Illinois
Fertilizer Conference Proceedings
January 22-24, 2001
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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 corn-soybean 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 corn-soybean 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 no-till system, but did not respond under chisel tillage (Rehm, 1997). Clearly, there needs to be additional information collected on P and K fertilization frequency and the proper fertilization needs of a corn-soybean rotation under different tillage systems and for conditions in southern Illinois.
The objectives of our study are:
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, and
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 on 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 in between these two extremes. Treatment 17 is equal parts of P and K applied annually to corn and soybeans, whereas treatment 18 is a check plot with no P and K applied to either 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 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
Because this is the first year for the study, only the first crop has been fertilized in the rotation. Therefore, the treatments are simply a P and K factorial rate study. The corn yields (Table 3) varied by tillage system, with NT producing the higher yields at DS and CT producing the higher yields at BV and BR. Only at DS with CT were check yields dramatically lower than the other treatments, and, for the most part, there were no P rate and K rate interactions, so most of the discussion will be on P or K main effects.
The main effects of P and K rates on corn yields were mixed (Table 3 and Table 4). There was a linear response to P rates at BR and BV for NT only. However, yields increased at BV as P rates increased, but yields decreased at BR with increasing P rates. In the BR case, yields were highly variable and were affected by weather factors of excessive rainfall in May and June. The yields for NT at BR increased with increasing K rates, up to 80 lb/acre. This site and the DS NT and CT sites all responded positively to increasing K rates. These were also the sites with the lowest soil test K levels, so the responses were not unexpected.
The soybean yield results for DS CT were similar to the corn results, with yields increasing as K rates were applied, except the largest response occurred with the first increment of K2O from 0 to 40 lb/acre (Table 5 and Table 6). The NT area at BR also had increasing soybean yields as K rates increased up to 80 lb/acre.
The higher rates of K for the DS chisel tillage area significantly increased corn and soybean yields. This area had a very low soil test K level, and the additional K provided by the biennial K application proved to be effective, especially in increasing corn grain yields. Results from the BR location were similar for the NT soybean yields. However, for the most part, there was little to no yield response to increasing P or K rates. This may be an indication that, for maintenance applications of P and K on soils already at proper P and K build-up levels, there will be no difference between annual and biennial fertilizer applications. But this is only the first year of study, and results may be very different in future years, where residual P and K may be important. 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.
1S. A. Ebelhar is Agronomist and A. H. Anderson is Research Specialist, Dept. of Crop Sciences, Univ. of Illinois; E. C. Varsa is Assoc. Professor, Dept. of Plant, Soil and General Ag., So. Illinois Univ.; T. D. Wyciskalla is Researcher, Dept. of Plant, Soil and Gen. Ag., So. IL Univ., 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.
