Efficiency of Nitrification Inhibitor DMPP under Different Levels of Wheat Straw Using 15N Tracer Isotope

Regarding the necessity of increasing organic matter in agricultural land (through application of crop residues to the soil) and due to net immobilization and temporary shortage of nitrogen sources in the soil, conducting more research on utilization of N resources is inevitable. In order to evaluate the effects of nitrification inhibitor DMPP on soil nitrate and ammonium accumulation and wheat yield production and fertilizer use efficiency, a greenhouse experiment was carried out in a factorial randomized complete block design (CRD) in three replications during two consecutive years (2014-2015). The first factor was three levels of wheat straw (zero, five and ten tons per hectare) and the second factor was three fertilization treatments (no-fertilizer, labeled 15N ammonium sulfate, and 15N fertilizers containing nitrification inhibitor). The results showed that DMPP could delay conversion of ammonium to nitrate for more than a month. The use of wheat straw (treated with ammonium sulfate) reduced yield and nitrogen fertilizer use efficiency. But, the addition of DMPP (mixed with ammonium sulfate fertilizer) changed the above process and led to increased yield and nitrogen fertilizer use efficiency. By the application of DMPP inhibitor, ammonium concentration in the soil (derived from fertilizer) increased and, consequently, soil microorganisms benefitted from ammonium nutritional source. Considering that absorption of ammonium is preferred by these microorganisms, it seems that presence of large amounts of ammonium affect microorganisms growth and, consequently, their competition with plant will decrease. The outcome of the above actions is over in favor of the plant and reduction in yield and nitrogen use efficiency (due to the net immobilization) partially adjusted (or neutralized).