Effect of sugarbeet by-products on the solubility and availability of ferrous sulfate in soil

Abstract

Ferrous sulfate solutions applied to crop or weed residues, prior to tillage and planting, have been shown to reduce iron (Fe) deficiency chlorosis of subsequent crops. The objective of this study was to determine if ferrous sulfate solutions applied with sugarbeet (Beta vulgaris L.) by-products, and other plant materials, would enhance Fe solubility and availability in soil. Four laboratory experiments and five field trials were conducted. In the laboratory, ferrous sulfate applied to a diversity of plant materials, prior to mixing with soil, increased the DTPA-extractable Fe in soil compared to ferrous sulfate applied alone. Sugarbeet molasses was found to be more effective in increasing Fe solubility than wheat (Triticum aestivum L.) straw, sunflower (Helianthus annuus L.) hulls, or sugarbeet pulp. Spent molasses (desugarized molasses, raffinate) was found to be as effective as regular molasses at increasing the solublility of Fe in the soil. Under field conditions, ferrous sulfate solutions applied in the fall to wheat straw, followed by tillage, increased Fe solubility in the soil over the control. Ferrous sulfate plus sugarbeet molasses applied to wheat straw, followed by tillage, gave the greatest DTPA-extractable Fe levels in soil. Iron deficiency chlorosis of soybean (Glycine max L. Merr.) the following year was slightly reduced by Fe fertilizer treatments at one of the sites, but seed yields were not improved. Further studies are warranted, to determine if solutions of ferrous sulfate plus molasses or spent molasses could alleviate Fe deficiency with other methods of application, such as broadcast and incorporated shortly before planting, or banded near the seed.