Ameliorating Sandy Loam Soils: Assessing Soil Nutrient Dynamics and Crop Performance under Variable Rates of Hydrogel, Humic acid and Biochar

Abstract

Background: Sandy loam soils are generally low in organic matter and have poor water and nutrient retention, which limits crop productivity. Soil amendments such as hydrogel, humic acid, and biochar are increasingly used to improve soil quality and enhance plant growth. However, their comparative effectiveness under sandy loam conditions is not well understood, making this study relevant for sustainable soil management. Aims: To evaluate the individual potential of variable rates of specific soil amendments -hydrogel, humic acid, and biochar, to improve the productivity and overall health of sandy loam soils, which are typically hindered by low organic matter and poor water retention. Study Design: Three set of pot culture experiments were carried out using hydrogel, humic acid and biochar. The design used was completely randomized design (CRD). Place and Duration of Study: Pot culture experiments were conducted at College of Agriculture, Padannakkad, Kasaragod, Kerala, India, from December 2024 to May 2025. Methodology: Three independent pot experiments were conducted with 5 replications and 4 treatments of hydrogel,8 treatments of humic acid (comprising variable rates of plant derived and synthetic humic acid) and 8 treatments of biochar (comprising variable rates of hardwood and rice husk biochar). Total number of pots used were 100. The test crop was chilli (var Anugraha). Results: The three amendments optimized soil health and crop growth in different way. Hydrogel application at 3 kg ha⁻¹ optimized soil aggregate stability, reduced bulk density, and also facilitated the reproductive growth, resulting in maximum dry matter production (35.3 g). Synthetic humic acid at 15 kg ha⁻¹ structurally stabilized the soil while significantly enhancing soil organic carbon (SOC), available nitrogen and available potassium. Among the biochar treatments, hardwood biochar consistently outperformed rice husk biochar, yielding significantly higher SOC, nitrogen availability, dry matter accumulation and final fruit yield. Conclusion: Optimal rate of application of these amendments significantly improved the physico-chemical properties of sandy loam soils, demonstrating that while biochar is most effective for crop yield, hydrogel and humic acid were superior for structural stability and moisture retention, offering a sustainable pathway for managing coarse-textured agricultural soils.