Discovering prosperity by planting diverse pastures
Landcare Research scientists have made an important discovery about the ubiquitous farming practice of letting grass grow under your gumboots. Soil scientist Dr Paul Mudge, in collaboration with DairyNZ, has discovered that the introduction of herbs into ryegrass pastures can increase annual dry matter production by 1.3 tonnes per hectare.
The impressive results, achieved by mixing the likes of chicory and plantain with ryegrass, were recorded in an experiment on DairyNZ’s Scott Farm near Hamilton. Mudge and Landcare Research researcher Dr Norman Mason, who brought his specialist ecological knowledge and modelling expertise to the project, identified the ecological mechanisms behind the enhanced production of these alternative pasture mixtures.
New Zealand farmers have been integrating diverse pastures into their farming systems for decades, but industry bodies, such as DairyNZ, are interested in understanding the potential economic and environmental benefits.
Farmers have good ryegrass/clover pasture production models, but currently they don’t have any way of modelling more diverse pasture mixes. Ongoing research aims to use predictive models linking productivity to soil and climate to identify the areas in New Zealand that are most likely to benefit from more diverse pastures. The ultimate goal of Landcare Research is to provide information for farmers to identify the optimal pasture species and species mixes for specific soil–climate combinations throughout New Zealand.
Mason thinks the goal is achievable, "And we have taken important first steps towards that thanks to some innovative thinking". Landcare Research studied climate data to model dry-matter yield for 14 pasture mixtures in a small plot trial from 2010 to 2013, run by DairyNZ at Scott Farm, Hamilton. They included the standard ryegrass–clover mix and a diverse mix also containing chicory, plantain, red clover, lucerne, prairie grass and timothy. DairyNZ measured botanical composition and above-ground biomass of each plot before grazing.
In addition, Landcare Research continued the trial for another year to allow measurements of plant functional traits, soil carbon and nitrogen cycling, and to develop a pasture production model.
DairyNZ were interested in using output from the model in their ‘whole farm model’, and they also supplied Landcare Research with pasture production data from an adjacent large-plot diverse pasture trial to validate the Landcare Research model. The final validated model was used to predict ‘diverse’ and ‘standard’ pasture growth from 1980 to 2013 at Scott Farm using climate data for the closest Virtual Climate Network station and water-holding properties of the three main soils found on Scott Farm.
Results suggest more diverse pasture mixtures can perform better than standard ryegrass–clover mixtures, especially in drier conditions. The deeper root systems of chicory, plantain and lucerne mean they tend to grow well during dry summer/autumn conditions and provide high-quality feed when traditional ryegrass and white clover pastures perform poorly. By increasing the resilience of pasture production to water deficits, more diverse pastures could reduce dependence on supplementary feed in drier areas, while helping farmers to adapt to increased water deficits expected under climate change. The combination of monoculture and mixture treatments in the trial is particularly useful because it allows tests on what mechanisms in more diverse pastures might enhance productivity (e.g. increased resource uptake or increased resource use efficiency).
By understanding these mechanisms, Landcare Research will be better able to predict when and where diverse pastures will be most beneficial to pasture production (e.g. what species or species mixes will be most suited to specific soil–climate combinations).
There are also potential environmental benefits from integrating more diverse pasture mixes into farm systems, such as increased carbon sequestration in soil; reduced N leaching and N2O emissions; improved water-use efficiency and resilience to drought stress; and less reliance on fertiliser inputs. The research also gave rise to other discoveries which showed increased microbial activity and accelerated carbon decomposition during summer in plots containing herbs.
Mudge has created climate- and soil-based predictive models which show that the more diverse ryegrass-based mixtures have similar long-term average production but greater long-term resilience in production than standard ryegrass–white clover mixtures. He is now working with Alvaro Romera (DairyNZ) and Graeme Doole (Waikato University) on a manuscript, in which ‘output’ from the diverse pasture model is being used in the Integrated Dairy Enterprise Analysis (IDEA) framework model to determine the role and economic value of more diverse pastures in dairy farm systems.
"In addition to existing models we propose to develop climate-soil-based models for dry matter production under monocultures of Lucerne," Mudge said. "This would draw on published data as well as data from the FRNL small plot trial at Scott Farm. We would use these models to predict (at the paddock scale across New Zealand) the level of irrigation required to maintain peak productivity for lucerne. These predictions would in turn allow us to compare the water use efficiency of lucerne to that of diverse and standard ryegrass-based mixtures across New Zealand".
NOTES ON FUNDING: the Diverse Pastures research programme was funded by MBIE Strategic Funding of: 2016 ($220,000), 2015 ($220,000) 2014 ($190,000).