Project Title: Quantifying the tradeoff between tree and crop productivity on farms

Project Supervisor: Peter Carberry

Funding Body: RIRDC/LWRRDC/FWPRDC

Admin Contact: Marshall Mackay

Commencement Date: 1 / 1 / 1999 Completion Date: 30 / 6 / 2001

In enabling landholder assessment of the productivity and risk of commercial agroforestry investment on grain farms in Australia’s medium to low rainfall regions, this project aims to:

i. add the capability to simulate tree-crop competition for light, water and nutrients to APSIM’s existing capacity to simulate the impact of windbreaks on crop production and its emerging capacity to simulate tree productivity;

ii. quantify the potential benefits and risks of planting trees in association with cropping land through an economic analysis of associated crop and tree yields predicted for the historical climate record at selected sites; and

iii. with landholders, extension officers and researchers, use this new capability to design and implement action learning activities that enable individual landholders to explore the viability of agroforestry investments for their own farms.

This project has four key activities:

1. APSIM development – APSIM has a well-establish capability to simulate cropping systems in Australia and the capability to simulate tree growth and productivity is currently being added by incorporating into APSIM the established 3-PG tree model [via Keating project - see linkages specified in B7]. The capacity to simulate the microclimate effects of windbreaks on crops has also been established [via Carberry windbreak project]. APSIM has the capability to simulate crop mixtures or intercropping systems (Carberry et al., 1996), a capability which, with further development, can be also employed in dealing with the simulation of tree-crop competition for light, water and nitrogen. The enhancement of APSIM to deal with tree-crop interactions will benefit from related progress in other modelling efforts in Australia and elsewhere [via Stirzaker/Landsberg project specified in B7]. The budget contains $15K in the first year to fund software engineering input into the design and implementation of the APSIM software to accommodate tree-crop interactions.
2. Testing APSIM – data on tree-crop interactions, incorporating measurements on productivity, and water and N balances, will be collated. Known data sources include the Esperence and Atherton National windbreak experimental sites and the SUDMEYER GRDC and STIRZAKER RIRDC projects specified in section B7. The budget contains $16.5K over three years to assist additional data collection at these established experimental sites. Further data will also need to be found from other sources. APSIM’s ability to simulate tree-crop interactions will be tested against this collated database.
3. Economic analyses – APSIM will be run for a range of tree-crop configurations over the historical climate record for key medium to low rainfall regions of Australia. Predicted wood production and crop yields (incorporating the aggregate effect of crop yield loss due to tree competition offset by yield increase due to windbreaks) will be used in economic analyses to assess profitability and risk of alternative system configurations. Analysis results will be reported in extension material and industry media.
4. Action learning activities – recent APSRU experience has demonstrated that simulation can provide a powerful learning tool in assisting farm managers to explore their farming system. As part of this project, a number of pilot "What IF Analysis & Discussion" sessions (WIFADs) using APSIM will be run with groups of landholders to enable the viability of agroforestry investments or retention of existing shadelines to be explored in the context of individual’s own farms. These WIFAD sessions will be conducted principally in the northern cropping region and will be coordinated by Peter Voller (DNR, Dalby) and other local agribusiness consultants and extension officers who interact with existing farmer groups interested in agroforestry. From these pilot activities, an action learning module may be developed for broader usage. The budget includes $9K over three years to fund farmer group facilitation.

Convincing evidence exists for long-term benefits of retaining or planting trees on farms to rehabilitate land and protect the soil from erosion or salinity problems. However, trees compete with commercial crops both for land area and resources, especially in the medium to low rainfall regions of Australia. The incentive for landholders to plant trees would increase if crop losses could be offset not only by the beneficial impacts of tree windbreaks on crop yields and resource sustainability but also by the economic returns gained from farm forestry products. A significant problem in encouraging landholders to act on this incentive is that it is difficult to quantitatively assess this tradeoff between crop and tree productivity for different regions and cropping systems, and almost impossible for landholders to do so in the context of their own farm.

A number of recent RD&E developments now provide the opportunity to enable the tradeoff between tree and crop productivity on farms to be quantified in a manner relevant to commercial farming practice. Firstly, via the RIRDC National Windbreak Program, the beneficial effects of tree windbreaks has been quantified and an ability to predict such effects has been developed. Secondly, the ability to predict tree productivity has progressed to a point that is now comparable to current crop simulation models. And thirdly, through the efforts of APSRU, considerable evidence now exists that simulation models can be regarded by farmers and consultants as viable and relevant tools in the management of their commercial farming enterprises. Many farmers on the Darling Downs, and several agribusiness firms, regularly use the APSIM model to quantitatively assess alternative cropping strategies in the context of their own farm or business. The major new R&D issue addressed by this proposal is to develop the capacity to simulate tree-crop competition - a key R&D issue identified by but largely not addressed in the National Windbreak Program.

Developing the capability to simulate tree-crop interactions will provide landholders with the opportunity to assess the productivity and risk of agroforestry for their farm. Identifying regions and, in particular, individual farms where agroforestry is well adapted to integration with crop production could provide significant economic, environmental and social benefits – as would also be the case if regions or farms unsuited to agroforestry were identified. By involving landholders, extension officers and agribusiness in action learning activities that utilise this capability, this project will be helping agroforestry realise some of these perceived benefits.