Topsoil samples were collected from more than 100 fields under organic management for 6 to 36 years. Fields were grouped in continuous vegetable cultivation (CVC), greenhouse vegetable cultivation (GVC) and cereals or pulse rotation with cereals or pulse every 3 years (3CP), vegetable and cereals or pulse rotation with cereals or pulse every 4-6 years (4to6CP), and continuous rice cultivation (CRC). Available P in the soil of CVC and GVC was much higher than the recommended range in conventional managements. Exchangeable K was also higher in the soil of CVC and GVC. These results were attributable to the dependence on animal composts and purchased organic fertilizers that are rich in P and K and to the lack of soil diagnosis. By contrast, available P, exchangeable cations and pH in the soil of 3CP and CRC were all within the recommended range. Available P, exchangeable cations and pH in the soil of 4to6CP were higher those of 3CP. We suggest to incorporate cereals and pulse as scavenger crops in vegetable cultivation every three years and/or to apply plant residue composts.
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