Maximum pasture production with perhaps 30 percent less phosphorus fertiliser use is an indicated outcome from a major national pasture research project.
A key aspect of the research is identifying pasture legume species and varieties that perform at maximum production, or near maximum production, with soil phosphorus levels lower than is generally considered necessary for clover-based pastures.
For example where a soil phosphorus reading of 35 ppm is needed for maximum sub clover growth (Colwell analysis, 0 – 10 cm depth), research has shown that about 20 ppm can give equivalent growth by some phosphorus-efficient legume species.
Dr Richard Simpson, CSIRO Agriculture and Food research agronomist, leads a national project looking at phosphorus efficient plants with other well know researchers such as Dr Suzanne Boshma Department of Primary Industries Tamworth and Richard Hayes Wagga.
Both pink (French serradella; Ornithopus sativus) and yellow serradella (O. compressus) are among a small group of legumes identified as far more phosphorus efficient than traditional species like sub clover.
Serradella is the most promising for use in permanent, mixed pastures indicating they can perform at near maximum production with phosphorus levels much lower than required by most sub clovers.
However serradella is not used as widely as sub clover in many environments. They are used in vast areas of Western Australia and on many lighter soils in the central and north west NSW slopes.
But in soils of the NSW southern tablelands and slopes they have not found wide acceptance. Some of the research is focused on identifying how serradellas might be better able to live up to their promise in such areas. So far, the research, which involves farmer trials, indicates productivity can be equivalent to sub clover in these areas given careful choice of varieties. In areas where serradella is well established, grazing management more suited to aerial seeding species is required. Research indicates that persistence of current varieties can be problematic, although Avila, a later maturing line, has so far persisted better than other varieties in a southern tablelands trial.
In other environments such as central west NSW shorter season yellow serradella (e.g. cultivar King) has for many years proven to be long term persistent as well as very productive, especially on acid soils, including acid sub soils.
Serradella is quite different to sub clover and requires different management for long term persistence.
Both are annual plants dependent on seed production for long-term persistence. However, serradella is aerial seeding, in contrast to sub clover which seeds at ground level and buries some of its seed. Care needs to be taken to allow for good seed set by serradella and to allow stands to build up good soil seed reserves.
The research has a strong focus on factors affecting persistence such as flowering and seed set, hard-seed levels and seed softening.
Richard Simpson notes Avila, for example, flowers about the same time as Goulburn sub clover, which is about right for the southern tablelands. The study is looking for similar persistence attributes in pink serradellas which is showing superior productivity potential in these environments.
Dr Simpson, a long-time soils researcher, is mindful of how important more phosphorus efficient plants would be to farming and grazing industries.
Much of the continent has inherent phosphorus deficient soils. Much of fertiliser phosphorus applied to correct this deficiency tends to lock up in plant unavailable forms. Plants more soil phosphorus efficient has the potential to save farmers a lot of money.
