Crop Models Richard Chynoweth chynowethr@far.nz

1. Crop Models Richard Chynoweth chynowethr@far.org.nz

2. Grower feedback • Help to answer the ‘what if’ questions • Delay applications • Reduce the amount • Miss an irrigation (wheat calc) • Dry season • Sow earlier • Save money • Increased knowledge • Confident decisions

3. Turning crop physiology into a tool for growers and advisers. They include; What happens How it happen Why it happens Two things to get right at the beginning are; Weather matters! Soil matters! Crop models are about

4. Components of a simulation model • Soil parameters • Climate variables • Crop parameters • Base temperature • Max photosynthetic rate • Radiation use efficiency • Leaf expansion rate • Grain partitioning rules

5. The Sirius Wheat Calculator software

7. Potential Yield of Maize

8. Potential Yield - Maize • Potential Yield: Maximum possible yield achievable for a given • Hybrid, sowing time, sowing location, population • Assumes no limitation from water, nutrient, soil quality, weeds, pests or disease

9. Potential Yield • Radiation drives biomass • Temperature drives development Green Leaf Area Yield Biomass HI RUE RUE = 16 kg DM/ha per 1 MJ/m2 absorbed

10. Radiation MJ/m2/day

11. Sowing Time Grain yield (t/ha)

12. Hybrid Grain yield (t/ha) CRM

13. Population Grain yield (t/ha) Population (/ha)

14. Potential Yield • Affected by: • Location • Sowing date • Hybrid • Population Green Leaf Area Yield Biomass HI RUE

15. Maize Nitrogen Requirements • Nitrogen is the nutrient most likely to be limiting in maize • Total crop uptake is about 1% (20T crop uses ~ 200 kg N) • In a mature crop, most end up as protein in grain

16. Maize Nutrient Uptake

17. Maize Nutrient Uptake

18. The Sirius Wheat Calculator

19. Reproductive development is triggered by daylengthand temperature. The model needs to know how. The canopy gathers light and holds nitrogen – The model needs to know how. The whole lot depends on the water supply – The model needs to know how. The only stuff we really want in the end is the grain. Until we get that there is no money in it In simple terms - Wheat

20. A crop needs enough time to grow a root system that can gather resources from the soil It needs leaves to gather sunlight and turn it into money It needs to synchronise its development with the season so that grain grows at the optimum time Therefore:

21. Wheat crops will use each megajoule of sunlight they can collect to produce about 1 gram of biomass A wheat crop will produce a new mainstem leaf about every 100 degree days above zero The final number of mainstem leaves depends on daylength and temperature during development Growth stages can be calculated from current leaf number and final leaf number. Some of the rules

22. Inputs • Soil information • Soil type • Mineral N (kg/ha) to 80cm or gravels • Cultivar & sowing date • Weather data (solar radiation, temperature, rain) • Historical data for future predictions • Daily data: local weather for predictions about today

23. Modules • Phenology based on leaf appearance and numbers • Biomass accumulation from light interception and radiation use efficiency • Canopy growth a function of thermal time, modified by stress • Evapotranspiration and water limitation • Soil model • Nitrogen uptake and redistribution • Grain production based on partitioning rules

24. Structure Green stuff Stem Grain Where does the N go? 1% of non-green biomass 0.5% of non-grain 15 kg/ha per unit green area 2% of Grain