Meta-Analysis of the Relationship Between Crop Yield and Soybean Rust Severity

Abstract

Meta-analytic models were used to summarize and assess the heterogeneity in the relationship between soybean yield (Y, kg/ha) and rust severity (S, %) data from uniform fungicide trials (study, k) conducted over nine growing seasons in Brazil. For each selected study, correlation (k=231) and regression (k=210) analysis for the Y-S relationship were conducted and three effect-sizes were obtained from these analysis: Fisher's transformation of the Pearson's correlation coefficient (Zr) and the intercept (β0) and slope (β1) coefficients. These effect-sizes were summarized through random-effect and mixed-effect models, with the latter incorporating study-specific categorical moderators such as disease onset time (DOT) (<R1 or ≥R1 reproductive crop stage), disease pressure (DP) (high=>70%, moderate=>40 and ≤70%, and low=≤40% S the check treatment), and growing season. The overall mean for r- (back-transformed Z-r) was -0.61, based on the random-effects model. DOT and DP explained 14 and 25%, respectively, of the variability in Z-r. Stronger associations (r-=-0.87 and -0.90) were estimated by mixed-effects models for the Zr data from studies with highest DP (DP>70%) and earliest rust onset (DOT<R1), respectively. Overall means (based on a random-effect model) for the regression coefficients β-0 and β-1 were 2,977 and 18 kg/ha/%(-1), respectively. In other words, S as low as 3% would reduce 60 kg/ha for an expected Y of 3,000 kg/ha. In relative terms, each unitary percent increase in S would lead to a 0.6 percentage point (pp) reduction in Y. The three categorical moderator variables explained some (5 to 10%) of the heterogeneity in β-1 but not in β-0 The estimated relative reduction in Y was 0.41 to 0.79 pp/%(-1) across seasons. Highest relative yield reductions (>0.73 pp/%(-1)) were estimated for studies with DOT<R1 and DP>70%; the latter possibly due to high fungicide efficacy when DP is low, thus leading to higher yield differences between fungicide-protected and nontreated plots. The critical-point meta-analytic models can provide general estimates of yield loss based on a composite measure of disease severity. They can also be useful for crop loss assessments and economic analysis under scenarios of varying DOT and weather favorableness for epidemic development.

Meta‐analytic modelling of the incidence–yield and incidence–sclerotial production relationships in soybean white mould epidemics

“…Two relationships, the yield–incidence and sclerotia–incidence, were explored and the estimated coefficients and statistics constituted the effect size within each study. Three effect sizes per study were summarized for each relationship, including the Fisher's Z ( Z r ) transformation of the Pearson correlation coefficient ( r ) that summarizes the strength of the relationship (Paul et al ., ; Dalla Lana et al ., ). Pearson's r was calculated for each study using the cor .…”

“…Traditionally, meta‐analysis is usually preceded by a systematic review of multiple literature sources (Shah & Dillard, ; Scherm et al ., ). However, results may also be obtained directly from researchers or extracted from summaries in non‐peer reviewed literature and analysed using data at the individual level (plots) or aggregated (treatment means) (Paul et al ., ; Dalla Lana et al ., ).…”

“…The latter is a quantitative method of combining and summarizing results of individual studies using a statistically robust framework (Madden & Paul, ; Scherm et al ., ). There are multiple examples across a range of pathosystems focusing on quantitative summaries of treatment effects on disease reduction and increases in yield (Ojiambo et al ., ; Ngugi et al ., ; Paul et al ., ) and on relationships between disease and agronomic‐related variables such as yield, disease severity and mycotoxin concentration in other pathosystems (Paul et al ., , ; Shah & Dillard, ; Madden & Paul, ; Dalla Lana et al ., ). Traditionally, meta‐analysis is usually preceded by a systematic review of multiple literature sources (Shah & Dillard, ; Scherm et al ., ).…”

Meta-analysis of the application effects of a biostimulant based on extracts of yeast and amino acids on off-season corn yield

“…In Brazil, meta-analysis has been used in many different agricultural studies (DALLA LANA et al, 2015;CALVO et al, 2016;FANTIN et al, 2016).…”

Meta-analysis of scientific studies related to pesticide application techniques - air assistance and adjuvant addition

“…Thus, meta-analysis is an important tool, since this scientific methodology weighs the results of different studies, considered the variance of these data, and produced a summary of the existing results (LUIZ, 2002). This methodology has been validated in studies involving the application of pesticides, especially those related to plant pathology (MADDEN & PAUL, 2011), such as the study developed by DALLA LANA et al (2015), which assessed the relationship between the severity of Asian rust in soybean and losses in productivity.…”