Difference in yield and persistence among perennial forages used by the dairy industry under optimum and deficit irrigation

Perennial ryegrass (Lolium perenne L.) is the dominant forage grazed by dairy cows in Australia; however, poor persistence has led to an increasing interest in alternative forages. This study was conducted to identify more productive and/or persistent perennial forage species than perennial ryegrass. We evaluated 15 perennial forages under optimum irrigation (I1) and 2 nominated deficit irrigation (I2, 66% of irrigation water applied to I1; I3, 33% of irrigation water applied to I1) regimes, over 3 years at Camden, NSW (34 degrees 3'S, 150 degrees 39'E), on a brown Dermosol in a warm temperate climate. The forages were: perennial ryegrass, cocksfoot (Dactylis glomerata L.), phalaris (Phalaris aquatica L.), prairie grass (Bromus catharticus M. Vahl), tall fescue (Schedonorus phoenix (Scop.) Holub), kikuyu (Pennisetum clandestinum Hochst. ex. chiov.), paspalum (Paspalum dilatatum Poir.), birdsfoot trefoil (Lotus corniculatus L.), lucerne (Medicago sativa L.), red clover (Trifolium pratense L.), strawberry clover (Trifolium fragiferum L.), sulla (Hedysarum coronarium L.), white clover (Trifolium repens L.), chicory (Cichorium intybus L.), and plantain (Plantago lanceolata L.). Under non-limiting conditions of water and fertility, tall fescue, kikuyu, and prairie grass had the highest mean annual yield over the 3 years of this experiment (24.8 25.5t dry matter (DM)/ha), which was significantly greater (P < 0.05) than perennial ryegrass (21.1t DM/ha). Kikuyu was significantly higher than all forages under the extreme I3 deficit irrigation treatment, with mean annual yields of 17.0t DM/ha. In contrast, the mean yield of white clover was significantly lower (P < 0.05) than of any other forage at only 5.0t DM/ha, a 70% decline in yield compared with I1. Lucerne was the most tolerant species to deficit irrigation, with a mean annual yield decline (P < 0.05) between the I1 and I3 treatment of only 22%. This study has shown that there are large differences in the relative yield potential of forages and, importantly, indicates the possibility of increasing yield of perennial forages by at least 2-fold on commercial farms, by improving water, and fertiliser management. However, while yield is an important criterion for choosing dairy forages, it is only one factor in a complex system, and choice of forages must be considered on a whole-farm basis and include water-use efficiency, nutritive value, costs of production, and risk.