| The lack of water resources and the dislocation with the key water demand stage of crops,extensive farming management and unscientific application of nitrogen fertilizer are the important reasons for the low yield and poor quality of grain crops in the dry farming area of southern Ningxia.How to efficiently use the natural precipitation during the potato growth period and accurately match the best fertilization amount and tillage depth to promote crop growth is the key technical means to solve the sustainable agricultural production in this area.Therefore,this study carried out a field positioning experiment from 2021 to 2022.By setting different tillage depths[plowing 20 cm(F20),subsoiling 30 cm(S30),subsoiling 40 cm(S40)and subsoiling 50 cm(S50)]and nitrogen application rates[no nitrogen application(NO),low nitrogen application(N90),medium nitrogen application(N180)and high nitrogen application(N270)],a two-factor split-plot experiment was conducted to explore the effects of different tillage depths combined with nitrogen fertilizer measures on soil structure,water and nutrients,potato yield and quality,in order to explore the yield-increasing mechanism of tillage combined with nitrogen fertilizer measures.It provides technical and theoretical reference for the development of dryland water-saving agriculture in southern Ningxia.The main results are as follows:1.Tillage depth significantly affected soil bulk density and porosity in 0-40 cm layer.In 2021 and 2022,S50N90 and S50N0 had the best improvement effect on soil bulk density in 0-20 cm layer,which were significantly reduced by 5.5%and 5.6%,respectively,compared with tillage without N rate.The soil bulk density(20-40 cm layer)was improved best by S50N180 and S50N0 in 2021 and 2022,respectively,which were significantly reduced by 3.0%and 5.8%compared with the control treatment.Tillage depth and nitrogen application rate could significantly affect the number of mechanical and waterstable aggregates in>0.25 mm particle size soil,while the interaction between them only had a significant effect on the number of water-stable aggregates in 0-20 cm soil layer.In the two years,the number of mechanical and water-stable aggregates in the 0-20 cm layer>0.25 mm particle size soil was the highest in the S30N180 combination treatment.Compared with the tillage without nitrogen treatment,the number of soil mechanical and water-stable aggregates increased significantly by 15.0%and 37.4%,respectively.Tillage depth,nitrogen application rate and their interaction had extremely significant or significant effects on soil compactness during potato growth period.In 2021,the soil compactness of S50N180 and S50N270 treatment was the best during the potato growth period,but S50N0 and S50N90 treatment were the best in 2022.Under the same nitrogen application rate,the soil compactness of potato at different growth stages showed S50<S40<S30<F20.2.Tillage depth and nitrogen application rate had extremely significant or significant effects on soil water storage(0-100 cm layer).In the key growth period of potato(60,90 and 120 days after sowing)in 2021,the water retention effect of S50N0 combination treatment was the best,which was significantly increased by 19.6%compared with the control treatment.In 2022,the combination of S40N0 and S50N0 has better water storage effect.Under the same nitrogen application rate,the soil water storage in the growth period of potato treated with S50 was the highest in both years.Compared with the F20 treatment,the average soil water storage was significantly increased by 15.4%in 2021,and the average soil water storage in 2022 was significantly increased by 8.4%.Under the same tillage depth,the soil water storage was the highest under no nitrogen treatment.3.After two years of tillage and nitrogen application,the interaction between tillage and nitrogen application can effectively improve the soil nutrients in the 0-60 cm layer.At the same tillage depth,the soil nutrient content of all treatments increased significantly with the increase of N rate.In all treatment combinations,the soil total nitrogen and alkali-hydrolyzable nitrogen content in the two years was higher in the combination treatment S30N270 and S40N270,while the tillage without nitrogen treatment was the lowest.In 2022,the content of available potassium(0-60 cm layer)was the highest in S30N270 treatment,which was significantly increased by 89.3%compared with the control treatment.The content of available phosphorus and inorganic nitrogen in 0-40 cm soil layer was basically the highest in the treatment of deep loosening 30 cm or 40 cm combined with high nitrogen(270 kg/hm2)in the two years.4.The yield of potato increased significantly under different tillage depths combined with nitrogen application,and it could effectively improve crop water use efficiency and economic net income.Tillagedepth and nitrogen application rate had extremely significant effects on potato yield in 2021 and 2022 years,while the interaction between tillage and nitrogen application only had extremely significant effects on potato yield in 2022.Compared with the control treatment,the potato yield was the best in the S30N180 combination treatment in 2021,with an increase of 90.2%,and the S40N180 combination treatment was the best in 2022,with an increase of 69.7%,while the economic benefit,water use efficiency and yield treatment results are consistent.The fitting results of tillage depth and nitrogen application rate with potato yield showed that the application of nitrogen fertilizer 149.1 kg/hm2 on the basis of subsoiling 36.6 cmwas beneficial to provide a good soil microenvironment for the area and ensure stable and high yield of potato.5.Tillage depth,nitrogen application rate and their interaction had extremely significant or significant effects on potato quality components.In 2021,the contents of crude protein,starch and Vc in potato were the best in S50N180 combination treatment,which were significantly increased by 23.8%,55.2%and 46.5%respectively compared with the control treatment.In 2022,the contents of crude protein and starch in potato were the best in S30N180 combination treatment,and the Vc content was the best in S50N180 combination treatment,which were significantly increased by 68.1%,4.5%and 38.2%respectively compared with the control treatment.6.Through the correlation and principal component analysis of potato and each index,it was found that the key factors affecting potato yield under different tillage depths combined with nitrogen application rate were the number of soil mechanically stable aggregates with particle size of>0.25 mm,available phosphorus and inorganic nitrogen.The key factors affecting the content of potato quality components were the number of soil aggregates with>0.25 mm particle size,total porosity,available nitrogen,inorganic nitrogen,available potassium,total nitrogen and available phosphorus.In summary,different tillage depths combined with nitrogen fertilizer treatment can significantly improve soil structure,regulate soil moisture and nutrient environment in potato fields,and increase potato yield and quality.C onsidering the effects of soil fertilization,structure improvement,water storage and cost,it is suggested to promote subsoiling 30 cm or 40 cm combined with nitrogen fertilizer 180 kg/hm2 in the actual production of southern Ningxia mountainous area,so as to achieve high yield and quality improvement of crops. |
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