Tillage and potassium placement effects on potassium utilization by corn and soybean

Farmers in the lower corn belt region of the United States need to know how to fertilize soils in order to optimize the efficiency of potassium (K) us e by plants under different tillage systems and with high yield management. A field study was conducted from 1994 to 1996 at the Dixon Springs Agricul tural Center (DSAC) on a Bonnie silt loam (fine-silty, mixed, mesic Typic F luvaquent) soil and at the SIU Belleville Research Center (BRC) on a Herric k silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) soil. No-till ( NT) and spring chisel tillage (CT) systems were compared in a corn (Zea may s L.)-soybean (Glycine max L.) rotation. Within each tillage system, K rate s of 56, 112 and 168 kg K ha(-1) as potassium chloride were combined with f our placement methods that included surface broadcast, 25-cm surface band o ver the intended row, surface dribble 15 cm to the side of the intended row , and starter placement of 28 kg K ha(-1) 5 cm to the side and 5 cm below t he seed at planting (with the remainder of the K surface broadcast). The br oadcast K placement most often produced the lowest whole plant K compositio n of corn or soybean tissue when sampled within a month after emergence. Th is indicated that the broadcast treatment was less efficient than other pla cement methods in providing K in the early stages of plant development. How ever, by the reproductive stage of development, there were no differences i n leaf K concentrations among the various placement methods for either crop . Increasing K rates almost always increased leaf K concentrations and usua lly increased early plant growth and yields. Early plant growth and grain y ield were affected to a greater degree in corn than soybean. Soybean yields appeared to maximize at 56 kg K ha(-1), whereas corn often showed higher y ields (although not always significant) with K rates of 112 and 168 kg ha(- 1). Corn usually requires more K than soybean, which would explain its grea ter responsiveness to K. For corn, the placement method of K was not as cri tical as rate, even for no-till, across the six site-years of this study. L ower yields occurred in 1996 at both locations with the long term banding o f K fertilizers over the intended rows of soybean. This is in contrast to a yield benefit from surface banding at other locations or crops as reported in the literature. Weather problems related to a wet spring followed by dr y conditions late in the season may have contributed to the atypical result s in 1996. These weather problems probably either lead to larger plants ear ly which ran out of water late in the season, or higher accumulated salt co ncentrations in the root volume which reduced water uptake late in the seas on.