Optimized nutrient management improves fruit yield and fertilizer use efficiency and reduces carbon emissions in pomelo production

Objectives Excessive fertilization is common in cash crop production, especially in orchards. We used pomelo Citrus grandis (L.) Osbeck cv. Guanximiyou orchards in Pinghe County of Fujian Province to study the potential of optimized nutrient management in increasing fruit yield and quality and alleviating carbon emission from the production cycle.

Methods A field experiment was carried out in Pinghe County of Fujian Province in 2019 and 2020; 10-year-old red pulp pomelo trees were used as test materials. Two fertilization models were designed, one was local farmer’s fertilization practice (N 1050 kg/hm², P₂O₅ 880 kg/hm², K₂O 870 kg/hm², and 7500 kg/hm² organic fertilizer, FFP), and the other was optimized nutrient management (OPTs). The OPT included three treatments, chemical fertilizer-reduced treatment (N 200 kg/hm²and K₂O 200 kg/hm², OPT1), soil acidity regulation based on OPT1 (N 200 kg/hm², K₂O 200 kg/hm², and CaO 2010 kg/hm², OPT2), and the substitution of chemical N fertilizer with 20% organic fertilizer based on OPT2 (N 160 kg/hm², K₂O 176 kg/hm², CaO 2010 kg/hm², and 2000 kg/hm² organic fertilizer, OPT3). The pomelo yield and sources of agricultural cost were investigated, and the fruit quality and nutrient contents in tree organs (i.e., new leaves, branches, and fruits) were measured. The carbon emission during the whole life cycle of pomelo production was analyzed.

Results Compared with FFP, OPTs reduced the total chemical fertilizer input by 86% but did not affect (P>0.05) pomelo yield in 2019. On the contrary, OPT3 (P<0.05) increased single pomelo weight and yield in 2020. The N and K₂O fertilizers’ partial productivity of OPTs was average increased by 5.49 and 4.75 times on average compared with FFP across 2019 and 2020, respectively. OPT2 and OPT3 decreased fruit acidity and increased (P<0.05) the solid acid ratio and vitamin C contents. Compared with FFP, OPTs (P<0.05) reduced N content in new leaves, branches, and fruits but did not affect their P and K content. OPT2 and OPT3 increased Ca and K contents in new organs and leaves, respectively, resulting in a more balanced nutrient ratio in pomelo trees. OPTs increased economic benefit by 12.80%, decreased production cost by 35.66%, and reduced the annual net carbon emission and carbon footprint by 89.89% and 90.18%, respectively.

Conclusions In optimized nutrient management, the type and quantity of NPK fertilizer are reduced in different ratios. The organic fertilizer was applied to replace 20% of chemical N input, achieving a total reduction of chemical fertilizer by 86%. Consequently, the fruit yield, quality, fertilizer use efficiency, and production efficiency were improved. The decrease in fertilizers reduced carbon emissions and carbon footprint during the life cycle of pomelo production. Thus, optimizing nutrient management according to local conditions effectively achieves stability, increases fruit yield, improves fruit quality and fertilizer use efficiency, and reduces carbon emissions in orchards.