Effects Of Conservation Tillage On Soil Physical Properties And Nutrient In Northwest Plateau Of Hebei Province

The northwest plateau of Hebei Province, which is a part of the Inner Mongolia Plateau, belongs to semiarid ecological region with cold and high elevation. It covers a land of 17.3 thousand km2, about 1/10 of total land areas in whole province. There are about 1.5 million hectares lands used as farming, livestock and forestry, accounting for 85% of total lands, higher than the acreage in province. Among the Lands influenced strongly by human, the farmlands are 0.727 million hectares, and grasslands are 0.513 million hectares. The sandy chestnut soil is accounting for above 65% of total cultivated lands. The climatic factors and human intervention destroyed vastly the dynamic balances of plant colonies and between colonies and environments. So wind and water erosion and soil erosion are serious, and soil degradation and drought occurred frequently. The ecological and economic problems of long-term low and unstable of agricultural production were caused. The conservation tillage could alleviate the soil wind erosion, but the yield of no-tillage was reduced largely. Therefore this trial uses the methods combining field location and micro-zone simulation to study the annual characteristics of soil mechanical composition, water stable aggregate, bulk density and porosity and the variation of soil available nitrogen, available phosphorus and available potassium under the treatments of conservation tillage, traditional tillage and the stimulating soil with different collocating ratio. The characters of soil mechanical composition and soil bulk density in no-tillage farmland, enclosed meadows and farming-withdrawn grassland was understood clearly, and the soil physical characters of the stimulating soil with different collocating ratio varied in a whole year with natural settled was cleared for exploring soil physical basis and nutrition effects of yields reduction caused by no-tillage.The main results were as follows:1. The natural productivity in dry-sandy farmland was very low. The highest yield was only 1026.07 kg·hm-2 in the past three years. The yield of naked oats was influenced by cultivating methods obviously and were increased by tillage.The yield in no-tillage (NT) treatment was reduced markedly and was lowered respectively 35.45% and 42.16% than that in conventional tillage (CT) and rotary tillage (RT) treatments. 2. The soil mechanical composition of dry-sandy farmland in this region was mainly sand and gravel that the contents are stable, which respectively were about 60% and 20%. Results showed that the soil texture was gravelly sandy soil in this region. The contents of gravel and find sand were reduced and thick sand wasb increased by cultivation. In 0-5cm soil layers the thick sand contents in rotary tillage (RT) and conventional tillage (CT) treatments were respectively raised to 8.81% and 22.74% than that in no-tillage (NT) treatment.3. The bulk density in NT, RT and CT treatments were 1.639 g·cm^-3, 1.520 g·cm^-3 and 1.496 g·cm^-3 in 0²0cm soil layers, and the soil porosities in the treatments were less than 50%. The bulk density was decreased and porosity was increased in 0¹0 cm soil layers in NT at harvest. The bulk density and porosity in NT and RT had short odds in 10²0 cm soil layers, but the bulk densities were larger than that in CT and the porosities were less than that in CT. bulk density and porosity in RT were changed in 10³0 cm soil layers. Different cultivation had the less influence on water stable aggregates.4. The contents of available N, P and K in the trial soil were 102.64mg·kg^-1, 10.34 mg·kg^-1 and 115.26mg·kg^-1 separately. And the soil nutrient contents mainly concentrated in 0¹0 cm soil layer. The soil nutrient contents in harvesting period were slightly higher than that in presowing period, and were influenced slightly by different cultivations. The average content of organic carbon was 9.16 g·kg^-1 that was very low And was influenced largely by different cultivations. The organic carbon was decreased with depth under three kinds of cultivations. In naked oats growing season, the organic carbon contents were gradually decreased in 0¹0 cm soil layer and were increased in 20³0 cm soil layer at some extent with the development process, and were higher at harvest than that in presowing period.5. The soil mechanical compositions were relatively stable under three land use types of no-tillage farmland, enclosed meadows and farming-withdrawn grassland and were changed less. The bulk density in 0¹0 cm soil layers in NT farmland was about 1.70 g·cm^-1 and significantly less than that in enclosed meadows and farming-withdrawn grassland. The bulk densities in other layers were variated less. Therefore the larger bulk density value was one of the reasons of causing sparse vegetation and lower yields.6. The bulk density of the stimulating soil with different collocating ratio was increased in a whole year with natural settled. The bulk density in treatment with 30% grit ratio was raised to 1.57 g·cm^-3.