By Caitlin Langley
Farmers and managers understand that one of the keys to the reduction of weed populations and increasing drought tolerance in pasture is getting away from conventional monoculture. Indeed many are progressing to the idea that by having multiple grass varieties in a pasture system by investing in greater pasture biodiversity it will encourage long term persistence. Biodiversity in pasture systems suppresses competition of unfavorable varieties that are either less palatable to livestock, as well as accounting for variation in the landscape.
When considering the investment such as establishing a new pasture, it may be that you are offered a range of options, including complex mixtures that will promise to achieve biodiversity. But how many of these selected varieties of plants ultimately survive to maturity when competing for resources during early growth establishment is often held to question, particularly in the instance of products such as the complex ‘shotgun mixes’.
What stands to question is if in the instance of establishing new paddocks, is using such mixtures for establishing pasture achieving efficient persistence for all species included? For many, the approach to establishing biodiversity is by sowing up to 7 to 8 species and ostensibly leaving the paddock to do the rest. But how effective is this method, and how uniformal is success for all selected varieties?
Image credit: Johan Fabius
Diversity of plant species in Australian grasslands has been the subject of extensive ecological studies over the last 25 years its primary focus has been that relating to biodiversity and its consequences. And while most of these studies comprehensively support the fact that in the instance of established pastures increased biodiversity results in greater plant productivity and and increased nitrogen (Hector et al 1999), other similar studies concluded that drought resilience and long term stability were also increased with biodiversity.
In a study conducted in the permanent pasture zone in southern NSW within the Murrumbidgee and Murray catchments in Spring 2005, a survey of 61 paddocks on over 35 farms was conducted to investigate persistence of establishment of new paddocks. In the study it was shown that despite farmers having sown on average 5 species per paddock, in most cases only two species could be found. In addition to these findings is was shown that in all of the paddocks surveyed that there was no appreciable persistence of the 5 species sown.
So aside from potentially ‘throwing away’ money in sowing species that were found in these studies to be unsuccessful at persisting to maturity in new paddock systems, does it then follow that there is a diminished productivity when paddocks sown with these multiple varieties experience the loss of the non-persistent species?
A further study of phalaris – the most persistent perennial species, demonstrated two significant factors relating to this question. The two discoveries were that pastures contained more phalaris if they were sown with fewer or no other perennial grass species, and were well fertilized.
So does it then come down to commercial interests driving the sale of multiple varieties for sowing new pastures? While this might not be the definitive answer, there is little (if any) legitimate studies that are able to provide evidence that it results in successful germination of all of the selected species. It is important to note that this particular study is region specific and may not be able to be readily applied to other regions, but it is worthwhile considering that the evaluation of many species selected by agronomists for these complex pasture mixes are usually evaluated in monoculture plots for their suitability – that is to say, it does not necessarily follow that these varieties are suited to or even complementary to growing with each other when put in an uncontrolled environment when they are potentially competing for resources.
In conclusion, while it is proven and acknowledged that in established pasture systems biodiversity leads to optimal persistence, it is important when considering pasture mixtures for establishing new pastures that the focus should be the persistence of the individual species best suited to your specific farming system, and for some farmers choosing to stick to simpler mixtures could be the key to establishing a robust pasture.
Image courtesy Virgona, J., & Hildebrand, S. (2007)
Virgona, J., & Hildebrand, S. (2007)
“Biodiversity and sown pastures: What you sow is not what you get”
Proceedings of the Grassland Society of Southern Australia, Echuca VIC