Improved soil and irrigation management for forage production 2. Forage yield and nutritive characteristics

Abstract

Pastures are the main source of energy and nutrients for dairy cows in the irrigated dairy region of northern Victoria, yet annual production and utilisation of pasture have remained static over the last 20 years. Previous small plot research has shown that pasture yields can be increased through systems of soil modification that improve soil structure and alleviate limitations to root growth. We compared the yield and nutritive characteristics of 4 forage species [tall fescue (Festuca arundinacea), lucerne (Medicago sativa), phalaris (Phalaris aquatica) and perennial ryegrass (Lolium perenne)] on soils which had been modified using commercially-available equipment and using spray irrigation at 2 frequencies. In year 1 (2000–01), annual yields of the forages were tall fescue: 21.2 t dry matter (DM)/ha; lucerne: 20.5 t DM/ha; phalaris: 19.8 t DM/ha; and perennial ryegrass: 20.8 t DM/ha. In the second year of the experiment, annual yields averaged 28.9 t DM/ha for tall fescue, 26.1 t DM/ha for lucerne, 31.6 t DM/ha for phalaris and 23.2 t DM/ha for perennial ryegrass. There was no consistent response in yield of any species to soil modification. The improvements in soil structure achieved with soil modification were probably not large enough to result in yield responses. Yields were greater when frequently irrigated, with the exception of perennial ryegrass in the second year. Most of the yield benefit due to frequent irrigation was limited to the summer months. No yield data showed significant soil by irrigation frequency interaction. There were significant differences in forage nutritive characteristics between the 4 species. The lower crude protein content of lucerne would be at least partly due to the frequent application of nitrogen fertiliser to the grasses. Tall fescue usually had similar nutritive characteristics to perennial ryegrass in terms of metabolisable energy, protein and NDF. Phalaris had high fibre contents and low metabolisable energy in summer. We conclude that it is not feasible, at this time, to improve yields of irrigated forages through soil modification on a commercial scale.