Technical Abstract: Potato yield in Maine has remained relatively constant for over 50 years. To identify and quantify constraints to potato productivity, we established Status Quo (SQ), Soil Conserving (SC), Soil Improving (SI), Disease Suppressive (DS), and Continuous Potato (PP) cropping systems under both rainfed and irrigated management. Each system is evaluated by our interdisciplinary team for plant growth and productivity, soil chemical-physical-biological properties, tuber diseases, soilborne diseases, foliar diseases, economics, and their interactions. In this particular analysis, we examined the impact of cropping system and water management on soil phosphatase, urease, and microbial biomass C. Activities of acPase, alPase, and diPase were 28, 80, and 86% higher, respectively, in the SI system than in the PP system. Irrigation also increased alPase, diPase, and urease activities. Under rainfed management, microbial C was highly correlated with phosphatase and urease activities. When measured under buffered conditions, urease activity was highly correlated with rainfed potato yield. To the extent that urease is an indicator of plant N availability, this may reflect the influence of N availability on yield. This study showed that both cropping system and water management influence the activities of several enzymes considered important for plant uptake of N and P.