Plant availability of an iron waste product utilized as an agricultural fertilizer on calcareous soil

Abstract

An Fe‐dust waste which accumulates as a by‐product from the steel industry poses a disposal problem. Since the waste material contains approximately 43% Fe, 5% Zn, and 2% Mn, it shows potential for recycling as an agricultural plant nutrient. The Fe waste was evaluated in laboratory experiments to explore solubility, availability and soil reaction relationships. Two forms of Fe waste (dust and pellet) were treated with various amounts of H₂SO₄ in an attempt to increase Fe solubility and enhance plant availability. The amount of Fe solubilized was directly proportional to the amount of acid used. Following Fe waste acidulation, the water soluble and DTPA soluble Fe was significantly higher from dust than from pellet, regardless of the acidulation. An incubation study of Fe waste (with and without H₂SO₄) in a calcareous Fe deficient soil indicated that Fe availability decreased sharply with soil reaction time. In a greenhouse experiment, the Fe waste material was evaluated to alleviate Fe chlorosis of sorghum grown in an Fe deficient calcareous soil. Two sorghum cultivars, Fe efficient and inefficient, were grown as test crops. The Fe waste (dust and pellet) with and without acid at a ratio of 1:2 (Fe:H₂SO₄), was mixed with the soil at 3 rates before planting. Sulfuric acid alone was also applied at the same rate directly to the soil as a comparison treatment. Plant dry matter yield of both cultivars as influenced by treatments followed the same order: acidified Fe dust > H₂SO₄ > acidified Fe pellet > Fe dust > Fe pellet = control. However, the dry matter growth response to added Fe was much more for the Fe inefficient than for the efficient cultivar. This lack of response to applied Fe by the Fe‐efficient cultivar indicates its greater capability to obtain sparingly soluble Fe from the soil. The Fe concentration in the efficient cultivar also was affected little by added Fe, whereas, with the inefficient cultivar Fe increased linearly with added Fe. Non‐acidified Fe pellet failed to alleviate Fe chlorosis in either sorghum cultivar apparently due to its less surface area for solubility in soil. The Fe dust waste exhibited effectiveness as a soil Fe amendment when used at high rates under greenhouse conditions.