Abstract
Estimating the precise nutritional status of crop nitrogen (N) after flowering period is not only important to predict deficiency but the excess that could be revised by fertilization in future crops. Critical N dilution curves describing the critical N concentration ([N]c) in plant tissues during crop growth have been used to estimate the N status of whole plants in cotton. Little is known, however, about the critical N dilution curve for specific plant organs such as cotton fruits. The objective of this study was to verify the feasibility of fruits-based critical N dilution curve as a useful diagnostic tool for diagnosing the N status of cotton crops. A 3-year field experiment was conducted with seven N application rates (0–360 kg N ha–1) using the high-yielding cultivars Jimian 228 and Lumian 28, which differ in maturity. The relationship between fruits dry mass (DM) and N concentration ([N]) was analyzed, and a model of [N]c for cotton fruits was constructed and validated. The results showed that fruits [N]c decreased with increasing fruits DM. The critical N dilution curve based on cotton fruits was described by the equation [N]c = 2.49 × DM–0.12 (R2 = 0.649, P < 0.0001) across cultivar-years. The N nutrition index (NNI) of the fruits (NNIf) with the N dilution curve was significantly related to the NNI of shoot DM, relative yield (RY), and boll density at most sampling dates. For an NNIf of approximately 1, the RY was nearly 95%, while it decreased with a decreasing NNIf below 1. The petiole nitrate-N (NO3-N) concentration was also linearly related to the NNIf, suggesting that the NO3-N concentration in the petiole was a good predictor of the NNIf. Therefore, fruits-based critical N dilution curve and the derived NNIf values will serve as a useful diagnostic tool for diagnosing N status in cotton crops.
Highlights
Cotton is the most important natural textile fiber crop worldwide
From the dilution curve developed for fruits dry mass (DM), the nitrogen nutrition index of fruits (NNIf) was calculated for all sampling dates
The NNIf values were highly related to the nutrition index of the shoot (NNIsh) for both cultivars in most cases, with the exception of Jimian 228 at the fourth sampling after the flowering period (Figure 6), indicating the strong synchrony between fruits and shoot N status
Summary
Cotton is the most important natural textile fiber crop worldwide. Cotton production provides income for approximately 100 million families and its economic impact is estimated to be approximately $500 billion yr−1 (Chen et al, 2007; Cotton Research Institute Chinese Academy of Agricultural Sciences [CRI], 2013). Cotton Fruits N Dilution Curve of raw cotton in the world. The yield is quite low (802 kg ha−1) in the Yellow River Valley of China compared with the national average (1720 kg ha−1) (United States Department of Agriculture [USDA], 2019; National Bureau of Statistics of China, 2020). One of the main reasons for such a low yield level may be inappropriate crop nutrient management, irrespective of cultivars and climatic variability (Cotton Research Institute Chinese Academy of Agricultural Sciences [CRI], 2013)
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