Abstract:

The effects of urease and nitrification inhibitor, and coated urea on soil nutrients and sunflower yield were evaluated in the Hetao Irrigation Area. An in-situ field experiment was established and six treatments with four replicates were set up, including no fertilization (Control), conventional N application (NPK), NPK plus urease inhibitor HQ and nitrification inhibitor DCD (HDN), NPK plus urease inhibitor NBPT and nitrification inhibitor DCD (NDN), 50% urea plus 50% coated urea (PCU1), and 30% urea plus 70% coated urea (PCU2). The results indicated that compared to the NPK treatment, HDN and NDN treatments significantly increased soil organic carbon (SOC), total nitrogen (TN), available phosphorus (AP), available potassium (AK) and inorganic nitrogen (IN) content by 2.4%-5.0%, 11.6%-12.1%, 36.7%-50.0%, 12.4%-13.2% and 24.0%-56.6%, respectively. In contrast, application of partial substitution of urea with coated urea did not affect SOC, TN, AP, AK and IN content. HDN and NDN treatments also increased soil dissolved organic carbon (DOC) content by 7.3% to 10.2%, while the application of coated urea did not have any effects on DOC content. Aboveground biomass (AGB) of sunflower was increased in HDN, NDN and PCU1 treatments when compared to the NPK treatment, in which HDN treatment resulted in the highest AGB. Compared to the NPK treatment, the HDN, NDN and PCU1 treatments significantly increased sunflower yield and nitrogen use efficiency, with the highest increase observed in the HDN treatment. In contrast, PCU2 treatment had no significant effect on sunflower yield and reduced nitrogen use efficiency. The application of conventional urea in combination with urease and nitrification inhibitor is a crucial management practice for enhancing soil nutrient retention capacity and sunflower yield in Hetao Irrigation District.

Key words: inhibitors, coated urea, soil nutrients, sunflower yield, nitrogen use efficiency, Hetao irrigation area