Thinking of the Southern USA conjures a mosaic of southern charm and hospitality, authentic cuisine, unique tourist destinations and a conservative culture, but more importantly thriving agricultural production systems providing food, feed, fibre and feedstock for regional and national consumption and trade. In fact, agriculture is the mainstay of the Southern economy responsible for job creation and income generation, rural development, regional and extra-regional trade. The southern region contributes 24% of 75 billion dollars to the annual US net farm income. In addition, Southern agricultural exports account for 26% of total US agricultural exports. Regional population growth which has doubled since the 1950s and inherently demands more ecosystem goods and services, therefore agricultural production systems have to continually evolve while aiming for higher productivity and efficiencies while maintaining environmental integrity and ensuring sustainable management of resources. In addition to exponential population growth, changes in precipitation frequency and intensity with simultaneous elevated temperatures have together reduced crop-water availability with significant impacts on crop yield, productivity and food security. Although water is a renewable resource, its availability as determined by precipitation, temperature, evaporation and runoff, is seasonally and spatially variable and limited. The south is nevertheless blessed with abundant water resources, being home to Lake Lanier, Lower Rocky River Reservoir, Lower Mississippi River, Mobile River and the Tennessee River, to name a few. However, excessive withdrawals and reduced precipitation was responsible for the 16 month drought which pitted Alabama, Georgia and Florida in legal battles over equitable distribution of water resources and even invoked the declaration of emergency by Georgia. This regional experience is not unique but a representation of a global phenomenon that recently attracted celebrity involvement in an effort to create awareness and sensitization of depleting fresh water resources in a meeting dubbed “Summit on the summit” hosted on Mt. Kilimanjaro in January, 2010. Of all the natural disasters, drought is the most chronic and therefore is the least respected until its effects are hard felt. Conservative models predict that these occurrences will continue unabatedly.
Since water resources are finite, it is prudent to develop an integrated water resource management strategy as a risk management rather than crisis management approach. Proactively assessing the holistic demand and supply capacity and the vulnerability of southern water resources as affected by social and climatic factors can allow for diligent, equitable and sustainable management. In 2005, daily southern fresh water withdrawals were partitioned among irrigation (19.8%), livestock (0.7%), aquaculture (2.1%), energy generation (54.9%), public supply (13.1%), domestic (1.1%), industrial (7.8%), and mining (0.5%) sectors. The increasing demands by domestic use, energy and industrial sectors limits agricultural water, thereby constraining food production. Apportioning values indicate that 55% of daily fresh water withdrawals are apportioned to thermoelectric power generation. Reducing fresh water consumption by substitution with recycled water or desalinized water may be a viable policy intervention. To reduce agricultural vulnerability in the South, there must be fundamental changes in current water management for sustainable food production.
Rainfall cannot be timed with the critical stages of plant development nor can it supply the optimum quantity of water required for growth. Therefore, during the yield determining stages of plant growth and development, supplemental irrigation is necessary to maximize or safeguard yield potential and quality during the summer months. Present genetics have the capacity to produce manifolds than average yields; therefore the manipulation of management practices at the farm level can aid water conservation, yield and sustainability. Changing current practices, however, will depend on the economics of the proposed changes. No tillage with stubble mulching improves soil aggregation, water-holding capacity and nutrient cycling while reducing soil water evaporation. Crops adapted to a no-tillage system should not be planted otherwise. Irrigation method, timing and frequency are in direct control by the farmer. The selection of highly efficient and economical irrigation systems can aid in water conservation. An assessment of the irrigation systems reveal that drip irrigation is 90-95% efficient in delivering water and nutrients to the plant relative to sprinklers (60-75%) and furrow irrigation (35-40%). Crop production in the south utilizes furrow irrigation (50%), sprinklers (44.5%) and micro-irrigation (5.5%). The efficiency of furrow irrigation can be increased if water is delivered in alternate rows rather than every row. The adoption of mechanistic crop models to determine crop water requirements based on plant water demand at critical growth stages is also a viable option to optimize water use without causing irreversible or considerable damage to the yield potential.
Although a farmer may invest in expensive irrigation equipment, the water required may not be legally available, the government may to fund and organize agricultural water user’s association responsible for rationing and monitoring water resources on a needs basis. In 2005, 75 and 25% of daily irrigation withdrawals were sourced from ground water and surface water, respectively. Aquifer management guidelines need to be developed to prevent indiscriminate withdrawals and reduce the burden on ground water sources. The government may also provide procurement subsidies for high efficiency irrigation systems such as surface and sub-surface drip variable rate irrigation systems. On farm rain capture in reservoirs or ponds for future use can be an alternative for farmers with the capacity to do so; however the costs involve may not justify such an investment. It may be more prudent for the states to develop such water capture facilities and monitor the release and rationing during periods its needed most.
Improving intrinsic crop water use efficiency can be achieved by deficit or supplemental irrigation, however, engineering plants with the capacity for enhanced canopy evaporative cooling under stressed conditions can render plants drought tolerant. In addition to physiological manipulations, agricultural research is required on improving crop water use efficiency with an emphasis on crop breeding for rainfed agriculture. Industry has responded to the need for improved plant tolerance genetics and precision irrigation management techniques and equipment. BASF, Syngenta and Monsanto have patents on a slate of climate-ready genes which will render a plant tolerant to changing climate variables by protecting the yield potential. Although these transgenic crops are not yet released, their safety must be intensely verified. ValleyIrrigation has patented the Farmscan Variable Rate Irrigation technology which controls the amount of water, fertilizer and other crop management inputs applied to areas as small as one square meter. FVRI takes into consideration field soil heterogeneity and differential plant demands for water and nutrients. Although these technologies can contribute considerably to water conservation and efficiency, the initial costs are prohibitive, therefore reducing procurement costs facilitated by research and new designs can foster adoption of these new technologies.
Maintaining the ‘greenness’ of southern agriculture in an era of climate change and increased demands for finite water resources, would require a synergistic approach by the government, state, farmers and industry to develop safe cost-effective technologies that can be applied to present production systems without much amendment.
Works Cited
Associate Press. Southern Drought Pits States Against Feds. 2007. Available online at: http://www.cbsnews.com/stories/2007/10/21/national/main3389403.shtml (accessed 5 April 2009)
Roberson, R. Southern agriculture facing water management crises. Available online at: http://deltafarmpress.com/mag/farming_southern_agriculture_facing/ (accessed 5 April 2009)
United States Department of Agriculture. National Agricultural Statistics Survey. Available online at: http://quickstats.nass.usda.gov/ (accessed 4 April, 2009)
Kenny, J.F., Barber, N.L., Hutson, S.S., Linsey, K.S., Lovelace, J.K., and Maupin, M.A., 2009, Estimated use of water in the United States in 2005: U.S. Geological Survey Circular 1344, 52 p.
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