Comparison of conventional and alternative vegetable farming systems on the properties of a yellow earth in New South Wales

Intensive vegetable farming has the potential to damage soil health, leadin g to poor productivity and large environmental impacts. This paper reports on changes in soil properties after three and a half years of vegetable cro pping and discusses the implications for sustainability. A vegetable fannin g-systems experiment began in 1992 at Somersby, in NSW, Australia. The aim of the experiment was to compare five different approaches to vegetable cro pping in terms of their productivity, profitability, soil effects and envir onmental impact. The experimental treatments represent whole production sys tems, intended to simulate real farms, but under more controlled conditions than is possible on farms. The systems are defined by the goals and values of the farmer rather than by the management practices employed. The actual management practices - nutrition, tillage, rotations, pest and weed manage ment, etc. - were selected to satisfy these goals and values. For instance, to satisfy the goal of 'maximise profit', fertilisers and pesticides were applied in excess to ensure high yields of large, undamaged produce which r eceive the best prices. Conversely, one of the management practices used to satisfy the goal 'optimise profit while minimising environmental impact' w as to grow cover crops regularly in rotation with vegetable crops. A range of chemical, physical and biological properties of surface soil (0-10 cm) f rom the farming-systems were measured and compared to baseline measurements . The two alternative systems, which received large inputs of compost, had higher soil organic carbon, microbial biomass. total nitrogen, total phosph orus, exchangeable nutrient cations, water-holding capacity and aggregate s tability than the conventional systems. The system that received the larges t mineral fertiliser inputs, and the most tillage, had the highest availabl e phosphorus levels, the lowest phosphorus sorption capacity and lower aggr egate stability than the alternative systems. Consequently this high input system had the greatest potential to lose sediments and phosphorus to the e nvironment. The two other conventional systems had smaller fertiliser input s and maintained a phosphorus sorption capacity that was no different from the alternative systems. These more carefully managed conventional systems offer hope that relatively small changes in management can have significant environmental benefits. Yet the broad improvement in soil health achieved by the biological approaches should provide better long-term fertility and lower off-site impacts. It may be wise to make use of both these approaches to management in attempting to balance the short and long-term viability o f intensive vegetable farming. (C) 2000 Elsevier Science B.V. All rights re served.