| Aiming at the problems of shallow soil available surface and low nitrogen fertilizer utilization in the drought-cultivated mountainous area of south Ningxia,a two-year localization experiment was conducted in the drought-cultivated mountainous area of south Ningxia to further explore the potential of potato yield increase.In the first year(2021),the field experiment of different tillage depth(ploughing 20 cm(F20),subsoiling 30 cm(S30),subsoiling 40 cm(S40),subsoiling 50 cm(S50))with nitrogen application rates(0 kg/hm2(N0),90 kg/hm2(N90),180 kg/hm2(N180),270 kg/hm2(N270))was set.In the second year(2022),based on the first year experiment,a 15N isotope labeled microzone experiment was set up.The study was conducted to investigate effects of potato growth and development,root characteristics,plant nitrogen uptake,accumulation,transport and yield under different tillage depth with nitrogen application rates,and further elucidate the influencing factors on tuber yield formation.The aim of this study was to explore the tillage depth with nitrogen application rates suitable for potato growth in the mountainous area of south Ningxia,so as to provide theoretical basis and technical reference for the healthy and sustainable development of upland potato industry in this area.The main research results are as follows:1.Subsoiling,nitrogen application and their interaction could significantly affected root morphological characteristics and physiological activities of potato at key growth stages(budding,tuber formation and tuber expansion).Under the same tillage depth,N180 treatment could significantly promote root growth,and under the same nitrogen application rate,S30 and S40 treatment could significantly promote root growth.Compared with F20 × N0 treatment,S30×N180 treatment had the best effect on root length,root surface area,root volume,root tip number,root activity and root absorption area in 2021,which were significantly increased by 28.82%,32.73%,38.29%,11.25%,15.40%and 38.31%.In 2022,S40 ×N180 treatment was the best,with significant increases of 30.75%,32.42%,35.18%,12.97%,14.48%and 34.05%compared with F20×N0 treatment,respectively.2.Subsoiling,nitrogen application and their interaction could improve potato emergence rate,and the emergence rate of potato under S30×N180 treatment was the highest,which was significantly increased by 23.43%compared with F20×NO treatment in 2 years.Under the same tillage depth,N180 treatment could significantly improve plant height,leaf area index,dry matter quality of above-ground and underground parts of potato during the whole growth period.In 2021,S30 × N180 treatment had the best effect,significantly increased by 39.61%,21.01%,51.64%and 104.47%compared with F20 × N0 treatment.In 2022,S40×N180 treatment had the best effect.Compared with F20×N0 treatment,it was significantly increased by 35.26%,19.60%,34.61%and 52.05%.In the key growth period of potato,the photosynthetic capacity of potato leaves could be improved by suitable nitrogen application.The net photosynthetic rate of leaves was the highest in S30×N180 treatment,which was 19.47%higher than that in F20×N0 treatment in 2 years.The transpiration rate of leaves treated with S30×N180 in 2021 and S40×N180 in 2022 was the highest,which significantly increased by 53.60%and 50.68%compared with F20×N0 treatment,respectively.3.Subsoiling,nitrogen application and their interaction could significantly increase potato yield.Under the same tillage,the yield of N180 treatment was the highest in two years.Under the interaction of the two,the total potato yield could be significantly increased by subsoiling of 30-40 cm combined with N180 treatment,and the yield of medium potato could be significantly increased by deep loosening of 50 cm.After fitting the total potato production,tillage depth and Nitrogen application rate in 2021 and 2022,it was found that crop yield increased first and then decreased with the increase of tillage depth and Nitrogen application rate.When the subsoiling of 30-40 cm and the Nitrogen application rate was 146.74-161.01 kg/hm2,the highest yield of potato could be obtained.4.Subsoiling,nitrogen application and their interaction could significantly affected nitrogen uptake,accumulation and distribution in potato organs.Under the same tillage practice,the nitrogen accumulation of plant organs under N180 treatment was the highest in two years.Under the interaction of the two treatments,the nitrogen accumulation under S30 × N180 treatment in 2021 and S40 × N180 treatment in 2022 was the highest,which significantly increased by 123.89%and 88.11%compared with F20×N0 treatment,respectively.The nitrogen accumulation was mainly concentrated in the stem and leaf at the expansion stage from seedling to tuber,and was mainly concentrated in the tuber at harvest stage.In all treatments,the subsoiling of 30-40 cm combined with the nitrogen application rate of 90-180 kg/hm2 could significantly improve the nitrogen harvest index,nitrogen agronomic use efficiency,nitrogen partial productivity,nitrogen physiological use efficiency and nitrogen use efficiency of potatoes.5.Subsoiling,nitrogen application and their interaction can significantly increase the nitrogen content in soil,so as to achieve the nitrogen balance of soil and plant..With the deepening of soil layer,the contents of total nitrogen,alkali-hydrolyzed nitrogen,nitrate nitrogen and ammonium nitrogen in 0-60 cm soil gradually decreased,but with the increase of nitrogen application rate,the contents of total nitrogen,alkali-hydrolyzed nitrogen,nitrate nitrogen and ammonium nitrogen in 0-60 cm soil gradually increased,with the nitrogen application rate of 270 kg/hm2 being the most significant increase.In 2021,compared with F20 × N0 treatment,total nitrogen,alkali-hydrolyzed nitrogen and nitrate nitrogen in 0-60 cm soil were significantly increased by 82.61%,69.36%and 145.28%under S30×N270 treatment,and ammonium nitrogen in 0-60 cm soil under S40 X N270 treatment was significantly increased by 234.11%compared with F20 ×N0 treatment.In 2022,compared with F20 ×N0 treatment,total nitrogen and nitrate nitrogen in 0-60 cm soil under S30 X N270 treatment significantly increased by 37.84%and 165.26%,and ammonium nitrogen in 0-60 cm soil under S40 × N270 treatment significantly increased by 313.79%compared with F20×N0 treatment.6.The optimal nitrogen application rate of deep roosting combined could significantly increase the percentage of 15N atom excess and Ndff(N derived from fertilizer)in each organ of the plant,and significantly promote the accumulation of 15N in tuber at swelling stage and harvesting stage.Among all treatments,S40 × N180 treatment had the highest 15N accumulation,and S40 × N90 treatment had the highest nitrogen absorption(15N)use efficiency.The contribution of fertilizer N to the nitrogen content of each plant organ was higher than that of soil N.With the progress of growth stage,the total fertilizer N of each plant organ increased gradually,and the ratio of soil N source decreased gradually.At harvest stage,the ratio of fertilizer N source was 1.09%-12.86%,and the ratio of soil N source was 87.15%-98.92%.The absorption,accumulation and distribution of fertilizer N and soil N in potato organs were significantly improved by tillage nitrogen application.In conclusion,subsoiling combined with proper nitrogen application could significantly improve the balance of plant fertilizer nitrogen and soil nitrogen,and enhance the absorption and transport of different nitrogen by plants.The physiological and physiological characteristics of root system,plant and plant nitrogen had significant positive correlation with potato yield and nitrogen use efficiency under deep roosting nitrogen application.Although total nitrogen in soil 0-60 cm had no significant effect on potato yield,it could significantly improve nitrogen use efficiency.The results showed that the number of root tips,root absorption area and dry matter weight were very important to improve potato yield,and the comprehensive score of principal components was the highest when combined with 180 kg/hm2 nitrogen application at subsoiling of 30-40 cm.Therefore,from the perspective of yield and high yield and efficient nitrogen use,the root and plant growth and physiological characteristics of potato can be significantly improved by subsoiling of 30-40 cm combined with nitrogen application rate of 180 kg/hm2,and the transfer of fertilizer nitrogen and soil nitrogen to tuber can be increased,so as to promote the growth of plant,tuber yield and efficient nitrogen use. |
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