Dynamics of Wet and Dry Aggregate Stability From a Three-Year Microalgal Soil Conditioning Experiment in the Field

Palmelloid, unicellular green microalgae in the genus Chlamydomonas were inoculated onto replicated plots at rates calculated to approximate feasibility through sprinklers (5 x 1011 log phase cells ha−1 yr−1) and with an airplane (5 x 107 ha−1 yr−1) to test their value as soil-conditioning agents. Applications were made to the same parcels of a Quincy loamy sand for three consecutive growing seasons. Highrate plots consistently showed significantly greater (5% level) stability to slaking of 0.92− to 1.68-mm sized aggregates from the surface (2 to 3 mm) algal veneer compared with low-rate and control plots, which were not different. This ranged from about 11 to 27% increased stability at the end of each season. After the 3rd yr, a significant difference of almost 12% was measured for wet aggregate stability of high-rate plot samples from the first 30 cm. Low-rate and control plots were never different. Dry aggregate stability to disruption by a Chepil-style rotary sieve was significantly greater (by 37%) for veneer samples from the high-rate plots after the second and third seasons. Low rate and control plots were not different. Similarly, dry stability of aggregates from the first 30 cm of the high-rate plots was significantly greater than comparable samples from the low-rate and control plots after the 2nd and 3rd yr (by 13%). Low-rate and control plots were not significantly different, suggesting a commercial potential for microalgal soil conditioners on light soils to which large inocula can be applied.