Ammonia emission and nitrogen use efficiency with application of nitrification inhibitor and plant growth regulator in a calcareous soil (Karaj, Iran)

Abstract

Ammonia volatilization (AV) is one of the main potential pathways of nitrogen (N) loss and re-deposited ammonia acts as an indirect source of N2O. The question arises how environmentally friendly inputs such as nitrification inhibitors (NI) and plant growth regulators (PGR) can affect AV in calcareous soils, while increasing nitrogen use efficiency (NUE) and crop yield. To answer this question, the effects of applying urea in combination with nitrapyrin (NP) as a NI and gibberellic acid (GA3) as a PGR on daily AV, winter wheat yield and NUE were evaluated. The treatments included a control treatment, urea and urea+NP + GA3 with five replications. Urea and urea coated with NP were applied in three equal split applications, and GA3 was foliar sprayed once. By using 15N-labeled urea and setting up three 15N microplots inside each plot, the nitrogen in the plant derived from fertilizer (Ndff) and the fate of N fertilizer were directly investigated. Ammonia emission factors and estimated values of indirect N2O-N produced from AV in urea and urea+NP + GA3 were 27% and 33%, and 0.38 and 0.45 kg N ha−1, respectively. The grain yield and 1000-grain weight in urea+NP + GA3 treatment were significantly increased by 15% and 13%, respectively, compared to urea. However, urea coated with NP increased AV and decreased Ndff by about 22% and 15%, respectively. The increase in AV caused by the addition of NP was relatively lower than amounts reported in previous studies. This could be due to the split application of N fertilizer on dry soil, the immediate incorporation and the ammonium fixation capacity of illite and vermiculite clay minerals presence in this soil and the reduction of readily available NH4+. The N difference method displayed 21% increase in NUE when urea was applied with NP and GA3 but tracking 15N showed that the combination of urea+NP + GA3 reduced NUE by about 8%. This suggests that NP may not be a viable option for increasing NUE in calcareous soils due to its ability to increase AV. Further research is needed to study the combination of other NIs with GA3 and investigate their effect on AV to simultaneously improve yield and NUE.