Finding the optimal fertilizer type and rate to balance yield and soil GHG emissions under reclaimed water irrigation

Water and inorganic nitrogen fertilizer have a notable impact on crop yield and greenhouse gas (GHG) emissions from soil. Reclaimed water (RW) is widely used for irrigation when there are shortages of water resources. It is very important to control yield and greenhouse gas emissions by fertilization under reclaimed water irrigation (RWI). The study consisted of a continuous test that evaluated three types of fertilizer treatments (urea, amine, and slow-release fertilizer) and a no-fertilizer treatment under three-year RWI and four fertilizer levels (150, 200, 250 and 300 kg.N.ha^-1) under one-year RWI to determine the best fertilizer to support maize production and reduce GHG (CO₂ and N₂O) emissions from soil; further, the applicability of RWI in the DNDC model was verified. For many years, GHG emissions under RWI showed an increasing trend, but the effect was not significant. A strong correlation was found between the GHG emissions flux and fertilizer amount, and a threshold fertilization amount existed between 220 and 260 kg.N.ha^-1 that minimized yield-scaled N₂O emissions and the ratio of GHG cumulative emission to yield (GHG/Y). The results indicated that the optimal amounts of SF and UF under RWI were 240 and 225 kg.N.ha^-1 by second-order equation and the DNDC model, respectively, and the rate better balanced the yield and GHG emissions.