Managing Nitrogen for Crabgrass Hay Production

Much of the forage produced in the subhumid areas of the USA is from cool-season species, which mature and become dormant in early summer. This results in minimal forage produced in mid- to late summer, a time referred to as a “summer slump.” ‘Red River’ crabgrass [Digitaria ciliaris (Retz) Koel.] is a productive warm-season annual that can fill this void, but optimum N fertilizer management for this species is unknown in much of the eastern plains of the USA. We tested N rates of 0, 50, 100, 150, and 200 lb N/acre from two sources, urea and ammonium nitrate, applied as single or split applications, on two cuttings during two years that contrasted in rainfall. A yield plateau was reached just above 100 lb N/acre both years, although yield was 2× higher in the moist year. However, forage fertilized with more than 100 lb N/acre generally had a higher N concentration than forage that received less N. Split application often resulted in less forage with a lower N concentration in the first cutting, but more in the second cutting than a single N application. Responses to N source were small, with application as ammonium nitrate yielding more than urea only in the second cutting at lower N rates.