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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Winter 1995 Pioneer 3732 Pioneer 3737 190 180 170 160 150 140 130 120 110 100 90 Yield - bu/A 0 40 80 160 K2O applied - lbs/A Figure 1. Corn yield in a ridge-till planting system as affected by hybrid and rate of applied potash, Oldham and Rehm, University of Minnesota, 1989. Larry Oldham and Dr. George Rehm Does Pattern of Root Development Explain Variances in Crop Response? Minnesota ridge-till studies suggest corn hybrids with shallower root system patterns may respond better to potash applications in early growth stages. Summary: Research conducted on ridge-till systems in 1991-92 seems to point to differences in development of corn root systems as an explanation for differing responses of young corn plants to potassium applications. In the early growth stages, hybrids with shallower root development patterns are better able to tap potassium close to the soil surface. However, differences in root development between hybrids seem to disappear as corn grows throughout the season. Other factors, such as changes in bulk density of soil, and changes in potassium chemistry as affected by moisture and temperature, may also be involved. More research is needed. Before 1988, several farmers who used the ridge-till planting sys tem suspected that corn yields were declining in comparison to the yields of neighbors who used conventional planting systems. The decline was noted more frequently after the ridge-till system had been used for three or four years. There were theories for this decline, but no easy explanations. In 1988, potassium deficiency symptoms appeared on corn grown in many ridge-till fields. These symptoms appeared even though soil tests for potassium were in the high or very high range. The severity of the symptoms also varied with hybrid. Thinking that reduced uptake of potassium resulting in visual deficiency symptoms could be the cause of the declining yields, research was initiated in 1989 to evaluate the effect of banded potash fertilizer on corn production in ridge-till systems. That research has continued through the 1994 growing season. Hybrid responses differ Initial research was started in Murray County in southwest Minnesota in the fall of 1988. Potash was knifed into the center of existing ridges to supply 40, 80, and 160 lbs/A of potassium. A coulter and knife assembly was used to place the fertilizer 3.5 to 4 inches below the soil surface. The assembly was also passed through the control plots where no fertilizer was used. The optimum rate of potash for Pioneer 3732 was 80 lbs/A of potassium. This hybrid also showed the most severe potassium deficiency symptoms (Figure 1). For Pioneer 3737, a hybrid that did not show potassium deficiency symptoms, the use of 40 lbs/ A of potassium produced the optimum yield. The soil test for potassium was 145 ppm, a high test by University of Minnesota definitions. Results from the research in Murray County show that banded application of potash in the center of existing ridges is a management tool that can be used to increase yields in these planting systems. There was, however, no easy explanation for the problem. It appeared that some hybrids were able to use soil potassium much more easily than others. This suggested there must be differences in the development of root systems in ridge-till as compared to conventional-till systems. Variance confirmed In 1990, potassium deficiency symptoms appeared on corn grown in
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