The Nutrient Reduction Index: A parsimonious and continuous measure of conservation practice adoption among farmers

A Nutrient Reduction Index (NRI) was developed to assist investigators who wish to explore the impacts of interventions, individual difference factors, and farm characteristics on nutrient-focused conservation practices. Comparing the effectiveness of different interventions or understanding the effects of different farm and farmer characteristics can be difficult in the absence of a single and standardized measure of conservation practices (Anderson 2020; Loken and Gelman 2017; Lilienfeld and Strother 2020). Across two data sets (N = 1,452), the continuous NRI was calculated by weighting several in-field practices (tillage, cover crops, and small grains in rotation) by their actual impact on nutrient reduction (Iowa State University 2019; Ha et al. 2020). The NRI was shown to have a smoother distribution than individual conservation behaviors, and convergent validity was demonstrated with conservation-related constructs like conservationist identity and use of filtering practices. The NRI also correlated with farm size, greater formal education, and lower farmer age, consistent with previous work regarding general conservation practices. This measure of nutrient reduction practices can help reduce error associated with dichotomization of practice adoption (MacCallum et al. 2002) and testing multiple measures (Banerjee et al. 2009; Anderson 2020), and its weighted nature better reflects the impact of practice adoption on actual nutrient reduction.