Sulfur for Kentucky Grain Crops: A Meta-Analysis.

What is the evidence of S need in Kentucky’s corn, soybean and wheat? A meta-analysis of 72 valid (three or more replications of each treatment) comparisons between a no-sulfur (-S) control and a +S treatment, with 9 wheat, 23 soybean and 40 corn studies completed between 2008 and 2012 was done. Sites were in 11 counties and added S rates ranged from 8.4 to 1230 kg S/ha. The yield range was 4.6 to 17.5 Mg/ha for corn, 1.1 to 4.8 Mg/ha for soybean, and 4.6 to 6.9 Mg/ha for wheat. Initial statistical analysis, by site-year, found no benefit to +S (P_F ≤ 0.10) due to insufficient replication, significant variation, or both. The incremental yield response to S, negative or positive, was expressed as a % of the -S yield, and ranged from -22.4 to +18.3 %, with a mean of +0.1 % and a median of +1.1 %; neither significantly different from 0.0 %. Subpopulation analysis suggested wheat might be responsive (mean of +2.6 %); Spindletop sites gave negative (-4.9 %) responses; the 2011 year gave positive (+1.5 %) responses; and there were ‘trends’ for positive response when soils were poorly drained or older (Ultisols). Though a positive trend, high yield was not associated with S need. Site-years with lower yield potential experienced greater variation in response to +S because of interaction with other limiting factors (water). The data, from individual experiments or aggregated, do not support a 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.