Nitrogen Management In Wheat/maize Strip Intercropping For Improving Soil Health And System Productivity Under Rainfed Conditions

The dry farming area of the Loess Plateau is an important grain producing area in China.In the context of scarce resources,steady and continuous improvement of farmland productivity is a challenging task in the Northwest arid region.Intercropping can offer a pragmatic solution as it involves the intensive utilization of agricultural resources and promotion of high and stable yield of crops.A 2-year fixed site field experiment was conducted in Yangling District,Shaanxi Province from 2019 to 2021.The experiment included three intercropping treatments viz.wheat-monocropping（WMC）,maize-monocropping（MMC）,and maize-wheat intercropping（IMW）,and two N application rates viz.control（-N）and full-dose of N(+N,basal application at 150 and 235 kg ha^-1for wheat and maize,respectively).The effects of intercropping pattern and fertilization on the growth and development of population crops,resource utilization and sustainable system productivity were evaluated,including the effects of soil chemical properties,nutrient acquisition,and enzyme activities.Crop physiological characters,yield,and related characters;and chlorophyll fluorescence,gas exchange characteristics,lipid peroxidation,antioxidant properties,and other related indicators,in order to provide a theoretical basis for the development of wheat/maize model in the Loess Plateau dry farming area were also assessed.The main results of the study are as follows:（1）Results showed that IM-W increased N accumulation by 19.87%and 7.20%,and16.63%and 6.58%,P accumulation by 73.05%and 78.80%,and 69.75%and 24.50%,K accumulation by 20.50%and 7.49%,and 17.70%and 7.22%（averaged for N rates）in 2019and 2020,as compared to that of the respective monoculture crops,respectively.As compared with WMC and MMC,IM-W increased total N by 9.36%and 6.95%,Olsen P by25.54%and 21.78%,and exchangeable K by 14.63%and 7.96%and nutrients use efficiency by 23.56%and 34.76%（averaged for N rates and years）,respectively.The mean increase in urease by 7.56%and 4.43%,acid phosphatase by 38.47%and 16.26%,nitrate reductase by64.60%and 44.17%,sucrase by 19.39%and 7.75%,catalase by 119.21%and 34.31%,polyphenol oxidase by 194.44%and 86.36%,invertase activities by 144.82%and 40.53%,and the overall enzyme activity index by 43.70%and 52.89%for intercropping treatment（averaged for N rates and both years）was recorded,over WMC and MMC treatments,respectively.（2）Furthermore,our results showed that IMW significantly improved the land use efficiency,dry matter accumulation,grain yield and yield characteristics of both crops under rainfed conditions.Intercropping with N application（+N treatment）resulted in the highest wheat grain yield with 70.37%and 52.78%increase as compared with monoculture and without N application in 2019 and 2020,respectively.The contribution towards increased grain yield was the highest by the border rows followed by the second rows.This increase was attributed to higher number of ears per square meter（10-25.33%more in comparison to sole crop without N application）during both years of study.The sole wheat crop without any N application recorded the least values for all yield-related parameters.Despite the absence of significant differences,the relative decrease in intercropped maize under both N treatments was over 9%compared to the sole maize crop,which was mainly ascribed to the border rows（24.65%decrease compared to the sole crop）that recorded 12.0%and 13.0%decrease in kernel number and thousand-grain weight,respectively than the sole crop.This might be attributed to the reduced photosynthesis and chlorophyll pigmentation in IMW maize crop during the blended growth period.（3）Moreover,we also noted that as compared with their respective monocropping treatments,IW and IM increased the chlorophyll fluorescence（Fo/Fm）by 18.35%and14.33%,PS-11 efficiency by 7.90%and 13.44%,photosynthesis by 14.31 and 23.97%,C-capacity by 32.05%and 12.92%,and stomatal conductance by 41.40%and 89.95%under without-and with-N application,respectively.The reductions in WUEi,i WUE,and MDA content in the range of 8.76-26.3%were recorded for IW and IM treatments compared with WMC and MMC,respectively.There was a significant（P<0.05）increase in overall water use efficiency for intercropping treatment as compared with monocrops.Compared with the WMC and MMC,IW and IM also triggered better antioxidant activities under both N rates.The better performance of intercropping treatments i.e.,IW and IM were also associated with improved osmolytes accumulation under rainfed conditions.As compared with control,N addition significantly improved the chlorophyll fluorescence,gas exchange traits,lipid peroxidation,and antioxidant enzyme activities under all intercropping treatments.To provide insights into the subsequent research on the molecular mechanism of crops’resistance to water stress,stably expression of enzymatic and non-enzymatic antioxidants-related genes were screened.Gene expression of both enzymatic and non-enzymatic antioxidants genes was relatively stable in different tissues of wheat and maize crops under water scares conditions.In conclusion,under the rain-fed condition of the Loess Plateau,wheat/maize intercropping population had advantages in utilizing the light energy,nutrients and the available moisture,which can improve the soil chemical and biological properties,enhance photosynthetic and antioxidant characteristics of crops,promote efficient nutrient acquisition of crops,and further promote dry matter accumulation and yield formation of crops.Therefore,this intercropping model can be successfully adopted for the subhumid prone arid regions and subhumid areas with annual precipitation of 450 mm-650 mm.