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, leading to poor productivity and large environmental impacts. This paper reports on changes in soil properties after three and a half years of vegetable cropping and discusses the implications for sustainability. A vegetable farming-systems experiment began in 1992 at Somersby, in NSW, Australia. The aim of the experiment was to compare five different approaches to vegetable cropping in terms of their productivity, profitability, soil effects and environmental impact. The experimental treatments represent whole production systems, 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 management, 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 receive the best prices. Conversely, one of the management practices used to satisfy the goal ‘optimise profit while minimising environmental impact’ was to grow cover crops regularly in rotation with vegetable crops. A range of chemical, physical and biological properties of surface soil (0–10 cm) from 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 phosphorus, exchangeable nutrient cations, water-holding capacity and aggregate stability than the conventional systems. The system that received the largest mineral fertiliser inputs, and the most tillage, had the highest available phosphorus levels, the lowest phosphorus sorption capacity and lower aggregate stability than the alternative systems. Consequently this high input system had the greatest potential to lose sediments and phosphorus to the environment. The two other conventional systems had smaller fertiliser inputs 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 of intensive vegetable farming. © 2000 Elsevier Science B.V. All rights reserved.