Effect of partial replacement of chemical fertilisers by manure on nitrogen loss from wheat-maize farmland in North China

Manure substitution for chemical fertiliser changed soil nitrogen transformation and losses. In order to explore the effects of organic fertilizer replacement of chemical fertilizers on different forms of nitrogen loss and nitrogen balance of agroecosystems, a field trial was conducted continuously for 2 years (2021-2023) at Luancheng Agroecosystem Experimental Station, Hebei Province, and 2 different manure fertilizers (cow and sheep manure) and 4 different replacement ratios field trials were designed: 100%/70% manure replacement of chemical fertilizers, 50% manure replacement of chemical fertilizers, 30% manure replacing chemical fertiliser, 100% chemical fertiliser, to study the differences of different manure replacement ratios on crop yield, different nitrogen losses and and nitrogen balance. The results showed that organic fertilizer substitution reduced soil N₂O emission to a certain extent relative to chemical fertilizer alone, especially reduced the cumulative N₂O emission by 13.86%-51.36% in the 2023 maize season, and reduced ammonia volatile nitrogen loss by 60.51%-65.43% and 13.05%-43.54% in the wheat and maize seasons, respectively, at the same time, but at the same time, it also increased soil CO₂ emission, comprehensive yield and greenhouse gas (GHG) emissions, and the nitrogen balance. CO₂ emissions, combined yield and GHG emissions analysis, manure substitution increased farmland GHG intensity at equal yields, relative to 30% and 50% sheep manure substitution treatments were the lowest environmental greenhouse effect of fertilisation practices at relatively high yields. Manure substitution also reduced the soluble nitrate nitrogen and total nitrogen content of the soil leachate, and the cow dung substitution treatment decreased by 7.45% and 7.50%, respectively, compared with the sheep dung substitution treatment. At the same time, with the increase of manure substitution ratio, the soluble organic nitrogen leaching ratio increased, and the ratio of soil solution organic nitrogen to total soluble nitrogen increased from 22.92% to 77.98%, increasing the risk of soil organic nitrogen leaching. Yields of wheat and maize with manure replacement also increased with the ability of manure replacement to improve soil nutrient-crop synergies. In particular, 30% sheep manure substitution was more beneficial for crop yield and nitrogen utilisation, while 30% cattle manure substitution was more suitable for improving soil nutrient status. The results of the study provide useful insights into the rational use of agricultural waste resources in the combined farming area of the North China Plain.