Effects of Vermicompost and Salinity on Proctor Optimum Water Content, Maximum Dry Bulk Density and Consistency of a Sandy Clay Loam Soil

ABSTRACT

Salinity and sodicity greatly influences ongoing physical processes in soils. Organic matter may rehabilitate physical and mechanical properties of soils. Vermicompost as an amendment influences moisture-related parameters including consistency (plastic – PL and liquid limit – LL) and compaction. This study was conducted on soils (sandy-clay-loam) treated with different salinity levels (0.58 (control – irrigation water quality, tap water), 4 and 8 dS m⁻¹) to investigate the effects of different vermicompost doses (0% (control), 2.5% and 5% w/w) on soil consistency limits and compaction. The pot experiment was carried out in a total of 27 pots, i.e. 3 (vermicompost doses) x 3 (salinity levels) x 3 (number of replicates). For Proctor compaction properties, maximum dry bulk density (MDD) reduced and optimum water contents (OWC) increased with increasing vermicompost doses under different salinity levels (p < .01). Increasing vermicompost doses under the lowest salinity level (0.58 dS m⁻¹) yielded increasing optimum water contents for control (LL = 35.93% and PL = 25.85%). Optimum water contents were determined as 42.19% (LL) and 29.93% (PL) for 2.5% vermicompost dose and as 47.33% (LL) and 36.01% (PL) for 5% vermicompost dose under the lowest salinity level. LL, PL, OWC and MDD were significantly affected by vermicompost x salinity interactions. The highest maximum dry bulk density (1.92 g cm³) and the lowest optimum water contents (13.50%) were obtained from 0% vermicompost under the 8 dS m⁻¹ NaCl level. Mean weight diameter (MWD) values ranged from 0.690 mm for 0% VC treatment under high Na salt level (8 dS m⁻¹ NaCl) to 0.821 mm for 5% VC treatment under lowest Na salt level (0.58 dS m⁻¹ NaCl). The correlations between aggregate stability (particle size group 1–2 mm) and optimum water content were 0.647*, 0.587* and 0.598* as compared to correlations of −0.512*, −0.470*, and −0.617** between aggregate stability (particle size group 1–2 mm) and maximum dry bulk density for the 0, 4 and 8 dS m⁻¹ NaCl levels, respectively. MWD was positively correlated with OWC (0.386*) and negatively correlated with MDD (−0.385*). The greatest (2.39%) and the lowest (0.32%) soil organic matter values were respectively observed in 5% VC under the lowest salinity level (0.58 dS m⁻¹) and 0% VC with at high Na salt level (8 dS m⁻¹ NaCl). It was concluded that vermicompost reduced compaction-induced damage in soils.

KEYWORDS:

• Liquid limit
• organic amendment
• plastic limit
• plasticity index
• Proctor compaction test
• salt stress

Acknowledgements

The author would like to thank the Soil, Fertilizer and Water Resources Central Research Institute in Ankara, Türkiye and Prof. Dr. Abdullah Baran and Dr. Çağla Temiz of Ankara University Agricultural Faculty for providing the working environment and facilities for this study. The author would like to thank editors and the anonymous reviewers for the helpful comments, corrections, and suggestions on the previous version of the manuscript.