EFFECTS OF 30 YEARS REPEATED FERTILIZER APPLICATIONS ON SOIL PROPERTIES, MICROBES AND CROP YIELDS IN RICE–WHEAT CROPPING SYSTEMS

SUMMARY Long-term fertilization experiment has been conducted since 1981 to study the effect of soil management practices on soil fertility, soil carbon and nitrogen sequestration, soil culturable microbe counts and crop yields at the Nanhu Experimental Station in the Hubei Academy of Agricultural Sciences (situated in the middle reach of the Yangtze River and the rice–wheat cropping system). The experiment was designed with the following eight treatments: (1) unfertilized treatment: Control; (2) inorganic nitrogen fertilizer treatment: N; (3) inorganic nitrogen plus inorganic phosphorus fertilizer treatment: NP; (4) inorganic nitrogen, inorganic phosphorus plus inorganic potassium fertilizer treatment: NPK; (5) pig dung compost (manure) treatment: M; (6) inorganic nitrogen fertilizer plus manure: NM; (7) inorganic nitrogen, inorganic phosphorus fertilizer plus manure treatment: NPM and (8) inorganic nitrogen, inorganic phosphorus, inorganic potassium fertilizer plus manure treatment: NPKM. The results showed that long-term application of organic manure in combination with inorganic fertilizer significantly (p< 0.05) increased soil organic C concentrations compared with the corresponding inorganic fertilizers alone. Soil organic C contents were significantly (p< 0.05) increased in balanced application of NPK fertilizers in comparison to unbalanced application of fertilizers. After 30 years of experiment, soil organic C and total N sequestration rate averagely were 0.48 t ha−1year−1and 28.3 kg ha−1year−1in the fertilized treatments respectively; nevertheless, it were 0.27 t ha−1year−1and 9.7 kg ha−1year−1in the unfertilized treatment. Application of organic fertilizer in combination with inorganic fertilizer significantly (p< 0.05) increased culturable microbial counts compared with the corresponding inorganic fertilizers alone. The balanced application of NPK fertilizers significantly (p< 0.05) increased culturable microbial counts compared with unbalanced application of fertilizers. The average grain yield of wheat and rice was significantly (p< 0.05) higher in organic manure combined with inorganic fertilizer treatment than in inorganic fertilizer alone and unfertilized control. Therefore, long-term application of organic manure combined with inorganic fertilizer and balanced application of NPK fertilizers could increase soil organic C and total N sequestration, culturable microbial counts and crop grain yields.