| The black soil region in Northeast China, where large amount of slope cropland distributes, is vast and fertile, thus has become one of the most important grain production base of China for a long time. For the reasons of long-term unreasonably excessive exploitation and utilization, as well as some natural factors which facilitate the occurrence of soil erosion have been continuing or even exacerbating, the situation of soil and water lose in this region is fairly serious nowadays, as a consequence the extensive deterioration of soil quality and agricultural nonpoint source pollution have been risen. Therefore to study the effects of different tillage measures, especially the conservation tillage measures within the maize seedling stage when the cover degree is relatively low is quite meaningful. This thesis will mainly focus on the effects of some different tillage measures on the redistribution of rainfall, the distribution of raindrop energy, changes of soil characters before and after the rain, soil erosion and migration of agricultural nonpoint source pollution on the slope cropland in black soil region within the period of maize seedling stage, and tries to explain the occurrences and processes of soil erosion and agricultural nonpoint source pollution and evaluates the measures depending on different requirements. The main results are as following.1. The effects of maize itself on the interception of rainfall are not evident, with only 6.51% of rainfall being redistributed; the rainfall interception capacity of maize is just based on the canopy density, therefore the VM (Vertical Maize) treatments, which have bigger canopy density perform better on the redistribution of rainfall. The maize at seedling stage can magnifies the diameter of raindrop, and reduces the kinetic energy of raindrop and the total energy of rainfall under the canopy; VM treatments also have better effects on these aspects.RC (Residue Coverage) can decline both the splash detachment rate and splash transport rate substantially.2. The effects of rainfall on changes of bulk weight of surface soil can almost be removed by RC treatments; the rainfall can unify the bulk weight of surface soil into about 1.30g/cm2 under all other treatments. The increment of upper soil layer water content raised by rainfall is far above the water content of subsoil layer; Hr (Horizontal ridge) and RC can strengthen this kind of water content uptrend. The water infiltration rates under the condition of big rain density are always higher than under the condition of light rain density; Vr (Vertical ridge) and RC can increase the water infiltration rate and the effects of Hr is more evident.3. The effect of maize itself on soil and water conservation is not evident. Normally Vr can intensify the situation of soil erosion when rains. Hr and RC can decline both the rate and amount of runoff and soil loss, but the soil and water lose rate will reach an obvious peak value when the ridge breaks. Evaluating from the viewpoint of water and soil conservation, Hr+RC should be the best maize tillage measure on slope cropland in black soil region.4. The main agricultural nonpoint source pollution in runoff is NH4-N, while in the sediment is organic matter. Commonly, the concentration of pollutions in runoff can be increased by RC and Hr treatments, but the total amount of migration of them in runoff can be decreased by these 2 measures markedly. RC will reduce the concentration of organic matter and soluble PO4-P in sediment, while the effects of other tillage measures on the concentration of organic matter and soluble PO4-P in sediment are not evident. Both the Hr and RC can effectively control the migration of pollutions in runoff and sediment.Cogitating systematically with the factors including water and soil conservation, soil characters and agricultural nonpoint source pollution, Hr+RC is the best choice of tillage measure on slope cropland in black soil region. |
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