Nitrogen mineralization as affected by temperature in calcareous soils receiving applications of dairy manure

Current data is lacking for prediction capability of N mineralization for the silty soils found in Southern Idaho receiving the repeated application of manures. The objectives of this experiment were to determine the effect of temperature on N mineralization from control and manured soils, develop N mineralization rate correction factors for temperature (Q10 and temperature factors), and create a simple model for predicting N mineralization as a function of cumulative heat units or growing degree days (GDD). Manured and control soils underwent a 49-d laboratory incubation at five different temperatures (-14, 4, 10, 23, and 30oC); soil inorganic N concentration was determined at 0, 1, 3, 5, 7, 13, 20, 28, 35, 42, and 49 d. Net N mineralization was fit to a zero-order model, where the rate coefficient (k) values for the manured soil ranged from 0.017 to 1.28 mg kg-1 soil d-1 over the five temperature treatments while k values in the control measured 0.028 to 0.53 mg kg-1 soil d-1. Calculated Q10 from -14 to 30oC were 2.7 and 2.0 for the manured and control soils, respectively. At low temperatures (-14 to 4oC), the Q10 for the manured soil was 5.1 compared to 1.5 for the control soil. This finding suggests that manure additions may lower the temperature threshold for N mineralization to occur under near frozen soil conditions. Manure treatment effects on temperature factor were not observed, suggesting that manure application history may not need to be considered when developing TF coefficients for N mineralization models