Weeds – Friend or foe? Increasing forage yield and decreasing nitrate leaching on a corn forage farm infested by redroot pigweed

Various weed management methods have been tested without complete success and still represent a major nuisance often negatively effecting yields. Therefore, it may be time to change attitudes about weeds and view them as friends of the agroecosystem rather than as foes. For the first time, field experiments were conducted to introduce and evaluate the yield and quality of corn–redroot pigweed mixture forage in a semi-arid region of Iran during 2010 and 2011. A randomized complete block design with a split factorial arrangement of treatments in four replications was subjected to low irrigation and full irrigation regimes. Subplots consisted of a factorial combination of four N levels (0, 150, 300 and 450 kg N ha−1) and two forage mixtures (corn monoculture and corn–redroot pigweed mixture). When averaged over both years, N addition (from 0 to 450 kg N ha−1) increased corn forage yield by 74 and 42% under full and low irrigation regimes, respectively. The forage yield increased by 121 and 69% in the corn–pigweed mixture for comparable treatments. In corn monoculture, the minimum required forage protein (90 g kg−1) occurred only where forage yields were lower than 10 t ha−1, whereas in the corn–pigweed mixture, all the treatments with 90 g kg−1 protein produced yield more than 11 t ha−1. N enhancement (0–450 kg ha−1) increased nitrate leaching loss (NLL) by 158 and 107 kg ha−1 in corn monoculture and 100 and 55 kg ha−1 in the corn–pigweed mixture under full and low irrigation regimes, respectively. However, an alteration in the NLL trend in response to N application grew in both forage types, but the NLL severity was reduced in the corn pigweed mixture. The integration of redroot pigweed (a major weed species on summer crop farms) with corn, rather than its removal, could be recommended to ensure an acceptable forage yield/quality in a poor sandy soil while also reducing N leaching.