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Sulfur for Kentucky Grain Crops: A Meta-Analysis John H. Grove University of Kentucky Department of Plant and Soil Sciences John H. Grove University of Kentucky Objectives What is the evidence of S need in Kentucky’s corn, soybean and wheat? Controversial, but lots of recent work The 3-4 rep field trials not definitive Use meta-analysis: Explore this alternative approach to data aggregation Department of Plant and Soil Sciences Outline Definition(s) of meta-analysis Agricultural meta-analysis examples interpretation strengths/weaknesses Grain crop response to S in Kentucky interpretation strengths/weaknesses Conclusions Department of Plant and Soil Sciences Defining Meta-Analysis “meta-” along with; after; beyond; transcending; higher “meta-analysis”, the analysis of analyses methods focused on contrasting and combining results from different studies more powerfully estimate the true effect size as opposed to a less precise effect size derived in a single study under a given single set of assumptions and conditions Webster’s Dictionary; Wikipedia Department of Plant and Soil Sciences Advantages of Meta-Analysis Combines several studies – can be less influenced by local bias; Shows whether the results are more varied than what is expected from the sample diversity; Is a generalization to the population of studies (the inference space); Has higher statistical power to detect an effect than individual studies. Wikipedia Department of Plant and Soil Sciences Disadvantages of Meta-Analysis Publication bias – file drawer problem; When a practice or product shows no effect you get under-reporting. Agenda-driven bias – cherry picking; The meta-analyzer might find reasons to exclude, rather than include (or explain). Inference space “is like beauty”; Meta-analysis expands inference space Meta-analysis dilutes inference space Department of Plant and Soil Sciences A Meta-Analysis Example “Plant health” (corn fungicide use) is scientifically controversial – results from individual trials “all over the place”. 12 Land Grant plant pathologists pull together response data from 212 ‘valid’ studies conducted in 14 states. Determine the average yield difference to fungicide use for each study. Arrange the yield difference data from most negative to most positive. Department of Plant and Soil Sciences 151 studies with Headline® individual study difference individual study standard error mean difference = 4.1 bu/A standard error = ± 0.6 bu/A significant at the 99.9% level of confidence Paul et al, 2011, Phytopathology 101:1122-1132 Department of Plant and Soil Sciences Other Summary Comments Mean yield difference was greater: On fields with lowest non-treated yields; On fields with higher disease severity. “Use of these foliar fungicides is unlikely to be profitable when foliar disease severity is low and yield expectation is high”. Paul et al, 2011, Phytopathology 101:1122-1132 Department of Plant and Soil Sciences Another Meta-Analysis Example Wadsworth (1987) conducted an experiment on a range of crops, over several years (66 studies). Did, or did not, add a small amount (24 gallon per acre) of water. No expected benefit to this small amount of water. Yield difference expressed as a percentage of the control. Department of Plant and Soil Sciences Response Range Was -22% to +33% 100% Cummulative distribution (%) Greatest response 75% 50% responses above zero Average response (-0.6% 2.3%) 50% 25% 50% responses below zero Lowest response 0% -40 Department of Plant and Soil Sciences 0 40 80 Response to water (%) 120 160 Cumulative Distribution (%) 100% 75% Fertiliser Phosphorus 50% Fertiliser N Products that raise yield move curve to the right 25% 0% -40 0 40 Response to Product (%) Department of Plant and Soil Sciences 80 120 160 Do Kentucky Soils Need S? Electric power: by-product gypsum (FGD) New company converts FGD dust to pelletized product for bulk blending Commissioner of Agriculture (recently elected and with gubernatorial aspirations) publicly linked to new company – states that there is general need for S in Kentucky soils Fertilizer retailers want new products Ag reporters for state’s 2 major newspapers ask UKAg about need for S: Department of Plant and Soil Sciences Do Kentucky Soils Need S? UKAg response is a quiet, but firm No Reporters return to Commissioner of Agriculture: Reply lacks perspective Fertilizer retailers worry: UKAg extension commands respect Grain growers desire general evaluation: Know many field trials have been done UKAg Dean commissions meta-analysis Department of Plant and Soil Sciences Grain Crop S Nutrition Meta-Analysis Between 2008 and 2012, 72 valid comparisons, within 34 field trials, that involved a –S control and a +S treatment valid = 3 or more replications per treatment 40-corn, 23-soybean, 9-wheat 11 counties spread widely across the state; mostly NT soil management +S rate ranged from 8.4 to 1230 kg S/ha Koch-Agrotain and Mosaic-MES product evaluation trials of particular value Department of Plant and Soil Sciences Grain Crop S Nutrition Meta-Analysis S sources were gypsum (CaSO4.2H2O); ammonium sulfate ([NH4]2SO4); or MES (10-40-0-10S) Wide yield (Mg/ha) range: 4.6-17.5 (corn), 1.1-4.8 (soybean), and 4.6-6.9 (wheat) +S response, as % of the –S check, ranged from -22.4% to +18.3%; mean of +0.11% No significant difference (probability of a greater F > 0.10) in any single study or when all grain species combined together Department of Plant and Soil Sciences Frequency of S Response - All Comparisons/Crops/Location-Years Cumulative Frequency (%) 100 50 0 -25 -20 -15 -10 -5 0 5 +S Response (%) Department of Plant and Soil Sciences 10 15 20 25 Numerical Evaluations 72 Grain Crop Comparisons Mean response to added S: + 0.11 %; not statistically different from 0% Median response to added S: +1.12 %; not statistically different from 0% 40 Corn Comparisons Mean response to added S: - 0.71 %; not statistically different from 0% Median response to added S: +0.57 %; not statistically different from 0% Department of Plant and Soil Sciences Numerical Evaluations 23 Soybean Crop Comparisons Mean response to added S: + 0.54 %; not statistically different from 0% Median response to added S: +0.82 %; not statistically different from 0% 9 Wheat Comparisons Mean response to added S: + 2.61 %; was statistically different from 0% Median response to added S: +1.77 %; not statistically different from 0% Department of Plant and Soil Sciences Other Numerical Evaluations Soil Order: Alfisols, Mollisols-Inceptisols, Ultisols; not different from 0.0 %. Year: 2008, 2009, 2010, 2011, 2012; not different from 0.0 %. Soil Drainage: well-drained, moderately well-drained, somewhat poorly/poorly drained; not different from 0.0 %. Fragipan: absence, presence; not different from 0.0 %. Department of Plant and Soil Sciences Department of Plant and Soil Sciences Conclusions No relationship of S response to yield, for any crop The data, from individual or aggregated experiments, do not support a general grain crop S recommendation There is no evidence of a need to begin field trials with the intent of developing an S fertilizer recommendation for Kentucky grain crops Department of Plant and Soil Sciences Acknowledgements Dr. Greg Schwab (now with Koch Agronomic Services, LLC) and Dr. Edwin Ritchey for contributed data Dr. Eugenia Pena-Yewtukhiw (West Virginia University) for assistance with the meta-analysis Department of Plant and Soil Sciences Thank You! Questions?