Volume 6, Number 46: 12 November 2003
Van Ittersum et al. (2003) note that a major problem associated with crop production in Australia is water loss below the plant root zone or deep drainage, which can lead to water-logging, soil acidification and dryland salinity. Hence, in an effort to learn how potential changes in the global environment might impact this problem, they performed a number of simulation experiments with the Agricultural Production Systems Simulator (APSIM)-Nwheat model in which they explore the implications of possible increases in atmospheric CO2 concentration and near-surface air temperature, as well as decreases in precipitation, for wheat production and deep drainage at three sites in Western Australia differing in precipitation, soil characteristics, nitrogenous fertilizer application rates and wheat cultivars.
The scientists' first order of business was to assess the impact of the ongoing rise in the air's CO2 content on the phenomena of interest. In doing so, they found that wheat grain yield increased linearly at a rate of 10-16% for each 100-ppm increase in atmospheric CO2 concentration, with only a slight concomitant increase in deep drainage (a big win-tiny loss outcome). For a likely future CO2 increase of 200 ppm, for example, increases in grain yield varied between 3 and 17% for low nitrogen fertilizer application rates and between 21 and 34% for high rates of nitrogen application, with the greatest relative yield response being found for the driest site studied. On the negative side, the increase in CO2 typically decreased grain protein content; "but in financial terms," say the scientists, "this was more than offset by the increase in yield in most cases."
When potential warming was factored into the picture, the results proved even better. The positive effects of the CO2 increase on wheat grain yield were enhanced an extra 3-8% when temperatures were increased by 3°C in the model simulations. These yield increases were determined to result in an increased financial return to the typical Western Australian wheat farmer of 15-35%. In addition, the imposition of the simultaneous temperature increase lead to a significant decline in deep drainage, producing a truly win-win situation that enhanced the average farmer's net income by another 10-20%. Consequently, it was found that the CO2-induced increase in temperature predicted by the world's climate alarmists could well increase the net profitability of Western Australian wheat farmers by anywhere from 25-55%, while at the same time mitigating what van Ittersum et al. refer to as "one of Australia's most severe land degradation problems."
If precipitation were to concurrently drop by 25% across the entire year, however, van Ittersum et al.'s analysis reveals a wider range of results. Although for some of the sites and soils they studied the financial benefits described above would be maintained, for others there could be financial declines of 15-90%. However, it should be remembered that one of the ancillary predictions of the same climate models that predict CO2-induced global warming is a significant increase in earth's hydrologic cycle, which would bring even more precipitation to most parts of the world than they currently receive.
All in all, the results of this impressive study of real-world agricultural operations in a significantly CO2-enriched atmosphere -- which is the only environmental change we can be confident will occur in the foreseeable future -- bodes well indeed for the financial well-being of Western Australian wheat farmers and the land that supports them.
| Sherwood, Keith and Craig Idso |
Reference
van Ittersum, M.K., Howden, S.M. and Asseng, S. 2003. Sensitivity of productivity and deep drainage of wheat cropping systems in a Mediterranean environment to changes in CO2, temperature and precipitation. Agriculture, Ecosystems and Environment 97: 255-273.