| Unscientific farming patterns and natural disasters have led to changes in the physical and chemical properties of sloping soils and damage to soil structure,resulting in serious soil erosion on sloping soils and affecting crop yields.As a conventional tillage pattern in black soil areas,the rainfall water infiltration and nutrient migration characteristics of cross-slope monopoly and downslope monopoly are directly related to black soil conservation and food production.Therefore,the study of the distribution of water and nutrients in soils under cross-slope monopoly and down-slope monopoly conditions can provide a scientific basis for the effective use and conservation of soil and water resources as well as agricultural production and livelihood.In this thesis,a field plot experiment was conducted to study the distribution characteristics of soil moisture and tracer Brand nitrogen nutrients in the 0-60 cm soil layer of soybean in the two slope treatments under rainfed conditions,and to analyse the differences in soil moisture and nutrient distribution between the cross-slope and down-slope monopoly conditions.The distribution of soil moisture and tracer Brand nitrogen nutrients in the 0-60 cm soil layer at different times during the soybean reproductive period were characterized.This paper provides a scientific basis for agricultural production and farmland environmental management.The main findings of this thesis are as follows:(1)Under natural rainfall conditions,the soil volumetric water content varied between 17.37%and 36.59% at six locations in the cross-slope monopoly treatment(i.e.up-slope monopoly furrow,up-slope monopoly side,monopoly platform plant centre,monopoly platform inter-plant,downslope monopoly side and down-slope monopoly furrow),and between 13.37% and 36.59% at four locations in the down-slope monopoly treatment(i.e.monopoly platform plant centre,down-slope monopoly platform inter-plant,monopoly side and monopoly furrow)during the soybean reproductive period.The soil volumetric moisture content varied between 13.71% and 33.67% in the downhill monopoly treatment.In both the cross-slope and down-slope monopoly treatments,the soil moisture in the furrow showed signs of migration to the deeper soil layer of the monopod as the soil depth increased.In the cross-slope monopoly treatment,the maximum soil water storage at different sampling periods was at the monopoly furrow.In the down-slope monopoly treatment,the soil water storage at the furrow location was still the highest,while the soil water storage at the side of the monopoly was the lowest among the three sampling locations at different sampling periods.The difference between the average soil water storage in the cross-slope monopoly and the downslope monopoly was higher than that in the down-slope monopoly at different times,with the largest difference between the two tillage patterns at the bulge stage and the smallest difference at the finish stage.(2)During the soybean growing period,the Br-concentrations in the soil ranged from 1.61 to878.11 mg/kg at different depths in the cross-slope monopoly treatment and from 1.79 to 872.06mg/kg in the downhill monopoly treatment.Under different treatment conditions,the peak Brcontent migrated from the top layer of the cultivated soil to the deeper 60 cm soil layer where leaching occurred over a period of about 60 days.In the horizontal slope monopoly mode,the Brcontent in the soil was mainly in the vertical direction in the first three samples(1st: 12 July;2nd:27 July;3rd: 11 August),but in the 4th sample(31 August),the Br-content was significantly higher in the slope direction,and the Br-content in the lower monopoly side was also the highest among the five locations in the slope direction.The Br-content in the centre of the monopoly was always higher than that in the inter-plant area at the bottom of the slope,and comparing the changes in the Br-content in the centre of the plant and the inter-plant area at the bottom of the slope,it was concluded that the Br-transportation intensity along the slope was increasing under the downhill monopoly conditions.The intensity of Br-migration along the slope was higher in the cross-slope monopoly than in the down-slope monopoly.The Br-content in the centre of the plant on the monopoly platform decreased by 49.53% to 62.21% each time,and the Br-content in the inter-plant area on the monopoly platform decreased by 16.64% to 36.82% each time under cross-slope monopoly cropping in the vertical direction.It can be inferred from the difference in the rate of reduction in soil Br-content between the two locations that the root system at the centre of the plant is the main player in nutrient uptake,while the nutrient uptake capacity at the inter-plant level is only half of that at the centre of the plant.Under downhill monopoly conditions,the Br-content of the soil on the side of the monopoly was higher for a longer period of time,which further proves that the amount of rainwater infiltration on the side of the monopoly is low and the relative loss of Br-is low.Comparing the Br-content in the centre of the plants in the cross-slope and down-slope monopoly,the Br-content in the centre of the plants in the cross-slope monopoly was higher than that in the down-slope monopoly on 12 July and 27 July,while the opposite was true on 11 August and 31 August,indicating that the cross-slope monopoly had a positive effect on nutrient supply in the early part of the crop,while the down-slope monopoly was beneficial to the nutrient supply of the plants in the later part of the crop.(3)The ammonium N content in the soil at different sampling locations of the cross-slope monopoly treatment ranged from 3.18 to 14.39 mg/kg,while the ammonium N content at different sampling locations of the down-slope monopoly treatment ranged from 3.26 to 13.99 mg/kg during the soybean fertility period without fertilizer application.The standard deviations of ammonium N concentrations at each location were small.Along the slope direction,the total ammonium nitrogen content was higher in the up-slope gullies and monopoly sides than in the down-slope gullies and monopoly sides in the cross-slope monopoly treatment.In the down-slope monopoly treatment,ammonium nitrogen began to migrate in the slope direction from the flowering stage.The analysis shows that the soil has a limited capacity to carry ammonium nitrogen and that ammonium nitrogen is also subject to slope migration.In the vertical,cross-slope monopoly treatment,the ammonium N content was higher in the centre of the plant on the monopole than in the inter-plant area,except for the six-node stage and the bulge stage.In the down-slope monopoly treatment,ammonium nitrogen began to migrate slopewards from the flowering stage,and the changes in ammonium nitrogen concentrations at the centre of the plant and at the inter-plant level at the bottom of the slope were found to be greater at the inter-plant level than at the centre of the plant in the 5-20 cm soil layer.The pattern of changes in ammonium nitrogen in the soil under different monopoly conditions was basically the same,showing a gradual decline from high to low,with a large change of more than 40% between the six-node stage and the flowering stage,and a smaller change of less than 20% in ammonium nitrogen nutrients during the subsequent fertility period.(4)The nitrate-nitrogen content of the soil in the cross-slope monopoly treatment without fertiliser ranged from 7.25 to 47.05 mg/kg,while that in the down-slope monopoly treatment ranged from 7.74 to 33.24 mg/kg during the soybean growing period.In the slope direction,the nutrient content in the 60 cm layer of soil in the cross-slope monopoly treatment remained at a high level from the six-node stage to the bulge stage,indicating that nitrate-nitrogen leaching was occurring in the soil;in the down-slope monopoly treatment,nitrate-nitrogen also began to migrate in the slope direction from the flowering stage.In the vertical direction,from the six-node stage to the bulge stage,the nitrate-nitrogen content was lower in the centre of the monopole than in the interplant area.The nitrate-nitrogen content was higher at the monopole from the bulge stage to the finish stage.The average nitrate-nitrogen concentrations in the cross-slope monopoly and the smoothbreakage monopoly showed the same trend and the same magnitude of change throughout the soybean reproductive period from the six-node stage to the pod stage.(5)The changes in ammonium and nitrate nitrogen in the 0-60 cm soil layer during the soybean reproductive period showed that the ammonium nitrogen content decreased from the six-node stage onwards,with the greatest change at the flowering stage.The soil ammonium nitrogen content decreases sharply during the flowering period.The significant increase in nitrate-nitrogen content during the flowering period further justifies this judgement. |
