Feasibility of Reducing Sulfosulforun Herbicide Application in Wheat (Triticum aestivum L.) by Nitrogen Application Management

Wheat is the main crop cultivated through out the world. Around 60 percent acreage of world farms belong to cereal crops from which, 33 percent belong to wheat production. In Iran wheat also is the dominant cereal crop accounting for almost 70 percent of cereal production. Iran wheat production in 2013 was about 14 million tones, and average grain yield 3750 Kg ha-1, is much lower than developing countries such as France ( 6800 Kg ha-1 ), Germany (7000 Kg ha-1 ) UK (7500 Kg ha-1 ) Japan ( 5000 Kg ha-1 ) and China (4900 Kg ha-1. The reasons for low yield include conventional planting methods, costly inputs, improper land preparation, imbalanced fertilizer application, lack of coordination between growers and mill owners, natural calamities and shortage of irrigation water and heavy weed infestation. Among these, poor management of fertilizers and weeds are the major cause of low wheat production in Iran. The use of herbicides for weed control in wheat is a common practice in management of weeds. But environmental and economical aspects, uncertainty in the long-term efficacy of chemical weed control methods are the most important issues that have caused researchers and farmers seeking to introduce an alternative to herbicides or to reduce the use of herbicides. Among herbicides, sulfonylurea’s such as sulfosulforun is one of the most important herbicides in wheat field. However, sulfosulforun is an effective herbicide for weed control. But its active soil residual, may damage rotational crops. Due to importance of nitrogen fertilizer management in wheat yield improvement, present study was designed to investigate the effect of nitrogen fertilizer application methods on weed management of wheat and reducing sulfosulforun herbicide under agro-climatic conditions of Mashhad, Iran.
In order to evaluate sulfosulforun reducing dose, by nitrogen application management, an experiment was performed as split factorial plot, based on randomized complete block design with three replications at research farm, Faculty of Agriculture, Ferdowsi University of Mashhad, in 2012. Treatments included, nitrogen application methods (Broadcast and Band), the amount of nitrogen application (100, 200 and 400 kg ha-1 )(46% urea source) equal to 46, 92 and 184 kg ha-1 nitrogen per hectare, as complete factorial plots and sulfosulforun doses (100, 75 and 50 % of recommended dose (26.6 g (75% EC (emulsifiable concentrate)) as sub plots, applied at wheat tillering stage. Weed density and relative frequency were recorded 149, 177 and 210 days after wheat planting. Wheat biomass and seed yield per 1 m-2 were recorded at the end of the experiments. Analysis of variance of data was carried out with SAS software and for means comparison LSD (p≤0.05) test was used.
Results showed that band application of nitrogen, reduced weed density and weed biomass significantly. By increasing nitrogen dose, mentioned parameters were increased significantly in both methods on nitrogen application. The highest weed density (29.27 plant m-2) were observed when sulfosulforun was not applied and the method of nitrogen application was broadcasted. The lowest weed density (12.78 plant m-2) observed at solfosulforun recommended dose and nitrogen band application treatment. The method of nitrogen application affected the amount of solfosulforun application. Based on the results, the effect of sulfosulforun at 75% and 50% of the recommended dose, didn’t effect significantly (p 0.05) on weed control when nitrogen applied in band with solfosulforun at recommended dose on weed control when nitrogen applied broadcast. Similar results were observed for wheat seed yield and wheat biomass. Wheat seed yield (343.40 g m-2) and wheat biomass (1141.50 g m-2) at solfosulforun recommended dose, when nitrogen applied in band, was not significantly different from 75% recommended dose of solfosulforun and nitrogen broadcast application method.
Based on the results of experiment, the amount of nitrogen and its application method concludes an acceptable approach for wheat integrated weed management. It can optimize nitrogen fertilizer and solfusulforun herbicide usage, which are the main concerns in wheat production economically and ecologically. However nitrogen band application reduced the amount of nitrogen fertilizer and solfusulforun herbicide. Due to various factors affecting the competitive relationship between weeds and crops, it is suggested that in future the use of other herbicides, in different places and different crops to be considered.