AREC, Quincy Research Report 81-1
NUTRIENT MA .AG T
FOR IRRIGATE A Uof Fd
By F M. Rhoads
Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
AREC, Quincy Research Report 81-1
IRRIGATED AGRONOMIC CROPS
By F. M. Rhoads'
Institute of Food and Agricultural Sciences
Agricultural Research and Education Center
1Professor of Soil Science, AREC Quincy, University of Florida, IFAS.
1. D. Teare,
Agronomist and Center Director
NUTRIENT MANAGEMENT OF IRRIGATED AGRONOMIC CROPS
F. M. Rhoads
University of Florida Agricultural Research
and Education Center, Quincy, Florida 32351
Nutrient management consists of making fertilizer nutri-
ents available to plants as needed for optimum rate of growth.
This includes matching the application schedule with the de-
sired rate of uptake as well as providing the total amount
needed for a profitable yield. The high mobility of certain
nutrient elements in sandy southeastern soils make it more
difficult to maintain adequate levels of plant nutrients in
the zone of maximum root activity than in regions having finer
textured soils. Fortunately, some nutrient elements move less
than others. Nitrogen in the form of NO- moves most rapidly
of the three major nutrients. However, moves significantly
in sandy soils (7). Plant nutrient elements that have a neg-
ative electrical charge associated with them move most rapidly
through the soil. Elements with negative charges include ni-
trogen, sulfur and boron. Nitrogen occurs in the NH+ form but
it is oxidized to the NO form within a few weeks after being
added to the soil.
Phosphorus accumulates in the surface of most soils while
potassium levels do not build to very high values in sandy
soils (Fig. 1). No P had been applied 12 months prior to sam-
pling but 50 ppm-K was applied a few weeks before. A soil
test value of 30 ppm P is equivalent to 67 kg-P/ha. Multiply
ppm in soil test by 2.24 to convert to kg/ha in the furrow
Soil Test (ppm)
40 80 120 160
o 60 -
Figure 1. Phosphorus and potassium distribution with depth
in a Troup sand.
Nutrient Uptake of Irrigated Corn
The logical approach in developing a nutrient management
system for a specific crop is to first examine factors affect-
ing nutrient uptake rates. Growth stage or plant size is im-
portant as well as plant population and date of planting.
Corn plants take up comparatively small amounts of plant
nutrients during the seedling stage but the rate of uptake
accelerates rapidly as the growing season progresses (Table
1). The average rate of N uptake between 7 and 9 weeks after
emergence was 44.5 kg/ha/week. This was the period of most
rapid uptake for all elements except Zn. About 2/3 of the
total Zn uptake occurred between 4 and 7 weeks after emergence.
Over 80% of the potassium was taken up between 4 and 9 weeks
after emergence. Less than 13% of the total K uptake occurred
after silking. Elements with over 40% of the total uptake oc-
curring after silking were N, P, and Mg. Therefore, deficien-
cies of these elements could occur during the filling period.
Table 1. Nutrient content of irrigated corn at each of four
growth stages for a yield of 14,550 kg/ha.
Weeks after Growth Nutrient Content (kg/ha)
emergence stage N P K Ca Mg Zn
4 46(cm) 31 3 25 1 3 .06
7 124(cm) 110 16 159 7 18 .26
9 silk 199 32 312 17 30 .26
14 mature 348 60 357 27 52 .31
The amount of K taken up after silking is usually very
small in comparison to the total uptake (11). Application of
K after silking did not increase the K uptake of corn on a
Troup sand (Fig. 2). Highest K uptake occurred when the to-
tal K fertilizer was applied by 6 weeks after planting. Yield
was positively correlated with rate of K uptake between 7 and
9 weeks after planting.
200 I Uptoke
it / Figure 2. Comparison between
S ^two fertilizer-K application
50- I / schedules and actual K uptake
Si/ of irrigated corn on a Troup
/\ /sand. Solid lines show ac-
oo /4 cumulated amount of K applied
/// over time and broken lines
o5- / show accumulated uptake. Dots
/ and triangles show application
dates on solid lines and sam-
o ii II I I pling dates on broken lines.
Higher plant populations take up larger amounts of nutri-
ents. Rate of N uptake was proportional to population and
fertilization level for irrigated corn between 35 and 70 days
after planting (Table 2). The effect of population was partly
hidden by increasing the total application of N in order to
maintain the same level of fertilizer N per 1000 plants. How-
ever, highest yields were obtained at three populations with
3 kg-N/1000 plants even though higher N levels were applied
Table 2. Effect of population and amount of fertilizer on
rate of N uptake by irrigated corn 35 to 70 days
Population Rate of N uptake Total N uptake
(plants/ha) kg/ha/day kg/ha
77,000 4.2 147
101,000 6.3 220
146,000 8.3 292
1/Nitrogen was applied to supply 3 kg/1000 plants.
Late planted corn emerges quicker and grows faster imme-
diately following emergence than early planted corn because
of the higher ambient temperature. Therefore, date of plant-
ing must be considered when scheduling fertilizer application
in a nutrient management program for irrigated corn. Corn
planted on March 8 contained 7 kg-N/ha 35 days after planting
while that planted on May 17 contained 63 kg-N/ha (Table 3).
The difference in total N uptake between the two planting
dates was reduced to 17 kg/ha at 70 days after planting.
Table 3. Effect of planting date on average rate of N uptake-
by irrigated corn for two growth periods (74,000
Planting Average N uptake (kg/ha/day)
date 0 to 35 days 35 to 70 days
March 8 0.2 4.2
May 17 1.8 3.
1/Nitrogen was applied to supply 3 kg/1000 plants.
Response of Irrigated Corn to Nutrient Management
The first consideration in a nutrient management program
is the total amount of nutrients to apply (10). This will
depend mainly on two things, the yield goal and crop response.
Crop response to three levels of fertilization is shown in
Table 4 for irrigated corn. Response was linear between the
low and medium level and started to decrease between the med-
ium and high level. The ratio of grain yield to applied N
was about 56 for the low and medium fertility treatments and
about 45 for the high fertility level.
Table 4. Effect of fertilization level on yield of irrigated
Fertilizer applied Yield
N P K
84 25 70 4,767
168 50 140 9,345
336 100 280 15,053
Nutrient management has as its primary goal to produce
crop yields equal to those expected if leaching losses of
nutrients did not occur. Protecting fertilizer nutrients
from leaching increased grain yield of irrigated corn on a
sand by more than 180% (Table 5). Plastic mulch gave com-
plete protection from leaching as indicated from soil samples
taken at the end of the growing season. However, the high
salt concentration in the fertilizer band prevented the plant
roots from taking up enough nutrients to produce a yield in
the 12,000 kg/ha or greater range.
Table 5. Effect of leaching protection on yield of irrigated
corn grown on Troup sand.
Type of Yield
None 2380 a*
Sulfur coated fertilizer 4700 b
Liquid water repellent 6210 bc
Plastic mulch 6720 c
*Means followed by the same letter are not significantly dif-
ferent (P = 0.05) according to Duncan's multiple range test.
Fertilizer application can be delayed as much as four
weeks after planting in some cases without a significant yield
loss (Table 6). These data are from late March plantings at
Quincy Florida on Orangeburg and Ruston soils (10). Nutrient
stress had developed at six weeks after planting to the extent
that yields were reduced by 14 to 18%.
Table 6. Effect of early season nutrient stress on yield of.
Date of first Relative
fertilizer application Year yield
(weeks after planting) $
Bi-weekly application of fertilizer increased grain
yield of irrigated corn on a sand by 39% (Table 7) above that
obtained with a preplant and two sidedress applications (8).
The increase would have been much greater in comparison to a
single preplant application.
Table 7. Effect of multiple fertilizer applications on re-
lative yield of irrigated corn.
Fertilizer Date of last Number of Relative
schedule application applications yield
Preplant and 8 3 7
Bi-weekly starting 12 7 100
Suggested Strategies for Nutrient Management
of Irrigated Corn
The following suggestions apply to mid-March planting
dates in North Florida. Application of P at planting will
provide adequate amounts for plant uptake throughout the
growing season on properly limed soils. Two applications of
K appear to be adequate if 1/3 of the K is applied at plant-
ing and 2/3's at 6 weeks after planting. Nitrogen, boron,
and sulfur can be applied together in equal proportions of
the total amount applied during the season. A specific sched-
ule that has worked well on soils with a sandy clay loam sub-
soil is to apply 1/4 of the N at emergence, 1/4 at 45 to
60 cm, 1/4 at 100 to 120 cm, and 1/4 at 180 cm plant height.
A suggested schedule for deep sands is 16% of the N at emer-
gence as a sidedress application and 12% per week with ferti-
gation at 4, 5, 6, 7, 8, 9, and 10 weeks after planting.
Enough water should be applied with each application of fertil-
izer to move it from the soil surface into the plow layer.
Nutrient Management for Peanuts, Soybeans and Cotton
Historically, peanuts have not shown dramatic responses
to specific fertilization techniques (3). Nitrogen fertili-
zation of peanuts is not needed because of symbiotic fixation.
It has been demonstrated that Ca is not translocated from roots
to the fruit of peanuts but must be in contact with pods to
prevent deficiency symptoms (1). Therefore, the application
of gypsum to peanuts during the pegging period is, perhaps, the
most significant example of nutrient management for this crop.
The application of nutrients through irrigation has not been
widespread for peanuts. Possibilities include B, S, K and Mg
for sandy soils.
The most recent example of intensive nutrient management
for soybeans was reported by Garcia and Hanway (2). Four ap-
plications of a foliar spray, containing total amounts of
N, P, K, and S of 80, 8, 24, and 8 kg/ha respectively, pro-
duced a yield increase of 1040 kg/ha. Sources of nutrients
were urea, potassium polyphosphate, sulfate of potash, and
ammonium sulfate. Application of these nutrients to soybeans
through irrigation has not been reported in the literature.
Tests in Florida with Cobb soybeans did not show any positive
response to foliar fertilization (6).
The monitoring of nitrate-nitrogen in cotton petioles has
been shown to be effective for managing the N nutrition of
cotton. Safe petiole levels of NO--N for irrigated cotton in
California are 16,000 ppm at early bloom, 8,000 ppm at mid-
bloom, and 2,000 ppm at late bloom (4). The University of
Arkansas offers an Extension Service program for monitoring
petiole NO- to cotton growers with recommendations for defi-
cient or excess N (5). The system is much more difficult to
apply to unirrigated than to irrigated cotton because of the
effect of soil-water content on N uptake.
1. Bledsoe, R. W., C. L. Comar, and H. C. Harris. 1949.
Absorption of radioactive calcium by the peanut fruit.
2.. Garcia, R. L., and J. J. Hanway. 1976. Foliar fer-
tilization of soybeans during the seed-filling period.
Agron. J. 68:653-657.
3. Harris, H. C. 1959. Research on peanuts during the
last twenty years. Soil and Crop Sci. Soc. of Fla.
4. Mackenzie, A. J., W. R. Spenser, K. R. Stockinger, and
B. A. Kratz. 1963. Seasonal nitrate-nitrogen content
of cotton petioles as affected by nitrogen application
and its relationship to yield. Agron. J. 55:55-59.
5. Maples, R., and W. N. Miley. 1979. Nitrate monitoring
to help improve nitrogen fertilizer efficiency on cotton.
Better Crops with Plant Food. Vol. LXIII (spring):15-17.
6. Nagel, D. H., W. K. Robertson, K. Hinson, and L. C.
Hammond. 1979. Foliar fertilization of Cobb soybeans in
Florida. Soil and Crop Sci. Soc. of Fla. Proc. 38:122-
7. Rhoads, F. M. 1970. Redistribution of fertilizer salts
in soil columns after leaching with water. Soil and
Crop Sci. Soc. of Fla. Proc. 30:298-304.
8. Rhoads, F. M., R. S. Mansell, and L. C. Hammond. 1978.
Influence of water and fertilizer management on yield
and water-input efficiency of corn. Agron. J. 70:305-
9. Rhoads, F. M., and R. L. Stanley, Jr. 1979. Effect of
population and fertility on nutrient uptake and yield
components of irrigated corn. Soil and Crop Sci. Soc.
of Fla. Proc. 38:78-81.
10. Rhoads, F. M. 1981. Plow layer soil water management
and program fertilization on Florida ultisols. Soil
and Crop Sci. Soc. of Fla. Proc. (in press).
11. Rhoads, F. M., and R. L. Stanley, Jr. 1981. Fertilizer
scheduling yield and nutrient uptake of irrigated corn.
Agron. J. (in press).
Conversion factors: from metric to English
ppm P x 4.54 = Ib/A P205 in furrow slice
ppm K x 2.41 = Ib/A K20 in furrow slice
kg/ha x 0.89 = Ib/A
kg/ha x 0.016 = bu/A
plants/ha 0.4 = plants/A