PurposeTo study the effects of continuous cropping time on the microbial biomass and extracellular enzyme stoichiometry of typical red sandy soils in a tobacco field in Yunnan Province, and combining with the physical-chemical properties to explore the underlying mechanisms, providing theoretical reference to alleviate the continuous cropping obstacle of tobacco.
MethodsThe red sandy soils with 1, 2, 4, 6 and 9 years continuous cropping of tobacco were studied. The soil physical-chemical properties, microbial biomass carbon, microbial biomass nitrogen, microbial biomass phosphorus, and the activity of extracellular enzymes driving the carbon, nitrogen and phosphorus cycles were measured. The relationship between soil fertility parameters and soil extracellular enzyme activities were analyzed by ecological stoichiometry and redundancy analysis (RDA).
Results1) With the continuous cropping time increasing, the contents of soil organic carbon, total nitrogen, total phosphorus, ammonium nitrogen and nitrate nitrogen decreased first, and then increased, with the lowest value at 4 years of continuous cropping. 2) The pH value of continuous cropping soil ranged in 5.68-6.43, with a decrease from 1 to 6 years of continuous cropping, and increased from 6 to 9 years. 3) RDA showed that the soil organic carbon, total phosphorus and pH value significantly correlated with extracellular enzyme activities. Stoichiometric analysis of soil extracellular enzymes showed that the soil microorganisms at 1, 2, and 6 years of continuous cropping were strongly limited by carbon sources, while the microorganisms in all continuous cropping soils were limited by nitrogen sources.
ConclusionAfter 4 years of continuous cropping, there are significant changes in soil pH value, carbon, nitrogen, and phosphorus, and the activity of extracellular enzyme driving nitrogen cycling increases, which converts organic nitrogen into inorganic nitrogen, to maintain the soil nitrogen balance.
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