Effects of organic and inorganic fertilizers on sloping-land citrus orchards with acid soils in Southern China

Fixed orchard trials were conducted to investigate the effects of different combinations of organic and inorganic fertilizers on fruit yield and quality of sloping-land citrus, and to analyze and compare the changes among the various treatments in quantity of soil culturable microorganism, C and N of soil culturable microorganism, content of active aluminum in rhizosphere and content of aluminum in citrus roots. The results indicate that quantities of bacteria, actinomycetes and fungi under the treatments of 20% organic manure + 80% chemical fertilizers (T1), 40% organic manure + 60% chemical fertilizers (T2), and 100% organic manure (T3) are significantly increased, and which are about 1.30, 1.40 and 1.46 times of those under the 100% chemical fertilizer treatment (CK) in average. The amounts of carbon and nitrogen of soil microbial biomass are significantly increased in the treatments with organic manure, and the amounts under the T3 treatment are increased by 45.6% and 63.3% compared with the CK. These indicate that the application of organic manure should flourish the communities of soil microorganisms and thus improve soil biological quality. It is observed that the application of organic manure can mitigate the influence of aluminum toxicity through significantly reducing root absorption and accumulation of aluminum from the soil, and in particular, under the T3 treatment, active aluminum content of rhizosphere is significantly decreased by 77.4% compared with the CK. The application of organic manure can promote the growth of root system, increase fruit yield, and ameliorate fruit quality of citrus significantly, with an average yield increase up to 18.5% over the CK.