Effect of potassium rate and placement on soil test variability across tillage systems

Experiments were conducted from 1994 through 1996 at the Dixon Springs Agri cultural Center of the University of Illinois and the Belleville Research C enter of Southern Illinois University to evaluate potassium rates (56, 112, and 168 kg K ha(-1) as liquid KCI formulations) and placement methods in a corn (Zea mays L.) and soybean (Glycine mau L.) rotation using chisel till age (CT) and no-tillage (NT) practices. Four placement methods were used: s urface broadcast, surface band (25 cm wide band over each row), surface dri bble (15 cm from each row), and banding 28 kg K ha(-1) las a starter) 5 cm to the side and 5 cm below the planted seed (remainder of the K rate was su rface broadcast). In April of 1997, at the Belleville Research Center only, soil cores in incremental depths of 0-5, 5-10, and 10-20 cm were collected in a 5-cm spaced transect across and perpendicular to the two center rows of plots of each placement method that received 112 kg K hdl. Four transect s were taken from each plot with the soil composited by layer and by positi on across the transect and relative to the rows. Nutrient stratification wa s evident with both the chisel and no-tillage systems. However, placements using no-tillage showed much higher levels of K in the 0-5 cm depth than ch isel, but the placements modified by chiseling (CT) had higher K levels in the 5-10 cm depth. This reflected the effect of mixing of the applied K int o the soil with tillage, whereas, the higher K levels at the surface with N T reflected no fertilizer disturbance. All of the placement methods had hig her K levels near the row and the levels decreased toward the middle of row s, even for the broadcast treatment. This was an indication that K was bein g redeposited near the row after the plants matured. This could also have b een associated with leaching from the plant after physiological maturity, o r from the breakdown and release of K from the plant after harvest, or both . The starter treatment with chisel tillage showed a definite K band near t he row in the 5-10 cm depth that did not show up in the no-tillage plots. T his may have been an indication that crops in the no-tillage treatment util ized more of the starter K than chisel tillage, perhaps because of a more r estricted rooting environment in no-till. The banded and dribble treatments with no-till showed very sharp peaks in the 0-5 cm depths due to a lack of incorporation via tillage, but this may also indicate a less efficient sys tem for K uptake later in the season when surface roots are less active in nutrient uptake.