Aiming at the issues of insufficient input of organic matters and high reliance on nitrogen fertilizers of wheat production in the Qinghai Plateau, the study investigated the influences of different incorporation methods of green manure after wheat combing nitrogen fertilizer reduction on wheat yield and soil quality, so as to provide the theoretical basis and practical guidance of efficiently and sustainably producing wheat in this area.

The experiment was conducted in the experimental field of the Academy of Agriculture and Forestry Sciences of Qinghai University from 2022 to 2023. A split plot design was adopted, and three nitrogen application levels were set up in the main plot of wheat season: conventional nitrogen application (225 kg·hm^-2, N2), nitrogen reduction by 30% (158 kg·hm^-2, N1), and no nitrogen application (N0). The subplot was setup as three green manure incorporation methods in the previous season: only green manure root returning (RR), overground straw returning via sheep digest combined with root returning (SDRR), and overground straw and root returning (OSRR).

The content of soil organic matter, total nitrogen, ammonium nitrogen, available phosphorus, and available potassium of treatment nitrogen reduction by 30% and overground straw returning via sheep digest combined with root returning (N1SDRR) were increased by 10.3%, 8.6%, 23.8%, 9.1%, and 8.4%, respectively, than those under nitrogen reduction by 30% and overground straw and root returning (N1OSRR). Meanwhile, the content of soil nitrate nitrogen under N1SDRR was 4.4% and 11.3% lower than that of treatment conventional nitrogen application and overground straw returning via sheep digest combined with root returning (N2SDRR) and N1OSRR, respectively. Additionally, the activities of soil alkaline phosphatase, sucrase, and urease under N1SDRR treatment were increased by 8.5%, 10.2%, and 3.7%, respectively, compared with the N1OSRR treatment; however, the activity of soil catalase was 7.1% and 10.0% lower than that under N2SDRR and N1OSRR, respectively. The soil quality index of the N1SDRR treatment was the highest (0.79), showing no significant difference from the N2SDRR treatment, but significantly increasing by 72.0% compared with the N1OSRR treatment. Furthermore, SDRR significantly enhanced the grain yield of wheat by 28.1% and 7.3% compared with RR and OSRR, respectively, and no yield reduction occurred even 30% nitrogen fertilizer was reduced. Linear regression analysis demonstrated a significant positive correlation between the soil quality index and yield. The random forest model indicated that the main factors influencing soil quality index were soil organic matter, available phosphorus, ammonium nitrogen, and total nitrogen, while the main factors influencing grain yield of wheat were soil organic matter, total nitrogen, ammonium nitrogen, available phosphorus, and urease activity.

Under the condition of 30% reduction of nitrogen fertilizer, the overground straw returning via sheep digest combined with root returning could effectively improve soil quality and wheat grain yield by reducing soil bulk density, increasing soil organic matter, total nitrogen, ammonium nitrogen, available phosphorus, available potassium content and alkaline phosphatase, urease and sucrase activity, which was a suitable management measure for sustainable wheat production in this area.

In the oasis irrigated agricultural region, the low resource utilization efficiency and the ratio of output/input are the most prominent constraints for crop production. In this study, the characteristics of light use efficiency, irrigation water productivity and economic benefit in different cropping patterns were investigated in the areas. Research on the sustainability of different cropping patterns would benefit crop production to save cost and increase income in this region.

A field experiment was carried out in a typical arid irrigation area, Wuwei, Gansu province, from 2018 to 2020, to determine the effects of different cropping patterns on leaf area duration, grain yields light utilization efficiency, irrigation water productivity and economic benefit of crops. The sustainability of different cropping patterns was evaluated based on the above indexes.

Multiple cropping of green manure after spring wheat harvested significantly increased the leaf area duration of the main-cultivate crops during the whole growth period. W-G//M increased leaf area duration of the main-cultivate crops by 7.7%-7.8%, compared with W//M. Compared with sole cropping and spring wheat-green manure multiple cropping, the intercropping increased the grain yield of main-cultivate crops and the inputs of production cost, simultaneously. There was no significant difference in the total grain yield between W-G//M and W//M in 2018 and 2019. However, W-G//M increased the total grain yield by 8.7% in comparison to W//M in 2020. Compared with M, W-G and W, W-G//M increased net return by 16.7%-26.5%, 78.5%-132.2% and 35.9%-78.8%, respectively. In two intercropping patterns, the net return of the W-G//M decreased by 7.2% in comparison to W//M treatment in 2018. However, the net return of two intercropping treatments showed not significantly different in 2019 and 2020, and the ratio of output/input showed a similar result. Multi-planting green manure after wheat harvested could significantly improve the light use efficiency of crops. W-G//M treatment increased light use efficiency by 7.2%-14.1% compared with W//M. The light use efficiency under W-G was increased by 23.5%-52.1% in comparison to W treatment. Compared with W, the productivity of irrigation water under W-G was significantly reduced by 48.6%-54.3% (irrigation water use efficiency) and 30.9%-39.8% (Economic benefit per cubic meter irrigation water), while there was no significant difference in the productivity of irrigation water under W-G//M and W//M. W-G//M had the highest sustainability index across three years.

Grain yield of main-cultivate crops and economic benefits were improved by intercropping and multiple cropping green manure after wheat harvested. The irrigation water productivity and light utilization efficiency were also increased, thereby improved the sustainability of this cropping pattern. Therefore, multiple cropping green manure after wheat harvested in wheat/maize intercropping could be used as a high-efficient utilization of resources and sustainable cropping pattern in arid irrigation areas.

The problem for film-mulched maize in the oasis irrigation region was an advanced nitrogen (N) requirement and led to the insufficient supply of N at the late growth stages. In this study, the effects of N-fertilizer postponing application on intercropped maize photosynthetic physiological characteristics and grain yield were studied, so as to reveal the photosynthetic mechanism of intercropped maize grain yield advantage in the experimental area.

From 2019 to 2021, the maize was used as experimental materials in Hexi oasis irrigation region. The split-plot experiment design was adopted, among which pea/maize intercropping and maize monoculture were the main factors, and three N fertilizer postponing application (postponing ration 20%, 10%, and traditional practice) were the secondary factors. Then, this field experiment was used to investigate the photosynthetic physiological characteristics and yield performance of maize under N-fertilizer postponing application and intercropping pattern.

The results demonstrated that the grain yield of intercropped maize under the postponing application of 20% N-fertilizer and 10% was increased by 28.5% and 13.8%, and biomass yield by 23.8% and 12.5%, respectively, compared with traditional N management practices. Similarly, compared with traditional N management practice, the grain yield of sole maize under the postponing application of 20% N-fertilizer and 10% was also increased by 29.7% and 13.3%, and biomass yield by 19.6% and 10.3%, respectively. Compared with the monoculture maize, intercropping could increase the grain yield by 33.2%-35.1% and biomass yield by 26.8%-31.5% under the same area. Furthermore, the postponing application of 20% N-fertilizer and 10% increased the population grain yield of intercropping pattern by 27.2% and 12.9%, respectively, compared with the traditional N management practice. The results showed that intercropping pattern could increase the grain yield of maize compared with the sole pattern, and the N fertilizer postponing application also boosted the improvement of grain yield in the intercropping system compared with the traditional N management practice. During the whole growth periods, the intercropping increased the net photosynthetic rate, stomatal conductance, transpiration rate, and decreased intercellular CO₂ concentration. Compared with traditional N management, the net photosynthetic rate under the postponing application of 20% N-fertilizer and 10% was increased by 12.8% and 6.0%, the stomatal conductance by 14.0% and 6.9%, and the transpiration rate by 20.5% and 9.5%, respectively, while the intercellular CO₂ concentration was decreased by 29.8% and 13.1%, respectively. The SPAD value under the postponing application of 20% N-fertilizer and 10% was increased by 7.5% and 3.7%, respectively. The principal component analysis results showed that the N-fertilizer postponing application and intercropping pattern could increase the grain yield via boosting the net photosynthetic rate, the stomatal conductance, the transpiration rate, and leaf SPAD value, and decreasing intercellular CO₂ concentration.

N-fertilizer postponing application 20% treatment (36 kg·hm^-2 N fertilizer was topdressing at maize jointing stage and 108 kg·hm^-2 at 15 d post-silking stage) had the advantage of improving the photosynthetic characteristics of intercropped maize, thereby boosting the grain yield improvement.

The aim of this study was to investigate the effects of green manure and wheat straw co-incorporation on water use efficiency of next season wheat (Triticum aestivum L.), which played an critical supporting role in the construction of water use efficient and sustainable production pattern of spring wheat in northwest irrigation region.

In this study, a randomized block design was adopted, with fallowing after wheat harvesting (W) as the control, wheat multiple cropping green manure with no-tillage sowing + green manure and wheat straw co-incorporation (W-NTGS), wheat multiple cropping green manure with no-tillage sowing + green manure incorporation (W-NTG), and wheat multiple cropping green manure shallow plowing for destroying stubble + single returning of green manure to the field (W-TG). The characteristics of water consumption, grain yield, water use efficiency (WUE) and irrigation water use efficiency (WUE_i) of wheat were investigated.

The soil water storage in 0-50 cm soil layer before wheat sowing was significantly increased by multiple cropping green manure compared under W. The soil water storage in 0-10 cm, 10-20 cm, 20-30 cm, and 30-50 cm soil layers before wheat sowing with W-NTGS was increased by 22.1%, 30.2%, 21.5%, and 11.1% compared with that of W-NTG, and 26.2%, 33.2%, 26.5%, and 16.4% increase compared with that of W-TG, respectively. However, there was no significant difference in soil water storage in 0-110 cm soil layer before wheat sowing between W-NTG and W-TG. Compared with fallow treatment, water consumption, evaporation, and ratio of evaporation to evapotranspiration of wheat decreased by 7.0%-7.1%, 11.7%-20.1%, and 5.2%-15.9%, respectively. The water consumption of wheat with W-NTGS decreased by 6.4% than that of wheat under W-NTG in 2021, and averagely decreased by 6.1% than that of wheat under W-TG in 2020 and 2021. Compared with W-NTG and W-TG, the evaporation of wheat under W-NTGS decreased by 9.7% and 13.6% on average, and the ratio of evaporation to evapotranspiration decreased by 6.2% and 11.3%, respectively. There were no significant differences in water consumption, evaporation, and evapotranspiration ratio between W-NTG and W-TG. Compared with W, the grain yield of wheat multiple cropped with green manure increased by 6.4%-16.8%. Meanwhile, the grain yield of wheat under W-NTGS increased by 6.6% and 9.8% on average compared with W-NTG and W-TG, respectively. However, the grain yield of wheat between with W-NTG and W-TG was not significant difference. Compared with W, the WUE and WUE_i of wheat multiple cropped with green manure increased by 11.9%-30.7% and 6.4%-16.8%, respectively. The WUE of wheat under W-NTGS increased by 10.9% and 16.8%, and the WUE_i increased by 6.6% and 9.8%, respectively compared with W-NTG and W-TG. There were no significant differences in WUE and WUE_i between W-NTG and W-TG.

The co-incorporation of green manure and wheat straw (W-NTGS) could significantly increase soil water storage in 0-50 cm before wheat sowing, and decrease the ineffective loss of soil water in wheat season, thus reducing the water consumption of wheat and increasing the grain yield, and ultimately significantly improving the farmland and irrigation water use efficiency, which could be used as a recommended technology for water efficient use of wheat multiple cropping with green manure in arid irrigation region.

In view of the severe water shortage of resource-based irrigation areas in the west of the river oasis and the large amount and low utilisation of mulch and water and nitrogen inputs in crop production, the effects of no-tillage and two-year use of mulch on the water utilisation characteristics of subsequent crops under water and nitrogen reduction conditions were explored to provide a practical basis for the construction of water and nitrogen reduction and efficient water utilisation technologies in the trial area.

From 2019 to 2021, a three-factor split plot experiment was carried out, with two tillage methods of conventional tillage (CT) and no-tillage (NT), two irrigation levels of 20% reduced irrigation (I1, 1 920 m³·hm^-2) and conventional irrigation (I2, 2 400 m³·hm^-2), and three N levels of 40% reduced N application (N1, 135 kg·hm^-2), 20% reduced N application (N2, 180 kg·hm^-2) and conventional N application (N3, 225 kg·hm^-2), to study the evapotranspiration, evaporation and water use efficiency of different treatments.

The one film for two years can optimize the soil water environment before wheat sowing and reduce the ineffective water consumption during wheat growth period. Compared to CT, NT was beneficial to increase soil water content and water storage before wheat sowing, which increased by 16.9%-23.0% and 14.5%-16.5%, respectively; It can reduce the evapotranspiration (ET), total evaporation (E) and proportion of evaporation to evapotranspiration (E/ET) of wheat in the whole growth period by 3.5%-4.2%, 19.0%-20.2% and 16.8%-19.3%, respectively. With the reduction of irrigation and N application, the three indicators of evapotranspiration, evaporation and E/ET decreased. Compared with I2, the three indicators decreased by 6.1%-6.4%, 10.8%-11.1% and 5.5%-6.0%, respectively; Compared with N3, N2 and N1 decreased by 2.2%-3.9%, 4.2%-10.9% and 1.7%-7.2%, respectively; Under the interaction of tillage and irrigation, evapotranspiration and E/ET of NTI1 decreased by 0.6%-6.6% and 17.4%-17.6% respectively compared with CTI1; Integrated water and nitrogen reduction for two years with no tillage and one film to further optimize water consumption structure, the three indicators for NTI1N2 were reduced by 11.0%-12.9%, 28.3%-47.6% and 22.5%-26.4% respectively compared to CTI2N3. Compared with CT, NT significantly improved wheat grain yield and water use efficiency by 4.8%-6.3% and 9.0%-9.5% respectively. Under NT and CT conditions, there was no significant difference in grain yield and water use efficiency (WUE) between I1N2 and I2N3, I2N2 wheat. Comparing wheat grain yield and water use efficiency under different treatments, NTI1N2 was the highest, increasing grain yield and WUE by 5.1%-6.6% and 5.7%-6.2%, respectively, compared to the control CTI2N3.

In the Hexi irrigation area, no-tillage and one-film two-year rotation of maize for wheat, irrigation of 1 920 m³· hm^-2 and N application of 180 kg· hm^-2 in the whole growth period, is a production technology suitable for water and nitrogen conservation, high wheat yield and efficient water use in this area.

In arid irrigation area, the problem of limited water resources, high nitrogen fertilizer input, and low water use efficiency (WUE) in maize production is serious, it’s necessary to investigate the viability of dense planting to compensate for the negative impact of reduced nitrogen application on the water use efficiency of maize, so as to provide academic foundation for the maize production with reduced nitrogen but high water use efficiency.

From 2019 to 2022, a split-plot experiment was carried out in Wuwei, Gansu Province. Two levels of nitrogen application rate, including reduced nitrogen application (N₁, 270 kg·hm^-2) and traditional nitrogen application (N₂, 360 kg·hm^-2) were set in the main plot. Three planting densities, including traditional density (M₁, 78 000 plants/hm²), medium density (M₂, 103 500 plants/hm²), and high density (M₃, 129 000 plants/hm²) were set in the split-plot, N₂M₁ was set as the control. The effects of nitrogen application, plant density and their interaction on water consumption characteristics and water use efficiency of maize were mainly studied.

In the trial year, the water consumption of reduced nitrogen application was 4.7% lower than that of traditional nitrogen application. The water consumption of the combination of reduced nitrogen application and medium density (N₁M₂) was not significantly different from that of the control. The water consumption of high and medium density treatments increased by 8.4% and 4.2% respectively compared with that of traditional density treatment. The grain yield of maize decreased with the reduction of nitrogen application. Medium density could increase grain yield compared with high density and traditional density. The combination of reduced nitrogen application and medium density increased the grain yield compared with the control. In the test year, the grain yield of the reduced nitrogen application treatment was 4.6% lower than that of traditional nitrogen application treatment, the grain yield of the medium density treatment was increased by 5.6% and 8.2% respectively compared with high density treatment and traditional density, and the grain yield of N₁M₂ was 4.3% higher than that of N₂M₁. Reducing nitrogen application reduced IWUE, but maintained the same WUE as traditional nitrogen application; Medium density was beneficial to improve WUE and IWUE, and could compensate for the WUE decrease caused by reduced nitrogen application. In the four study years, the IWUE decreased by 4.5% due to reduced nitrogen application, and there was no significant difference in WUE between the two nitrogen application levels; Compared with the traditional and high density treatments, the IWUE of the medium density treatment increased by 8.6% and 6.4%, respectively, and the WUE increased by 4.5% and 10.1%, respectively; The compensation effects of medium density on the IWUE and WUE were 4.3% and 5.2%, respectively.

In arid irrigation area, applying nitrogen of 270 kg·hm^-2 and density of 103 500 plants/hm² during the whole growth period of maize can increase the yield and water use efficiency compared with the existing water and nitrogen management measures, which is a production technology for nitrogen saving and water efficient utilization of maize in this area.