Effect of nitrogen, farmyard manure and metribuzin on nitrogen transformation

In recent years, several types of herbicides are being used to control weeds for higher crop production. However, indiscriminate use of herbicides may affect the activities of beneficial soil microorganisms and consequently nitrogen transformation processes in soils. Therefore, a laboratory incubation study was conducted to investigate the effect of weedicide (metribuzin) on nitrogen transformation in sandy loam soil. The NH₄-N content in soil increased up to one week of incubation in all the treatments and then declined thereafter. Application of metribuzin helped in releasing higher NH₄-N content in soil than control at first week of incubation that remained visible up to 5th week. The NO₃-N content in soil increased after first week of incubation under all the treatments, but increase was relatively higher between 5th and 7th week of incubation and it became stable onwards. Application of nitrogen and farmyard manure (FYM) increased NO₃-N content in soil and maximum increase was observed between first and second week of incubation. Application of metribuzin caused decrease in NO₃-N content in the soil. The increase in ammonification with a concomitant decrease in nitrification indicated that nitrifying bacteria were sensitive to the application of metribuzin.