Crop Growth and Production Responses to Commercial Humic Products in U.S. Midwestern Rainfed Conditions.

Humic products (humic and/or fulvic acids) have been in use for over 100 years, yet published  research is scant on crop responses to humics under differing soil and weather conditions. We initiated field research experiments on corn (Zea mays L.) in Iowa in 2009 and have since expanded to multiple U.S. Midwest states investigating products from three  companies for also soybean (Glycine max L.) and sugar beet (Beta vulgaris L.). Our results examined the consistency of crop responses to humic products.  A three-year (2009-2011) on-farm survey of 95 corn production fields showed significant (P<0.001) gain in hand-sampled grain weight with humic product application, on average by 6.5% above the control. Grain weight increased numerically in about 80% of the fields. Yield components analysis attributed the yield gain to longer ears. Despite this overall consistency, environmental effects on yield responses were noted in more intensively studied fields. For the same corn production field, grain yield response to a humic product as measured by combine ranged from +2.2 to +39.9% (P=0.02) by landscape position/soil organic matter content (P<0.001) during a severe drought (2012), while during ideal growing conditions (2014) corn grain yield response varied from only -2.8% to +8.4% (P=0.47) due to much higher grain yields in the control. Leaf area frequently increased with humic product application by up to 6% even in the absence of appreciable grain yield gains. In another field experiment, soybean grain yield improved by 6.3% to 7.5% (P=0.05) during a mild drought year (2013), but only 1.3% to 6.8% (P=0.20) under near ideal growing conditions (2015). Yield component measures attributed the yield increases to higher numbers of seed filled pods. From our eight years of field experiments, crop growth and yield responses to the application of humic products can vary with soil organic matter content and weather patterns (i.e., rainfall and temperatures), with the greatest crop responses occurring under drought stress conditions and in soils with lesser organic matter contents. Because these factors create significant variability and crop response to humic products in fertile soils may be less than a 10% increase, it is particularly important for field research designs to minimize other potential sources of error, including landscape anomalies and previous management artifacts. As global populations continue to grow, more pressure will be put upon marginally productive soils to feed people and livestock, and increased drought incidence with climate change exacerbates this problem. Humic products can serve as a tool to better manage crops under these pressures.