Improved soil and irrigation management for forage production 3. Plant - soil - water relationships
A field experiment was conducted from January 2000 for 2.5 years, at the Department of Primary Industries, Kyabram, in northern Victoria. The experiment determined the effect of soil modification, with and without subsurface drainage, on the yield and water use of tall fescue (Festuca arundinacea), lucerne (Medicago sativa), phalaris (Phalaris aquatica) and perennial ryegrass (Lolium perenne) under 2 irrigation frequencies. The soil was a red-brown earth. The forages were spray irrigated from August to May when evaporation minus rainfall (E – R) reached 45–50 mm (frequent) or 90–100 mm (infrequent). The depth of irrigation water applied was equal to the soil water deficit (SWD) of each treatment, measured before each irrigation. Soil modification did not change the plant available water content of the soil (about 115 mm). The apparent depth of water extraction was initially different between soil management treatments but, over time, these differences disappeared. There were consistent differences between the forage species in the apparent depth of soil water extraction. Lucerne extracted water from deeper in the soil than phalaris followed by tall fescue and then perennial ryegrass. In general, the infrequently irrigated forages extracted water from deeper in the soil than did the frequently irrigated forages. The frequently irrigated treatments received slightly more water than did the infrequent treatments. The depth of water applied to the control and modified soil was similar, whereas the drained soils received more water than did the undrained treatments. There were differences between the forages in the depth of water applied, with lucerne receiving up to about 1500 mm/year and the grasses about 1100 to 1300 mm/year. Water use efficiency [kg dry matter (DM)/ha.mm] of the forages ranged from 14 to 18 kg DM/ha.mm in 2000–01 and up to 24 kg DM/ha.mm in 2001–02. The relatively high water use efficiencies were largely due to the high yields achieved, as water use was similar to that of district farms.