Soybean maturity group selection: Irrigation and nitrogen fixation effects on returns

Soybean (Glycine max [L.] Merr.) production tradeoffs across maturity group (MG) I through V were analyzed using data on irrigation applied, harvest index (HI), yield, and nitrogen (N) fixed in crop residue at two locations and a range of years. Water use efficiency (WUE), defined as grain yield/water (irrigation and rainfall) and nitrogen (N-2) fixation prediction equations allowed analysis of tradeoffs between irrigation use and N-2 fixation by MG under both irrigated and non-irrigated conditions. Analysis of partial returns by year and location revealed; (i) no consistent optimal MG choice under irrigated conditions; (ii) that irrigated soybean always outperformed non-irrigated production; and (iii) that non-irrigated MG V soybean had higher yields than earlier MG. Further, WUE, averaged across location and study years, was highest for MGs II and III with less loss in yield potential with restricted irrigation compared to MG IV and V. N-2 fixation was inversely related to HI and positively correlated with Y. MG V compared to MG I, II and III thus displayed multi-fold increases in N-2 fixation regardless of irrigation. Adding N fertilizer value for a subsequent crop from N-2 fixation and potential implications of net GHG emissions to partial returns did not modify optimal MG choice. (C) 2015 Elsevier B.V. All rights reserved.