Using Growing Degree Days to Predict Nitrogen Availability from Livestock Manures

Abstract

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 NO3 and NH4 concentrations were determined at weekly or biweekly intervals. The rate of NO3 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, , while N was immobilized by incorporation of beef manure. The disappearance of NH4 was a linear function of time and of GDD. A single predictive equation was sufficient for dairy, poultry, and swine manures, in the form , with soil NH4 reaching zero at ≈350 GDD. These laboratory data indicate that GDD can be used for predicting NO3 accumulation and NH4 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.