Illinois Fertilizer
Conference Proceedings
January 27-29, 2003
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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 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 to 15 bu/acre yield advantage over biennial P applications in a no-till system, but did not respond under chisel tillage (Rehm, 1997). Clearly, additional information needs to be 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:
1) 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
2) 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 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 through 15 represent all possible combinations 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 or 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 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.
The corn yields for 2002 (Tables 3 and 4) did not vary significantly between tillage systems. Check plot yields were significantly lower than the other treatments only for CT at DS, indicating that the other fields still had enough residual P and K to support yields in 2002. It should be pointed out that there was too little rainfall at BR during the growing season, and yields will not be reported. 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
generally increased with increasing K rates, especially for the low soil test
site at DS. It appears that the biennial application of P and K to corn (BP
and BK) resulted in the highest corn yields for CT, but the annual P and K applications
(AP and AK) resulted in the highest yields for NT.
Soybean Yields
The soybean yield responses to P and K rates were very small and non-significant
(Tables 3 and 5). Check yields
were lower only for DS CT, again an indication of low soil test K levels.
Corn Ear-leaf P and K Composition
There were very slight differences among treatments for ear-leaf P concentrations
(Tables 6 and 7). Increasing
P rates at DS for CT increased the ear-leaf P concentrations. Lower ear-leaf
K levels for DS and BV CT were associated with lower grain yields for these
studies. Increasing K rates significantly increased ear-leaf K levels for CT
at both locations, resulting in an increase in yield.
Trifoliate leaf P and K Composition
Increasing P rates increased trifoliate leaf P levels for CT at both locations (Table 8). Lower K levels for check plots for CT at DS were associated with a slightly lower yield. Increasing K rates at DS for CT and 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
9). 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 when
this occurred. For NT, biennial application of P and K to corn would work, but
the best treatment was annual P and K applications to both corn and soybeans.
However, when one fertilizes with a variable-rate spreader to vary P and K rates
across the field, it would require two trips across the field each year (one
for P and one for K) if the variable-rate spreader were single ingredient.
1S.A. Ebelhar is an agronomist
and A.H. Anderson is a research specialist, Department of Crop Sciences, University
of Illinois; E.C. Varsa is an associate professor, Dept. of Plant, Soil and
General Ag., So. Illinois University; T.D. Wyciskalla is a researcher, Dept.
of Plant, Soil and General Ag., So. Illinois University; C.D. Hart is a visiting
research specialist, Dept. of Crop Sciences, University 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
