acid acid rain aeration agricultural lime agronomy aluminium sulfate ammonia ammonium nitrate ammonium phosphate ammonium sulfate anthropogenic arable land aral sea aswan dam australia bacteria calcium capillary action carbohydrate carbon cycle cast chemistry contour line cover crop crop rotation dam decay desertification detritus drylands earthworm egypt environmental chemistry environmental health environmental remediation erosion europe evapotranspiration evergreen extremophile feces floodplain groundcover guinea herbicide heterotroph humic acid hydrocarbon hydrology insecticide irrigation keyline design land degradation legume magnesium metabolism meteorology microbiology microorganism monopotassium phosphate mushroom natural resources conservation service nigeria nitrate nitrogen nitrogen fixation nitrogenase nodule north america organic compound overpopulation ph peru pesticide phoenicia phosphate phosphorus poros potash potassium potato rhizobia root saline salinity savanna shifting cultivation shrub slash and burn soil soil contamination soil ph soil salinity soil science soils retrogression and degradation solvent species sulfur surface runoff unintended consequence united states united states department of agriculture urea urea phosphate vegetation water table windbreak