The effect of nitrification inhibitor DMPP and fertilizer nitrogen rate on agronomic characteristics in wheat

Nitrogen (N) more than other mineral essential nutrients is required for plant growth and its shortage limit the growth and yield of crops. Nitrogen losses in different ways, reducing soil fertility, as well as increasing the yield potential of new cultivars, including bread wheat cultivars (Triticum aestivum L.), has increased the need for N fertilizer application. Today, using fertilizers containing nitrification inhibitors has been considered as one of the ways to reduce N losses and optimize N nutrition of crops. However, no study has been carried out in this context under field conditions in Iran.

In this study, the effects of different sources of N include: a) ammonium sulfate, b) ammonium sulfate containing nitrification inhibitor DMPP, c) urea, and d) ammonium sulfate containing DMPP plus urea at 50:50, and different rates of fertilizer N including 0 (control), 50, 125 and 200 kg N ha-1 on yield and yield components of wheat were evaluated. The experiment was conducted as a factorial based on randomized complete block design with four replications in Gorgan University of Agricultural Sciences and Natural Resources.

The results indicated a linear and significant increase in yield components, grain and biological yield and reduction in harvest index with increasing nitrogen fertilizer rate. The mean grain and biological yield in control (0 kg N ha-1) were 3882.2 and 8016.2 kg ha-1. A kilogram increase in nitrogen fertilizer resulted in 13.5 and 30.55 kg increase in grain and biological yield, respectively. Grain and biological yield were reached to 6477 and 13964 kg ha-1 , respectively, in the treatment of application of 200 kg N ha-1. According to the results of this experiment, grain yield changes were mainly due to changes in the number of spikes per square meter and partly due to changes in the number of grains per spike, and grain size fluctuations had no considerable effect on grain yield changes. Grain yield in ammonium sulfate containing DMPP was 2.8% and 4.2% higher than urea and ammonium sulfate, respectively. But, this increase was not statistically significant. In terms of grain yield components, biological yield and harvest index, there was no difference between nitrogen fertilizers containing DMPP and conventional fertilizers.

Under the environmental conditions of this experiment, despite a significant linear increase in yield components, and grain and biological yield of wheat in response to increasing nitrogen fertilizer rate, the use of nitrogen fertilizer containing nitrification inhibitor did not result in significant improvement in grain yield probably due to soil characteristics, low number of irrigation (only two time), irrigation time (late in the growing season of wheat), as well as the spliting and application of fertilizer in three stages. Therefore, due to the high cost of these fertilizers, their use is not recommended.