Plantation Field Laboratory Mimeo Report PFI65-2. -
Mg and P Fertilizer Study With Peppers-/
-H. Y. Ozaki .and J.. R. Iley/ -
The retention of phosphorus and magnesium by the sandy soils of'the lower east
coast of Florida is largely governed by the solubility of material applied to, or
formed in the soil. Most of the soils in cultivation have been limed to a PH above
6.0 where the retention of applied soluble phosphate is due.to the formation of
.calcium phosphate. Therefore, the availability of retained phosphate is due to the
solubility of this material, which is relatively -low.
The usual procedure inland preparation for cultivation, and maintenance df a
higher pH, is to use some neutralizing material, usually calcium and magnesium, for
example dolomite. : Additional water soluble magnesium is applied in the fertilizer
and, together with..the neutralizing material, presumably supplies the needed mag-
nesium for the growing crop. Soil test values for magnesium by acid extracting
Sreagents do'not distinguish between excahngeable magnesium and magnesium released
from a neutralizing material, which could be considered as extremely low in avail-
ability at this pH.
There is a need for a combination of materials, or materials which will assure
San adequate supply. of both phosphorus and magnesium to the plant. This will re-
quire the determination of the amounts of materials used, or used in a combination
to give the desired results.
The purpose of this study was to evaluate 3 rates each of superphosphate and
magnesium sulfate fertilizers and.several other magnesium and/or phosphorus ferti-
:Experimental. Procedure. --.
A randomized complete block experimental design containing.a 3 x 3 factorial
of superphosphate and magnesium sulfate rates plus treatments of other phosphorus
and magnesium materials in 4 replications was used on Pompano and Arzell fine sands.
The treatments are listed in Table 1. Early Calwonder pepper was seeded in double
rows, 16 inches apart on 68-inch beds and later thinned to a 9-inch spacing. Totals
of'300 pounds of nitrogen and 300.pounds of potash were used in 6 applications for
the remaining required fertilizer components. Micro-nutrients zinc and iron were
applied early in the season as pesticides. Standard pesticide control procedures,
including materials containing copper and manganese, were followed during most of
the growing season. .. .
SData were taken on the weight of plant material removed at thinning, the total
and graded pounds of pods of first and all harvests, and graded yields of marketable
pods of the 3 x 3 factorial of all harvests.
1 This presentation of the results of a fertilizer study prepared for research
and industry. Results herein neither constitute nor pl mendation of any
Assistant Horticulturist, Plantation Field laborato, Uiivers f ida.
3 Assistant Soils Chemist, .verglades Experiment St ion, u asity o
":r.. 1 : ." ;:,' : ."". J ,' .' ," :
Results and Discussion.
At thinning, in late February, young plant growth differences were highly sig-
nificant. Treatment 14, magnesium ammonium phosphate-potassium ammonium phosphate,
highly increased the transplant weight above other treatments (Table 2). From data
of the factorial (treatments 1-9), it can be seen that the increase in transplant
weight was partially due to phosphorus (Table 2).
There are several other possibilities why magnesium ammonium phosphate-potassium
ammonium phosphate .(Treatment 14) increased early plant growth above all other treat-
ments in this experiment. This material is more resistant to leaching by excessive
rainfall than the ammonium nitrate-potassium sulfate fertilizer. Thus, in this
test it supplied nutrients throughout a period of early plant growth that received
considerable rainfall. In addition, it was the only treatment that had part of the
nitrogen and potassium fertilizer broadcast and rototilled at planting time. The
seedlings probably were supplied with more nutrients immediately after sprouting.
In other treatments, surface applications of nitrogen and potash, which were irri-
gated in several inches from the seed row,, may not have supplied sufficient nutrients
to the immediate seed zone area in the early growing period.
Soil analyses from a preliminary eggplant study gave high values for phosphorus
and magnesium where.magnesium ammonium phosphate was used., These high values were
probably due to its increased solubility in an acetate solution. Its low solubility
in water does not.hilnder its availability to plants, since eggplant leaf analyses
values for phosphorus and magnesium were higher than treatments where superphosphate
The first and total harvests resulted in significant differences among treat-
ments in pounds of pepper pods produced (Table 3) at the 1 percent level of statisti-
cal significance. Again, the magnesium ammonium phosphate-potassium ammonium
phosphate treatment (Treatment 14) yielded higher than other treatments but was not
significantly different from most treatments where the higher rate of phosphorus
was applied. Here, it can be seen that phosphorus was the factor governing increased
yields in the soil with 2-5 pounds of water soluble phosphorus or 5-28 pounds of
ammonium acetate soluble phosphorus per acre. Phosphorusfrom superphosphate in the
factorial was responsible for the increase in poundage of total, U. S. fancy and
marketable (fancy + U. S. #l) pods of the first harvest, and total, U. S. fancy and
marketable pods of all harvests (Table 4). Because most of the yields on the first
harvest were fancy, the marketable yields are not listed.
There were not any significant differences in weight of transplants, yield of
pods or yield of graded pods due to magnesium derived from dolcmite, basic slag, or
basic slag plus chelating agent. Evidently sufficient magnesium for yields was
present in these soils since performance of the treatment where magnesium was not
applied (Treatment 16) was among the highest in each case. Soil test values of 60
to 100 pounds of magnesium per acre were obtained by an 0.5 N acetic acid soil ex-
Magnesium-potassium ammonium phosphate fertilizer (Treatment 14) resulted in
slightly better quality pods than the other treatments, especially in the early
harvests. Quality ratings, based largely on outside appearance, were made on each
of the 4 harvests. The quality of pods from the 50 and 500 P 0 treatments was
also better than quality of pods from the 5 P20 treatments. In the factorial
treatments, the quality of pods from 550 PO and 60 Mg (Treatment 9) was rated
slightly better than the quality of the ot&e; treatments (1-8).
,^. i ,"*
........A factorial-with differentrates of. superphosphate-and-magnesium sulfate rates
plus treatments of other phosphorus and magnesium materials resulted in significant
differences in weight of transplants, yield of pods and yield-of graded pods of
Early Calwonder pepper.
Magnesium ammonium phosphate-potassium ammonium phosphate gave a highly signi-
ficant increase in transplants weight which was probably due to the immediate
availability of nutrients to the sprouting seed,or seedlings. The resistance of
this material to leaching made this possible during a period of early growth which
was dominated with excessive rainfall.
In the factorial, increased rates of phosphorus were responsible for increased
transplants weights and yields..
The use of magnesium ammonium phosphate-potassium ammonium phosphate also re-
sulted in the highest yield but it was not significantly different from most treat-
ments where the high rate of phosphorus was applied. It resulted in slightly better
quality fruit on the first harvest. .
Dolomite, basic slag and basic slag plus a chelating agent, as sources of mag-
nesium did not increase, weights of transplants or yields, but a treatment not
,containing any. applied.magnesium indicat-ed that these- soils-'contained sufficient '
amounts for this crop. ..
Table 1. Treatments of P-Mg study with Peppers.
P. P0 Mg : : :. .:.Broadcast and rototilled : :
Treatmer-nt ~~ : Lbs Ar I *-'prior to bedding
8 Q' 500
S* o ...5006 :
'Yes, but only-- of MgOlo
S" '.Y..'." es, but only of Mgo .,:: .
Yes, but only J-ofMgO .
......Yes, but only ; of MgO...
Yes, but only ut Mg%00
.... Yes, but only rof MgO. -.. ..
Yes, but only 1,
Yes, but only of Mgo
. .. ..... .. Y e s .. . .. ... .. -
Yes ... ..
" '" ": "" .. .... 'Y e s b u : : .. i. 1 0
S(Rototilled) ... ..
2 Superphosphate, 20% P 0.
SMagnesium sulfate, 28 MgO.
3 Dolomite, 17.2% MgO.
SBasic slag, 35 P 0c, and superphosphate.
6 Basic slag, 8% Mg05 (giving 49.6 pounds of mn, 460 Ca, 402 pounds of Fe per acre)
SChelated basic slag, 3% P and superphosphate.
SChelated basic slag, 8>% /05 giving 49.6 pounds of Mn, 460 Ca and 402 pounds of Fe
8 per acre.
Magnesium ammonium phosphate-potassium ammonium phosphate, 42% P205 and 24% MgO,
The remaining I was applied one month later as broadcast sidedressing and culti-
LO The remaining 3/4 was applied 1/4 each at 1. 2, and 3 months as broadcast side-
dressing and cultivated.
Table 2. Weight of transplants thinned from 25-foot bed in pepper P-Mg study.
Treatment ...Transplant eight9
No. P20 go oz. -
1 1 1 ... 1.. ........ .. ... .. .
16. 500 o 39.5 b
5. 50 50 38.6 b
9. 50 100 37.9 be
7. 500o 25 .. 37.3 be
12. 500 1725 33.6 bc
8.. 500 50 ., 32.0 bc
11. 500 172 31.9 be
13. 500 1726 29.1 bc
10. 50 172 26.9 bc
4. 5 25 21.5 be
3. 52 100 21.0 bc
6. 50. 10o0 18.8 be
1._ 5 25 12.0 be
2. 2 50 50 12.0 be
15. o o 8.7 c
- !*, Magnesium -ammonium phosphate-potassium-anmoniumn phosphate,
W. R.. Grace & Co.).:.
" (Mag "Amp with" K-" '-
Magnesium. sulfate ,(Emjo-Berkshire Chemical, Inc.)
B. asic slag and superphosphate.
SBasic slag, (Fairfield of Florida Agr. Slag. Corp.)
Dolomite ............ .
Chelated basic slag and superphosphate (Fairfield of Florida Agr. Slag. Cor.)
Chelated basic slag
Average of 4 replications.
Means:followed by,, same letter are not significantly different from each other.
,,''1-: :~ "
..,i -.. : -. .;.
Table 3. Total pounds of pepper pods harvested per 20-foot bed from first and
all harvests in pepper study.
Treatment Number First Harvest* All Harvests*
.... .... .- .Lbs,- Lbs.
14 34.8 a 92.2 a
8 25.4 ab 78.6 ab
16 25.6 ab 80.8 ab
7 23.0 ab 80.2 ab '
1 24.0 ab 82.0 ab '
12 22.6 ab ,: 75.2 abc
9 20.2 abe 81.4 ab
5 : 17.8 abed 69.0 .'- abed
: 13 1 :: 18.2 abcd 74.8 abe
10 ,' 12.0 bcd 67.0 bcde
4 '" 10.6 bcd 65.4 bcde
6 9.8 bcd 68.2' bcd
3 8.2 bed 54.4 cde
1 3.6 cd 50.0 de.
2 2.6 cd 54.2 cde
..5.-.......... .. .-- -.. -. .--...-...- .. .o.8- .-. .. .. .. .......... ........ 4 8 '.'. e. e
* Average of 4 replications.
**Means followed by same letter are not
significantly different from each other.
Table 4. Effect of rates of superphosphate and magnesitii sulfate on poundage of
fancy pods of first harvest, total pods of all harvests,. U. .S. fancy pods
of all harvests'and marketable (fancy + U. S' No.- 1i)pods from all harvests.
Treatment First Harvest*
P205 MgO .U, s.' .Fancy All Harvests*
Lbs/A bs/A : U. S. Fancy Marketable Total
1. 5 25 1.352 8,308 16,946 19,485
2. 5 50 973 8,619.:. 17,384 gl2o61
3. 5 100 3,055 8,998 17,977 21,178
4. 50, .2.5 ....: 4,027. -, : 12,578 21,810 .. ':. 25,458
5. 50 50 6,654 13,639 23,464 26,859
6. 50 100 3,541 14,252 22,919 26,577
7. 500 25 8,658 16,577 27,783 31,188
8. 500 50 9,446 17,199 27,005 30,595
9. 500 100 7,685 18,007 28,425 31,694
* Average of 4 replications, linear response to P205 highly significant.