Rational biochar application rate for cotton nutrient content, growth, yields, productivity, and economic benefits under film-mulched trickle irrigation

Abstract

Biochar application to soils has been proven to be an efficient way for yield enhancement in agricultural systems. However, what is the most economical biochar application rate (BCAR) for cotton in saline-alkali soils in arid and semi-arid zones remains unclear. To narrow the gap, this study aims to investigate how biochar application affected the nutrient content, growth, yield, quality, and productivity of cotton, and to find the rational BCAR. The three-year field experiments of biochar application combined with plastic film mulched drip irrigation were conducted for cotton in Xinjiang, China. The biochar was continuously applied to the farmland at 0 (in 2018)+ 0 (in 2019)+ 0 (in 2020), 10 + 10 + 10, NT (no test)+ 25 + 25, 50 + 50 + 30, and 100 + 100 +NT t ha−1 during cotton growth period of 2018–2020. The cotton growth, yield, and quality indicators were observed and used for computing water-fertilizer productivity. The cost-benefit analysis was referred to recommend a rational BCAR. All four biochar application treatments increased the leaf/stem/root nutrient (N, P, and K) content than control during different cotton growth stages. The daily relative content of chlorophyll increased with the increasing BCAR and were larger at biochar treatments of 50 and 100 t ha−1 than 0, 10, and 25 t ha−1. The growth and yield-related indicators (plant height, stem diameter, leaf area index and seed yield), irrigation water productivity, and partial fertilizer (N, P, and K) productivity consistently increased than control under biochar application conditions, and the BCAR of 10 t ha−1 showed the greatest advantages in enhancing germination rates, cotton yields, water-fertilizer productivities, and financial income than biochar treatments of 0, 25, 50 and 100 t ha−1. However, neither cotton fiber quality indices (length, Micronaire, strength or uniformity index) were significantly affected by biochar applications. Based on the economic analysis, the rational BCAR was 10 t ha−1 each year (continued for three years) for cotton planting, which was a best dose that could be applied to arid zones and have not been reported before.