Illinois
Fertilizer Conference Proceedings
January 24-26, 2005
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S. A. Ebelhar, E. C. Varsa, J. D. Hernandez, T. D. Wyciskalla and C. D. Hart
1
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 × 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 a) 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 b) determine the economics of annual versus biennial fertilizer applications to corn and soybeans in rotation.
Field studies were initiated in 2000 at two locations in southern Illinois. These locations included the University of Illinois, Dixon Springs (DS) Agronomy Research Center 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. In 2004, the DS no–till (NT) P2O5 and K2O rates were also increased to 180 and 240 lb⁄acre, respectively, due to the lack of soil test P and K buildup after four years of 120 lb–acre rates. 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.
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 rates below, we are referring to the P or K rates applied this season, kno wing 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.
Corn Ear–leaf P and K Composition. There were slight differences among treatments for ear–leaf P concentrations (Table 3). Overall, there were lower corn leaf P levels with check treatments, and slight increases in leaf P concentrations as P rates increased. Increasing K rates significantly increased ear–leaf K levels for NT at both locations and CT at DS. Increasing K rates actually decreased leaf P concentrations slightly at DS. Leaf K concentrations of check plots were significantly lower that fertilized plots and led to lower yields at DS but not BV. At BV, even though the ear–leaf K levels were lower in the check plots, they were close to or above the critical level of 1.7%.
Trifoliate leaf P and K Composition. Increasing P rates slightly increased trifoliate leaf P levels for CT and NT at DS only (Table 4). There were lower K levels for check plots for both tillage systems at DS and NT at BV, which was associated with a significantly lower yields. Increasing K rates resulted in increased trifoliate leaf K concentration for both tillage systems at DS only. For the DS CT site, increasing P rates increased leaf K concentrations but increasing K rates decreased leaf P concentrations. This is probably a dilution effect associated with the growth limiting effect of low K levels.
Corn Yields. The corn yields for 2004 (Table 5) varied significantly between tillage systems with NT out–yielding CT at DS and CT out–yielding NT at BV. Planting date and stand differences accounted for these effects. Check plot yields were significantly (8–30 bu/acre) lower than the other treatments at DS, but not BV, indicating that the BV fields still had enough residual P and K to support yields in 2004. 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.
The main effects of P and K treatments on corn yields were mixed and in most cases slight. Increasing P rates decreased yields at DS for NT and increased yields at BV for CT. Corn yields increased significantly with increasing K rates for the CT site at DS and the NT site at BV. When averaged over the four-year period, 2001–04, check yields are lower for DS CT and NT, and for BV NT (Table 6). Increasing K rates increased yields at these locations and tillage combinations. In 2004, the BP and BK (soy) treatment had the lowest yield for DS CT and both CT and NT at BV. This matches many observations in years past which have shown that when there was at least some K applied to corn at DS, yields were usually higher than where all of the K was applied to soybeans (Table 7).
Soybean Yields. The soybean yield responses to P and K rates were small (Table 5), but with NT at both locations, yields increased with increasing P rates. Check yields were lower in most cases than where fertilizer was applied, indicating that P may be becoming limiting. There were no effects of increasing K rates nor was there an effect of annual versus biennial fertilization. This matches observations over several years (Tables 6 and 7).
Economics. Simple economics are shown in Table 8. Gross returns were calculated for the various yields associated with fertilizer treatments using $1.98⁄bu corn and $5.00⁄bu soybeans. In general, differences in treatments are larger for the corn than for soybeans. The four–year returns for the BP and BK (soy) treatment were lowest for CT at DS and BV and averaged $100⁄acre less than the BP and BK (corn) treatment. For NT, both treatments involving BK to soybeans were $70–100⁄acre less than the BK corn treatment or the annual K treatment. The corn versus soybean BP treatments were not different from each other or from the AP treatment. Economically, the BP treatment on corn would be better if DAP were used as it provides a cheap source of nitrogen for the corn.
Results suggest that the best overall method of fertilizing CT may be the biennial application of P and K to corn and letting the soybeans be fertilized by the residual (Table 7) or the annual application of P and K to each crop. Our data also indicate that the biennial application of fertilizer should not be on the soybean crop as there was significant yield loss of corn under both NT and CT when this occurred. For NT, any treatment that resulted in some K fertilizer applied directly to the corn worked best.
Table 2. List of treatments for each tillage.
Table 8. Gross returns, 2001–04.
1 S. A. Ebelhar is an agronomist, Dept. of Crop Sciences, Univ. of Illinois; E. C. Varsa is a professor and J. D. Hernandez is an assistant. professor, Dept. of Plant, Soil and General Ag., So. Illinois Univ.; T. D. Wyciskalla is a researcher, Dept. of Plant, Soil and Gen. Ag., So. IL Univ., nd C. D. Hart is a research specialist, Dept. of Crop Sciences, Univ. of Illinois
