B.PAS.0360 - Not enough nodules: impact of herbicides, pesticides and other farm management

Summary

Recent surveys of paddocks in southern Australia revealed more than 90% had legumes that were inadequately nodulated. Without sufficient and effective nodulation, legumes are unlikely to meet expected nitrogen fixation targets which then have the capacity to affect pasture production, pasture quality and ultimately livestock production. As a result of this project, we were able to identify gaps in knowledge and identify key areas for future investment to improve legume function in pastures which will likely increase pasture production and potential for improvement of livestock production.

Objectives

This project will achieve the following objectives:
1. A review of the information concerning herbicide, insecticide, fungicide use and soil management to improve legume-rhizobia symbiosis to distil what is known about individual and multiple stresses on the formation of an effective symbiosis and the quantity of N fixed.
2. Report to MLA the results of consulting with industry (red meat producers n=80 and advisers n=40) to quantify contemporary use practices with regard to use of soil inputs (e.g. fertiliser, lime), herbicides, insecticides and fungicides in pasture paddocks and results/observations on legume production.
3. With direction from MLA Technical Contact, develop draft extension materials to mitigate issues with nodulation and N-fixation arising from the use of herbicides, insecticides, pesticides and/or sub-optimal soil management.
4. Describe re-inoculation strategies for existing pasture contexts across southern Australia to increase N-fixation.
5. Develop an investment strategy to improve N-fixation and red meat production.
6. Make recommendations to MLA on candidate investment and delivery partners to undertake recommended work, which may include the research organisation at its discretion.

Key findings

The literature review and industry survey identified numerous gaps likely to be limiting pasture legume performance. Gaps identified aligned well with industry identified needs for future investment.

Traditional legumes are failing to meet producer expectations in terms of livestock production goals at least half of the time.

Coupled with the need for development of new legume germplasm is the need for improved technology to support dry sowing.

Literature analysis with respect to the impact of herbicides on legume and rhizobia function identified many gaps.

The conclusion from the literature review and consultation with industry was that the highest priority for investment is in the mixed farming zone. This zone is extremely dynamic with much change in farming systems and as such there is capacity to positively influence outcomes for legume function. Improvements in legume function are likely to see greater capacity to attain livestock production goals and also to positively impact the whole farming system through provision of increased quantities of biologically fixed nitrogen.

Benefits to industry

Legumes are pivotal to the supply of nitrogen for non-legume pasture components and are largely responsible for the responses observed where phosphorus and sulphur-based fertilisers are applied to pastures. However, these pivotal functions are not a given and rely on adequate and effective nodulation and nodule function for pasture legumes. Additionally, pasture legumes contribute positively to improvement in soil conditions including supporting of increases in microbial biomass and therefore nutrient turnover rates. Legumes have the capacity to contribute to achievement of sustainability goals on farm and by industry more widely (e.g. ecocredentials, attainment of carbon-neutrality). There are now legumes available with improved adaptation to climatic and soil physiochemical challenges prevalent across southern Australia. Investment in the RDE&A priorities identified in this project will close the gap between actual and potential nitrogen fixation by pastures legumes resulting in increased pasture growth and livestock production.

MLA action

MLA used the outcomes of this project to inform options for new investment and create adoption material. Included, were further investigations of R&D in the mixed farming zone with GRDC.

Future research

Potential future investments may include but are not limited to;
1. Development of legume and rhizobia germplasm to overcome the shortcomings of traditional legume adaptation to changing soil, climatic and farming system requirements.
2. Improved technology to support dry sowing which includes investment in appropriate germplasm (plant and rhizobia) and rhizobia delivery technology.
3. Investment in improving the understanding of herbicide impacts on pasture legumes particularly with respect to the use of herbicides in contemporary and future farming systems. This area of investment was rated a 9.5/10 by industry.