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Biochar application improves soil environment and thus enhances crop yields. However, its optimum application rate is site- and crop-specific. Our aim is to determine the optimum biochar application rate (OBAR) in sugar beet by investigating its influences on economic profit. A 3-year field biochar application test for sugar beet was conducted in Xinjiang, China. Plastic film mulch and drip irrigation were applied. Five treatments of biochar application rates were made. For each treatment, same biochar rates (i.e. 0, 10, 25, 50 and 100 t ha−1) were applied in each year from 2018 to 2020 with a few exceptions where biochar rates were manipulated according to the results of the first two years. The physiological ecology indicators, irrigation water and fertilizer productivities and economic profit were analyzed. The N, P and K uptake during growth stages of sugar beet, the physiological ecology indicators (e.g. aboveground and underground biomass, leaf area index) and sugar content increased with increase in biochar application rate. The irrigation water and partial fertilizer productivities and economic benefits were the greatest at the biochar application of 10 t ha−1 for each year, which was recommended as the best dose for sugar beet planting. For sugar beet planting in arid and semi-arid zone, continuous application with OBAR of 10 t ha−1 had the maximal economical profit, the net profit increase was 6.94 billion dollars compared with no biochar application. Therefore, considering the comprehensive responses of the nutrient uptake, salt absorption, yield, and the economic benefit of various biochar application rate, the biochar application rate of 10 t ha−1 year−1 was recommended as the optimum dose. There were complicated interactions of soil, biochar and crops, further studies involving multi-discipline overlap are needed to reveal the yield, quality and productivity increase mechanics of sugar beet affected by biochar. • The biochar applications increased the N, P and K uptake during different growth stages of sugar beet. • The growth and yield related indicators were significant increased under biochar application conditions. • Yield components were the largest under biochar application rate of 10 t ha−1. • The biochar application rate of 10 t ha−1 was recommended as the optimum dose for sugar beet planting. [ABSTRACT FROM AUTHOR]