02 Feb 2011

Agronomic Practices and Input Use Efficiency

Presentation made in India, "Preparing for Climate Change"

“Preparing Agriculture for Climate Change”
February 6-8, 2011 at the Punjab Agricultural University, Ludhiana, India.
Agronomic practices and input-use efficiency
Robert Norton, Regional Director, International Plant Nutrition Institute, Australia and New Zealand;
Dr Norton and Dr Hillel in conference sessions.
Extended Summary
The 2050 IPCC emissions scenario A1B indicates that atmospheric carbon dioxide will reach 550 ppm, and this change along with increases in other “greenhouse” gases seems likely to create further perturbations in global weather patterns. It is virtually certain that future climates will have warmer days and nights, fewer cold days, more frequent hot days and nights, while it is likely that there will be larger areas affected by droughts. Current climate models suggest that annual rainfall in the grain production regions of Australia will decline by 50–100 mm and annual mean surface temperatures rise by 1-2oC.

Productivity growth in agriculture is the key indicator to meet food security and the impact of science has been to improve grain yields, without recourse to expanding production areas. The increase in production over the Green Revolution – into the Evergreen Revolution – is a case study in ecological intensification which has delivered increasing food supply as well as preserving land for wildlife and non-agricultural pursuits. These changes have come about by improvements in efficiency of resource use – such as water, nutrients and radiation – through agronomic and genetic adjustments to production systems.

As a consequence of changes in climate and the need to maintain and improve productivity, over the past 20 years in south-eastern Australia, farmers have changed their management practices by a combination of increasing pasture or fallow frequency, reducing plant density, selecting shorter season crops and increasing residue retention. The application of these basic agronomic changes using existing technology should provide some adaptation to climate change in the short to medium term. Additional technologies such as precision or site-specific management and better climate forecasting offer further improvements in resource use efficiency.

Although there are several ways that resource use efficiency can be defined, there has been considerable improvement in agronomic efficiency of – for example - nitrogen use. It has been reported for corn in the US that agronomic efficiency has increased by 50% and this is a consequence of adopting balanced nutrition with the right product at the right rate, in the right place and the right time. Such strategies will continue to deliver improvements in nutrient use efficiency.

While it is expected that higher temperatures and lower water availability will adversely affect grain production, the higher atmospheric carbon dioxide concentration is likely to moderate the impacts. The two major effects of higher carbon dioxide in C3 plants are to increase crop growth (fertilization effect) and decrease water use, which combined suggests higher water use efficiency even for unadapted cultivars. Experiments from Free Air Carbon Dioxide Enrichment (FACE) facilities have helped to quantify the impact of the interaction of high temperatures, changing water supply and increased [CO2], and the data from the Australian Grains FACE suggests that this fertilization effect occurs even with otherwise adverse growing conditions.

Elevated [CO2] increases photosynthetic rates by increasing RuBisCO activity in C3 plants and decrease transpiration by closing stomata in both C3 and C4 plants. The rise in photosynthetic rate is most often accompanied by a decline in leaf N, and as a result photosynthetic N use efficiency rises, termed photosynthetic acclimation. Together, these give a CO2 “fertilisation effect” to plants that has been reported to increase in grain yield of wheat between 15% and 31%. The response tends to be larger under drought and but is also affected by N supply. There appear to be opportunities to select better adapted cultivars to elevated [CO2] by investigating differences in acclimation response and changes in source/sink balances. Such improvements would improve both nutrient use efficiency as well as radiation use and water use efficiency, reducing the adverse effects of climate change in the medium term.

However, in the longer term, improved efficiency alone is not likely to ensure future food security. Whole system changes may be needed to develop new products or to relocate landuse activities to different areas as new agroecological zones develop.
2011 02 PAU TALK Norton.pdf (size: 2.57 MB)

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