Nitrogen Mineralization of Anaerobic Swine Lagoon Sludge as Influenced by Seasonal Temperatures

Abstract

As anaerobic swine lagoons approach maximum sludge storage capacity, producers must periodically remove sludge and apply it to nearby fields. Information regarding the availability of nitrogen (N) in sludge as a nutrient source applied at different seasons of the year could improve crop-use efficiency. A 12-month laboratory study was conducted to quantify the effects of seasonal temperatures on mineralization of N in lagoon sludge. Sludge was mixed with a Coastal Plain soil (Arenic Kandiudult) and incubated for one year at weekly fluctuating temperatures based on Winter, Spring, Summer, and Fall application dates, ranging from a Winter low temperature of 9°C to a Summer maximum temperature of 30°C. Samples were analyzed monthly for NO3-N and NH4-N in 1.0 M KCl extracts of sludge amended soil. Sludge N availability (sum of NO3-N plus NH4-N concentration in 1.0 M KCl extract) was fit to a nonlinear regression model for a first-order reaction. Net N mineralization rate constants (k) derived from these models for the initial season of application increased in the order Fall (0.07) < Winter (0.075) < Spring (0.22) < Summer (0.36). While initial rates of net N mineralization differed, N availability predicted from first order equations was similar for all temperature regimes after one year of incubation and averaged 74% of the total N applied. Forty-two to 53% of the organic N in the sludge was mineralized during the one-year incubation.