A Meta‐Analysis on the Effect of Agricultural Conservation Practices on Nutrient Loss

Abstract

Conservation practices are widely used to reduce N and P loads from agricultural fields and minimize their impact on water quality, but research using field‐scale data to model the national average impact of conservation practices for different forms of N and P is needed. Thus, we quantified the effects of conservation practices (grassed waterways, terraces, contour farming, filter strips, and riparian buffers) on total, particulate, and dissolved N and P runoff from farmlands. Specifically, we conducted a meta‐analysis of the Measured Annual Nutrient loads from AGricultural Environments (MANAGE) database using propensity score matching and multilevel modeling to remove the influence of confounding factors. There is no best method for addressing this influence, so we applied two alternative methods because similar results increase confidence in our findings. Propensity score matching found that conservation practices reduced total P, particulate P, and particulate N loading by an average of 67, 83, and 67%, respectively. Multilevel modeling estimated reductions of 58, 76, and 64% for the same nutrients. Although the propensity score method only yields a mean rate of reduction, multilevel modeling further estimates the reduction for different subgroups (i.e., different crops and fertilizer application methods) when such groupings are feasible. The multilevel models indicated that conservation practices affected row crops the most (e.g., corn [Zea mays L.] and soybean [Glycine max (L.) Merr.]) and fields with injected or surface‐applied fertilizers. Our analysis used field‐scale data to estimate the average effectiveness of conservation practices in reducing N and P runoff, providing valuable insight for regional and national decision making. Core Ideas Balancing confounding factors enabled us to conclude the effect of conservation practices. Total P and particulate P and N had >50% reductions in loading due to conservation practices. Conservation practices are most effective at reducing the loading of particulate P and N.

Conservation Agriculture as a Sustainable System for Soil Health: A Review

“…According to Belay et al [261], in supplementary irrigation vegetable production systems, CA practices can optimize nutrient use by decreasing nutrient losses through runoff and leaching. In this respect, several studies show that CA practices reduce the loss of nutrients via runoff or nutrients adsorbed in sediments lost by water erosion [176,[262][263][264][265]. In this context, Jordan et al [266] registered an 81% decrease in total P loss and a 94% decrease in organic nitrogen with non-inversion tillage compared with plow.…”

Increasing the Effectiveness and Adoption of Agricultural Phosphorus Management Strategies to Minimize Water Quality Impairment

“…Once this difference was accommodated, the researchers determined that particulate P was reduced by 58% and total P by 76% when CPs were used either individually or in combination. Daryanto et al (2017) demonstrated the importance of cropping system to P loss, as did Nummer et al (2018).…”

“…Often, addressing P losses at the field scale will require implementation of multiple CPs that address different P loss pathways. Nummer et al (2018) used a meta‐analysis approach to evaluate the effects of CPs (namely, conservation tillage, buffers, grassed waterways, and terraces), implemented alone or in combination, on P losses using data from the Measured Annual Nutrient loads from AGricultural Environments (MANAGE) database. Initial analysis revealed that more fertilizer was applied to fields in the database with CPs (e.g., cropland vs. pasture), thus confounding results due to the opposite effects of fertilizer application and CPs.…”

Updates to the MANAGE database to facilitate regional analyses of nutrient runoff

“…Specifically, Harmel (2015a, 2015b), Christianson et al (2016), and Hertzberger et al (2019aHertzberger et al ( , 2019b added data from 79 studies of drainage N and P concentrations and loads mainly from the midwestern and eastern United States. In addition, the MANAGE database has been used for meta-type analyses of management impacts on drainage nutrient losses (Flores et al, 2021;Hertzberger et al, 2019a;Liu et al, 2021;Zhao et al, 2016) and on the impact of agricultural conservation practices on nutrient losses in surface runoff (Nummer et al, 2018;Qian & Harmel, 2016;Reckhow et al, 2009). The database has also been used to evaluate modeling tool predictions of best management practices effectiveness, regional water balances, and regional ranges of runoff, sediment, and nutrient loss (e.g., Merriman et al, 2009;White et al, 2010White et al, , 2015aWhite et al, , 2015b.…”