Study On The Cultivated Grassland Construction In Loess Hilly-gully Areas Based On Water Balance

Through the pot culture together with the field experimentation, in this paper, bird's-foot and gramineous herbage usually growing in the loess hilly-gully areas have been tested to study the effect that individual and colonial herbages have on the precipitation, the use of soil moisture and the soil water balance;meanwhile, the researches of the adaptabilities of individual and colonial herbage to water, such as, transpiration, water consumption, water absorption efficiency, drought resistance, growth under the water different conditions , accumulation of biomass, etc. have been conducted to explain the theory of herbage drought-resistant adaptability. Based on the above research, this paper has also probed into some principles of constructing the cultivated grassland under the condition of water balance to provide scientific theoretical basis for deciding the soil water-carrying capacity of grassland and keeping up the sustainable development of the grassland in the Loess Hilly-gully Areas, and to lay a theoretical foundation for a high yield of grassland and for the ecological and economic construction under the condition of soil moisture balance. The research results are as follows:I. Analyzing of the function about grassland in loess hilly-gully areas and rote of water in grasslandBased on the Analyzing of the function about grassland in loess hilly-gully areas and role of water in grasslan, the grassland was regarded as the key of developing economy and entironment in this area. The unbalance of water in the grassland is one important cause. These made keeping the balance of soil water a key, but all of this, must be based on the characters of pasturag's drought resistance and consuming water.II. Drought Resistance of Different HerbageThere exists a distinct difference in transpiration and stoma resistance among different varieties of alfalfa, whose transpiration graph has three types: double-peaked, single-peaked and climbing types. The transpiration of plant and the surface evaporation affect the humidity among alfalfa on the land growing alfalfa: the humidity among higher alfalfa and in thecorolla will reduce the value of air pressure in and outside the pores, which can affect the transpiration of alfalfa.Compared with gramineous herbage, the moisture content of the tissues of bird's-foot is quite stabler and the air permeability of its cell membrane is lower than gramineous herbage, and bird's-foot contains more proline in the environment where there is less water. Thus, the reason that bird's-foot can resist drought is that it not only has a developed root system but also its tissue has a stronger drought resistance. In the droughty environment, the fact that the chlorophyll B content of herbage reduces faster than that of chlorophyll A content showed that chlorophyll A was extremely unstable when the loss of water happened.In the droughty environment, alfalfa can strongly synthesize the protein, but there exists a difference in protein synthesis among different varieties of alfalfa. For four varieties of alfalfa, their abilities to synthesize protein are closely related to soil moisture and are becoming weak while soil contains less water. During the early period of protein synthesis, there exists a less distinct difference in the protein synthesis among these varieties, however, during the late period of the protein synthesis, this difference is increasingly distinct, especially when the soil moisture content is less than 5%, for example, the contents of dissociative amino acid of alfalfa, such as Algonquin and Farmer's Treasure are clearly higher than those of the "Emperor" and the "Venal".Drought makes proline, cystine and histidine in alfalfa change greatly and the contents of these amino acids will increase when water content reduces in the soil. If soil moisture content is less than 5%, the content of those substances will increase rapidly. Among these substances, the change of histidine is the greatest one and the variation coefficient of " Farmer's Treasure" can amount to 200%.ID. Moisture Absorption Characteristics of Herbages of Different KindsThe results of the experiment conducted in the fields have shown that:Growing bird's-foot in the Loess Hilly-gully Areas certainly caused the loss of soil moisture, even in the year when the precipitation is very plentiful, but there existed a distinct difference in water consumption among different varieties of herbage. To five selected varieties of bird's-foot, the "Emperor" is suitable for being grown in the Loess Hilly-gully Areas because it can germinate and become green more earlier next year and grow faster than the other selected varieties, and because it has a higher yield and a higher precipitation utilization efficiency.Compared with the alfalfa without stubble, if the stubble of alfalfa is kept 5cm high, the stubble will help improve the yield of alfalfa;but if its stubble is kept 10cm high, the soil moisture consumption will increase and the yield of alfalfa will decrease. The land havinggrown alfalfa with standing grain for one year certainly causes the loss of soil moisture, but the varieties of standing grain, the time for growing these varieties, etc. need studying further to make sure the validity of this intercropping.The results of pot experiment are as follows: compared with bird's-foot, in the morning, the transpiration rate of gramineous herbage decreases when there is a serious shortage of moisture in the air, however, the transpiration rate of bird's-foot extremely decreases when there is a moderate shortage of moisture in the air;and as usually, in the afternoon, the transpiration rate of gramineous herbage is higher than that of bird's-foot. This fact showed that transpiration of bird's-foot was more sensitive to the loss of soil moisture and bird's-foot itself could more strongly control the transpiration.The calculation result of moisture utilization efficiency has indicated that there exists a great difference between individual and colonial plants. Therefore, the moisture utilization efficiency of unifoliate horizontal plant could represent a underlying moisture utilization efficiency of plants and the moisture utilization efficiency of colonial plant could be an apparent one, but these viewpoints awaited to be verified further. However, in practice, two sides should be considered to decide the variety of herbage suitable for growing.Besides these, there exists a distinct difference in studies on the photosynthesis and the moisture absorption characteristics of individual herbage between the above and under leaves.IV. Analysis of the Cause of Low Survival of Alfalfa Seedling kt the Loess HiBy-gnlry Areas All alfalfa seedlings can easily survive when the soil water content is more than 10%, butalfalfa seedling cannot easily survive when the soil water content is less than 10%. For this reason, more than 10% of soil moisture content can make alfalfa seedling survive better in the Loess Hilly-gully Areas.When there are more winds, alfalfa seedlings has a higher photosynthesis velocity and their fresh rate is higher than that of seedlings affected by wind;in addition, with the increase of soil moisture content, the biomass of Alfalfa seedlings can gradually increase and their root system is more vital in the environment of good water. Blowing can decrease their calyptrogens ratio, and increase the transpiration rate and the stomatic conductance;at the same time, blowing can make their root system vitality become weak and make plants lose water much easier. When soil moisture content ranges from 10% to 12%, their root system and the transpiration are so strong that more soil moisture is dissipated, which causes the great loss of soil moisture. More winds in the field can make it easier that alfalfa seedlings lose moisture and more difficult that alfalfa seedlings absorb moisture, which brings about water imbalance. These changes can be a reason that alfalfa seedlings are difficult to survive.V. Effects of Different Land Utilization on Soil MoistureIn the 0-30cm deep soil layer, the evaporation affects soil moisture so directly and seriously that this layer could unsuitably be used to study soil water, however, plants with a short growing period and plants with short roots can be grown there in order to fully use the limited soil water resources.Compared with the different forms of land utilization, the soil growing alfalfa clearly contains less water, and the longer the time of growing alfalfa is, less water the soil contains. Therefore, the research showed that , if alfalfa is long grown , the loss of soil moisture is serious;and that the supplementary of the amount of soil moisture storage of the natural grassland is more than that of the land growing alfalfa;and that , as far as the amount of storing soil water is concerned, the amount of soil water storage of cultivated land is more than that of the orchard, and the amount of soil water storage of the orchard is more than that of natural grassland , and the amount of soil water storage of natural grassland is more than that of the land growing alfalfa.VI. The Principles of Water Balance, Carrying Capacity And Construction of Cultivated Grassland in The Loess Hilly-gully AreasIn the Loess Hilly-gully Areas, under the condition of normal precipitation, the full yield of alfalfa is 10,000kg fresh ratexhm2 and its potential yield can reach 50,000kg fresh ratexhm2. In these areas, because the lower water-carrying capacity of grassland has limited the high yield of alfalfa, there has existed a great difference between the full yield and the potential yield of alfalfa, even in the same condition of soil. According to the research of water, characteristics of common herbage and water-carrying capacity of the grassland, here some principles have been suggested to construct the cultivated grassland in the Loess Hilly-gully Areas: the sustainable development of deciding the varieties of grass based on the water and deciding the kind of livestock on the basis of the varieties of grass;the principle of developing ecological environment economy together;at the same time, the principle of adjusting measures to local conditions, paying attention to diversity and making some relevant policies.