Head and stover contribution to digestible dry matter yield on grain and dual-purpose sorghum crop

Sorghum is becoming an important forage crop in many regions of Argentina due to its productivity and ability to utilize water more efficiently. The use of new grain sorghum hybrids, including dual-purpose types, has generated a need for information on hybrid choice and time of harvest. We studied the yield and quality changes during the grain filling period of grain and dual-purpose sorghums intended for whole-plant forage. Four commercial sorghum hybrids were evaluated in four rainfed environments of Buenos Aires milk basin, Argentina. Forage yield and quality traits were determined on head, stover and whole-plant. Quality measurements were performed by NIRS. No interactions were detected for all variables of forage yield, except for harvest index, in which the environment interacted with maturity. Effects of maturity and hybrid were detected in most variables of forage yield. Particularly, stover dry matter (DM) content had a maximum value at early milk stage and then declined, but whole-plant and head DM content increased throughout maturity. Regarding to quality, head in vitro DM digestibility, head digestible energy and digestible whole-plant DM yield were affected by maturityxhybrid interaction. Effects of maturity and hybrid were observed for most quality traits; however the environment did not influence any of them, except for head crude protein. Both grain and dual-purpose hybrids presented a window for harvest starting at early milk and concluding before physiological maturity. However, whole-plant DM yield and whole plant digestibility reached a maximum at hard dough stage, without changes up to physiological maturity.