Effects of Phosphorus and Potassium Fertilization on Septoria Glume Blotch of Wheat

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Abstract
A single application of P and K in the fall for wheat-soybean [Glycine max] multiple cropping systems is a common practice that can result in excessive fertilization for wheat. The effects of applied and residual P and K and their interactions on Septoria glume blotch, lodging and yield of wheat were evaluated in a minimum tillage system. In 1978 lodging increased as P levels increased but it was not entirely related to increased vegetative growth. Glume-blotch severity was positively correlated with P rates (R2 = 0.76); 1000 kernel weight and grain yield were negatively correlated with P rates, glume blotch and lodging. In 1979 glume blotch ratings decreased at residual soil P levels from 7 to 25 kg/ha (additional P and K were not applied in 1979) and then increased as residual soil P levels increased to 45 and 141 kg/ha. Lower plant height at the 2 lowest P levels probably contributed to greater glume blotch in these treatments. In 1979 1000 kernel weight was inversely related to glume blotch on heads. S. nodorum infection of seed was not significantly related to P, K, glume blotch, yield, or lodging in either year. S. nodorum in seed remaining on the soil surface during the summer declined to nearly zero by Sept. and was not a significant source of inoculum for the next crop. K and P .times. K interactions did not affect any variable measured except grain yield in 1978 when increasing K rates lessened the detrimental effect of applied P. Excessive P enhances glume blotch and reduces yield of wheat, but this relationship is not entirely related to lodging and vegetative growth.

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