Effect of Continuous Application of Low-Acidulent Fertilizer on Acidification of an Andisol and Plant Growth

Abstract

Our objective was to prevent the soil acidification caused by the NH₄ ⁺ and the accumulation of SO₄ ²⁻ and Cl⁻ using a low acidulent urea based fertilizer applied in an Andisol that initial pH was adjusted to pH5 (named LAF5) or pH6 (named LAF6) in comparison with the continuous application of a rapidly soluble ammonium based fertilizer (RSF) applied on the same soils (named RSF5 and RSF6, respectively). Komatsuna (Brassica campestris var. maruha) and barley (Hordeum vulgare L.) were used as test plants. After three successive Komatsuna cultivations, barley seedlings were grown for 7 days to evaluate the degree of soil acidification. A rate of 0.2 g N kg⁻¹ soil of each fertilizer was applied in each Komatsuna culture. No accumulation of sulfate and chloride ions was found in the soil continuously treated with the LAF. However, the continuous applications of RSF accumulated both sulfate and chloride, and lowered the soil pH remarkably compared to those of LAF. Initial soil extractable SO₄ ²⁻ contents in pH5 and pH6 treatments were 510 and 573 mg kg⁻¹, respectively. After three Komatsuna cultivations, the soil extractable SO₄ ²⁻ in RSF5 and RSF6 treatments increased to 2833 and 2374 mg kg⁻¹ in RSF5 and RSF6 treatments, respectively; and changed to 407 and 635 mg kg⁻¹ in LAF5 and LAF6 treatments. The continuous application of low acidulent fertilizers lowered the soil pH of 0.22 and 0.41 units in LAF5 and LAF6 treatments, respectively, and the continuous RSF application lowered the soil pH of 0.89 and 0.77 units, in RSF5 and RSF6 treatments, respectively. Both dry matter and root length of barley were drastically reduced in the RSF treatment and showed typical symptoms of aluminum toxicity, i.e., brown roots and deformed root tips. The root tips of barley with LAF treatment showed weaker hematoxylin staining than those with RSF treatment.

Keywords:

• Acidification
• Aluminum toxicity
• Chloride
• Low-acidulent fertilizer
• Sulfate

Acknowledgments