Nitrogen mineralization in beef- and pig-manure-amended soils measured using anion resin method

A major challenge facing the widespread use of manure is the uncertainty about its fertilizer equivalence. This study was carried out to determine the fertilizer equivalence of locally available manures in two soils in Manitoba. A randomized complete block design was adopted with six treatments [nitrogen fertilizer, a liquid swine manure (LSM), three solid beef manures (SBM) and a control] and four replicates. Each treatment was applied to a cylindrical soil column installed at the site at the rate of 100 kg ha(-1) of "available N", and leached NO3-N was captured by resin bags at the bottom of the cylinder. The soils and resin bags removed from the cylinders were sampled at 0, 1, 2, 4, 6, 8, 10, 14, and 18 wk following treatment application. Ammonium nitrogen in the amendments was nitrified within the first 2 to 3 wk with significant build-up of NO3-N in the soil above the control (P <0.05). The greatest available N was in the fertilizer treatment, followed by the LSM and the smallest was in the SBM. The available N in the three SBM was statistically similar (P > 0.05). Approximately 50% of the inorganic N in LSM was available during the growing season, while 68 to 100% of SBM inorganic N was available. Between 4 and 25% of the organic N in the three SBM was mineralized during the growing season. High soil moisture hindered N mineralization and enhanced N loss in the clay soil. LSM has the greatest fertilizer equivalence, with a mean of 65 to 68%, of the four manure types used. The fertilizer equivalence of the three SBM ranged between 42 and 59% and was influenced by the manure C:N ratio and the soil environmental conditions. Our study suggests the need to revise the assumptions regarding manure N availability by considering soil environmental factors in the estimation of available N.