Soil Quality and Profitability in Sodic, Grey Clay in Merah North, NSW, due to sowing Rotation Crops and Applying Gypsum
Sustainability in any farming system is dependent upon a number of interacting factors which include climate, soil quality, plant nutrition, management, weed and disease incidence, and economic factors. In cotton-based fanning systems it has been assumed that a "sustainable" system is represented by a cotton-rotation crop sequence, whereas a "degradative" system is exemplified by continuous cotton (Cooper 1999). As a consequence many cotton growers sow rotation crops after irrigated cotton assuming that they will improve soil quality, minimize disease incidence and maintain profitability of cotton (Cooper 1999). The crop most commonly sown in rotation with cotton is wheat, although legumes such as dolichos, faba bean and chickpea have become more popular in recent years (Cooper 1999). Although past research has addressed issues such as soil structure, nitrogen and water use (MCGarity et al 1984; Constable et al. 1992), information on the comparative advantages and disadvantages of a range of rotation crops, and the sustainability of such crop sequences over extended periods has been limited. Several long-term on-farm experiments were, therefore, established during 1993 in New South Wales and Queensland to evaluate the sustainability of selected rotation crop-cotton sequences with issues such as soil quality (physical, chemical and biological), weeds and disease incidence, cotton agronomy and economic benefits receiving a high priority (CRC for Sustainable Cotton Production 1994). The objective of the study reported in this paper was to quantify the changes in soil quality, cotton lint yield and profitability from 1993 to 1999 of six irrigated cotton-rotation crop sequences sown in a sodic grey clay in Merah North, NW NSW. Crop sequences were selected following discussions with local cotton growers. The indices used to evaluate sustainability included soil quality, soil microbiology and disease incidence, yield and profitability. This paper presents data on soil properties (soil organic C, structure as air-filled porosity of oven-dried soil, eXchangeable Ca, Mg, K and Na, pH, electrical conductivity (EC) and EC /exchangeable Na in the 0-0.6 in depth), lint yield and profitability (as gross margins/ha and gross margins/ML of irrigation water).