Differences in soil water content between perennial and annual forages and crops grown under deficit irrigation and used by the dairy industry

Water for irrigated agriculture is becoming increasingly scarce worldwide and this has led to interest in deficit irrigation (DI) as a means of reducing forage and crop water requirements. While perennial ryegrass (Lolium perenne L.) dominates the forage base on Australian dairy farms, its ability to extract water from the soil profile under DI compared to other species has not been documented under best practice management. Changes in soil water content (SWC) of twenty two perennial and annual forage and crop species were evaluated over three years to assess the ability of these forages to extract water from the soil profile compared to perennial ryegrass under DI on a brown Dermosol, over three years at Camden, Australia. Seven perennial and three annual forage species created a greater (P < 0.001) soil water deficit (SWD) to 150 cm than perennial ryegrass. Paspalum (Paspalum dilatatum Poir.) created the largest SWD to 150 cm of 226 mm, which was 78 mm greater than perennial ryegrass for the same year. Estimated plant root depth was greater than 150 cm for 11 of 12 perennial forage species, but less than 150 cm for seven of 11 annual forage species. This study showed that there were large differences between values of maximum extractable water for the range of forage species evaluated, which has implications for reducing irrigation requirements and reducing recharge.

► 22 forage and crop species were compared for differences in soil water extraction over three years.
► There were large differences in soil water extraction between forages and crops.
► The C4 perennial paspalum had the greatest soil water extraction.
► Over all forages soil water extraction was poorly correlated with forage production.