Evaluating the Effect of Deficit Irrigation on Yield and Water Use Efficiency of Drip Irrigation Cotton under Film in Xinjiang Based on Meta-Analysis.

Water scarcity constrains the sustainable development of Chinese agriculture, and deficit irrigation as a new irrigation technology can effectively alleviate the problems of water scarcity and water use inefficiency in agriculture. In this study, the drip irrigation cotton field under film in Xinjiang was taken as the research object. Meta-analysis and machine learning were used to quantitatively analyze the effects of different farm management practices, climate, and soil conditions on cotton yield and water use efficiency under deficit irrigation, to investigate the importance of the effects of different factors on cotton yield and water use efficiency, and to formulate appropriate optimization strategies. The results showed that deficit irrigation significantly increased cotton water use efficiency (7.39%) but decreased cotton yield (-15.00%) compared with full irrigation. All three deficit irrigation levels (80~100% FI, 60~80% FI, and 40~60% FI; FI: full irrigation) showed a significant decrease in cotton yield and a significant increase in water use efficiency. Under deficit irrigation, cotton yield reduction was the smallest and cotton water use efficiency increased the most when planted with one film, two tubes, a six-row cropping pattern, an irrigation frequency ≥10 times, a nitrogen application of 300~400 kg·ha-1, and a crop density ≥240,000 per hectare, and planted with the Xinluzhong series of cotton varieties; deficit irrigation in areas with average annual temperature >10 °C, annual evapotranspiration >2000 mm, annual precipitation <60 mm, and with loam, sandy soil had the least inhibition of cotton yield and the greatest increase in cotton water use efficiency. The results of the random forest showed that the irrigation amount and nitrogen application had the greatest influence on cotton yield and water use efficiency. Rational irrigation based on optimal management practices under conditions of irrigation not less than 90% FI is expected to achieve a win-win situation for both cotton yield and water use efficiency. The above results can provide the best strategy for deficit irrigation and efficient water use in drip irrigation cotton under film in arid areas.

Different Responses in Root Water Uptake of Summer Maize to Planting Density and Nitrogen Fertilization.

Modifying farming practices combined with breeding has the potential to improve water and nutrient use efficiency by regulating root growth, but achieving this goal requires phenotyping the roots, including their architecture and ability to take up water and nutrients from different soil layers. This is challenging due to the difficulty of in situ root measurement and opaqueness of the soil. Using stable isotopes and soil coring, we calculated the change in root water uptake of summer maize in response to planting density and nitrogen fertilization in a 2-year field experiment. We periodically measured root-length density, soil moisture content, and stable isotopes δ18O and δD in the plant stem, soil water, and precipitation concurrently and calculated the root water uptake based on the mass balance of the isotopes and the Bayesian inference method coupled with the Markov Chain Monte Carlo simulation. The results show that the root water uptake increased asymptotically with root-length density and that nitrogen application affected the locations in soil from which the roots acquired water more significantly than planting density. In particular, we find that reducing nitrogen application promoted root penetration to access subsoil nutrients and consequently enhanced their water uptake from the subsoil, while increasing planting density benefited water uptake of the roots in the topsoil. These findings reveal that it is possible to manipulate plant density and fertilization to improve water and nutrient use efficiency of the summer maize and the results thus have imperative implications for agricultural production.

Greenhouse gas emissions from the wheat-maize cropping system under different tillage and crop residue management practices in the North China Plain.

With increasing attention being placed on mitigating global warming and achieving agricultural sustainable intensification, conservation agriculture practices have gradually been implemented in the North China Plain (NCP). However, there are still knowledge gaps on the effects of conservation practices on greenhouse gas (GHG) emissions in this area. In this study, a four-year field experiment was conducted from 2014 to 2018 to assess the effects of tillage and crop residue management practices on the emissions of nitrous oxide (N2O) and methane (CH4). Subsequently, crop yields, area-scaled and yield-scaled total non-carbon dioxide (CO2) GHG emissions were assessed. Our research found that no-till (NT) decreased N2O emissions by 22.6% compared with conventional tillage (CT) in winter wheat (Triticum aestivum L.) seasons, but there was no difference between tillage practices in summer maize (Zea mays L.) seasons. Crop residue retention practice (+R) increased N2O emissions by 28.1% and 26.7% compared with residue removal practice (-R) in winter wheat and summer maize seasons, respectively. The NT soils took up more CH4 compared with the CT soils in summer maize seasons. Area-scaled total non-CO2 GHG emissions showed trends similar to those of N2O emission. Since crop residue retention improved the maize yield compared with the residue removal treatments, yield-scaled total non-CO2 GHGs emission did not differ between residue management practices in summer maize seasons. Our four-year field measurements indicated that no-till practice could be more useful as an option to mitigate non-CO2 GHG emissions in the wheat - maize cropping system.

Effects of different nitrogen application rates on soil water stable aggregates and N2O emission in winter wheat field.

Excessive nitrogen application would deteriorate soil structure and increase greenhouse gas emission. We set up six treatments, i.e., N0, N120, N180, N240, N300and N360(nitrogen application rates of 0, 120, 180, 240, 300 and 360 kg·hm-2, all straws returned into the field in situ) in the nitrogen fertilizer experimental site to investigate the effects of different nitrogen application rates on soil N2O emission, soil water-filled porosity (WFPS), soil temperature, nitrate and ammonium contents, composition and stability of water stable aggregates in winter wheat filed in 2018-2020. The results showed that there was a significant positive correlation between soil N2O emission and nitrogen application rate. There was no correlation between WFPS and nitrogen application rate. Soil temperature in the 0-10 cm layer decreased significantly with the increases of nitrogen application rates. There was a significant positive correlation between nitrate and ammonium contents and nitrogen application rate. With the increases of nitrogen application rates, the content of water stable aggregates with diameter >2 mm decreased, while that of water-stable aggregates with diameter <0.5 mm increased. The particle size of soil water-stable aggregates also decreased gradually. There was a significant negative correlation between nitrogen application rate with mean weight diameter (MWD) and geometric mean diameter, while no correlation with fractal dimension. The fitting equation between MWD and N2O emission flux was y=3928.3e-2.171x (R2=0.55, P<0.001), indicating that N2O emission increased markedly as MWD decreasing. The increases in nitrogen application rate reduced soil temperature in the 0-10 cm layer, increased nitrate and ammonium contents, decreased the average particle size of soil water stable aggregates, and the stability of soil aggregates, and increased soil N2O emission.

Suitable nitrogen application mode and lateral spacing for drip-irrigated winter wheat in North China Plain.

To propose an appropriate nitrogen application mode and suitable drip irrigation lateral spacing, a field experiment was conducted during 2017-2018 and 2018-2019 growing seasons to quantify the different drip irrigation lateral spacings and nitrogen fertigation strategies effects on winter wheat growth, yield, and water use efficiency (WUE) in the North China Plain (NCP). The experiment consisted of three drip irrigation lateral spacing (LS) (40, 60, and 80 cm, referred to as D40, D60, and D80 respectively) and three percentage splits of nitrogen application modes (NAM) (basal and top dressing application ratio as 50:50 (N50:50), 25:75 (N25:75), and 0:100 (N0-100) respectively). The experimental findings depicted that yield and its components, and WUE were markedly affected by LS and NAM. Fertigation of winter wheat at N25:75 NAM notably (P<0.05) increased the grain yield by 4.88%, 1.83% and 8.03%, 4.61%, and WUE by 3.10%, 3.18% and 5.37%, 7.82%, compared with those at NAM N50:50 and N0:100 in 2017-2018 and 2018-2019 growing seasons, respectively. LS D40 appeared very fruitful in terms of soil moisture and nitrogen distribution, WUE, grain yield, and yield components than that of other LS levels. The maximum grain yield (8.73 and 9.40 t ha-1) and WUE (1.70 and 1.95 kg m-3) were obtained under D40N25:75 during both growing seasons, which mainly due to that all main yield components in D40N25:75 treatment, such as spikes per unit area, 1000-grain weight, and grains per spike were significantly higher as compared to other treatments. The outcomes of this research may provide a scientific basis of lateral spacing and nitrogen fertigation management for the production of drip-irrigated winter wheat in NCP.

Application of Exogenous Protectants Mitigates Salt-Induced Na+ Toxicity and Sustains Cotton (Gossypium hirsutum L.) Seedling Growth: Comparison of Glycine Betaine and Salicylic Acid.

Soil salinization adversely affects agricultural productivity. Mitigating the adverse effects of salinity represents a current major challenge for agricultural researchers worldwide. The effects of exogenously applied glycine betaine (GB) and salicylic acid (SA) on mitigating sodium toxicity and improving the growth of cotton seedlings subjected to salt stress remain unclear. The treatments in a phytotron included a control (CK, exogenously untreated, non-saline), two NaCl conditions (0 and 150 mM), four exogenous GB concentrations (0, 2.5, 5.0, and 7.5 mM), and four exogenous SA concentrations (0, 1.0, 1.5, and 2.0 mM). The shoot and roots exposed to 150 mM NaCl without supplementation had significantly higher Na+ and reduced K+, Ca2+, and Mg2+ contents, along with lowered biomass, compared with those of CK. Under NaCl stress, exogenous GB and SA at all concentrations substantially inversed these trends by improving ion uptake regulation and biomass accumulation compared with NaCl stress alone. Supplementation with 5.0 mM GB and with 1.0 mM SA under NaCl stress were the most effective conditions for mitigating Na+ toxicity and enhancing biomass accumulation. NaCl stress had a negative effect on plant growth parameters, including plant height, leaf area, leaf water potential, and total nitrogen (N) in the shoot and roots, which were improved by supplementation with 5.0 mM GB or 1.0 mM SA. Supplementation with 5.0 mM exogenous GB was more effective in controlling the percentage loss of conductivity (PLC) under NaCl stress.

Linking exogenous foliar application of glycine betaine and stomatal characteristics with salinity stress tolerance in cotton (Gossypium hirsutum L.) seedlings.

BACKGROUND: Glycine betaine (GB) plays a crucial role in plants responding to abiotic stresses. Studying the physiological response of cotton seedlings to exogenous GB under salt stress provides a reference for the application of GB to improve the resistance of cotton seedlings under salt stress. The purpose of this research is to examine the impacts of foliar-applied GB on leaf stomatal structure and characteristics, gas exchange and chlorophyll fluorescence characteristics and plant growth indicators of Gossypium hirsutum L. under NaCl stress conditions. RESULTS: Under the salinity of 150 mM, the four concentrations of GB are 0, 2.5, 5, and 7.5 mM, and the control (CK) was GB-untreated non-saline. Salt stress negatively affected leaf stomata as well as gas exchange and chlorophyll fluorescence and decreased plant growth parameters of cotton seedlings. The treatment with 5 mM GB significantly increased the evolution of photosynthetic rate (Pn), transpiration rate (Tr), intracellular CO2 concentration (Ci) and stomatal conductance (gs) compared to the GB-untreated saline treatment. The Exogenous foliar-applied GB has sustainably decreased the carboxylation efficiency (Pn/Ci) and water use efficiency (WUE). The concentration of 5 mM GB leads to a significant improvement of leaf stomatal characteristics. The leaf gas exchange attributes correlated positively with stomatal density (SD), stomatal length (SL) and stomatal with (SW). CONCLUSION: The overall results suggested that exogenous foliar supplementation with GB can effectively alleviate the damage of salt stress to cotton seedlings. The effect of applying 5 mM GB could be an optional choice for protecting cotton seedlings from NaCl stress through promoting the stomatal functions, photosynthetic activities and growth characteristics.