Phosphorus, potassium, chloride, and fungicide effects on wheat yield and leaf rust severity

Plant nutrition and disease suppression are among the most important manage ment tools for producers of hard red winter wheat (Triticum aestivum L.) in the central and southern Great Plains. This study was conducted to examine the effects of phosphorus (P) (0, 15, and 30 kg ha(-1)) and potassium 0() (0, 37, and 74 kg ha(-1)) fertilization, foliar fungicide application, and cultivar disease tolerance on wheat yield, yield components, and severity o f leaf rust (Puccinia triticina Eriks.). Compared with no P, fertilizing wi th P increased yield by as much as 60% (>1.3 Mg ha(-1) increase). Yield of cultivars susceptible to leaf rust was nearly 0.6 Mg ha(-1) less without K than with K fertilization. Fungicide application resulted in mean yields of 4.8 Mg ha(-1) for both resistant and susceptible cultivars, however, yield of susceptible cultivars was suppressed more than yield of resistant ones without fungicide. Although P fertilization had a moderately suppressive ef fect on leaf rust, the increased yield was primarily due to production of a bout 50% more heads m(-2) apparently from more prolific tillering. Similarl y, K fertilization appeared to reduce leaf rust severity and improve yield by increasing kernel weight, but this response may have been related partia lly to chloride (Cl) in the KCl fertilizer. Correlations suggested that imp roving dry matter production and N, P, and K uptakes at the boot stage by P and K fertilization can reduce leaf rust severity later in the growing sea son and increase wheat grain yield. These results indicate that especially P fertilization, but also K fertilization and fungicide application, are im portant management tools for reducing disease and increasing winter wheat y ield.