The aim of this study was to investigate the effects of green manure combined with wheat straw returning application on grain yield and leaf photosynthetic characteristics of spring wheat (Triticum aestivum L.) under different nitrogen reduction levels, which could provide theoretical basis and technical support for establishing spring wheat multiple cropping with green manure saving and efficient production pattern.

The experiment was conducted at the Wuwei Oasis Agricultural Experimental Station of Gansu Agricultural University in 2022 and 2023. The split-plot designed experiment was adopted. The main plot was designed with different returning materials at three levels, including green manure and wheat straw combined returning application (W-GS), green manure returning application alone (W-G), and fallowing after wheat harvesting (W-F). The split plot was designed with four nitrogen application levels, including conventional nitrogen application rate (N1, 225 kg N·hm^-2), nitrogen application rate reduced about 15% (N2,190 kg N·hm^-2), about 30% (N3,155 kg N·hm^-2), and about 45% (N4, 120 kg N·hm^-2). The chlorophyll value (SPAD value), photosynthetic characteristics and grain yield of the top expending leaf of spring wheat was measured, and the leaf water use efficiency and light energy utilization efficiency was analyzed.

Negative effect of nitrogen reduced application was observed on the grain yield of spring wheat, however, this effect was compensated even the grain yield of spring wheat was increased by green manure combined with wheat straw returning application. With the same nitrogen application rate, compared with that of W-F, the grain yield of spring wheat under W-GS and W-G increased by 15.3% and 9.4%, respectively, and the grain yield of spring wheat with W-GS was increased by 5.4% than that of W-G. The grain yield of spring wheat under W-F was decreased by the decreasing of nitrogen application rate, while that of W-GS had no significant difference between N3 and N1. The grain yield under W-GSN3 was not reduced compared with that under W-GSN1 and W-FN1. The photosynthetic characteristics of spring wheat leaf with nitrogen reduced application rate was improved by green manure combined with wheat straw returning application. The SPAD value, net photosynthetic rate (P_n), stomatal conductance (G_s), transpiration rate (T_r) and leaf water use efficiency (LWUE) of spring wheat leaf under W-GS were significantly increased, respectively, compared with that of W-G and W-F under the same nitrogen application rate. With the decreasing of nitrogen application rate, the SPAD value, P_n, G_s, T_r and LWUE of spring wheat leaf under W-F was decreased significantly, however, there was no significant difference between N3 and N1 in W-GS. Comparison between combined treatments, there was no significant difference in photosynthetic characteristics of spring wheat under W-GSN3 compared with W-GSN1 and W-FN1. The light use efficiency (LUE) of spring wheat was significantly increased by 5.2% W-GS than that of W-F. The LUE of spring wheat with W-F decreased by the decreasing of nitrogen application rate, however, the LUE of spring wheat with W-GS was not significant difference between N3 and N1. There was no significant difference was observed in the LUE of spring wheat under W-GSN3 compared with that under W-GSN1 and W-FN1. The results of the path analysis indicated that, the grain yield of spring wheat was mainly determined by thousand kernel weight, which was affected by the regulation on net photosynthetic rate and transpiration rate via stomatal conductance of spring wheat leaf.

The green manure and wheat straw combined returning application mainly increased the thousand kernel weight of spring wheat by improving the photosynthetic characteristics of spring wheat leaf, and finally did not reduce the grain yield of spring wheat under 30% nitrogen reduced application rate. Therefore, the green manure and wheat straw combined returning application under nitrogen application rate of 155 kg·hm^-2 was recommended as a nitrogen saving and efficient production pattern of spring wheat multiple cropping with green manure in arid oasis irrigation region.

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.

This study aimed to clarify the response of maize growth and yield with different nitrogen application rates to intercropped green manure, so as to provide the basis for establishing maize production pattern with nitrogen fertilizer saving via green manure in arid irrigation area.

A split plot experiment design was adopted, and two planting patterns of maize intercropping with common vetch (MV) and sole maize (SM) were set up in the main plot. Five nitrogen application rates were set up in the split plot: the recommended nitrogen application rates were N360: 360 kg N·hm^-2, application rates reduced with 25% (N270): 270 kg N·hm^-2, and that reduced with 50% (N180): 180 kg N·hm^-2, reduced with 75% (N90): 90 kg N·hm^-2, and no nitrogen application (N0). Leaf area index (LAI), daily leaf volume (LAD), light energy utilization rate, dry matter accumulation and yield of maize were investigated.

In 75-150 days after maize emergence, the LAI, total LAD and light use efficiency of maize with reduced nitrogen application rate (N270, N180, N90, N0) were increased by intercropped green manure. The maize LAI, total LAD and light use efficiency under M||V with N270, N180, N90, and N0 were significantly increased by 9.8%, 8.2% and 4.6% than that under SM, respectively. The maize LAI, total LAD and light use efficiency under M||V with N270 was not different with that with N360, in 75-150 days after maize emergence, and which was greater than that of other treatments. Somehow, the maize LAI, total LAD and light use efficiency of SM was decreased with reduced nitrogen application rate. The dry matter accumulation of maize under N270, N180, N90, and N0 was significantly increased by intercropped with green manure than that of sole maize, in 90-150 d days after maize emergence, which was increased by 4.6%. In 75-130 days after maize emergence, the growth rate of maize under M||V was significantly increased by 5.9% compared that with SM. With the same reduced nitrogen application rate (N270, N180, N90, and N0), the maize grain yield under M||V was significantly increased by 8.5% than that under SM. The grain yield of intercropped maize under N270 was significantly higher than that of sole maize under N360. Compared with SM, the kernel number per ear and 1000-grain weight of maize under M||V were significantly increased by 6.0% and 6.3%, respectively. The results of the fitting curve showed that the greatest grain yield of maize intercropped with green manure was 14 876.4 kg·hm^-2 with nitrogen application rate 261.4 kg·hm^-2. While the greatest grain yield of sole maize was 14 012.5 kg·hm^-2 with nitrogen application rate of 348.6 kg·hm^-2. The effect of reducing nitrogen application on the fresh yield and nitrogen accumulation of green manure was significant. The fresh yield of green manure under M||VN270 was significantly higher than that under M||VN360, M||VN90 and M||VN0 by 3.8%, 4.6%, and 9.7%, respectively, while the nitrogen accumulation with M||VN 270 was significantly higher than that with M||VN90 and M||VN0 by 5.3% and 11.9%, respectively. The total dry matter accumulation of maize with reduced nitrogen applied rate was increased by intercropped green manure, and then the number of grains per ear and thousand grains weight of maize was increased. Therefore, the intercropped maize could obtain a greater level of grain yield with the condition of reduced nitrogen application rate.

The treatment of 25% reduced nitrogen rate with intercropped green manure could make maize obtain higher yield than sole maize with the recommended nitrogen application rate. This pattern could be used as a recommended production method for chemical nitrogen fertilizer reduced application of maize in the research region and even similar ecological region.