The effect application of different organic residues on soil aggregate stability, carbon sequestration in sandy soil.

Abstract

     This study aimed to investigate the effects of different organic residues on soil aggregate size distribution and stability, as well as organic carbon accumulation within soil aggregates in salt-affected sandy soil. The experiment was conducted in a salt-affected paddy field of the Kula Ronghai soil series (Typic Natraqualfs) at Ban Ngio Kao, Non Pradu Subdistrict, Sida District, Nakhon Ratchasima Province, Thailand. A randomized complete block design (RCBD) was used with six treatments: control, groundnut stover, vetiver grass leaves, rice straw, rice husk, and cow manure, with three replications. Organic residues were applied at a rate of 1.6 t rai⁻¹. Soil samples were collected after 52 weeks. Soil aggregate size distribution and stability were determined using the wet-sieving method, while organic carbon in soil and soil aggregates was determined using the Walkley–Black method. Data were analyzed using analysis of variance, and treatment means were compared using the Least Significant Difference (LSD) test.

     The results showed that the amounts of large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), microaggregates (0.106–0.25 mm), and particles (<0.106 mm) ranged from 1.85–4.25, 1.49–3.41, 28.71–31.23, and 56.67–62.65 g per 100 g soil, respectively. The distribution of aggregate size fractions did not differ significantly among treatments. However, mean weight diameter (MWD) differed significantly, with the highest value observed in soil amended with vetiver grass (0.314 mm), compared with 0.185 mm in the control. Regarding organic carbon accumulation, cow manure showed the highest organic carbon content in aggregates >2 mm (0.075 g kg⁻¹ soil), whereas rice husk showed the highest values in the 0.25–2, 0.106–0.25, and <0.106 mm fractions, with values of 0.160, 0.111, and 0.171 g kg⁻¹ soil, respectively. In addition, the C/N ratio was positively correlated with organic carbon accumulation in the <0.106 mm fraction (r = 0.6334, p < 0.05), while the lignin/N ratio was positively correlated with organic carbon accumulation in the 0.25–2 mm (r = 0.6989, p < 0.05) and 0.106–0.25 mm fractions (r = 0.6930, p < 0.05).