Nitrogen Fertilization Effects on Quality of Organic Matter in a Grassland Soil

Organic matter is important to sustain and improve soil quality and productivity. A field experiment determined the effects of 27 annual spring surface-broadcast applications of ammonium nitrate at 0, 112 and 224 kg N ha−1 year−1 to bromegrass (Bromus inermis Leyss) on light fraction organic matter (LFOM), total amino acids, amino acid C (AAC) and N (AAN), ammonium–N (NH4–N) and, total organic matter (TOM) in a thin Black Chernozemic loam soil at Crossfield, Alberta, Canada. The concentration and mass of LFOM, AAC and AAN in the 0–5, 5–10 and 10–15 cm soil layers increased with N rate, with greatest increase in the 0–5 cm layer. The response to N application was much greater for LFOM than for TOM. The changes in soil LFOM, AAC, AAN, NH4–N and TOM suggest that N application increases the quantity of light fractions and improves the quality of total organic matter in the soil.