Economic Potential of Compost Amendment as an Alternative to Irrigation in Maine Potato Production Systems

Potato productivity in the northeastern US has been relatively constant for over 50 years, raising questions about what factors are limiting productivity. Research was initiated in 2004 to identify key constraints to potato productivity by evaluating Status Quo (SQ), Soil Conserving (SC), and Soil Improving (SI) cropping systems under both rainfed and irrigated management, and it was found that addition of compost or irrigation substantially increased yield. In this study, we employed partial budgeting to determine cost differences and their impact on net revenue for these cropping systems. Differences in systems were primarily associated with rotation length, tillage operations, compost and application expenses, and water management practices. When compost (as composted dairy manure) was annually applied at 19 Mg·ha and evaluated over the entire 3-year crop rotation cycle, the compost-amended rainfed SI system was more expensive to maintain than the irrigated SC system if compost cost exceeded $3.63 Mg. Average marketable yields were used to calculate gross and net revenue for each system. Because average potato yield for the irrigated SQ system (28.4 Mg·ha) equaled that in the rainfed SI system (28.3 Mg·ha), we were able to compare cost of irrigation versus compost for achieving comparable yield. The compost-amended SI system under rainfed management generated more net revenue from the potato crop than the irrigated SQ system when compost costs were less than $7.42 Mg. When compared to the commonly used rainfed SQ system, rainfed SI achieved higher net revenue as long as compost cost was less than $22.95 Mg. The rainfed SI system achieved higher net revenue than the irrigated SC system when compost cost was $9.43 Mgor less, but generated greater net revenue than the rainfed SC system regardless of compost costs, due to substantially higher yields associated with compost amendment. This investigation demonstrates that compost is a potentially viable substitute to irrigation for potato in the northeastern US; however, such potential is highly dependent on suitable compost sources and application costs.