Irrigation and Other Management Effects On Soybean Yield.

With occasionally dry conditions, including the widespread drought across much of the U.S. Corn Belt in 2012, the response of soybean to irrigation, and whether or not irrigation affects responses to other management inputs, is of considerable interest.  Over seven irrigation trials conducted at several locations in Illinois, we found yield responses to irrigation ranging from an increase of 510 kg/ha (12.9%) to a decrease of 321 kg/ha (6.3%).  While four of the trials showed a positive yield response, at only two sites were these statistically significant.  One of three negative responses was significant. Irrigation was most effective when precipitation was much below normal in August, especially where soils had lower water-holding capacity.  The effectiveness of different management inputs was not affected by irrigation.  Input combinations that included fungicide typically proved the most effective at increasing yield; fungicide produced significant yield increases in four of seven trials, and increased yield by 243 kg/ha across all sites.  Nitrogen application significantly increased yield in two trials.  There was no synergism between fungicide and N in their effect on yield. These trials have shown that though irrigation can increase yield modestly, its effect on yield over a range of sites was not very consistent.  For those who do irrigate, it does not appear that changing other management inputs will enhance the response to irrigation.