Research on Soil Management System Taking Account of Soil and Nutrient Component Losses in Agricultural Land

旱地土壤养分流失不仅影响耕地生产力，而且影响下游水环境。本研究的目的是评价地表进水口与草地缓冲带的组合对减少土壤和养分流失的作用，并建立适合旱地土壤和养分成分的沉降池结构。此外，本研究还对该系统在泰国北部梯田的可接受性进行了调查。经过3年的研究，得出以下结果：(1)旱地土壤和养分流失观测2年旱地土壤和养分流失观测结果表明，旱地土壤和养分流失颗粒总氮和总磷的损失率分别为88.8 ~ 94.3%和98.4 ~ 99.6%。根据通用的土壤流失方程，根据氮磷迁移系数和计算的土壤流失量，可以预测养分流失。(2)评价杂草覆盖下保护性耕作减少土壤和养分流失的效果。保护性耕作采用杂草覆盖下立轴耕作（SW），常规耕作采用浅旋耕（RSB）和深旋耕（RDB）。另外，裸地免耕（NB）作为对照。施用RSB和RDB虽然降低了土壤的干密度，但降雨后孔隙结构并未持续。然而，西南杂草根部形成的压力即使在降雨后仍能维持，并增强了土壤中的渗透作用。因此，西南地区地表径流量和土壤、全氮、全磷损失量均低于西北地区、西南地区和西北地区。(3)评价地表进水口与草地缓冲带联合减少土壤和养分流失的效果人工降雨坡面模型样地的试验结果表明，由于控制了地表径流通过草地缓冲带的流量，将多余的地表径流划分到地表进水口，草地缓冲带对土壤和养分流失的捕获效率可以保持在较高水平。有地表进水口和无地表进水口的草地缓冲带和沉降池样地土壤总流失量、全氮和全磷均无显著差异。有地表进水口的地块沉降池泥沙量是无地表进水口的0.42倍。认为草地缓冲带和沉降塘结合地表进水口的水土保持系统可以完善各项水土保持策略，从维护角度控制土壤和养分流失是有效的。(4)改进沉降池结构实验结果表明，反重力流多孔沉降池对排水流量的减少幅度小于重力流，反重力流多孔沉降池对悬浮物的控制也有足够的作用。另外，通过反重力流多孔沉降池进行冲蚀处理，可以有效地减少排水流量。(5)调查泰国北部梯田土壤管理制度的可接受性根据对沟蚀点的调查结果或农民的保护策略，修复沟蚀点是防止沟蚀的重要措施。对于沟蚀地的修复，土壤的压实密度应在1.3g/cm^3左右。少

Soil and nutrient losses in upland fields affect not only agricultural land productivity but also water environment in down streams. The objectives of this research were to evaluate the combination between surface inlet and grass buffer strips on reducing soil and nutrient losses, and to develop the suitable structure of settling pond for catching soil and nutrient components from upland fields. In addition, the investigation on acceptability of this system in terrace fields of Northern Thailand included in this research. The following outcomes were obtained through 3 years research.(1) Observing the soil and nutrient losses in upland fieldsThe results of 2 years observation on soil and nutrient losses showed that particulate total nitrogen and phosphorus losses respectively ranged 88.8 to 94.3% and from 98.4 to 99.6% of total losses. Also, nutrient losses could be predicted on the basis of the coefficient of nitrogen and phosphorus transfer along with the calculated soil loss based on … More the universal soil loss equation.(2) Evaluating the conservation tillage under weed cover on reducing soil and nutrient lossesShaft tillage under weed cover (SW) was applied as conservation tillage, and shallow rotary tillage (RSB) and deep rotary tillage (RDB) were as conventional tillage. Additionally, no tillage under bare soil (NB) was set up as control. Although the soil applied RSB and RDB decreased dry density, the pore structure was not sustained after the rainfall. However, the pres formed by weed roots in SW were sustained even after the rainfall, and enhanced percolation in the soil. So, there was a tendency for surface runoff and the losses of soil, total nitrogen and phosphorus in SW to be lower than RSB, RDB and NB.(3) Evaluating the combination between surface inlet and grass buffer strips on reducing soil and nutrient lossesThe experimental results of the slope model plot with artificial rainfall indicated that the trapping efficiency of soil and nutrient losses by grass buffer strips could be kept under high level, because the surface runoff discharge through grass buffer strips was controlled to divide the excess surface runoff by surface inlet. On the other hand, there was no significant difference between the plots combing grass buffer strips and settling pond with surface inlet and without surface inlet in total losses of soil, total nitrogen and total phosphorus. However, sediment amount of settling pond in the plot with surface inlet was 0.42 times of that without surface inlet. It was judged that soil conservation system combing grass buffer strips and settling pond with surface inlet could be improved the each conservation strategy and was effective for controlling soil and nutrient losses from the viewpoints of the maintenance.(4) Improving the settling pond structureThe experimental results showed the decrease in drainage discharge through the porous settling pond of inverse gravitational flow was smaller than that of gravitational flow, and the porous settling pond of inverse gravitational flow has also a sufficient function to control suspended solids. Additionally, it was judged that a washout treatment was effective for improving the decrease in drainage discharge through the porous settling pond of inverse gravitational flow.(5) Investigating the acceptability of soil management system in terrace fields of Northern ThailandAccording to the results of investigation of rill erosion sites or farmers' conservation strategies, rehabilitating rill erosion site is important for preventing gully erosion. For rehabilitating rill erosion site, it was concluded that soil should be compacted at around 1.3g/cm^3. Less