An Economic Analysis of the Nashua Tillage Study: 1978–1987

Yields and returns per acre for corn (Zea Mays L.) and soybeans (Glycine max L.) were evaluated under four alternative tillage systems in northeast Iowa from 1978 to 1987. The four tillage systems were moldboard plow (NB), chisel plow (CP), ridge-till (RT), and no-till (NT). Each tillage system had two rotations; continuous corn (CC) and a corn (RC)soybean (SB) rotation. The goal of this analysis was to evaluate the perception that the use of conservation tillage lowers economic returns. A secondary goal, made possible by the experimental design, was to determine if adopting conservation tillage necessitates a significant increase in chemical use. The moldboard plow system had the highest yield over the 10-year period regardless of rotation. No yields, regardless of system, declined over the period indicating that reduced tillage does not lead to decreasing yields. Additionally, yield stability (i.e., variation between years) was no different between the conventional and conservation systems. The rotation will have an impact on the returns associated with the alternative tillage systems. For continuous corn the moldboard plow had the highest average returns whereas the chisel plow system produced the highest return under the corn-soybean rotation. Evaluation using hourly labor charges of $4, $10, $20, and $50 did have an impact on which systems were significantly different. How each conservation system does depends on the opportunity cost for labor. Returns to conservation tillage systems saving relatively more labor (in time) increased more rapidly as labor charges were increased. This study has shown that the adoption of conservation tillage practices can be accomplished without lowering economic returns and significantly increasing chemical use. The particular tillage system to use will depend on the rotation and hourly opportunity cost of labor used by the farmer.