A spring-wheat field trial (2001～2002)was carried out to investigate the effects of different organic or inorganic fertilizer applying manner on the physical, chemical or biological characteristics of the
degraded soil and the interactions among the soil
fertility factors in central Tibet. A 4×4 split-plot design was employed. Organic fertilizer (sheep manure containing 7 g/
kg N, 4.9 g/kg P_2O_5, 2.8 g/kg K_2O and 267g/kg O.M respectively) was the main treatment which included four (0、7.50、26.25、45.00 t/(hm~2·a) levels. At each main treatment, four subtreatments, N_0P_0K_0(0-0-0 kg/(hm~2·a) as N-P_2O_5-K_2O), N_1P_1K_1(60-24-12 kg/(hm~2·a), N_2P_2K_2(120-48-18 kg/(hm~2·a) and N_3P_3K_3(180-72-24 kg/(hm~2·a), were set using urea, calcium superphosphate and potassium sulphate as fertilizers. The results were shown that the applying of inorganic or organic fertilizers enhanced the formation of soil aggregates, particularly, the larger aggregates, while bulk density and porosity of soil were not affected. Comparing with non-fertilized treatment soil organic matter was increased by
fertilization by 85.6% in plough
layer, but decreased by 10% in 31~60 cm layer. In calcareous soil, all fertilization treatments had higher available P but lower total N and available K in the soil of plough layer, the available P level was as high as 21.74 mg/kg in average while the total N and available K were only 0.177 g/kg and 45.57 mg/kg respectively. The organic matter content in plough layer or the content of total N, available N, total P, available P in different depth of
soil profile showed higher net increasing by fertilizations. Propagation of fungi and N fixing bacteria in the layers of 2~30, 31~60 cm and of actinomyces in 2~30 layer cm
Soil layer were suppressed by fertilization. Bacteria was dominant group in biome of the soil microbe community in all layers of the soil profile. Nitrogen-fixing bacteria reduced by the increase of the cellulose-decomposing bacterium in different horizon. Fertilization increased the proportion of bacteria in soil, the increment in deep layer was higher than that in plough layer. Applying of inorganic fertilizer increased the organic matter by 62.0%, soil total N by 300.0%, total P by 74.0%, available N by 73.5% and available P by 217.0% respectively; soil bacteria amount was increased by 57.5% in average. The effects of fertilization on crop yield showed similar trend as on soil fertility. It is concluded that the recovering of soil fertility would take long term without fertilization in central Tibet. All different fertilizing manners had significant and prompt effectiveness on the coordinating of soil environment, on promoting the process of bacteria-dominating propagation of soil microorganism, on enhancing the accumulation of soil organic matter and the reconstruction of soil structure, and on increasing the pool of N and P comparing with non-fertilization. The changing of physical, chemical or biological characteristics of the degraded soil showed similar ways among the different fertilizations. Soil fertility showed a significant recovering trend after applying of fertilizers, which demonstrated the possibility and potential of recovery of soil fertility and reconstructing of soil structure in relative short period.
Published: January 25, 2004
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