Modelling legume yield

What are we doing for farmers?

The purpose of this research area, led by Derrick Moot (Lincoln University) and Edmar Teixeira (Plant & Food Research), is to develop robust methods to estimate the yield and suitability of forage legumes across New Zealand. To do this, a real-time (daily time step) model, the Agricultural Production Systems sIMulator (APSIM) model, is being developed that can answer questions around environmental impacts, climate change, nutrient leaching and carbon sequestration on legume-based pastures. APSIM is described as "a comprehensive model developed to simulate biophysical processes in agricultural systems, particularly as it relates to the economic and ecological outcomes of management practices in the face of climate risk".

At this stage, the APSIM model is being used to assess forage legume yield from a national perspective using lucerne as a proof of concept due to the extensive data available. This model will also simulate lucerne growth under dryland conditions and from that provide input data that can be used to assess environmental impacts of using high quality forages on soil and water quality.

The 3 key achievements of this research to date are:

  1. Development of a validated lucerne model for irrigated conditions that can be used to assess yield and quality of lucerne grown on farms in high rainfall and irrigated conditions. This work aims to empower farmers to consider using lucerne in areas of their farm that can be cultivated or irrigated to complement uncultivable hill country areas. This model will be made publicly available.
  2. A national yield map, at a gross scale that uses maps of soils and climate that has been validated across New Zealand. Once validated with previously published results, the output gives confidence that the model can be used to inform policy around climate change, environmental impacts and compared with empirical models such as Overseer to test the accuracy of current and future on-farm nutrient budgeting. 
  3. A manuscript has been published with a simple thermal time (TGM) model of lucerne growth based on temperature. This provides a farmer-friendly option for individual farmers to assess potential yields of lucerne on their farm from their own temperature and rainfall data.

Ongoing and planned research

  • Work on the national datasets and the APSIM model is ongoing. At the end of the programme it is planned that the APSIM model will be suitable for addressing environmental and policy-relevant questions at a national scale (e.g. climate change and resource use). 
  • Comparison between the APSIM and the thermal time-based model is being validated with data from the national forage database. Reasons for any anomalies are being interrogated, and a manuscript is being prepared that compares the findings. Further work on the rainfed ASPIM model is ongoing.