Atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] retention by standing and flat wheat (Triticum aestivumL.) stubble was determined over time. Immediately following an application of 1.7 kg/ha atrazine, approximately 60% of the herbicide had been intercepted by the stubble and 40% was found in the underlying soil. After 3 weeks and 50 mm of rainfall, atrazine on standing and flat stubble had decreased by 90 and 63%, respectively, while atrazine in the soil increased nearly twofold. No atrazine was found in stubble 9 weeks after application, and only 17% of that originally applied remained in the upper 4 cm of the soil. Successive alternate-day applications of 12.5, 25, or 50 mm water on14C-atrazine retention by stubble was determined. Atrazine loss from stubble was greatest during the first water application, but there was no linear relationship between water application rate and retention of the herbicide. Atrazine loss from stubble decreased significantly following the second water application in all treatments. The amount of water applied did not influence atrazine loss following the third washing. Subsequent loss after the fourth, fifth, sixth, and seventh washings was not significant at any water application volume. After the seventh washing, atrazine residues were greatest on stubble which had received the least amount of water.

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A three-year ®eld experiment was undertaken to evaluate the effects of tillage methods on grain yield and yield components of wheat (Triticum aestivum) in continuous cropping. The experiment was conducted on a Ramjerd, ®ne, mixed, mesic, typic Calcixerepts soil. Wheat was sown: (1) after burning residues followed by conventional tillage, (2) after complete residue removal followed by conventional tillage, (3) after soil incorporation of residues followed by conventional tillage, (4) into untilled residues, (5) using chisel seeder after ®eld irrigation, (6) using chisel seeder plus herbicide application, and (7) after disking. Residue burning and removal increased spikes per square metre, grain per spike, 1000±grain weight, grain yield and harvest index compared with other treatments. This was due primarily to weed interference and lack of uniform crop establishment in the presence of residues. Reduced tillage methods retained more residues on the soil surface, which provided unsuitable conditions for crop emergence and growth. The incorporation of residues led to a build up of carbon in the soil, with lower grain yields compared with residue burning and removal, but these yields were higher than those of chisel-seeded plots.

Field studies were conducted to investigate the effects of different rates of herbicides on weed control, agronomic characteristics, and quality of sugar beet at Shiraz, Iran, in 2000 and 2001. Separate and combined applications of herbicides, including 14 combinations and different rates of grass and broadleaf herbicides, at two rates were used. Herbicides reduced weed biomass compared with the weedy check. In both years, maximum reduction in weed biomass was observed with desmedipham plus phenmedipham plus ethofumesate at 0.23 + 0.23 + 0.23 kg ai/ha and desmedipham plus phenmedipham plus propaquizafop at 0.46 + 0.46 + 0.1 kg ai/ha. Efficacy of grass herbicides was reduced when they were combined with pyrazon. Highest crop injury in both years was observed with desmedipham plus phenmedipham plus ethofumesate at 0.23 + 0.23 + 0.23 kg/ ha. Highest and lowest root yields in both years were produced in weed-free and weedy check plots, respectively. All herbicide treatments produced lower sugar beet yields than the hand-weeded check. Of the herbicide treatments evaluated, the highest sugar beet yields were with desmedipham plus phenmedipham plus propaquizafop at 0.46 + 0.46 + 0.1 kg/ha in 2001 and with desmedipham plus phenmedipham plus ethofumesate at 0.23 + 0.23 + 0.23 kg/ha in 2000. Sucrose content and other sugar beet brei characteristics were not affected by the herbicide treatments.