Effects of substituting chemical nitrogen fertilizer with organic fertilizer on apple yield, quality, and greenhouse gas emissions

Objectives We studied the effects of consecutive replacement of chemical fertilizer nitrogen with organic fertilizer on apple yield, quality, and the greenhouse gas emission and warming potential of orchard soil in field experiments during five consecutive years, so as to provide a theoretical and technological basis for high quality and environmental friendly apple production.

Methods A field experiment was conducted in the orchard of Xingtai City from 2016 to 2021, using 13-years-old Fuji apple trees as test materials. The four treatments were local farmers’ practice (CT), recommended fertilization (OPT), replacing 25% and 50% of chemical nitrogen fertilizer in OPT with organic fertilizer (OPT25 and OPT50, respectively). Apple yield and quality were measured every year, and the greenhouse gas emissions were monitored in the fifth year.

Results 1) Compared with CT, the yield of apple treated with OPT and OPT25 increased significantly in the next three years (P<0.05). Yield produced by OPT, OPT25, and OPT50 treatments were similar, while OPT25 obtained a 28.42% higher yield than CT in 2021. 2) Organic substitution promoted apple quality. With the increasing experimental years, OPT50 conferred more significant effect on quality improvement. Organic fertilizer substitution significantly increased vitamin C, sugar content, and the ratio of sugar to acid, thus significantly reducing the acidity. 3) OPT25 had the lowest cumulative N₂O emission in soil (2.40 kg/hm²), which was 6.98% lower than CT (P<0.05), while OPT50 had the maximum cumulative CO₂ emission from soil (3987.93 kg/hm²), which was 2.16% higher than CT. The orchard soil was a weak CH₄ sink in all the four treatments. Compared with CT, OPT and OPT25 decreased the greenhouse gas emission intensity (GHGI) by 12.65%, 15.16%, with OPT25 having the lowest GHGI (0.071 kg/kg).

Conclusions Organic fertilizer substitution markedly improves the yield and quality of apple fruit, but the effect of high substitution rate (50%) reduces with the experimental years. Organic fertilizer substitution reduces soil N₂O emissions and GHGI, but high substitution rate increases soil CO₂ emissions. It is recommended that 25% of the conventional chemical fertilizer for apple production in this region be replaced with organic fertilizer.