Illinois
Fertilizer Conference Proceedings
January 26-28, 2004
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S.A. Ebelhar, E.C. Varsa, 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 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 three 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.
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.
The corn yields for 2003 (Table 3) varied significantly between tillage systems with NT out-yielding CT at BV and CT out-yielding NT at DS. Planting date and stand differences accounted for these effects. Check plot yields were significantly (20–35 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 2003. 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 this season, 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. There were no significant responses to P treatments at any location for any tillage system. Corn yields increased significantly with increasing K rates for the NT site at DS. At DS, it appears that the annual application of P and K to corn (AP and AK) treatment resulted in the highest corn yields for CT, but the BP(soy) and BK(corn) P and K applications resulted in the highest yields for NT. Any time there was at least some K applied to corn at DS, yields were higher than where all of the K was applied to soybeans. At BV, treatments had no effects.
The soybean yield responses to P and K rates were small (Table 4), but in all cases, there was a tendency toward higher yields with the BP and BK (corn) treatment. This indicates that for at least part of the time, fertilizing the soybeans directly had either no effect or the effect was negative. Check yields were lower only for DS CT, again an indication of low soil test K levels at this site, but with NT at BV, check yields were highest. For this treatment, increasing P rates decreased yields.
There were slight differences among treatments for ear-leaf P concentrations (Table 5). For NT at both locations, there was lower corn leaf P levels with check treatments. Increasing K rates significantly increased ear-leaf K levels for NT at both locations and CT at DS, but these differences did not result in yield increases except for the NT field at DS.
Increasing P rates increased trifoliate leaf P levels for CT at DS only (Table 6). There were lower K levels for check plots for both tillage systems and both locations but most dramatic for CT at DS, which was associated with a significantly lower yield. Increasing K rates at BV for NT resulted in significantly higher leaf K levels, but with no apparent effect on yields.
We are still monitoring the long-term aspect of this study. Early indications 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.
1 S.A. Ebelhar is an agronomist, Dept. of Crop Sciences, Univ. of Illinois; E.C. Varsa is a 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. Illinois Univ., and C. D. Hart is a 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.
