Comparison of fertility characteristic in paddy soils of different ages in Cixi, Zhejiang

A pot-culture experiment was carried out to investigate the growth and production of rice cultivated in five paddy soils in use for 50 to 2000 years, and the effects of rice cultivation without fertilization on microbial biomass and enzyme activities in paddy soils were determined. The shoot length of rice cultivated in paddy soils tended to increase with years of use (p 0.10), while the biomass of straw, root and grain all increased significantly (p 0.05). Though the available nutrients were distributed with different ratios in different plant parts, the total N content in grain tended to increase with years of use (p 0.10), while the total P and K contents in straw increased significantly (p 0.05). Soil microbial biomass and activities of invertase and urease all tended to decrease after pot-culture experiment, while the correlations between these biochemical properties and field ages were similar to those before this experiment, suggesting that rice cultivation without fertilization consumed part of soil microbial biomass, decreased soil enzyme activities correlated with C and N transformation, and affected soil nutrients status disadvantageously. These results indicated that the fertility quality and the sustainable utilization of paddy soils were based on the recycling of crop available nutrients by straw returning or fertilization.