Establishment of a critical nitrogen dilution curve for drip-irrigated cotton under reduced nitrogen application rates

Abstract

The goal of this study was to establish the feasibility of using the critical nitrogen (N) dilution curve of cotton leaves for diagnosing N nutrition, so as to provide a theoretical basis and guidance for accurate fertilization in drip-irrigated cotton fields. We conducted field experiments using Lumianyan 24 under four different reduced N treatments including (506 kg hm−2 (N1), 402.5 kg hm−2 (N2), 299 kg hm−2 (N3), and 195.5 kg hm−2 (N4)) between 2018 and 2019. We subsequently measured N concentration and leaf dry matter (LDM). We also calculated the critical N concentration (Nc) dilution model, allometric growth model, N nutrient index (NNI), and N accumulation. Our results revealed that with the development of growth period, the leaf NNI and N accumulation displayed an increasing trend followed by a decreasing pattern in 2018. On the other hand, the leaf NNI in 2019 showed a similar performance as presented in 2018, while the N accumulation depicted a gradually increasing trend. We also found that NNI and N accumulation of cotton leaves reduced with decreasing N application. The Nc dilution curve model for drip-irrigated cotton fields was Nc = 5.163LDM−0.171 (LDM > 1.65), Nc = 4.7% (LDM ≤ 1.65), R2 = 0.933, with a highly significant fit and RMSE = 0.374, accompanied by excellent model simulation performance. In conclusion, this study established the Nc dilution curve model. Additionally, the calculated NNI can efficiently diagnose the status of N nutrients, thus providing a valuable theoretical basis for accurate fertilization of drip-irrigated cotton fields.