Nitrogen fertilizer is one of the key elements to increase the yield and significance of winter wheat. The experiment was established in the split zone design and was repeated three times. The nitrogen application level is set to 4 treatments, 75, 150, 225 and 300 kg ha −1 are arranged in the main plot, and different nitrogen application ratios are arranged in the sub-plots, respectively 5:5 (50%+50%) and 6: 4 (60%) + 40%). Nitrogen fertilizer was applied before sowing, jointing stage, flowering stage and filling stage. The experimental plot is 12 m2 (3 m × 4 m). The results showed that under the conditions of 225 kg/hm2 nitrogen application and 60%+40% nitrogen application rate, the yield of Jintai 182 was the highest compared with other treatment groups. With the increase of nitrogen application rate, the number of ears, grains per ear, thousand-grain weight and grain yield all increase first and then decrease. Each factor reached the highest 225 N kg / hm2, 417.17, 30.74, 40.96 g and 6182.11 kg / hm2. Compared with 75 kg/hm2 topdressing fertilizer, 225 kg/hm2 is a more suitable nitrogen fertilizer application rate for winter wheat. Within a reasonable range of nitrogen fertilizer application, there is a significant positive correlation between nitrogen content and winter wheat yield. By studying the amount of nitrogen fertilizer and a reasonable ratio of base fertilizer to topdressing, the utilization rate of nitrogen fertilizer can be maximized and excessive application of nitrogen fertilizer can be avoided.

Plant growth, nutrient uptake and yield can be sustained by the application of potassium fertilization. A pot experiment was conducted to study the effect of macronutrients accumulation of wheat about different potassium rates.The results revealed that the effect of different potassium levels on the growth and grain yield of wheat was significant. The application of potassium at 100% increased the most of the growth, yield components and accumulation of nutrients in wheat crop from 20−50% as compared to (control) the plots receiving no potassium application. In comparison to control, potassium application at 75% also significantly increased growth and yield components from 8−40%, however, potassium application of 50 and 25% increased the growth and yield components by 4−20%. As compared to plots receiving no potassium, application of potassium resulted 3−6% higher nitrogen content in grain and 2−11% higher nitrogen content in straw. While, potassium application increased the potassium contents by 50−154% in grain and 70-140% contents of potassium in straw as compared to control plots. However, in comparison to plots without potassium nutrition, application of potassium fertilization improved phosphorus contents by 2−10% in grain and 3-50% in straw of wheat crop. Among potassium levels of 25%, 50%, 75% and 100% were significant indicating that potassium at the rate of 100% was an optimum level for obtaining maximum grain yields in wheat crop. This study concluded that application of potassium nutrition increased the all growth, yield comonents and accumumation of nitrogen, phosphorus and potassium contents in grain and straw of wheat crop.

Wheat is the third most producing crop in China after maize and rice. In order to enhance the nitrogen use efficiency (NUE) and grain yield of winter wheat, a two-year field experiment was conducted to investigate the effect of different nitrogen ratios and doses at various development stages of winter wheat (Triticum aestivum L.). A total of five N doses (0, N75, N150, N225, and N300 kg ha−1) as main plots and two N ratios were applied in split doses (50%:50% and 60%:40%, referring to 50% at sowing time and 50% at jointing stage, 50% at sowing time + 50% at flowering stage, 50% at sowing time + 50% at grain filling stage, and 60% + 40% N ratio applied as a 60% at sowing time and 40% at jointing stage, 60% at sowing time and 40% at flowering stage, and 60% at sowing time and 40% at grain filling stage in subplots). The results of this study revealed that a nitrogen dose of 225 kg ha−1 significantly augmented the plant height by 27% and above ground biomass (ABG) by 24% at the grain filling stage, and the leaf area was enhanced by 149% at the flowering stage under 60 + 40% ratios. Furthermore, the N225 kg ha−1 significantly prompted the photosynthetic rate by 47% at the jointing and flowering stages followed by grain filling stage compared to the control. The correlation analysis exhibited the positive relationship between nitrogen uptake and nitrogen content, chlorophyll, and dry biomass, revealing that NUE enhanced and ultimately increased the winter wheat yield. In conclusion, our results depicted that optimizing the nitrogen dose (N225 kg/ha−1) with a 60% + 40% ratio at jointing stage increased the grain yield and nitrogen utilization rate.

A variable selection method based on random frog, variable filtering and variable interval expansion.

Avoidable or inappropriate nitrogen (N) fertilizer rates harmfully affect the yield production and ecological value. Therefore, the aims of this study were to optimize the rate and timings of N fertilizer to maximize yield components and photosynthetic parameter of soybean. This field experiment consists of five fertilizer N rates: 0, 75, 150, 225 and 300 kg N ha −1 arranged in main plots and four N fertilization timings: V 5 (trifoliate leaf), R 2 (full flowering stage) and R 4 (full poding stage), and R 6 (full seeding stage) growth stages organized as subplots. Results revealed that 225 kg N ha −1 significantly enhanced grain yield components, total chlorophyll (Chl), photosynthetic rate ( P N ), and total dry biomass and N accumulation by 20%, 16%, 28%, 7% and 12% at R 4 stage of soybean. However, stomatal conductance ( g s ) , leaf area index (LAI), intercellular CO 2 concentration ( C i) and transpiration rate ( E ) were increased by 12%, 88%, 10%, 18% at R 6 stage under 225 kg N ha −1 . Grain yield was significantly associated with photosynthetic characteristics of soybean. In conclusion, the amount of nitrogen 225 kg ha −1 at R 4 and R 6 stages effectively promoted the yield components and photosynthetic characteristics of soybean.

No abstract

Rapid and non-destructive estimation of leaf nitrogen accumulation (LNA) is essential to field nitrogen management. Currently, many vegetation indices have been used for indicating nitrogen status. Few studies systematically analyzed the performance of vegetation indices of winter wheat in estimating LNA under different irrigation regimes. This study aimed to develop a new spectral index for LNA estimation. In this study, 2 years of field experiments with different irrigation regimes were conducted from 2015 to 2017. The original reflectance (OR) and three transformed spectra [e.g., the first derivative reflectance (FDR), logarithm of the reciprocal of the spectra (Log(1/R)), and continuum removal (CR)] were used to calculate two- and three-band spectral indices. Correlation analyses and univariate linear and non-linear regression between transformed-based spectral indices and LNA were performed. The performance of the optimal spectral index was evaluated with classical vegetation index. The results showed that FDR was the most stable transformation method, which can effectively enhance the relationships to LNA and improve prediction performance. With a linear relationship with LNA, FDR-based three-band spectral index 1 (FDR-TBI1) (451, 706, 688) generated the best performance with coefficient of determination (R2) of 0.73 and 0.79, the root mean square error (RMSE) of 1.267 and 1.266 g/m2, and the ratio of performance to interquartile distance (RPIQ) of 2.84 and 2.71 in calibration and validation datasets, respectively. The optimized spectral index [FDR-TBI1 (451, 706, 688)] is more effective and might be recommended as an indicator for estimating winter wheat LNA under different irrigation regimes.

Lack of water can lead lower chlorophyll concentrations and yields. Based on the hyperspectral reflectance of winter wheat (Triticum aestivum L.), we analyzed the relationship between the canopy hyperspectral reflectance and the waterstressed winter wheat. The correlation analysis (CA), partial least squares regression (PLSR), and successive progressions algorithm (SPA) were used to extract the important bands. Then the hyperspectral estimation models for chlorophyll density (ChD) by characteristic variables were established. The results showed that the reflectance in the visible regions increased gradually with an increasing water stress. In the near-infrared (NIR) region, reflectance decreased with stress intensity. We extracted five and seven important waveband regions by CA and PLSR. Then we extracted right and nine important bands through SMLR, and 11 important bands were extracted by the method of SPA. We found that 427, 434, 749, and 814 nm contained important information about ChD of winter wheat after water stress. The model established by CA+SMLR was generally realized, whereas the ChD estimation models established by PLSR+SMLR and SPA with multiple linear regression had better performance, and the performance of the validation model was accurate and robust. The results of this study could provide theoretical basis and practical reference for accurate estimation of ChD in winter wheat after water stress.