| The Weibei Plateau, a part of the Chinese Loess Plateau, covers about 5.0×104 km2 with the cultivated area of 160×104 hm2. Its climate is semiarid, with annual precipitation ranging from 400-700 mm and most of the precipitation (50– 60%) falls as rain during July to September. Due to less rainfall and strong wind in spring, it often says Spring droughts in 9 of 10 years. Groundwater resources are sparse and deep, so the farmland on the Weibei Plateau is dryland and must, therefore, rely solely on rainfall. Therefore,water shortage is the most limited factor for crop production. Sustaining the agricultural production in the Weibei Plateau is very important to ensure that sufficient food is produced for the growing population.In this thesis, a brief review of the latest progress of research on dry land farming was given. To meet the natural resources, climate condition and production characteristics in this region, different types of conservation tillage were applied to winter wheat and spring corn, and their effects on soil water dynamics, soil nutrients, diseases, pests and weeds etc. in wheat field were also investigated. The results obtained were as follows: (1) Various mulching techniques relative to conventional practice significantly increased yields of spring corn and winter wheat, soil water storage and soil temperatures (except straw mulching), decreased temperature difference between day and night, prevented soil from impacts of rain drops, soil erosion and soil compaction, improved soil structure. In comparison with conventional tillage, permeable plastic film and straw mulching increased corn yield by 6.4% and 23.6%,the water use efficiency by 23% and 16%; yield of winter wheat by 43.1% and 40.4%, the water use efficiency by 43.0% and 2.0%,respectively. Furthermore, straw mulching could also remarkably increase soil organic matter and soil fertility. In addition, permeable plastic film had the same effectiveness of increasing soil temperature compared with common plastic film. However, when air temperature was higher than 35℃, permeable plastic film had the function of adjusting the extreme temperature. On the other hand, long-term mulching would promote mineralization of soil organic nitrogen and had a potential possibility for nitrate leaching. (2) Among various conservation tillage techniques, no-till with mulching and high stubble, and mulching with sub-soiling and high stubble were the most effective techniques to increase crop's yield by 37.5% and 34.9%, respectively, compared with conventional tillage. Moreover, no-till (or sub-soiling) with mulching and high stubble could also save working time and energy, and made a comprehensive social, economic and ecological effects. (3) The conservative tillage techniques had a remarkable delay of occurring runoff and improved water infiltration relative to conventional tillage. Especially, the sub-soiling with high stubble and mulching showed the best effectiveness in dry years, such as in the year of 2003 and 2004, water storage increased by 9.13% and 11.23%, yield of winter wheat increased by 38.6% and 58.8%, and water use efficiency increased by 1.8 kg·hm-2·mm-1 and 4.1 kg·hm-2·mm-1, respectively, compared with conventional tillage. (4) Under the conservative farming system, winter wheat infected with some diseases, for example,Bipol aris Sorokiniana, Puccinia striiformis West and Ustalago tritici(Pers)Jens, appeared to be more severe and a trend to spread widely, and two types of conservation tillage, mulching with high stubble and mulching with sub-soiling and high stubble, had the highest incidence of infection. Generally speaking, winter wheat under conservative tillage was easy to be infected by diseases in wet years, and rhizosphere of wheat had larger number of bacteria and microbe communities changed, correspondingly. These were potential constraints to wheat production. (5) Under different conservative farming systems, weed species and amounts were affected significantly. There were the most diversity and most numbers of weeds under no-till treatment compared with treatments of conventional, mulching with high stubble and sub-soiling, and mulching with sub-soiling. While mulching with high stubble and sub-soiling, and mulching with sub-soiling would be an effective measure for controlling and inhibiting weed's growth in the field. (6) Under different conservative farming systems, the species and relative abundance of weeds were changed, the diversity indices of Shannon's H and Margalef's DMG were difference. It was due to different ecological environment, amounts of available soil nutrients and available soil water which maybe have different impacts on the growth of different weeds.All in all, conservative farming systems were more suitable for crop production than conventional practice in Weibei Plateau. Hence, it is importance that educating farmers to apply the conservative farming system, which enables to obviously improve the integrated production capacity of the region. |
