Illinois
Fertilizer Conference Proceedings
January 27-29, 1992
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Michael J. Mainz and Glenn A. Raines1
Soils don't always respond to added P & K fertilizer by increasing soil
test levels or increasing crop yields. After 11 years without any fertilizer
applications P1 soil tests dropped 5-91bs/a and exchangeable K tests dropped
0-361bs/a at Perry. At Monmouth P1 soil tests decreased 10 lbs/a in one field
and increased 13 lbs/a in the other. Exchangeable K tests decreased 21 lbs/a
in Field B-2 and increased 33 lbs/a in B-4 after 8 years without added P or
K. Soil tests were expected to decrease more than what occurred, especially
at Monmouth. Soil test levels at both locations are below recommended values
and yield increases would be expected to occur when fertilizer is applied. Yield
increases generally occur at the lower P & K rates for all crops, but not
significantly. Wheat yields at ORC have responded significantly when the new
P & K rates have been applied to the old rates. The new P & K rates
affected corn and soybean yields more than the old rates, although not always
significantly.
Phosphorus (P) and potassium (K) rate studies were started in 1980 and 1982 at the Off (Perry) and Northwest (Monmouth) Research Centers, respectively. Rates of 0, 60, 120 and 180 lbs/a of P2O5 and 0, 100, 200 and 300 lbs/a of K2O were applied annually to corn, soybeans and wheat at the Orr Center. At Monmouth, of 0, 40, 80 and 120 lbs/acre of P2O5 and K2O, respectively were applied only in the years when the respective fields were planted to corn. Applying the P & K rates every other year was done to slow the rate of increase in soil tests. Generally, fertilizer rates have been applied in the fall at Perry and the spring at Monmouth. Fertilizer is surface broadcast with a Gandy dry fertilizer spreader.
The P & K studies at Perry are usually chisel plowed, except that the entire are is moldboard plowed once every 3 years. Moldboard plowing is done after wheat harvest. From 1982 through 1985, corn stalks were fall chisel plowed and soybean residue was tilled with a field cultivator in the spring at Monmouth. From 1985 to 1990, the fields were in a ridge till system with ridges reshaped during cultivation when the respective field was in corn. Then in 1990 the ridges were disked down and the fields converted to a chisel/Dyna Drive tillage rotation.
When these studies were established in 1979 and 1982 field sizes were selected
to allow for future rate divisions. Main rate plots were divided into 4 subplots,
even though the splits were not made until 1990. Each of the main plots were
split so that each of the 4 fertilizer rates would now be on each of the 4 old
rates. Each of the subplots were treated as a plot from the start even though
the splits were not made. This gave a total of 48 plots for each crop and nutrient
rather than 12 (4 fertilizer rates and 3 replications). The 4 rates were applied
annually to all plots at ORC and every other year at NWRC.
Soil test levels dropped in the zero rate plots the first 11 and 8 years respectively at Perry and Monmouth, respectively (Table 1 & 3). Field changes were more consistent at Perry than Monmouth. Initial soil test levels were low to very low at Perry for both P & K. At Monmouth initial tests were near or slightly above recommended levels. Annual application rates were designed to check fertilizer recommendations and soil response. At both locations, soybeans were the preceding crop when the initial samples were taken. Crop rotations have an effect on soil tests that is difficult to separate out of these results.
At Perry (ORC) the areas for the P & K rate studies have all 3 crops growing in one field for each study, but for identification purposes Field #1 was corn in 1990, Field #2 was soybeans and Field #3 was wheat. These crops/fields are in a corn-soybean-wheat rotation and have been since the studies inception. Phosphorus rates are 0, 60, 120 and 180 lbs/a P2O5 annual for all three crops. Annual Potassium rates are 0, 100, 200 and 3001bs/a K2O.
Initial soil test levels were higher than we wanted so it was decided to use lower P & K rates than at Perry and to apply them only every other year rather than annually. Fertilizer was applied to fields B-1 (P) and B-2 (K) in 1982, B-3 (P) and B-4 (K) in 1983 and then every other year until 1990 when annual applications were started. At Monmouth the fields are in a cornsoybean rotation with each crop being grown in both studies each year. B-1 and B-2 were corn in 1982 and B-3 & B-4 were soybeans. Application rates were 0, 40, 80 and 1201bs/a of P2O5 and K2O.
Both the zero rate and full rate values are compared to the initial soil tests for the respective plots at each location. Soil test levels should have decreased for the zero and 40 lbs/a rates and stayed relatively the same at the 801b/a rate at Monmouth. Only the full rate should have built up soil test levels. At Perry similar results should have occurred, but with higher application rates the soil tests should build faster and to a much higher level. The zero rate plots should have dropped significantly for both P and K at both locations since they were not fertilized for 8 and 11 years at Monmouth and Perry, respectively. Drawdown is difficult to estimate as the plant utilizes P & K from both the soil and applied fertilizer. There is room for error as both tests are affected slightly by sampling time, moisture content of the soil at sampling, crop rotation, and sampling technique. These errors may account for some of the changes in the zero rate plots, but not totally.
Every other year applications of 1201bs/a (full rate) of either P2O5 or K2O at Monmouth should have increased soil test levels only slightly (+13 lbs/a for P, and +30 lbs/a for K). Annual applications of 180 lbs/a P2O5 and 300 lbs/a of K2O should have increased soil tests approximately + 155 and +721 for P, and K, respectively. Actual changes were only half of the expected values. These predicted changes in soil tests assumed an increase of 1 lb/a for every 9 lbs/a of P2O5 and 4 lbs/a of K2O applied, subtracting that which was estimated to be removed by the crop. Crop usage was estimated since grain analysis was not completed every year of the study prior to 1990.
Possible explanations for the differences in predicted versus actual soil tests can be partially explained with the soil test and sampling themselves. Both locations are in the high P & K supplying regions of the state. Subsoils at both locations (16-24 inch depths) have high to very high P & K levels. These high P & K levels at Monmouth have allowed the plants to utilize fertility below the surface 8 inches thereby allowing the fertilizer applications to buildup the soil tests in the plow layer.
At Perry there is a layer of tight soil (shale?) in the 8-16 inch sampling depth that has apparently prevented crop roots from getting to the high P & K fertility below it. This may restrict the crops to using only the fertilizer that is applied. There is also the possibility that some of the fertilizer applied-, especially K, is tied up in the soil and not available for crop use.
Crop yields were not affected by either P or K application at either location (Graphs). This is the second year for the new fertilizer rates being applied to each of the old fertilizer rates. Last year, 1990, there were more responses to the old rates and very few to the new rate. This year, 1991, all the significant yield responses were to the new rates.
At Perry (ORC), there was a significant yield increase to the new rates of both P and K. Yields increased for each added increment (601bs/a) of P2O5 for the new rates for each of the 3 lower old rates. There was very little yield response for added P once soil test levels reached 90+. Wheat response to K soil tests and added K fertilizer was very erratic, although there was a significant response to the new rates.
Phosphorus and potassium soil test levels at Monmouth are high or very high
for P and near the recommended level (3001bs/a) or slightly above for K. There
doesn't appear to be much yield response for either nutrient. At Perry (ORC)
both the P and K soil tests for the old zero rate plots are below to much below
recommended levels. Even at the 15-23 P, soil test levels added P did not give
a significant yield increase. At the low 150-200 exchangeable K levels and at
higher levels the corn crop produced significantly higher yields with the new
K ,rates. The greatest response occurred when soil tests were below 3001bs/a
exchangeable K.
Soils at Monmouth have been built up to a high level for both P and K. Yield
responses generally have been very large to added fertilizer. This year yield
responses were very flat for both nutrients, but there was a significant yield
decrease to the high (1201b/a) K rate. Soil test levels at Perry (ORC) are below
recommended levels for both P and K, especially at the zero and low old rates.
Even at these low soil tests there wasn't a significant yield response to added
P or K fertilizer.
This marks the 9th and 12th year for the studies at Monmouth and Perry, respectively. Unfortunately soil, leaf tissue and grain samples have not been taken from every plot each year of the study. These past 2 years all crops have been sampled and data analyzed. In addition to the surface 0-8 inch depth, samples have been taken at the 8-16 and 16-24 inch depths. Without these additional sampling depths we would not have identified the hard pan (shale soil layer) in the 8-16 inch layer at Perry. It appears that this layer has prevented most of the crops roots from moving and into the fertile soil below. Yield reductions have occurred several years in the past 12, possibly as a result of the impenetrable layer.
Subsoil levels are high in both P & K at Monmouth. It is evident that the
crops are bringing up nutrients from below the plow layer (normal sampling depth).
Soil tests increases in the zero plots can only occur if nutrients are moved
between layers in a very fertile soil or by sampling errors. After this seasons
soil samples are analyzed we will be better able to see any trends that might
be developing in buildup or drawdown patterns. Responses on the fertile, high
CEC soils of Western Illinois to added P & K as well as other nutrients
has not always been according to the text book. Factors that we haven't considered
may be more important than originally thought.
Table 1: Effect of no fertilizer applications on soil test levels, Perry
Table 2: Effect of Full Rate fertilizer applications on soil test levels, Perry
Table 3: Effect of no fertilizer applications on soil test levels, Monmouth
Table 4: Effect of Full Rate fertilizer applications on soil test levels, Monmouth
Figure 1. Phosphorus Rate Study, 1991 ORC (corn yields)
Figure 2. Potassium Rate Study, 1991 ORC (corn yields)
Figure 3. Phosphorus Rate Study, 1991 NWRC (corn yields)
Figure 4. Potassium Rate Study, 1991 NWRC (corn yields)
Figure 5. Phosphorus Rate Study, 1991 ORC (soybean yields)
Figure 6. Potassium Rate Study, 1991 ORC (soybean yields)
Figure 7. Phosphorus Rate Study, 1991 NWRC (soybean yields)
Figure 8. Potassium Rate Study, 1991 NWRC (soybean yields)
Figure 9. Phosphorus Rate Study, 1991 ORC (wheat yields)
Figure 10. Potassium Rate Study, 1991 ORC (wheat yields)
1Michael J. Mainz and Glenn A. Raines are both Agronomists with the University of Illinois and Superintendents of the Northwest and Off Research Centers, respectively
Mainz, M.J., and J.J. Sutor. 1983-90. Phosphorus and Potassium Rate Study. Northwestern Illinois Agricultural Research and Demonstration Center, Report of Research Results.
Peck, T.R., and et.al., 1991-92. Illinois Agronomy Handbook. Circular 1311. University of Illinois, College of Agriculture, Cooperative Extension Service.
Raines, G.A., and T.E. Halock. 1981-90. Phosphorus and Potassium Rate Study. Orr Agricultural Research and Demonstration Center, Report of Research Results.
Fox, R.H., G.W. Roth, K.V. Iverson, and W.P. Piekielek. 1989. Comparison of soil and tissue nitrate tests for predicting soil nitrogen availability to corn. Agron. J. 81-971974.
Magdoff, F.R., D. Ross, and J. Amadon. 1984. A soil test for nitrogen availability to corn. Soil Sci. Soc. Am. J. 48: 1301-1304.
Magdoff, F.R., W.E. Jokela, R.H. Fox, G.F. Griffin. 1990. A soil test for nitrogen availability in the northeastern United States. Commun. in Soil Sci. Plant Anal., 2:(1316), 1103-1115.
Magdoff, F. R. 1991. Understanding the Magdoff pre-sidedress nitrate test for corn. J. Prod. Agric. 4:297-305.
Nafziger, E.D., R.L. Mulvaney, D.L. Mulvaney, and L.E. Paul. 1984. Effect of previous crop on the response of corn to fertilizer nitrogen. Journal of Fertilizer Issues. 1(4): 136-138.
Vitosh, M.L., D.D. Warnchke, D.R. Christenson, and J.G. Hall. 1988. Soil nitrate
testing : a guide for adjusting Michigan nitrogen recommendations for corn.
Proceedings of the 18th N. Central Extension-Industry Soil Fertility Workshop,
Nov. 9-10, 1988. Potash & Phosphate Institute, Manhattan, KS.
