Establishment of an NPK nutrient monitor system in yield-graded cotton petioles under drip irrigation

BACKGROUND: The determination of nutrient content in the petiole is one of the important methods for achieving cotton fertilization management. The establishment of a monitoring system for the nutrient content of cotton petioles during important growth periods under drip irrigation is of great significance for achieving precise fertilization and environmental protection. METHODS: A total of 100 cotton fields with an annual yield of 4500–7500 kg/ha were selected among the main cotton-growing areas of Northern Xinjiang. The nitrate nitrogen (NO(3)(−)–N), inorganic phosphorus (PO(4)(3−)–P) and inorganic potassium (K(+)–K) content and yield of cotton petioles were recorded. Based on a yield of 6000 kg/ha as the dividing line, a two-level and yield-graded monitoring system for NO(3)(−)–N, PO(4)(3−)–P and K(+)–K in cotton petioles during important growth periods was established, and predictive yield models for NO(3)(−)–N, PO(4)(3−)–P and K(+)–K in petioles during important growth periods were established. RESULTS: The results showed found that the yields of the 100 cotton fields surveyed were normally distributed. Therefore, two yield grades were classified using 6000 kg/ha as a criterion. Under different yield-graded, the NO(3)(−)–N, PO(4)(3−)–P and K(+)–K content of petiole at important growth stages was significantly positively correlated with yield. Further, the variation range of NO(3)(−)–N, PO(4)(3−)–P and K(+)–K content in petioles could be used as a standard for yield-graded. In addition, a yield prediction model for the NO(3)(−)–N, PO(4)(3−)–P and K(+)–K content of petioles was developed. The SSO-BP validation model performed the best (R(2) = 0.96, RMSE = 0.06 t/ha, MAE = 0.05 t/ha) in the full bud stage, which was 12.9% higher than the BP validation model. However, the RMSE and MAE were decreased by 86.7% and 88.1%, respectively. CONCLUSION: The establishment of NPK nutrition monitor system of cotton petioles under drip irrigation based on yield-graded provides an important basis for nutrition monitor of cotton petiole under drip irrigation in Xinjiang. It also provides a new method for cotton yield prediction.