Better performance of compound fertilizers than bulk-blend fertilizers on reducing ammonia emission and improving wheat productivity

Compound fertilizer and bulk-blend fertilizer are two major types of fertilizers used in wheat production. However, it remains unclear which type of fertilizers has lower ammonia (NH3) emission and greater wheat productivity. We conducted a field experiment in Hefei, China during 2018-2019 and 2019-2020 wheat growing seasons. The objectives were to assess the effects of three compound fertilizers and three bulk-blend fertilizers on NH3 emission and wheat growth, and elucidate the mechanisms involved. The seven treatments included the control test without N application (CK), bulk-blend fertilizer (BF), bulk-blend fertilizer with bentonite (BFb), bulk-blend fertilizer with humic acid (BFh), compound fertilizer (CF), compound fertilizer with bentonite (CFb), and compound fertilizer with humic acid (CFh). Results showed that compared with bulk-blend fertilizers, the corresponding compound fertilizers decreased total area-scaled NH3 emissions by 10.2%-19.2% and yieldscaled NH3 emissions by 12.8%-23.5%, increased average soil nitrification rate by 7.2%-20.9%, and reduced average soil NH4+ content by 7.2%-16.8% and average soil pH by 0.3%-1.0%. Greater soil nitrification rate in compound fertilizer treatments was partly responsible for the decreases in soil NH4+ content, soil pH, and NH3 emission, and then led to the increases in soil inorganic N content, grain yield, and N use efficiency. Compared with bulk-blend fertilizers, the corresponding compound fertilizers increased grain yields by 2.3%-12.2% and N use efficiency by 8.6%-43.9% (except for CF in 2019-2020). Overall, compound fertilizers had better performances than bulk-blend fertilizers in reducing NH3 emission (area-scaled and yield-scaled) and improving wheat productivity; while adding functional materials (e.g., bentonite and humic acid) and using proper application methods (e.g., banded application) are possible strategies for decreasing NH3 emission from bulk-blend fertilizers.