Water stability of earthworm casts in manure- and inorganic-fertilizer amended agroecosystems influenced by age and depth

Earthworm casts can contribute significantly to surface soil structure in a groecosystems. We suggest that the water stability of such earthworm casts depends on the earthworm food source, and the depth at which casts are made . We studied the effects of fertilizer inputs to cropping systems as earthw orm feedstocks, and depth of cast placement on cast water stability and tex ture. We collected air-dried earthworm casts from manure and inorganic fert ilizer-amended agroecosystems. Cast water-stability index and the cast text ure were measured at 1, 2, 4, 8, and 16 weeks. We found that fertilizer tre atments did not account for all of the variation in the measured water stab ility of earthworm casts. The placement of casts at 10 cm depth resulted in small changes in the water-stability index with time, while casts placed n ear the soil surface were degraded rapidly in terms of both water stability , and textural attributes. This was less marked in the inorganic treatment than in organic treatments. The differences in casts from different earthwo rm species, especially in terms of ecological groupings, may have affected the stability of the casts collected. Our results suggest that the form of fertilizer inputs can influence cast stability to some extent. However, cas t placement in terms of depth, which is largely a function of earthworm eco logical group, may be more important overall.