposition with heat, a decrease in
nitrate content having been found to take place at 1500 C., while
at 2000 or 2500 C. practically total destruction of nitrates took
(9) One of the noteworthy effects of soil heating is the production
of ammonia, which at 2000 C. was formed in abnormally large
amounts. Soil subjected to heat from brush burned in the field
was found to undergo stimulated ammonification after heating.
Nitrification, on the other hand, was not restored after the lapse of
(10) Heating to 2000 C. caused a loss of approximately 25 per
cent of the total nitrogen. A loss of nitrogen and the ammonia
formed by the action of heat came largely from the monamino
acid group, while the amids and diamino acid sustained much less
(11) The results of these studies are believed to throw important
light on the subject of soil aeration and consequently have a direct
bearing on the practical question of soil management.
. ": iiiii
- r ii
.. ..E :iEJ i
UNIVERSITY OF FLORIOA
3 1262 08929
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