1. California Organic Foods Act of 1990,1990
2. Losses and transport of nitrogen from soils;Blackmer,1987
3. Distribution and temporal changes of mineral nitrogen in soil supporting annual and perennial crops;Bergstrom;Swedish Journal of Agricultural Research,1986
4. Determination and isotope-ratio analysis of different forms of nitrogen in soils: III. Exchangeable ammonium, nitrate and nitrate by extraction-distillation methods;Bremner;Soil Science Society of America Proceeding,1996
5. Residual effects of interseeded hairy vetch on soil nitrate-nitrogen levels;Brown;Soil Science Society of America Journal,1993