تأثیر اسیدیته بر هم کاهی یون آهن (III) در کارایی علف کش نیکوسولفورون

In a preliminary test, it was observed that antagonism of nicosulfuron on barnyard-grass and velvetleaf as Fe3+>>Ca2+≥Mg2+. Addition of Fe3+ to the spray carrier reduced pH significantly. In order to study whether it was the presence of Fe3+ or the lower pH that antagonized nicosulfuron, two dose response experiments was conducted at Aarhus University in Denmark in 2011. Factors included were: Fe3+ at three levels (0 (DW), 0.002, and 0.01 M), buffer solution at three levels (no buffer, pH 4, and pH 7), and seven nicosulfuron doses (0, 4, 8, 16, 32, 64, and 128 g a.i. ha-1) in mixture with 0.2% v/w Contact (non-ionic surfactant) at three times replication. Nicosulfuron was applied post emergent at the 2-3 leaf stage of the weeds in a spray volume 160 L ha-1. ED50 doses were estimated on basis of shoot fresh and dry weights. pH variation of herbicide dissolved in DW did not affect barnyard-grass or velvetleaf biomass production, but addition of 0.002 or 0.01 M Fe3+ to the spray solution decreased nicosulfuron performance significantly. However, in the presence of Fe3+ buffering of the spray solution increased herbicide performance significantly. When Fe3+ concentration was 0.01 M ED50 values of 18.7, 3.3, and 1.2 g a.i. ha-1 were estimated for no buffer, pH 4, and pH 7 for barnyard-grass dry weight, respectively. The corresponding ED50 values for velvetleaf were 35.1, 30.0, and 16.9 g a.i. ha-1. Our results indicated that FeCl3 antagonism on nicosulfuron efficacy was due to a reduction in pH and not the presence of Fe3+ ions.