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

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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