Long‐Term Manure Application Effects on Nutrients and Selected Enzymes Involved in Their Cycling

Abstract

Core Ideas We assessed long‐term manure rates and application times on soil nutrients and enzymes at two sites. Increasing manure rate enhanced soil fertility but hydrolase enzymes showed a quadratic trend. Manure application prior to period of heavy rainfall (spring and fall) was associated with phosphorus losses. Peroxidase and phenol oxidase activities declined with increasing manure application rates. Oxidative enzyme activities were good indices of long‐term soil organic carbon storage. We investigated how soil nutrients (soil organic carbon [SOC], nitrogen [N], and Mehlich‐3‐extractable phosphorus [P‐M3]) and enzymes involved in their cycling were impacted by 10 yr of beef cattle manure application at two sites in Nova Scotia, Canada: a dikeland site (silty clay loam) and an upland site (sandy loam site), under timothy (Phleum pratense L.) cover. Manure was applied at four rates (from 0 to 300 kg total N ha−1) at different times (spring, summer, early fall, and late fall). Activities of hydrolytic enzymes: β‐glucosidase (BG), cellobiohydrolase (CB), leucine aminopeptidase (LAP), and phosphomonoesterase (PME) and oxidative enzymes: phenol oxidase (PO), peroxidase (PP), were quantified. We hypothesize that manure application will increase soil nutrients and BG, CB, LAP, and PME activities and will decrease PO and PP activities. After 10 yr of manure application, compared to a control, soil pH, SOC, N, and P‐M3 increased linearly by 41, 45, and 125%, respectively, with increasing manure rate, while BG, CB, PME, and LAP activities showed a quadratic response. Conversely, enzymes degrading less labile components (PP and PO) declined with increasing manure rate. Higher SOC and P‐M3 contents and higher LAP activity were found at the upland site, whereas higher PME, PP, and PO activities were found at the dikeland site. Inverse relationships between PME activity and P‐M3 content and between PP activity and SOC or N content were found, whereas a positive correlation between N content and LAP activity was observed. Regular manure application is a good way to sustain soil fertility, with the extent of soil C storage controlled by soil type. The optimal rate and timing of manure application is essential, since application prior to periods of heavy rainfall is associated with phosphorus losses. Our results demonstrated that oxidative enzymes (PP and PO) are good indices of long‐term SOC storage. The lower their activity, the higher is the SOC sequestration.