Is the agricultural intensification of sand dunes sustainable?

The length of coastal areas around the globe is over 1.6 million kilometers, skirting approximately 150 countries.  Many of them are in the tropics with sprawling cities along the coast not far from rural populations.  Farmers may be adapting environmentally unsustainable agricultural practices similar to what is being adapted in Keta and Kalpitiya, two coastal regions that are continents apart.  Is this level of intensification ecologically sustainable?

Fisherman in Kalpitiya, Sri Lanka working together. Photo: S.A. Prathapar/IWMI

Despite being continents apart, there are many similarities between the two.  Keta is east of Accra, Ghana, and Kalpitiya is north of Colombo, Sri Lanka.  Both are between the equator and 8 degrees N, about 150 km away from their respective capital cities along the coast, receive an annual rainfall of about 1000 mm, and have an average temperature range between 28 and 33 degrees Celsius.  Being closer to the equator, tropical vegetable production flourishes throughout the year, and their proximity to their capitals provides ready access to markets.  A range of short duration vegetables are grown, planted in adjacent plots a few weeks apart, so that a continuous harvest, and uninterrupted supply of vegetables is assured.  Almost all agronomic practices are done manually, providing employment not only to locals, but also for migrant labour.

But there are challenges for managing available land and water resources.  The land that is available for cultivation is of sandy texture, lacking structure and organic matter.  Loads of un-processed organic matter from dairies and poultries are tilled into the soil every two to three months, just ahead of a new planting.  Partially decomposed organic matter timidly binds sand grains and provides anchorage for vegetable crops with small canopies or with tubers and bulbs.  Tall crops with broad canopies are easily dislodged by winds from surrounding seas, despite the presence of coconut groves which act as wind breaks.

Farmers rely on the freshwater lens floating on saline groundwater for irrigation. Crops have to be irrigated daily, if not twice a day because of poor water holding capacity of soils, and high evaporative demands.  Significant fractions of groundwater drawn from fresh water lenses are returned with added nutrients and pesticides.  Because of the need for high frequency irrigation and increasing costs of labour, farmers have developed low-cost low-pressure sprinklers for irrigation.

Sprinklers are better suited for these soils than drips, because they cover larger areas than the drips.  Surface irrigation is impractical because of high conveyance losses.  Local design of sprinklers keeps the costs low, although they result in poor uniformity in soil water content.  Groundwater pumps which support sprinkler irrigation are of low horsepower.  They are relatively inexpensive and adequate to pump groundwater from shallow depths of groundwater.  Involuntarily, their low capacity minimizes the risk of salt-water intrusion.  However, during dry months, as the thickness of the fresh water lens shrink, there are occasions when the salinity of pumped water increase beyond unacceptable levels.

Is this level of intensification of a fragile environment sustainable?

The practices in these dunes are certainly profitable to farmers, despite the yields of crops are a lot less than their genetic potential.  The quality of the produce is not great either; even the farmers will admit that the vegetables have unacceptable levels of residues of pesticides.  Farmers know very well that the groundwater quality is beyond the limits of safe drinking water quality.  They purchase better quality water from villages away from theirs, and where there’s no intensification of agriculture as is in their villages.

It appears that the farmers have ‘accepted’ that the groundwater in the area is ‘good’ for irrigation and ‘bad’ for drinking.  Have they adapted a new paradigm of water management – acceptable quality of adequate quantity – for the intended purpose?

Is this the future of financially and socially sustainable-intensification? After all, their practices are meeting the demand for cheaper vegetables in the cities, employ unskilled labour in rural areas and make profits for themselves.  This offers opportunities for researchers to contribute and improve the situation. What can be done to promote environmentally sustainable practices, which are financially and socially sustainable along coastal areas?

What are the appropriate managed aquifer recharge methods, which can increase the thickness of the freshwater lenses?  How can the design of sprinklers be improved to provide better uniformity and less leaching at an affordable cost?  What can be done to organic manure so that the release of nutrients is gradual and slow?  What can be done to increase yields to be closer to their genetic potentials so that the area under cultivation may be reduced?

Pursuit of answers to the above and more will transform financially and socially sustainable intensification into ecologically sustainable intensification.