| Popis: |
Soil chemical parameters including total N, exchangeable ammonium, soluble nitrate, and extractable phosphate, potassium, calcium and magnesium, were compared between conventional and no-tillage treatments on land which had been left fallow in old-field vegetation for 12 years. Tillage treatments were also compared to an adjacent old-field which was not cropped. The study was carried out on the Georgia Piedmont for 2 years following the fallow period. Soil nutrient availability was related to chemical concentrations in the soil solution, plant nutrient uptake and litter decomposition. During 1978–1979, soil nitrate concentrations were highest in plowed systems and lowest in the old field. Extractable cation concentrations were generally higher in conventional tillage than in no-tillage soil during the 1st year after fallow (1978). However, during the 2nd year, higher cation concentrations in no-tillage soil prevailed. Nitrate concentrations in the soil solution at 60 cm depth were generally highest in conventional tillage, followed by no-tillage and lowest in old-field systems. During 1978–1979, total nutrient uptake by crops (grain sorghum and rye) and weeds was higher in conventional than in no-tillage systems. From 1978–1979 to 1979–1980, uptake decreased in both cropping systems, but proportionately more in conventional tillage systems so that uptake in 1979–1980 was similar in the two cropping treatments. Higher nitrate concentrations in leachate of conventional than in no-tillage and old-field systems suggested that plowing stimulated nitrification processes. |
