1. Summer crops will use more soil water than a clean fallow where winter crops fail due to waterlogging.

2. Once established, perennial plants use more water.

3. To maximise water use, sow early and use long season forages. Modelling results have shown that summer crops use from 0 to 30mm more water than the traditional summer fallow, which loses water from the soil through evaporation. This additional water use is expected to reduce leakage below the root zone (150cm) that can contribute to groundwater recharge. In species trials on the south coast of Western Australia, forage sorghum and other long season species, such as Nutrifeed forage millet, appeared to dry the soil profile the most. Grain sorghum and White French millet were also useful. However, a weedy fallow can use the same amount of water as a summer crop while a clean fallow will use from 7 to 45mm less than a summer crop.

The point of summer cropping however is to use the water usefully, rather than growing weeds! In a comparison against other summer active options, trials in the medium rainfall zone showed that sorghum water use was equivalent to lucerne in its first year of growth (see Table 2). However, in subsequent years, the established lucerne used significantly more water, so perennials such as this remain our premier water use option. An interesting aspect to the water use story is how much dry matter or grain plants produce per unit of water (their Water Use Efficiency or WUE). Past research shows vast differences in WUE between plants and one interesting comparison is that between forage sorghum and lucerne. Forage sorghum is around three times more efficient than lucerne at producing dry matter per mm of water available from rain or soil (see Table 3). This explains the photos you might see of huge sorghum stands being compared to a rather less impressive paddock of lucerne. These plants fill different niches in our farming system; lucerne is leguminous, perennial, uses the most water once established and offers high quality feed (but less of it), while forage sorghum can produce large amounts of feed in the same season as sowing and will regenerate each spring if frosts are mild (but the feed quality is variable). Use what suits your system, or both since lucerne and forages all respond best to rotational grazing. Water use research in winter and summer crops has shown that time of sowing is an important influence.

During the 2004 summer, a trial showed that the water use of sorghum, Nutrifeed forage millet and Shirohie Japanese millet was significantly increased with earlier sowing in October rather than December. Acknowledgement: This article was provided by Andrea Hills and Sally-Anne Penny, Development Officer WA Department of Agriculture Esperance, Ph: 08 9083 1111.