Can lucerne ( Medicago sativa L.) strips improve soil quality in irrigated cotton ( Gossypium hirsutum L.) fields?

Abstract

The effects of sowing lucerne ( Medicago sativa L.) strips in irrigated cotton ( Gossypium hirsutum L.) fields on soil quality was evaluated in a Vertisol at the Australian Cotton Research Institute (ACRI), and in a Vertisol and an Alfisol at two on-farm sites in New South Wales, Australia, from December 1995 to February 1997. Chemical (pH, EC, CEC, exchangeable sodium percentage, organic C), physical (air-filled porosity, plastic limit, dispersion index, soil strength), and biological (earthworm activity) indicators of soil quality were measured in each site. Overall soil quality in cotton and lucerne strips was evaluated using a `soil health condition report card' format to award a score to each soil quality indicator and summing up the individual scores to give a single value for each crop at any one site. The decision to award a particular score to any one indicator was based on a value range derived from the literature. In comparison with cotton, lucerne strips had higher air-filled porosity and organic C in the sub-soil of both on-farm sites, but had no significant effect at ACRI. However, lucerne did result in higher organic C in the soil surface at ACRI. Soil strength was higher and EC lower within lucerne strips in all three sites. Sowing lucerne strips resulted in higher earthworm activity at ACRI and at one commercial site, with highest numbers of earthworm burrows being observed in the former. We suggest that this has affected liquid flow patterns at ACRI where preferential flow mediated via the earthworm burrows appears to dominate. Overall soil quality was improved by lucerne strips only at ACRI, whereas that in the on-farm sites was not affected.