Short-term nitrogen mineralization during transition from conventional to organic management is unchanged by composted dairy manure addition in perennial forage systems

Abstract

This study was conducted to determine the effect of composted dairy manure (CDM) addition on nitrogen (N) mineralization in perennial forage production system undergoing transition to organic management. A field experiment was carried out on a Gray Luvisol of northeastern Colorado (40°39′N, 104°59′W) in 2008 and 2009, using the in situ resin core method. CDM was top-dressed onto two mixtures of perennial grasses at 22.4 and 11.2 Mg ha−1 in 2008 and 2009, respectively. Additionally, a control with no CDM addition was included. In 2008, N mineralization was unchanged following the addition of CDM compared to unamended control, irrespective of grass mixture. In 2009, N mineralization was greater in CDM-amended plots than controls, but these differences were only marginally significant (P < 0.1). There were, in general, no significant total dry matter (DM) yield or N uptake differences between grass mixes that received CDM and those that did not regardless of year, but generally total DM yield declined in 2009 compared to 2008. No significant differences in N mineralization, total DM yield or N uptake between controls and CDM-amended soils suggests that CDM-derived N mineralization rates were considerably lower than expected and thus may not keep up with N demand of perennial forage grasses in the short term, as evidenced by low total DM yield in 2009. Thus, we suggest that high application rates of CDM, in addition to quality, may be needed for at least 3 years until a reserve of organic N pool that will mineralize over time is built, particularly for a soil in transition to organic management.