Response Of Primary Productivity Of Degraded Grassland To Manure Addition And Its Mechanism

Nutrient deficiency is an important factor to limit the productivity of the arid and semi-arid grassland in north China. In recent years, chicken farming developed in northern grassland in our country has both ecological and economic advantages, among which the nutrients addition effects has been paid attention to. In order to explore the nutrient addition effects of farming chickens in the semi-arid sand grassland, we designed a relevant test about different gradient chicken manure addition which is,500,1000,1500,2000,2500, and 3000 kg ·ha-1·yr-1 and with no addition (CK) as contrast, to explore the effects of the soil physical and chemical properties, the community ecological system and the physiological properties of advantage specie which was Agropyron cristatum by the chicken manure addition in the HunShanDaKe sand in north China.1. The effects of nutrient addition on sandy soil physical and chemical propertiesThis study showed that the surface soil(0-20 cm) average pH was 7.5,showed that the soil of experimental zone was alkaline soil. The pH value was significantly reduced by chickens manure addition on the surface soil. But the pH value of deep layer soil (20-40 cm) was obvious variation. These showed that chickens manure addition can improve the pH value of the surface soil. The contents of soil organic matter, N, P and K and the stoichiometry rates of C:N, C:P and N:P etc., were significantly increased by the nutrients addition and the extremum were in between 1500-2500 kg·ha-1 ·yr-1. With the increase the number of nutrients addition years, soil organic matter content were almost rising accordingly in the same manure addition gradients. Therefore, there were an upper threshold of the addition nutrients in sand grassland to improve the soil physical and chemical environment, which could promote natural degradation of grassland soil improvement, and the threshold there may been between 1500-2500 kg ·ha-1·yr-1.2. Ecological effects of nutrients addition on vegetation communityChicken manure additions significantly (P< 0.05) increased the net primary productivity, vegetation coverage, species richness and long-term WUE. Compared to control, the largest improvement in such parameters occurred at the addition rate of 2000 kg·ha-1·yr-1, over which the improvement were reduced, moreover, the species richness was decreasing. We found that NUE was increased significantly with the increase of nutrients addition rates, but tended to a balance when nutrient rates over 1500 kg·ha-1·yr-1. The changes of root-shoot ratio of vegetation showed negatively correlated with the nutrient addition rates. These results indicated that chicken manure additions could promote vegetation recovery of natural degradation sand grassland, but there might be an upper threshold of the addition nutrients at 2000 kg·ha-1·yr-1 in the degraded sand grassland for the improvements of vegetation community structure.3. Nutrient addition effects on the eco-physiological characteristics of a dominate plant species, Agropyron cristatum, in the degraded sandy grassland.Chickem manure addition improved nitrogen content in leaves, Pn, Gs, Tr and leaf pigment content, Fv/Fm,φPSⅡ, ETR, the number of heads per plant, ripening rate, weight of 1000-seeds and the germination rate etc.. Therefore, the physiological characteristics of dominant species, Agropyron cristatum, were changed significantly by chicken manure fertilization in arid and semi-arid sand, which indicated that the viability and reproduction of Agropyron cristatum would be improved. But there might exist a nutrient upper threshold of 2500 kg·ha-1·yr-1.In conclusion, a certain intensity range of chicken manure addition could improve the soil physical and chemical environment of semi-arid sandy grassland, which made it more suitable for grass growth. Chicken manure additions could change the vegetation community structure, which made it to develop in the recovery succession direction. Physiological characteristics of dominant species could also be changed, indicating that their ability of survival and reproduction would be improved. That was to say, nutrient addition would play a positive role in promoting ecological restoration of the degraded grassland. What is more, according to the comprehensive analysis and from both ecological and environment viewpoints, the suitable chicken manure addition rate was suggested to be 2000 kg·ha-1·yr-1, and correspondingly, the suitable stocking rate of farming chickens was 666 chickens·ha-1.