Comparative effects of soil amendments and their hydrophobicity on stability of soil aggregates

Abstract

The stability of soil aggregates is an important soil attribute, which is known to be affected by soil hydrophobic conditions that result from the presence of organic materials. Organic and inorganic soil amendments may have hydrophobic properties that could influence aggregate stability. The objective of this study was to determine how the hydrophobicity of soil amendments affects the stability of soil aggregates. The experiment was conducted using four soil amendments, cattle manure (CM), hydrophobic leaf-litter (Casuarina equisetifolia, CE), biochar of CE leaf-litter (BCCE), and quick lime (CaO). Sieved (2 mm) surface soil was mixed with 3% CM, CE and BCCE and 1% CaO. Surface soil without amendments was used as the control. The samples were moistened to 80% of field capacity and incubated for 5 weeks. The moisture content was maintained by spraying water on moisture-loss basis. After 5 weeks, aggregates were separated into 3 size categories (<3, 3-6, 6-10 mm) and the percentage of water-stable aggregates (%WSA) was determined. The highest %WSA values of all three aggregate size categories were recorded with 3% CE amendment, showing ~37% increment compared with the control. The %WSA of <3 and 3-6 mm size categories were significantly higher (p<0.05) for treatments with CE, CaO and CM (26–37% increment compared with control), whereas the %WSA of 6-10 mm category was significantly higher in all four treated amendments (7–36% increment). Results revealed that the hydrophobic litter material (CE) was the most effective soil amendment in improving %WSA. Further experiments are necessary to identify the long-term impacts.