The split injection of water-soluble fertilizers effectively reduces N2O, CH4 and NH3 emissions while simultaneously improving rice yield and harvest index

Mitigating environmental impacts while enhancing grain yield is essential for sustainable rice production. One-time urea deep placement (UDP) has been recognized for its potential to reduce nitrogen (N) loss and improve rice yield. However, this method applies an excessive amount of nitrogen as a basal fertilizer, which increases N₂O emissions during the mid-season aeration (MSA) phase and promotes straw biomass over grain yield, consequently reducing the harvest index (HI). The split injection of water-soluble fertilizers (IF) could present a viable alternative solution. Nevertheless, no studies have yet investigated the environmental and agronomic effects of IF in rice production fields. Therefore, a three-year field experiment was conducted with six treatments: three-split urea broadcasting (BU), one-time UDP (UDP(10:0)), one-time IF (IF(10:0)), two-split IF with a 6:4 ratio (IF(6:4)), two-split IF with a 5:5 ratio (IF(5:5)), and a control without N (CK) in an intensive rice cropping system in China. Results showed that one-time UDP produced the lowest HI and increased N₂O emissions by 146 % compared to BU, due to surplus N provision until the MSA stage. In contrast, two-split IF treatments increased straw biomass by 7 %-9 % while improving rice yield by 13 %-14 % compared to BU and resulting in the highest HI, due to the reduced injection dosage of basal fertilizer and sufficient spike fertilizer injection, which in turn avoided surplus N at the MSA stage, thus decreasing total N₂O emissions by 15 %-28 % compared to BU. All deep fertilization treatments reduced CH₄ emissions by 43 %-67 % compared to BU. All IF treatments produced the parallel highest net economic benefit (NEB) of all treatments. Moreover, IF(6:4) reduced greenhouse gas intensity (GHGI) by 56 % compared to BU, and completely eliminated NH₃ volatilization. In conclusion, a two-split IF with a basal and spike fertilizer ratio of 6:4 is a promising strategy for reducing GHGI and NH₃ emissions while simultaneously improving rice yield, HI and NEB in paddy rice fields. Expanding split IF technology will greatly contribute to the green development of rice production.