UD Laboratory Studies Suggest that Humic/ Fulvic Acid Additives are Not Effective at Increasing P Bioavailability

Lauren Mosesso, DENIN Graduate Fellow; Amy Shober, Professor and Nutrient Management/Environmental Quality Extension Specialist; ashober@udel.edu and Jarrod O. Miller, Assistant Professor and Extension Agronomist, jarrod@udel.edu

Many Delmarva farmers indicate that they experience issues with phosphorus (P) uptake with corn and winter wheat due cool soil temperatures early in the growing season. In some cases, these crops can benefit from the addition of starter P fertilizers. Humic/fulvic acid additives have been successful in some greenhouse studies to increase P bioavailability for wheat uptake (Tahir et al., 2011), while unsuccessful for others (Jones et al., 2007). We evaluated two humic acid (HA) additives in a laboratory incubation study to determine if these additives could increase P plant availability and eliminate the need for starter P fertilizer on high P Delmarva soils.

Two HA additive products were added to five Delmarva soils with Mehlich 3 P concentrations >150 FIV at rates of 0, 20, 330, or 650 gal ac-1. The applied rates were much higher than recommended on the product labels. The experiment was carried out with three replications for each treatment. Soils were maintained under moist conditions (approximately 80% of field capacity). We collected soil subsamples from each cup at 0, 7, 14, and 56 days after HA additives were applied and analyzed for water extractable P and Mehlich-3 P.

In the absence of growing plants, we found no significant changes in water extractable P or Mehlich-3 P when measured at 7, 14, or 56 after HA application. These results were similar for all soils evaluated. As such, we have no evidence to support the claim that humic acid soil additives will enhance P solubility when applied Delmarva fields with Mehlich 3 concentrations exceeding 150 FIV. However, we recognize that results may vary in systems with actively growing crops.

Tahir, M., M. Khurshid, M. Khan, M. Abbasi, and M. Kazmi. 2011. Lignite-Derived Humic Acid Effect on Growth of Wheat Plants in Different Soils. Pedosphere 21(1):124-131.

Jones, C., J. Jacobsen, and A. Mugaas. 2007. Effect of Low‐Rate Commercial Humic Acid on Phosphorus Availability, Micronutrient Uptake, and Spring Wheat Yield, Communications in Soil Science and Plant Analysis, 38(7-8): 921-933, DOI: 10.1080/00103620701277817.