Study On Soil Acidification And Structure Stability Of Tea And Bamboo Plantation Soils

Tea and bamboo shoot are high value economic crops in Zhejiang province. Soil acidification and degradation of soil structure have been increasing serious because of intensive agricultural utilization, which have become the limiting factors of affecting normal growth and quality of tea and bamboo shoot, and the main obstacle factors of affecting sustainable high production and efficiency of tea and bamboo garden under intensive management. In this study, soil samples were collected from famous Longjing tea garden in Hangzhou and bamboo forest in Linan under intensive management to clarify tea and bamboo plantation soil acidification and possible soil factors inducing the bamboo withering by analyzing acidity features, nutrients changes, pH buffer capacity, stability of soil aggregates and the exchangeable acidity distribution in water-stable aggregates. And we also studied the main factor of affecting aggregate stability by selectively extracting organic matter and different morphological iron. The main results were summarized as follows:1. The significant topsoil (0-20cm) acidification was found in tea plantation soils. The lowest pHH2O in the tea plantation soils was as low as4.0. The tea plantation topsoil was characterized by higher soil organic matter and available phosphorus content. The highest available phosphorus was as high as138.2mg-kg-1. The topsoil acidification occurred after bamboo plantation. The pHH2o values of the topsoil were obviously lower than those of lower soil layers. The lowest pHH2o in the bamboo plantation soils was as low as3.75. The bamboo plantation topsoil was characterized by higher organic matter and available phosphorus content. The highest available phosphorus content of the topsoil was as high as350mg-kg-1. According to the analysis of aluminum chemical species, organic complexed aluminum was higher in the topsoil, decreasing from the surface layer to lower soil layer. Content of exchangeable aluminum was extremely significantly negative correlation with pHH2o and pHKCL and the increase of exchangeable aluminum may increase the harm to bamboo roots. Content of organic complexed aluminum was extremely significantly positive correlation with organic matter and available phosphorus. The average pH buffer capacity in tea plantation topsoil was10.98mmol-kg-1and the average pH buffer capacity in bamboo plantation topsoil was11.12mmol-kg-1. The pH buffer capacity of0-20cm layer was higher than that of20-40cm layer in tea garden. Soil organic matter was maybe the main factor of affecting the pH buffer capacity of bamboo plantation soils.2. Dry and wet-sieving analysis of aggregates indicated that tea plantation soils had high macro-aggregate content. The water-stability of aggregate in surface soil was higher than deep soil. The distribution of acidity in different size aggregates demonstrated that the contents of exchangeable acidity and exchangeable Al3+decreased as the particle size decreased, and had no significant difference between0-20cm layer and20-40cm layer. In>0.25mm water-stable aggregates of0-20cm layer, exchangeable Al3+was higher than exchangeable H+, but exchangeable H+was higher in0.106-0.05mm water-stable aggregates. In aggregates of20-40cm layer, exchangeable Al3+was always higher than exchangeable H+. Dry and wet-sieving analysis of aggregates indicated that bamboo plantation soils had good aggregate structure. Surface soil had higher water-stability than deep soil. The distribution of acidity in different size aggregates demonstrated that the contents of exchangeable acidity and exchangeable Al3+decreased as the particle size decreased, and had no significant difference between0-20cm layer and20-40cm layer. In>0.5mm water-stable aggregates, exchangeable Al3+was higher than exchangeable H+, but exchangeable H+was higher in<0.05mm water-stable aggregates. The percentage of exchangeable acidity, exchangeable Al3+and exchangeable H+in different water-stable aggregates showed that they were mainly existed in>2mm and2-0.5mm water-stable aggregates, and the quantity of water-stable aggregates was the main factor affecting the percentage of exchangeable acidity.3. Soil samples under tea plantation were separated into different water-stable aggregates using a wet-sieving procedure to identify their main aggregating agents. Content variation law of particle composition, total organic carbon, total phosphorus and different forms of iron oxides in different aggregate was different for the difference of soil parent materials. Content of organic carbon, total phosphorus and different forms of iron generally increased with increasing aggregate size in clayey soil derived from quaternary red earth, and its distribution showed preferential enrichment in the larger macro-aggregate fraction. Content of organic matter, total phosphorus and different morphological iron generally decreased at first, then increased with decreasing aggregate size in sandy soil derived from diluvium, except for higher content of total iron in0.5-0.25mm and0.25-0.106mm aggregates. Content of organic matter, total phosphorus and amorphous iron in different aggregate of surface layer was significantly higher than that of bottom layer.The organic matter and iron oxides of aggregates of0.5-0.25and0.25-0.106mm was oxidized with hydrogen peroxide, and chemical selective agents (dithionite, citrate, oxalate, bicarbonate). The particle size distribution of these treated aggregates was determined. Results indicated that organic matter had the least influence to the stability of0.5-0.25mm and0.25-0.106mm aggregates of clayey soil. The free iron oxide had the most importance role in aggregate stability mechanism of clayey soil. For sandy soils, both organic matter and free iron oxide had important role in aggregate stability of0.5-0.25mm and0.25-0.106mm aggregates in surface layer, the effect of organic matter and different morphological iron on the aggregate stability of0.5-0.25mm and0.25-0.106mm aggregates in20-40cm layer had no significant difference.