| Cultivated grassland is important base for modern husbandry. Ningxia, located in arid and semiarid zone in China, is one of the most serious desertified provinces in China. Desertification is seriously affecting ecological environment of local grasslands, meanwhile restricting the harmonious development between society and economy. So, establishment of cultivated grassland not only the request for accelerating the development of husbandry in Ningxia, but also the request for improving local ecological environment. Based on the comparatively abundant forests resources such as ecological shelter forests distributed in Ningxia but the lots of branches, leaves and other organic materials from those forests are not reused scientifically, this study selected local most common tree material poplar branches firstly, and during 2012 to 2015 studied the effects of different amended patterns used tree branches and different irrigated conditions on water and fertilizer of soil before and after cultivated grassland established and the growth of alfalfa. From 2014 to 2015, the microcosm experiments set up to study the amended effects when soil incorporated poplar branches and other organic materials, incorporated different amounts of poplar branches and amended with different applied patterns used poplar branches. The main results as follows:1) Field study from 2012 to 2015 showed, different amended patterns used tree (poplar) branches had positive effects on enhancing soil water storage and nutrients when compared to control before and after cultivated grassland established, and the tendency among treatments presented as ground branch incorporation+unground branch mulch (GBI+UBM)> ground branch incorporation (GBI)> grinded branch mulch (GBM)> control (CK) in irrigated plots, but changed as GBI+UBM> GBM> GBI> CK in unirrigated plots. However, the increase of soil physical properties (bulk densitu, porosity and water holding capacity) and nutrients contents and decrease of pH value among treatments both in irrigated and unirrigated plots changed as GBI+UBM> GBI> GBM> CK. However, the changes of total K were no significant among treatments no matrer in irrigated and no irrigated plots during experimental period (P> 0.05). And the content of available N changed the same with most other nutrients in irrigated plots but presented as GBI+UBM> GBI> CK> GBM, which showed microbe fixed nitrogen under treatment GBM in unirrigated plots.2) Field study in 2015 showed, different amended patterns used tree(poplar) branches had different effects on alfalfa yield and quality, and the change was different from the changes of physical and chemical properties of soil. No matter in irrigated or unirrigated plots, the yield of alfalfa was highest in GBM. The yield both in GBI and GBI+UBM had no difference with CK in irrigated plots, but lower than CK in unirrigated plots. To alfalfa quality, all three amended patterns effectively improved alfalfa quality compared to CK, but there were no significant difference among them.3) Field study in 2015 also showed, all three amended patterns had positive effects on increasing the contents of microbial C and microbial N and enhancing five enzymes activities when compare to CK both in irrigated and unirrigated plots. GB1+UBM had the best effects on increasing microbial C. microbial N and enzymes activity, but there those indices not changed uniform between GBM and GBI, and most of not significant difference between GBM and GB1. The result of bacterial community among treatments, measured by high-throughput sequencing method, showed that branch amendment could increase the relative abundance of proteobacteria(34.5%) and bacteroidetes(7.0%), and the order among treatments presented as GB1+UBM> GBI> GBM> CK. Additionally, the relative abundance of proteobacteria and bacteroidetes had positive correlation with nutrients content, microbial C content, microbial N content and enzymes activity, but negative correlation with pH value.4) The results of microcosm experiment conducted for studying the effects of incorporated seven organic amended materials on water retention of desertified soil showed that incorporated poplar branches and wheat straws had best effect on retaining soil water. Further study showed that water holding capacity of soil increased as incorporated tree branches increased. When compared different amended patterns, GBM was best in retaining soil water, but GBI+UBM was best in field study, and this mainly because mulched branched were very thick in field than in microcosm tubes.5) The results of microcosm experiment conducted for studying the effects of incorporated seven organic amended materials on soil chemical property, microbial characteristics and wheat growth showed, when compared to CK, all incorporated organic materials increased most of soil nutrients content. However, only except cow manure not decreased available N compared to CK, other six organic materials decreased available N, available Zn and available Cu, which showed microbe fixed nitrogen. However, cow manure significantly increased EC value compared other treatments and CK. In the other hand, all incorporated materials enhanced soil respiration, microbial C content, microbial N content, catalase activity and cellulose activity, but only cow manure increases urease activity and other materials had a tender to decrease it. To wheat growth, wheat straw and four kinds of tree branches had positive effects on wheat photosynthesis and biomass accumulation, but there were not obvious changes between them. Overall, wheat straw, poplar branches and locust tree branches were the best organic materials among all materials for desertified soil amendment.6) The results of microcosm experiment conducted for studying the effects of incorporated different proportion (2%-11%) of poplar branches on soil chemical property, microbial characteristics and wheat growth showed, soil pH value and most of nutrients (organic matter, total N, total P, total K, available P, available K, available Fe, available Mg, available Mn) content increased as incorporated branches increased, however available N decreased. Soil respiration, microbial C, microbial N, catalase activity and cellulose activity also increased as incorporated branches increased, but urease decreased. Photosynthetic rate, stomatal conductance, transpiration rate, SPAD value, plant height, tiller number and biomass of wheat increased firstly and then decreased, and the peak values presented at 5% poplar branched incorporated.7) The results of microcosm experiment conducted for studying the effects of different amended patterns (GBM, UBM, GBI, GBI+UBM) used poplar branches on soil chemical property, microbial characteristics and wheat growth showed, four patterns decreased EC, available N and available Cu, but increased pH value, SOC, total N, total P and total K; and 2 kinds of mulches decreased available P, available K, available Fe, available Mg and available Zn. However, mulches increased microbial activity but GBI and GBI+UBM decreased urease activity. To wheat growth, all amended patterns enhanced photosynthesis and biomass accumulation of wheat, but GBM and GBI+UBM better than UBM and GBI. Especially, GBM had positive effect on wheat tiller.In conclusion, both tree branches and crop straws are good materials for cultivated grassland amendment, especially the poplar branches, which were most common tree branches in Ningxia, are good organic materials for local cultivated grassland amendment in theoretical feasible as follows:5% amounts would be feasible dose when poplar branches used as incorporated pattern to amend cultivated grassland; however, branches mulch would better than incorporation on soil water retention and crop growth, but less effect than incorporation on soil physical and chemical properties improvement. We also need to know that both tree branches and crop straws will incur the imbalance of ratio of carbon and nitrogen, and lead to microorganism to fix nitrogen. So, it necessary to adjust ratio of carbon and nitrogen when use those organic materials to amend soil. |
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