Mitigating magnesium deficiency for sustainable citrus production: A case study in Southwest China

Abstract

Citrus is the biggest fruit crop in the world. Magnesium (Mg) deficiency is becoming a major limiting factor for sustainable citrus production globally, especially in China. Acidified soil, low Mg availability and poor nutrient management by small growers impact citrus fruit yield and quality, and its ecological environments. Grower surveys were therefore conducted to evaluate the extent and the underlying causes of Mg deficiency in the citrus orchards in Danling County, a typical citrus production county in Southwest China. A large, detailed citrus grower survey, along with soil and plant analyses, revealed that 73% of orchard soil and 93% of citrus leaf samples were Mg-deficient in the study region. Further, more than 50% of the local agrochemical technology providers did not identify citrus Mg deficiency symptoms. As a result, the orchard soil had negligible input of Mg (average 11 kg MgO ha−1), but received a large excess of nitrogen (average 712 kg N ha−1), phosphorus (average 364 kg P2O5 ha−1), and potassium fertilizers (average 565 kg K2O ha−1) annually. This unbalanced fertilization aggravated soil Mg depletion in 89% of citrus orchards. To rectify Mg deficiency, field experiments with crop nutrient demand and supply-based optimal nutrient management, including Mg application and reduced rates of NPK fertilizer (OPT+Mg), were conducted in two orchards over two cropping seasons. Compared with farmer practices, OPT+Mg treatment resulted in higher fruit yield (average 3.7 t ha−1), nutrient use efficiency, fruit quality and gross profit, with reduced environmental costs. In summary, this case study helped develop a social and technological strategy to mitigate Mg deficiency for profitable and sustainable citrus production in the major citrus producing region in China, and possibly in other counties with similar soil and environmental conditions.