Land use induced changes in cation anion balance of southern laterite soils of Kerala

Abstract

The study entitled “Land use induced changes in cation anion balance of southern laterite soils of Kerala” was conducted in the Department of Soil Science and Agricultural Chemistry, College of Agriculture, Vellayani during 2024-2025 with the objective of assessment of variability in the distribution of cations and anions as influenced by land use systems and seasons in the southern laterite (AEU 8) of Kerala. Georeferenced soil samples were collected from twenty different locations of four major land use systems (LUS) of the southern laterite soils of Kerala viz., banana, coconut, vegetable and uncultivated fallow lands, from the surface (0–15 cm) and sub-surface (15–30 cm) layers during both the pre- monsoon and post-monsoon seasons. The collected soil samples were analysed for physical properties, electrochemical properties, biological properties and cation- anion concentrations. An incubation experiment was conducted with the samples collected from the pre monsoon season to find out the effect of moisture content on cation anion concentration. During the incubation period, the concentrations of cations viz., NH₄⁺-N and Fe²⁺ displayed a pronounced decrease with the reduction in moisture content and the values recorded were statistically significant. Among the anions, NO₃⁻, SO₄²⁻ and PO₄³⁻ exhibited significant reduction with decrease in moisture content. Out of the five locations of the banana, coconut, vegetable and fallow land use systems, three were classified as sandy clay loam, one as silty clay loam and one as clay loam in texture. No variation in texture was observed in the sub surface layers. During the pre and post monsoon season in surface soil, significantly higher bulk density was noticed in the samples from banana LUS (1.20 Mg m-3) which was on par with coconut and uncultivated fallow LUS and lowest was observed in vegetable LUS (1.03 Mg m-3). Coconut LUS showed the highest pH (5.67) at 0-15 cm depth for pre and post monsoon. Significantly higher CEC (6.30 cmol(+) kg⁻¹) was recorded in the surface soils of coconut land use system. Conversely, vegetable LUS registered the maximum AEC (0.719 cmol(– ) kg⁻¹) in surface. Irrespective of the season and depth, the uncultivated fallow land showed the lowest values for pH, CEC and AEC.

Coconut LUS recorded the significantly higher contents of Ca²⁺ (298 and 268 mg kg⁻¹, respectively), Mg²⁺ (98 and 78 mg kg⁻¹, respectively), Na⁺ (58 and 40 mg kg⁻¹, respectively) and Mn²⁺ (33.00 and 35.83 mg kg⁻¹, respectively) during pre- and post- monsoon seasons, with values generally on par with the vegetable LUS in surface soil. Surface Cu²⁺ content was also highest in coconut soils (2.66 mg kg⁻¹) and was comparable to banana and vegetable systems. Vegetable LUS showed significantly higher K⁺ (144.00 and 125.50 mg kg⁻¹, respectively) and NH₄⁺-N (34.72 and 52.08 mg kg⁻¹, respectively) in surface and sub-surface. It also had higher Fe²⁺ (28.52, 18.34 mg kg⁻¹) and Al³⁺ (7.37, 7.84 mg kg⁻¹), along with the highest surface Cu²⁺ (2.66 mg kg⁻¹, on par with banana and coconut) and consistently highest Zn²⁺ in both seasons. Uncultivated fallow land recorded the lowest concentrations of Ca²⁺, Mg²⁺, Na⁺, K⁺, NH₄⁺-N, Fe²⁺, Al³⁺, Cu²⁺, Mn²⁺ and Zn²⁺ during both the pre- and post-monsoon seasons. Irrespective of the land use systems, the concentration of cations tends to decrease with the depth. Irrespective of the season, concentration of anions like nitrates (84.56 and 64.40 mg kg⁻¹, respectively), sulphates (31.15 and 28.15 mg kg⁻¹, respectively) and silicates (29.69 and 32.54 mg kg⁻¹, respectively) were significantly higher in the surface soils of vegetable LUS. MoO₄²⁻ content was also greater under this system, measuring 389.85 μg kg-1 in surface pre and post monsoon and 350.10 μg kg-1 in sub surface pre and post-monsoon. However, banana LUS recorded the highest PO₄³⁻ levels in both seasons in surface, with 18.97 mg kg⁻¹ in surface soil and 16.55 mg kg⁻¹ in sub surface soil. Similarly, BO₃³⁻ concentrations were highest in banana LUS, with values of 0.667 mg kg⁻¹ in surface soil pre and post monsoon and 0.618 mg kg⁻¹ in sub surface pre and post-monsoon. Irrespective of the land use systems, the concentration of anions tends to decrease with the depth. Across the land use systems, CAB values remained positive which indicates surplus of cations over anions implying a change in ionic balance in these systems, which may lead to nutrient imbalances. The CAB values were in the order of coconut ˃ vegetable ˃ banana ˃ uncultivated fallow which signifies that CAB in soil is influenced by both soil and crop

characteristics. Proper soil management practices are essential to maintain CAB and to optimize soil health and crop productivity.