Long-term effects of balanced fertilization on grass forage yield, quality and nutrient uptake, soil organic C and N, and some soil quality characteristics

Many soils in the Parkland region of the Canadian Prairie contain insufficient amounts of plant-available S and N for high crop yields. Two field experiments (Experiment 1 1980–2005 and Experiment 2 1996–2005) were conducted on a Dark Gray Chernozem (Boralfic Boroll) loam soil at Canwood in north-central Saskatchewan, Canada, to determine the effects of long-term N, S and/or K fertilization to grass on mean forage dry matter yield (DMY), nutrient (N, S and K) concentration and nutrient uptake (averaged over years), and root mass, soil pH, total organic C (TOC) and N (TN), light fraction organic matter (LFOM), C (LFC) and N (LFN), mineralizable C and N, and extractable ammonium-N and nitrate-N in May 2006 (after 26 or 10 growing seasons). Experiment 2 additionally compared the effects of ‘hay-on’ (cut hay not removed) versus ‘hay-off’ (hay removed) on the plant and soil parameters. Experiment 1 had annual treatments of no fertilizer, N, NS and NSK fertilizers from 1980 to 2005, and Experiment 2 received no fertilizer, N, S and NS fertilizers from 1996 to 2005 under ‘hay-on’ and ‘hay-off’ conditions. While DMY, nutrient uptake and root mass were little affected by application of N or S alone compared with the unfertilized treatment, they were substantially increased by application of both N and S together. Co-application of N, S and K fertilizers increased DMY, nutrient uptake and root mass compared with NS application in Experiment 1. Nitrogen concentration in forage was highest in the N only treatment, followed by NS, and then nil, S or NSK treatments. The concentration of K in forage decreased in the order of treatments: NSK > nil or S treatment > N or NS; and of S: NS or S treatment > NSK treatment > nil treatment > N only treatment. Nutrient uptake was influenced more by forage DMY than nutrient concentration. In Experiment 2, DMY and N and K uptakes were greater under ‘hay-on’ than ‘hay-off’ conditions. Soil pH to 15-cm depth was decreased by NSK fertilization. The amounts of TOC, TN, LFOM, LFC, LFN, and mineralizable C and N in the 0–10 cm soil were increased considerably by the co-application of N and S fertilizers. The increase in soil C correlated well with the increase in DMY or root mass resulting from balanced fertilization. Not removing hay resulted in substantially increased LFOM, LFC and LFN contents in soil. The accumulation and downward movement of nitrate-N in the soil profile was decreased with NS application compared with N alone. In conclusion, application of N and S fertilizers together to soil deficient in both N and S produced high forage yield, nutrient uptake and root mass while also reducing soil pH, increased C and N sequestration in soil, and minimized accumulation and downward movement of nitrate-N in the soil profile.