Fig. 2 Panel A: Soybean yields from 1972 to 1997 in the irrigated and rainfed production systems in Nebraska, plus U.S. yields. Panel B: A comparison of irrigated corn and soybean yields in Nebraska from 1972 to 1997. All trend lines in these two graphs were derived from linear regression analyses as displayed in the legend boxes (Y = yield, T = year)

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