Cumulative Effects of Nitrogen, Phosphorus, and Potassium Fertilizer Additions on Soil Respiration, pH, and Organic Matter Content

Abstract

AbstractCumulative effects of annual additions of NH4NO3 (111 kg/ha N), treble superphosphate (55 kg/ha P), and KCl (111 kg/ha K) on aspen (Populus tremuloides Michx.) soil respiration, pH, and soil organic matter content were examined. Total fertilizer additions from fall 1969 through spring 1975 were 777 kg/ha N and K and 385 kg/ha P.The main effect of N and P additions was to increase soil biological activity by up to 42% and 33%, respectively, with the greatest increases occurring at the 15‐ to 30‐cm soil depth. For K, a 21% reduction in soil biological activity occurred at 0‐ to 15‐cm, while a 20% increase was found at 15‐ to 30‐cm. Fertilization with N and P increased but K showed no effect on surface soil organic matter content. Subsurface soil (15‐ to 30‐cm) organic matter content was not affected by any treatment. Higher soil organic matter content probably resulted largely from greater aspen growth response to N. Increased soil biological activity was attributed to a combination of increased soil organic matter content and improved levels of soil N and P.Treatment with N, K, or N + K reduced soil pH, possibly because of microbial nitrification of NH4+ associated with uptake by aspen of NH4+ and K+ with replacement of H+ in the soil.