Comparative Responses of Early-maturing and Late-maturing Soybean Culitvars to an Irrigation Gradient.

Drought stress reduces late-maturing soybean [Glycine max (L.) Merr.] yields in Arkansas and the mid-southern USA. Irrigated early-maturing soybean cultivars with narrow rows and high population have similar yields to late-maturing soybean cultivars, but require less irrigation. However, there is little information on how early-maturing soybean cultivars will respond to suboptimal irrigation compared with late-maturing soybean cultivars. We hypothesized that early-maturing soybean cultivars would reduce yields more than late-maturing soybean cultivars when drought occurs. A field study was conducted at Fayetteville, AR to evaluate yield responses of early-maturing and late-maturing soybean cultivars to seven irrigation treatments from optimal to minimal irrigation. Two soybean cultivars from each of the maturity groups (MG) I, II, III, IV and V were used. Under optimal irrigation conditions, AG2802 (MG II) and S31-V3 (MG III) produced similar yields to MG IV and V cultivars, but required 18% and 20% less irrigation, respectively. Yield was regressed as a function of seasonal irrigation plus rainfall from emergence to R6 (full seed development) using cultivars and MGs as covariates. There was no difference between cultivars within each MG in yield response to seasonal irrigation plus rainfall, but MGs differed significantly. Yields of MG I, II, III, IV and V all decreased linearly as total amount of irrigation plus rainfall from emergence to R6 decreased, but regression slopes tended to be steeper for early MGs. These results demonstrate that yields of early-maturing soybean cultivars all reduced more than late-maturing soybean cultivars when drought occurred.