Tillage and Potassium Placement Effects on Potassium Use Efficiency in a Corn-Soybean Rotation

Illinois Fertilizer Conference Proceedings
January 23-25, 1995

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Tillage and Potassium Placement Effects on Potassium Use Efficiency in a Corn-Soybean Rotation

S.A. Ebelhar and E.C. Varsa¹

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Introduction

Potassium (K) fertilizer placement and mixing within the soil Ap horizon can influence its availability for plant uptake. Other factors affecting uptake are root growth of plants, diffusion rate of K to roots, K fixation, environmental conditions and tillage. Previous work by Kovar and Barber (1987) at Purdue suggested the possibility for optimizing potassium uptake and utilization by corn based on optimal placement and soil mixing of K fertilizers. Fertilizing too large of a soil volume (i.e. broadcasting and mixing in the Ap horizon) could result in the excessive fixation of K in soils which fix K. Fertilizing too small of a soil volume may create a situation where the plant roots, which occupy only about one percent of the soil volume, do not occupy enough of the fertilized volume for optimal fertilizer utilization.

Farmers in Southern Illinois need to utilize no-tillage and reduced tillage management practices on highly erodible land. This limits their ability to mix fertilizer throughout the plow layer. For this reason, farmers need to know how to best fertilize no-till areas to enhance optimum K uptake by plants. By comparing different K placement methods we can determine if stratification, low K utilization and reduced yields would warrant the periodic tillage of these soils.

The objectives of this study are to:

Determine the placement method which optimizes potassium utilization for corn and soybeans under no-till and reduced tillage systems.
Determine effects of using K in starter fertilizer.
Determine effects of potassium rate and placement on potassium uptake and yields of com and soybean.
Evaluate monthly sampling of selected plots at each location to measure variance among samples and seasonal effects on soil test K values.
Determine soil K stratification after 3 years of K placements.
To include a final report at the conclusion of this project to address each of the objectives stated above

Materials and Methods

No-till (NT) and chisel tillage (CT) treatments were used in a corn:soybean rotation at the Dixon Springs Agricultural Center (DSAC) and at the SIU Belleville Research Center (BRC). Before any tillage occurred, soil samples (0-7") were taken on each plot for analysis of pH, P and K. Also, on selected plots, soil samples were taken in 2" increments to 12" and 6" increments from 12-24". These soil samples were analyzed for pH, P, K, Ca, Mg, and O.M.

An average of the top 8" of soil for each location is shown in Table 1. Lime, at a rate of 4 tons per acre was spring applied to the DSAC site before tillage was performed in 1994. A finely ground lime (54% passed #60 mesh sieve) was chosen for quick reaction. Chisel tillage was performed at DSAC on 11 May and at BRC on 13 May. Tillage systems were blocked (whole plots) within each replication. A factorial arrangement of K rates and K placements plus a zero K check (subplots) were randomly placed within each tillage block in a split-split plot design. K rates consisted of 60, 120 and 180 lbs K₂O per acre. K placement methods consisted of surface broadcast (BC), 8-10" surface band (BD) over intended row, surface dribble (DR) 6" to side of intended row, and starter (ST). The starter treatment placed 30 lbs of K₂O 2" to the side and 2" below the seed and was applied at planting. The remainder of the K rate with the starter treatment was surface broadcast. These treatments were applied to both corn and soybeans at DSAC and BRC with 4 replications per crop per location.

The K treatments were applied in solution form by dissolving potash (0-0-60) in water. The treatments were applied after chiseling but before disking to provide some mixing of the fertilizer with the tillage treatment. Corn (Pioneer 3394 variety) was planted on 13 May at DSAC and 23 May at BRC at a seeding rate of 26,000 seed acre. The corn had to be replanted at DSAC on 27 May due to poor stands. Soybeans (Pioneer 9443 variety) were planted on 25 May at DSAC and 26 May at BRC at a planting rate of 10 seeds per foot in 30" rows (175,000 seeds per acre).

Phosphorus fertilizer was broadcast across all plots prior to planting. Nitrogen was sidedressed on corn at a rate of 150 lbs N/acre at 4 weeks after planting. Corn ear-leaves were sampled from each plot at mid-silking and the uppermost fully developed trifoliate leaves of soybeans were sampled at early bloom for nutrient analysis. Grain yields, grain moisture, and final plant stands were measured after physiological maturity.

Results and Discussion

Tissue Data

Increasing K rates increased the K uptake by corn plants at both DSAC and BRC, as measured by the ear leaf K concentrations at silking (Tables 2, 3 and 4). In most cases there was a measurable increase in leaf K above the check plots, especially as the rate increased to 120 lb K₂O/acre. Placement had no significant effect on leaf K (Table 5) nor were there any significant interaction effects involving placement with either K rates or tillage. Soil test K levels were slightly below 200 at each location (Table 1) but it does not appear to be low enough for a placement response. Perhaps the high amount of rainfall received at each location during June kept the roots active in the high K areas such that K never became positionally unavailable to the plants. Tillage also had no significant effect on leaf K at either location, although there was a strong indication of higher K levels with no-till at DSAC. A high degree of variability in soil K levels across the experimental area may account for some of the variability in the leaf K data. We are currently working on the analysis of this data. Once the soil data is obtained, we can use this data for covariance analysis to smooth out the data set.

Corn leaf nitrogen concentrations were also measured at each location. At DSAC, the chisel treatment had higher N levels than no-till, but at BRC the no-till was higher. Also at DSAC, BC and BD K placements increased the leaf N concentrations above where the K was applied either as DR or ST. There appears to be some synergistic relationship between K placement and N uptake, but perhaps these plants grew poorer and produced less dry matter therefore increasing the % of N. We really don't have an answer for this phenomenon at this time.

Increasing K rates tended to increase soybean leaf K at early bloom (Tables 7 and 8). Overall at BRC, BD gave better leaf K concentrations; whereas at DSAC a trend toward higher K levels occurred only with the 1201b K rate. There also appears to be a starter response at DSAC for K levels in leaves for the chisel tillage system only. These leaves tended to have higher concentrations of K at the 60 lb K rate. Soybean leaf N concentrations were unaffected by K rates, placement or tillage, although there tended to be higher concentrations of N under no-till at both locations.

Grain Yields and Plant Stands

Corn grain yields were higher for the BD treatment for the 120 and 180 K rates at DSAC but only for the 601b K rate at BRC (Tables 9, 10, 11 and 12). There seems to be a large increase in corn yields with the ST treatment at BRC for no-till. This could be an indication of a compaction problem causing poor root growth under no-till especially during the low rainfall period in May. There was a trend toward a linear response to K but not significantly different. Again, there appears to be a large variability across the plot areas and with soil sample analysis we may be able to reduce this variability using covariant analysis.

Corn plant stands were affected little by K rates and placement at either location (Table 13). Notill had significantly fewer plants for no-till at BRC but not at DSAC. Again, this could be an indication of a compaction problem at this location or perhaps the soil was cooler and wetter at planting due to excessive rainfall in April at this location. These plant stand differences by tillage at BRC could account for the tillage effect on leaf N at BRC.

Soybean yields and plant stands were hardly affected by any treatments at either location (Tables 12, 13, 14 and 15).

Soil K Data

Much of the soil data, including the monthly sampling of selected plots to a depth of 7", has yet to be analyzed. These results show some indication of a variability across the plot area because of the "intended" tillage differences. These samples were taken prior to any tillage and differences shown are purely random. One should note that even with some history of prior tillage, there is a large degree of stratification at both locations. Also it is interesting to note an increasing soil test K trend below 10" at BRC but not at DSAC. This may be a product of previous tillage effects on nutrient placement below the plow layer or may be inherent to the soil type at each location.

Summary

After only one year of study, it is almost impossible to draw any definite conclusions at this time. Apparently, there were some yield benefits from some of the placement methods but it was very difficult to pick up changes in plant K uptake derived from placement method.