DYNAMICS OF NITROGEN IN SOILS RECEIVING CHEMICALLY TREATED DAIRY MANURE

摘要

An incubation study was conducted to determine the effect of chemically treated (3 treatments: alum - Al; FeCl_3 - Fe; lime- Ca) manure addition on short- and long- term dynamics of NO_3~- and NH_4~+ in soils. Two manure application rates were used in addition to a control sample (no manure). Sub-samples were analyzed for pH, electrical conductivity (EC), water-extractable NO_3~-, NO_2~-, and K~+-extractable NH_4~+ after 1 d, 1 & 2 w, 1,3 & 6 m, and 1 & 2 y. Soil pH increased significantly for the application of Ca-treated manure after all incubation periods and was sensitive to the application rate. It, however, decreased (sharply between 1 d and 1 or 2 w) or remained unchanged (compared to control) for the other treatments. Nitrate release was controlled by the treatment type (untreated > Al-treated > Ca-treated > Fe-treated > control) and increased sharply between 1 d and 1 or 2 w and then slowly at longer incubation periods. Although more NO_3~- was extracted at the higher manure application rate, both the rates of addition had similar percent of the total applied N released as NO_3~- (P_(WENO3)). The trend in EC followed that of water-extractable NO_3~- resulting in an excellent correlation (r~2 = 0.96) between the two variables. In contrast to NO_3~-, K~+-exchangeable NH_4~+ exhibited a sharp decrease between 1 d and 1 w of incubation and then remained relatively constant for up to 2 y. The decrease in exchangeable NH_4~+ during the 1st week followed this order: untreated > Al-treated ≥ Fe-treated > Ca-treated > control. Application of chemically treated manure appears capable of decreasing the extent of initial rapid nitrification. Besides short-term effects, FeCl_3 addition is effective in lowering P_(WENO3) even after 2 y of incubation.