Spanish researchers have devised a method of boosting almond harvests by depriving the trees of water during the dry summer.

This discovery, which comes as Spanish agriculture is wilting under the effects of prolonged drought, could help develop almonds as a cash crop.

Spain has been suffering from drought for the past four years - a cause of widespread concern in a country where farming is still a way of life for many.

In the south, water rationing has been imposed in major cities and farmers have been banned from watering their crops. Agriculture accounts for up to 80 per cent of water used nationally and is seen as a key factor in the fight to save water. Yet farmers are often accused of wasting this precious resource by using inefficient methods of irrigation.

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The research team is headed by Joan Girona of the regional Catalan government's Institute for Agro-Food Industry Research and Technology and Elias Fereres, professor of plant production at the southern University of Cordoba. Their idea is to see whether almond trees will produce more if watered just the right amount at key times. "We cannot use more water as it is a limited resource," says Dr Girona, "we decided to use this water in much smaller quantities, which, if we know exactly when to use it, can make the crop more profitable."

The team's first step was to determine how much water almond trees need to produce the maximum possible crop. Using a control plantation of 190 trees, they measured soil moisture, drainage and evaporation and plants' transpiration and photosynthesis rates for three years to provide a precise picture of the almond tree's life cycle.

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An optimum level of irrigation was then worked out which allowed production per hectare to be boosted tenfold to 2,800 kilograms. The scientists also found that while at certain times of the year irrigation is of vital importance, at others it makes little difference to the yield.

Almonds are traditionally farmed as a dry crop on marginal land. Although Spain devotes some 650,000 hectares to growing almonds, the largest area in the world, productivity lags far behind that in the United States. California produces some 70 per cent of world production, using just 20 per cent of the land farmed by Spain.

"The only difference is irrigation," says Dr Girona. Spanish farmers tend to irrigate very sparingly, if at all, and even then only in the dry summer months. The IRTA-Cordoba research indicates that irrigation is needed in spring when the tree grows rapidly, and in the autumn when reserves of water are accumulated for the following year. Since from mid-July onwards, all growth stops and the tree concentrates on ripening its fruit, irrigation at this point will have no effect.

Watering in the summer is thus not only wasteful, but can damage or kill the trees if drainage is poor.

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