Long-term influence of compost on available water capacity of a fine sandy loam in a potato rotation

An improved soil physical structure, associated with organic amendments in crop rotations, can be viewed as an emergent property. A study was conducted to evaluate the effect of applied compost on soil water retention and available water capacity, and other associative soil properties in a long-term 3-yr potato rotation established on a Charlottetown fine sandy loam (Orthic Humo-Ferric Podzol) in Prince Edward Island. Soil samples (0-10 cm) were obtained from two crop phases (barley and potato) during the fourth cycle of the rotation (after four compost applications) in the 12th year of the experiment. Except for particulate N, compost had little effect on soil organic matter. In comparison to the barley phase, a combination of compost and surface tillage in the potato phase was associated with improved soil porosity parameters and increased soil water contents at -33 kPa ("field capacity"), -100 and -300 kPa. matric potential, compared with the no-compost control. These results indicate that compost stabilized the tillage induced soil aggregates and macro-porosity in the potato phase. Regression analysis showed that soil volumetric water content at both -33 and -1500 kPa matric potential was significantly related to soil C concentration, although the soil available water capacity remained unchanged. The results imply that the "non-nutrient" compost effect on potato productivity was related to soil water retention.