5Barzegar A R,Yousefi A,Daryashenas A.The effect of addition of different amounts and types of organic materials on soil physical properties and yield of wheat[J].Plant and Soil,2002,247:295-301.
6Mozafar A.Enrichment of some B-vitamins in plants with application of organic fertilizers[J].Plant and Soil,1994,167(2):305-311.
7The Commission of the European Communities.Commission regulation (EC) No 197/97 of January 1997,setting maximum levels for curtain contaminants in foodstuffs[J].Official Journal of the European Communities,1997,31:48-50.
8Torstensson G,Aronsson A.Nitrogen leaching and crop availability in manured catch crop systems in Sweden[J].Nutrient Cycling in Agroecosystems,2000,56(2):139 -152.
9Pechova B,Prugar J,Medved M,et al.Process of nitrate accumulation in vegetables crops[J].Scientia Agricultural Bohemica,1998,29(2):93-118.
10Muramoto J.Comparison of nitrate content in leafy vegetables from organic and conventional farms in California[EB/OL].http://www.agroecology.ory / people/ joji/ research/leaf nitrate.pdf,1999-06.