Evaluating pest-regulating services under conservation agriculture: A case study in snap beans

Abstract

Although conservation agriculture (CA) practices including strip-tillage (ST) and cover cropping are promoted largely for their potential benefits for soil quality, uncertainty surrounding their short-term effects on pests often constrains adoption. Quantification of ecosystem services or dis-services associated with pests is an important step in identifying research and policy priorities for improving the performance of CA practices. Using insect, weed and yield data from snap beans in a three year vegetable rotation, we estimated the value of pest-regulating services associated with the adoption of CA, and compared it to establishment and management costs associated with implementing CA.Experimental factors included tillage (full-width tillage [FWT] or ST), cover crops (winter rye [R] or none [NR]) and weed management intensity (low or high). The value of pest-regulating services associated with adoption of CA practices was estimated based on pesticide cost savings associated with reductions in pest densities given action thresholds typical of commercial snap bean production in the North Central United States. CA practices had no detectable impact on snap bean yields relative to FWT-NR, but resulted in significant tradeoffs in weed and insect abundance. For example, in at least one of two years, ST-R had lower densities of potato leafhopper, Powell amaranth and winter annual weeds, but greater densities of tarnished plant bug and large crabgrass compared to FWT-NR. CA practices had variable effects on natural enemies including ladybeetles, spiders and parasitoids, with no consistent impacts relative to FWT-NR. We estimated that CA practices resulted in net pest-regulating dis-services with costs of $33ha−1 for FWT-R, $25ha−1 for ST-NR, and $14ha−1 for ST-R. Under partial adoption of CA (ST-NR), pest-related costs were completely offset by savings in tillage costs, resulting in estimated short-term increases in net returns of $26ha−1. In contrast, complete adoption of CA (ST-R) resulted in greater pest and cover crop management costs that outweighed savings due to reduced tillage, resulting in estimated short-term losses of $165ha−1. In production systems for which effective, low-cost pesticides are unavailable (e.g. low-income countries) or prohibited (e.g. organic systems), the economic impact of pest regulation services is likely to be greater than our estimates suggest. Although CA practices provide several potential long-term ecosystem services at both the farm and landscape level, short-term impacts on pests and yields relative to the costs of implementation are likely to be the major determinant of grower adoption.