Illinois
Fertilizer Conference Proceedings
January 21-23, 2002
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S.A. Ebelhar, E.C. Varsa, A.H. Anderson, T.D. Wyciskalla, and
C.D. Hart1
While it appears to be cost effective and easier to apply fertilizer only to the corn in a cornsoybean rotation, there is some evidence that fertilizer applied to soybeans directly provides a significant yield increase, even on medium- to high-testing soils. Ebelhar and Varsa (1996) found significantly higher soybean yields with low rates of K even on soils testing in the 250 lb/acre range. There seemed to be some advantage to the annual application of K in a cornsoybean rotation, perhaps due to the greater availability of nutrients from freshly applied fertilizer (or less time for fertilizers to become tied up by the soil). High and very high rates of K tended to lower soybean yields, an indication that too much fertilizer may cause salt injury to sprouting soybeans.
Results out of Minnesota showed a definite tillage x fertilizer frequency interaction. Annual applications of P showed a 10-15 bu/acre yield advantage over biennial P applications in a notill system but did not respond under chisel tillage (Rehm, 1997). Clearly, additional information must be collected on P and K fertilization frequency and the proper fertilization needs of a corn-soybean rotation under different tillage systems for conditions in southern Illinois.
Our study has two objectives. The first is to evaluate annual versus biennial P and K fertilizer applications in a corn-soybean rotation for optimum nutrient use efficiency and grain yields under no-till (NT) and chisel-tillage (CT) conditions. The second is to determine the economics of annual versus biennial fertilizer applications to corn and soybeans in rotation.
Field studies were initiated in 2000 at three locations in southern Illinois: the University of Illinois Dixon Springs (DS) and Brownstown (BR) Agronomy Research Centers and the Southern Illinois University Belleville Research Center (BV). Soil types and initial soil test values are presented in Table 1. Soil test P levels ranged from 20 to 107 lb/acre, and K levels ranged from 97 to 330 lb/acre. Recommended fertilizer rates were based upon these soil tests for buildup and yields for maintenance for a two-year period (biennial needs).
However, in order to simplify our efforts, a uniform P2O5 and K2O rate was used across locations whenever possible. For this reason, P2O5 and K2O rates consisted of 120 lb/acre except for the DS chisel tillage (CT) area, where the rates were 180 and 240 lb/acre, respectively. Treatments consisted of either none, 1/3, 2/3, or all of the P and K applied to corn and the remainder applied to soybean, with P and K being handled separately (see Table 2 for a complete list of treatments). Treatment 1 represents all of the P and K applied to corn, and treatment 16 represents all of the P and K applied to soybeans in a corn-soybean rotation. Treatments 2-15 represent all possible combinations between these two extremes. Treatment 17 is equal parts of P and K applied annually to corn and soybeans, and treatment 18 is a check plot with no P and K applied to corn or soybeans.
It should be noted that because some of the soil tests were not performed until after the study was initiated, the rates of P and K application may be less than recommended by the build-up and maintenance guidelines in the Illinois Agronomy Handbook, but rates are sufficient for maintaining a high-yield environment and represent a practical farming operation. Rate changes, if deemed appropriate, will occur after the second year.
Now that we are in the second year of the study, we can compare annual versus biennial fertilization in the rotation. The corn yields (Table 3 and Table 4) did not vary by tillage system except at BR, where CT produced the higher yields. Check plot yields were lower than the other treatments for NT at BV and BR and for CT at DS. It should be pointed out that there was tremendous variability among plots at BR for CT and interpretation of this data set is prohibitive. For the most part, there were seldom P rate and K rate interactions, so most of the discussion will be on P or K main effects.
A point of clarification: All treatments received the same "rate" of P and K except for the check plots. When we refer to P or K rate, we are referring to the P or K rates applied in 2001, knowing full well that the remainder of the P or K "rate" is supposedly provided by the P or K (residual) application from a year ago.
The main effects of P and K treatments on corn yields were mixed and, in most cases, slight. Yields increased at BV as P rates increased for NT only (similar to the response in 2000); however, for the remaining sites and tillage, there were no significant responses to P treatments. The yields for NT at BR, NT at DS, and CT at DS all increased with increasing K rates. These were also the sites with the lowest soil test K levels, so the responses were not unexpected. It appears that the biennial application of K to soybeans (BK) treatment resulted in lower corn yields for many of the locationtillage combinations.
The soybean yield responses to P rates were very small and mixed (Table 3 and Table 5). Yields decreased with increasing P rates at DS for CT, but they increased with increasing P rates for BV NT. There were no responses to K rates. Check yields were lower only for DS CT, BV CT, and BR CT, an indication that soybean in the NT areas may be more efficient in P and/or K uptake.
Lower ear-leaf P and K levels for DS CT and lower P levels for BV NT are all associated with lower grain yields for these studies (Table 6 and Table 7). For the most part, P and K rates had little effect on ear-leaf P or K levels. For trifoliate leaf P and K levels (Table 8), lower K levels for check plots for CT at DS and BV are associated with lower yields. At DS for CT, there was a significant decrease in leaf P with increasing K rates but no apparent effect on yields.
Because there were several responses of increased corn yields with increasing K rates and a tendency for lower corn yields where the K was applied to soybean (allowing the corn to use residual K), early indications are that biennial application of K to corn would be preferred. There were no effects of annual versus biennial P applications, indicating that P could be applied at any time during the rotation.
While this is the second year of the study, this is only the first year in which we could compare annual versus biennial P and K applications, and results should be used cautiously. We are also monitoring soil test P and K levels over the course of this study to determine if annual or biennial fertilizer applications have any impact.
1 S.A. Ebelhar is Agronomist and A.H. Anderson is Research Specialist, Dept. of Crop Sciences, Univ. of Illinois; E.C. Varsa is Professor, Dept. of Plant, Soil and General Ag., So. Illinois Univ.; T.D. Wyciskalla is Researcher, Dept. of Plant, Soil and Gen. Ag., So. Illinois Univ., and C.D. Hart is Visiting Research Specialist, Dept. of Crop Sciences, Univ. of Illinois.
Ebelhar, S. A. and E. C. Varsa. 1996. Tillage and potassium placement effects
on potassium use efficiency in a corn-soybean rotation. In R G. Hoeft (ed.)
1996 Illinois Fertilizer Conference Proceedings, pp 23-40.
Rehm, G. W. 1997. Phosphate fertilizer management for corn and soybean production in two contrasting tillage systems. In 1997 Fluid Fertilizer Foundation Forum Proceedings, pp 57-66.
