NITROGEN, PHOSPHORUS, AND POTASSIUM EFFECTS ON GRAIN SORGHUM PRODUCTION AND STALK ROT FOLLOWING ALFALFA AND BIRDSFOOT TREFOIL

Abstract

Grain sorghum [Sorghum bicolor (L.)], grown on the often infertile claypan soils of the eastern Great Plains, requires attention to soil fertility. Experimental objectives were to determine the effects of phosphorus (P) and potassium (K) fertility levels, N application, and legume residual on grain sorghum production and stalk rot. Following alfalfa and birdsfoot trefoil, first-year sorghum yield was 7 Mg ha⁻¹ and not affected by N fertilizer. In subsequent years, yield increases due to N were less than 20%. Sorghum yield increased at low P and K rates, especially with nitrogen (N) fertilization and was greater following birdsfoot trefoil than following alfalfa. In 1995 when fertilized with N, lodging and stalk rot severity were increased by P and reduced by K. In 1996, stalk rot severity was reduced by K fertilization. Grain sorghum, grown after legume crops, required minimal levels of P and K, especially when N fertilizer was added.

Keywords:

• fertilization
• legumes
• disease

ACKNOWLEDGMENTS

Contribution no. 10-064-J, Kansas Agricultural Experiment Station. This research was funded in part by the Kansas Fertilizer Research Fund and the Foundation for Agronomic Research. The authors would like to acknowledge and thank David Kerley and the late Phillip Markley for their assistance with this project.