NITROGEN AND SOLUTION DYNAMICS IN SOILS RECEIVING CHEMICALLY TREATED DAIRY MANURE

摘要

An incubation study was conducted to determine the effect of chemically treated manure addition on short- and long-term N dynamics in soils. Three treatments (alum -- Al, FeCl ₃ -- Fe, and CaO -- Ca) and two manure application rates were used in addition to a control sample (no manure). Subsamples were analyzed for pH, electrical conductivity (EC), water-extractable NO ₃ - (WENO ₃ ), NO ₂ - , and K + -extractable NH ₄ + after 1 day, after 1 and 2 weeks, after 1, 3, and 6 months, and after 1 and 2 years. Soil pH increased significantly only for the application of Ca-treated manure after all incubation periods and was sensitive to the application rate; however, soil pH decreased sharply between 1 day and 1 to 2 weeks or remained unchanged (compared to the control) for the other treatments. Nitrate release was controlled by the treatment type (untreated chemically treated manure control) and increased sharply between 1 day and 1 week and then increased slowly at longer incubation periods. Based on the percent of applied inorganic N released as WENO ₃ (P _WENO3 ), differences between chemical treatment types mostly followed this order: untreated Al-treated Ca-treated Fe-treated. Doubling the manure application rate had no effect on P _WENO3 . The trend in EC followed that of WENO ₃ , resulting in an excellent correlation (r 2 = 0.94) between the two variables. In contrast to NO ₃ - , K + -exchangeable NH ₄ + exhibited a sharp decrease between 1 day and 1 week and then remained relatively constant for up to 2 years. Untreated manure had the highest ratio of exchangeable NH ₄ + to applied inorganic N after 1 week, and the differences between chemical treatment types were insignificant. Application of chemically treated (especially Fe- and Ca-treated) manure appears capable of decreasing the extent of initial (up to 1 week) rapid nitrification. Besides short-term effects, FeCl ₃ addition is effective in lowering WENO ₃ even after 2 years of incubation