Nitrogen Management Affects Sorghum Grown for Grain and Forage

Producers have to maximize crop production to stay economically viable. After grain harvest, sorghum [Sorghum bicolor (L.) Moench] stalks may be utilized for animal feed. The objective of this study was to determine the effect of fertilizer N rate and timing on yield, N concentration, and N removal in grain and the remaining stover of a stay-green sorghum hybrid harvested immediately after grain or left until a killing frost. Sorghum grain yield responded to N rates up to at least 120 lb/acre, but was unaffected by fertilizer N timing. Nitrogen removed in the grain increased linearly with N rate and was about 25% of the applied fertilizer N. Stover yield and N removal was reduced by applying two-thirds of the fertilizer N as a sidedress at the eight-leaf stage compared with applying two-thirds or more N preplant. Stover yield was greater when cut immediately after grain harvest than after a killing frost partly because of poor post-harvest growth. Small amounts of post-harvest plant growth resulted in greater stover N concentration, especially at higher N rates. Total N removal by stover and grain responded linearly to increasing N rates and was greater if stover was harvested after grain harvest and if post-harvest growth did not occur. Nitrogen management is important for sorghum grain, as well as for stover used for feed.