Using Growing Degree Days to Predict Nitrogen Availability from Livestock Manures

Predictive tools are needed to better match N release from manure with crop demand. Growing degree days (GDD) have been successfully used to predict N release from crop residues and other amendments. A 112‐d incubation experiment was conducted at 10, 17, and 24°C to evaluate GDD (0°C base temperature) predictions of N transformations from beef ( Bos taurus ), dairy, poultry ( Gallus gallus ), and swine ( Sus scrofa ) manure. Manure was incorporated at rates estimated to provide 150 kg N ha −1 (or 75 mg N kg −1 soil). Soil NO 3 and NH 4 concentrations were determined at weekly or biweekly intervals. The rate of NO 3 accumulation increased with increasing temperature, and could be predicted across temperature regimes using GDD. This predictive ability could be generalized across dairy, poultry, and swine manures using an exponential equation,NO 3 = 54.10 [ 1 − exp ( − 0.006 GDD ) ], while N was immobilized by incorporation of beef manure. The disappearance of NH 4 was a linear function of time and of GDD. A single predictive equation was sufficient for dairy, poultry, and swine manures, in the formNH 4 ( as percentage of   input ) = 0.703 − 0.0021 GDD ( R 2 = 0.66 ), with soil NH 4 reaching zero at ≈350 GDD. These laboratory data indicate that GDD can be used for predicting NO 3 accumulation and NH 4 disappearance from a range of livestock manures. If successfully extended to the field, this predictive capability may allow for improved management of N from animal manures.