Searching for synergism in dryland cropping systems in the central Great Plains

Previously published research reported a “synergistic effect” of corn (Zea mays L.) on winter wheat (Triticum aestivum L.) and proso millet (Panicum miliaceum L.) water use efficiency (WUE) when corn (C) was the preceding crop for dryland cropping systems in the central Great Plains, i.e., less water was required to grow a unit of wheat (W) or proso millet (M) when corn was the preceding crop. A similar synergistic effect of field pea (Pisum sativum L.) for seed (P) or forage (FrP) on winter wheat water use and yield has also been reported. The purpose of this study was to examine a long-term cropping systems yield and water use data set in order to determine if WUE is altered by rotational sequence (i.e., previous crop). Yield and water use data (computed by water balance using neutron probe and time-domain reflectometry measurements) were acquired from a crop rotation study conducted at Akron, CO from 1996 to 2011 using the following rotation sequences: W-fallow (F), W-C-F, W-M-F, W-C-M, W-M, W-W-C-M,W-C-M-F, W-C-M-P, W-C-M-FrP and W-M-Sunflower (S, Helianthus annuus L.)-F. Water use efficiency was computed as grain yield divided by water use. Changes in WUE due to crop rotation were also evaluated based on slopes of water use/yield production functions. The analysis of these data did not support a conclusion that corn has a synergistic effect of improving WUE of wheat or millet production nor the conclusion that pea has a synergistic effect on wheat.