Nitrogen and solution dynamics in soils receiving chemically treated dairy manure

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, FeCl3 - 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 NO3-(WENO3), NO2-, and K+-extractable NH4+ after 1 day, after 1 and 2 weeks, after 1, 3, and 6 months, and after I 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 I day and I 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 WENO3 (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 WENO3, resulting in an excellent correlation (r(2) = 0.94) between the two variables. In contrast to NO3-, K+-exchangeable NH4+ 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 NH4+ 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 I week) rapid nitrification. Besides short-term effects, FeCl3 addition is effective in lowering WENO3 even after 2 years of incubation.