Leaf dry matter outperforms leaf area index in developing critical nitrogen dilution curves for nitrogen management of drip-irrigated high-density maize

The critical nitrogen (N) dilution curve is a suitable analytical tool for in-season estimation of N status to implement precision N management. This study was undertaken for a comprehensive comparison of N dilution curves in Japonica and Indica rice to investigate, whether a single curve can be used for both rice ecotypes and to determine the most robust plant index for assessing N status in rice ecotypes. The different N dilution curves were developed based on plant dry matter (PDM), leaf area index (LAI), leaf dry matter (LDM) and stem dry matter (SDM) for N diagnosis in Japonica and Indica rice. The comparison of N dilution curves of two rice ecotypes showed non-significant differences, therefore a single/unified curve can be used to assess plant N status for precision N management in both rice ecotypes. The relationships between PDM based, with LAI, LDM, and SDM based N nutrition index, accumulated N deficit and N requirement, indicated that leaf based approaches could be used as substitutes for PDM approach. The lower coefficient b values of LDM based curve (due to efficient physiological N use in leaves) implied that LDM was the most appropriate approach for developing N curve as compared to other approaches.

Determination of critical nitrogen dilution curve based on leaf area index for winter wheat in the Guanzhong Plain, Northwest China

Analyzing uncertainty in critical nitrogen dilution curves

The critical nitrogen (N) dilution curve, which expresses whole-plant critical N concentration as a function of shoot biomass, can be used as a N management diagnostic tool for cereals. The objectives of this research were to develop a critical N dilution curve for wheat grown in calcareous soils and to formulate a model for estimating N fertilizer requirement of wheat crop at different growth stages. Six N fertilization rates (0–250 kg N ha−1) were used to induce variability in plant growth throughout six site-years (three locations at West Delta of Egypt and two seasons [2020/21-2021/22]). Aboveground shoot biomass (W; Mg DM [dry matter] ha−1) and N concentration (Nc; g kg−1 DM) were determined on five sampling dates during the growing season. A critical N dilution curve was developed as: {N}_{mathrm{c}}=50.141 {mathrm{W}}^{-0.424}. The Nc dilution curve was then used to develop a N fertilizer topdressing strategy. The study relied on N nutrition index inferred from the Nc based on N uptake, and instead of relying on a single N recovery efficiency coefficient, a variable N recovery efficiency was developed. This approach increased the hypothetical N requirements at low N application rates while decreased requirements at high N application rates, implying that the Nc dilution curve can be used successfully to estimate the rates of supplemental N application. The developed strategy will provide a solid basis for precisely managing N fertilizer, though challenge ahead at the farm level will be in determining the actual shoot biomass and N concentration.

Determination of critical nitrogen dilution curve based on leaf area index in rice

Key variable for simulating critical nitrogen dilution curve of wheat: Leaf area ratio-driven approach

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.

In order to investigate the feasibility of using rice critical nitrogen concentration as a nitrogen nutrition diagnosis index, a two-year positioning field gradient experiment using four rice varieties and four nitrogen levels (0, 75, 150, 225 kg·ha–1 for early rice; 0, 90, 180, 270 kg·ha–1 for late rice) was conducted for early and late rice. The critical dilution curves (Nc%) of the double-cropped rice based on leaf dry matter (LDM) were constructed and verified using the field data. Two critical nitrogen dilution curves and nitrogen nutrition indexes (NNI) of rice LDM were constructed for early rice [Nc% = 2.66LDM−0.79, R2 = 0.88, NNI ranged between 0.29–1.74, and the average normalized root mean square error (n-RMSE = 19.35%)] and late rice [Nc% = 7.46LDM−1.42, R2 = 0.91, NNI was between 0.55–1.53, and the average (n-RMSE = 15.14%)]. The relationship between NNI and relative yield was a quadratic polynomial equation and suggested that the optimum nitrogen application rate for early rice was sightly smaller than 150 kg·ha–1, and that for late rice was about 180 kg·ha-1. The developed critical nitrogen concentration dilution curves, based on leaf dry matter, were able to diagnose nitrogen nutrition in the double-cropped rice region.

In order to investigate the feasibility of using rice critical nitrogen concentration as a nitrogen nutrition diagnosis index, a two-year positioning field gradient experiment using four rice varieties and four nitrogen levels (0, 75, 150, 225 kg·ha-1 for early rice; 0, 90, 180, 270 kg·ha-1 for late rice) was conducted for early and late rice. The critical dilution curves (Nc%) of the double-cropped rice based on leaf dry matter (LDM) were constructed and verified using the field data. Two critical nitrogen dilution curves and nitrogen nutrition indexes (NNI) of rice LDM were constructed for early rice [Nc% = 2.66LDM-0.79, R2 = 0.88, NNI ranged between 0.29-1.74, and the average normalized root mean square error (n-RMSE = 19.35%)] and late rice [Nc% = 7.46LDM-1.42, R2 = 0.91, NNI was between 0.55-1.53, and the average (n-RMSE = 15.14%)]. The relationship between NNI and relative yield was a quadratic polynomial equation and suggested that the optimum nitrogen application rate for early rice was sightly smaller than 150 kg·ha-1, and that for late rice was about 180 kg·ha-1. The developed critical nitrogen concentration dilution curves, based on leaf dry matter, were able to diagnose nitrogen nutrition in the double-cropped rice region.

Establishing critical nitrogen dilution curves based on leaf area index and aboveground biomass for greenhouse cherry tomato: A Bayesian analysis

The critical nitrogen (N) dilution curve is widely used to diagnose crop N status, but no such model has been developed for sugar beet. This study evaluated the effects of irrigation amount and N rate on sugar yield, N use efficiency, and soil nitrate-N (NO3-N) residue of drip-fertigated sugar beet in the arid southern Xinjiang of China. A reliable N nutrition index (NNI) for sugar yield was also established based on a critical N dilution curve derived from the dry matter of sugar beet. A three-year field experiment was established with six N rates (25–480 kg N ha−1) and three irrigation levels based on crop evapotranspiration (ETc) (0.6, 0.8, and 1.0 ETc in 2019 and 2020, and 0.4, 0.6, and 0.8 ETc in 2021). Results showed that sugar yield and N uptake increased and then generally stabilized with increasing N rate, while N use efficiency decreased. Most soil NO3-N was mainly distributed in the 0–60 cm soil layer, but increasing irrigation amount reduced residual NO3-N in the 0–80 cm soil layer. Additionally, the established critical N dilution curve of sugar beet was considered stable (Normalized RMSE = 16.6%), and can be used to calculate plant N requirements and further N rates during sugar beet growth. The results indicated that the optimal NNI was 0.97 under 0.6 ETc for sugar yield production of sugar beet in this study. This study provides a basis for efficient water and N management in sugar beet production in arid and semi-arid regions globally.

In order to verify the applicability of critical nitrogen (N) dilution curve for summer maize in North China Plain, and the feasibility of N nutrition index (NNI) in evaluating N nutrition status of maize plant, a 2-year experiment with five N-fertilizer treatments (0, 60, 120, 180, and 240 kg N ha –1 ) was conducted using the cultivar Zhengdan 958. The results showed that the above ground biomass (W) increased significantly with increasing N-fertilizer application within a certain range. The data of above ground biomass and corresponding N concentration for each sampling stage were divided into N limited group and N non-limited group based on the statistical results, then the critical N concentration (N c ) was calculated and the critical N dilution curve model (N c =34.914W –0.4134 ) for summer maize was established, and the model parameters had a good similarity to these reported. NNI calculated based on the critical N dilution curve model had a significant correlation with relative N uptake amount, or relative above ground biomass or relative yield. Therefore, critical N dilution curve and NNI can be used to predict plant N c and characterize plant N status in summer maize in North China Plain.

In-season estimation of rice grain yield using critical nitrogen dilution curve

Critical nitrogen (Nc) dilution curve and its extended N nutrient index (NNI) in previous study was only be applied to wheat for N status diagnosis. This research improved this model and further established the N topdressing model which can be quantify the N topdressing rate when NNI < 1. To facilitate the estimate of the Nc concentration, the determination of basal stem tissue sap nitrate (Nit) concentration as a rapid and operational way was used to characterize N status in this study. The results revealed that N dilution curve in this study specific to winter wheat could be used to establish the N nutrition status. There was significantly positive relationship between the Nit concentration and whole plant N concentration at each growth stage. Moreover, the Nit concentration linearly and positively correlated to the N fertilizer application rate, then deducing the N fertilizer topdressing rate per 100 Nit unit, which finally established the N fertilizer topdressing model: N topdressing rate = (critical Nit − actual Nit) × N topdressing rate per 100 Nit unit. The N dilution curve-based model will offer technical support for managing the precise application of N during the growth period of wheat crops.

Determination of a Critical Nitrogen Dilution Curve for Winter Wheat Crops