The Influence of a Microalgal Conditioner on Selected Washington Soils: An Empirical Study

Chemical and physical analyses of four Columbia Basin soils were used to evaluate the effects of repeated annual inoculation with the mass cultured microalgal soil conditioner Chlamydomonas mexicana ‘Lewin’. Carbohydrate concentrations were consistently, though not significantly, greater in both the surface 10 mm and in the upper 300 mm of treated portions of a Quincy loamy fine sand, a Quincy loamy sand, and a Warden silt loam compared to untreated portions from the same soil mapping units. Treated soil samples from the two Quincy soils contained from 0.12 to 0.40 g/kg more carbohydrate than did untreated samples, while differences of about 1.0 g/kg of soil were measured in the Warden silt loam. Using locations as replicates, increases in water retention from treatments were significant (0.05% level), ranging from 2 to nearly 5% above untreated soils. Wet sieving of 0.92‐ to 1.68‐mm natural aggregates showed striking differences (significant at 0.1% level) between treated and untreated samples of the three soils. Stability in water was increased from 54.4 to 76.1% for the Quincy loamy fine sand, from 44.5 to 63.4% for the Quincy loamy sand, and from 82.1 to 86.1% for the Warden silt loam. Disruption of natural 0.92‐ to 1.68‐mm aggregates by rotary dry sieving was significantly different (0.05% level) between algal‐treated and untreated samples. Disruption to particles < 0.42 mm was 75.1 and 87.2% of treated and untreated samples, respectively, of Quincy loamy fine sand. Corresponding values for the Quincy loamy sand were 81.3 and 97.6%, and for the Warden silt loam, 60.9 and 78.8%. Moisture is implicated as the factor most likely controlling growth and polysaccharide production by the microalgal inoculum from the fact that differences in these chemical and physical properties could not be measured between treated and untreated samples from a dryland Ritzville silt loam.