| The relationship between soil nutrients and crop yields is S-shaped and non-linear, thus, identifying threshold value of nutrient index is crucial for scientific fertilization and comprehensive evaluation of soil fertility.With extensive gradient data on nutrients and yields over the past 30 years, long-term fertilization experiments have emerged as optimal platforms for studying nutrients threshold. Based on the monitoring data from long-term fertilization experiments conducted with fertilizer and manure in reddish paddy soil, and with fertilizer in red upland soil at Jinxian county, Jiangxi province, we used different methods including frequency accumulation curve, growth effect curve and experts achievement reference to systematically determine the threshold values of organic matter(OM), total nitrogen (TN), available nitrogen (AN), total phosphorus(TP), available phosphorus(AP), total potassium(TK), available potassium(AK) and pH value.The results showed significant or extremely significant growth-effect relationship(obtained corresponding simulation equations) between nutrient indexes and crop yields.The determined thresholds were OM 30g/kg, TN 2.0g/kg, AN 200mg/kg, TP 1.2g/kg, AP 20mg/kg, TK 14g/kg, AK 100mg/kg and pH 4.5 (low) and 6.5 (high),respectively.These findings can serve as a reference for fertilization practices and soil fertility assessments in red soil region. |
