Litter mass and nitrogen disappearance in year‐round nitrogen‐fertilized grass and legume–grass forage systems

Abstract

AbstractPlant litter is an important nutrient pool in grasslands. Most estimates of N return from litter are based on incubation of attached plant material (live or senescent) instead of dead, detached material on the soil surface. Our objective was to quantify mass, chemical composition, and N disappearance from soil‐surface litter for year‐round forage systems based on N‐fertilized grasses (GN) (290 kg N ha–1 yr–1) or legume–grass mixtures (LG) (30 kg N ha–1 yr–1) when grazed or harvested for hay. Litter mass and composition were measured in winter and summer over 2 yr, and litter was incubated for 180 d to quantify N disappearance. Summer litter mass was greater for GN than LG under grazing (2,840 vs. 1,730 kg ha–1) and hay management (2,780 vs. 1,240 kg ha–1). Cool‐season litter mass for GN was also greater than LG (1,990 vs. 1,200 kg ha–1). Initial litter N concentrations for GN and LG were 26 vs. 23 and 21 vs. 20 g N kg–1 organic matter in summer and winter, respectively. Litter lignin concentration and C/N and lignin/N ratios remained relatively constant. At the end of incubation, remaining litter biomass ranged from 63 to 85%. Nitrogen disappearance was greater for GN than LG, averaging 43 vs. 19 kg ha–1 yr–1, respectively, due to greater herbage accumulation and litter mass for GN. We conclude that year‐round forage systems including legumes contribute important quantities of N via aboveground litter decomposition, but amounts are likely less than for grass systems receiving relatively large N fertilizer inputs.