Sorghum Bicolor Hay Options for Limited Irrigation and Rainfed Conditions In Semiarid Subtropical Regions.

Producers in semiarid regions must maximize sorghum forage yield under varying irrigation constraints. Harvest management is often determined by available equipment, which is usually limited to that used for hay production. Annual dry matter yields of furrow-irrigated sorghum forage types [conventional and photoperiod-sensitive sorghum-sudangrass (SS and PS, respectively) and forage sorghum (FS)] all drilled for hay were compared from years of full irrigation (600 mm yr^-1 + 321 and 332 mm May – October precipitation in 1997 and 1998, respectively; two harvests; PS were not included in these years), limited irrigation (300 mm yr^-1 + 295 and 352 mm May – October precipitation in 2002 and 2006, respectively; two harvests), and no irrigation (302 and 275 mm precipitation in 2003 and 2005, respectively; one harvest). A significant year x irrigation x sorghum type interaction existed for annual yield because SS outyielded FS when irrigation was available with irrigation timing and precipitation distribution having a role. Generally, poor regrowth by FS led to the difference; however, with sufficient precipitation, second cut FS yields equaled first cut yields and FS total yields equaled SS total yields (11.60 vs. 12.62 Mg ha^-1 for FS and SS total yields, respectively, P > 0.30). When precipitation was not sufficient, the annual yield difference exceeded 3.50 Mg ha^-1 (8.71 vs. 12.23 Mg ha^-1 for FS and SS, respectively, P < 0.05). Although not significant, FS and PS yields were higher than SS in unirrigated years when July and September precipitation were sufficient. July and September precipitation appeared to have the greatest influence on productivity in each year without regard to irrigation status in addition to the poor regrowth by FS in multiple-cut systems. With irrigation ≥300 mm yr^-1, multiple-cut PS or SS is best. Under unirrigated conditions, single-cut FS or PS are best.