Water usage in subtropical crops: the path from efficiency to sustainability

Water usage in subtropical crops: the path from efficiency to sustainability

Agriculture is an economic and social engine that makes it possible for millions of families to develop their way of life in Europe. To be more specific today (April 2020), according to European Union data, agriculture provides regular employment for 20 million people¹.

Farmers, government and consumers are increasingly aware of the importance of a sustainable agricultural sector both in terms of employment and environment.

The geographical characteristics of the coastal strip of the provinces of Malaga and Granada, protected by mountain ranges, create a subtropical climate that is unique within the Mediterranean climate. The mountain chains parallel to the coast retain both the humidity from the sea and the heat generated by the sun, providing stable temperatures throughout the year. This creates a subtropical climate that provides optimal growing conditions for tropical fruits. These conditions have been used by the farmers of these provinces to grow fruits such as avocado, mango or cherimoya for more than two centuries. In Málaga, tropical fruits have been cultivated since 1770². 

In other regions of the Iberian Peninsula such as the Valencian Community, western Andalusia and the southern coast of Portugal, areas have been detected where frosts never occur and winds are not problematic so avocado has also begun to be cultivated as an alternative to other less profitable crops for the farmer.  

The Mediterranean climate is associated with low rainfall and periods of drought, which unfortunately tend to be accentuated by climate change. Lack of water is one of the main factors limiting agricultural production and is also a concern for consumers who are looking to generate a positive environmental impact with their food purchases. 

Technology is a key factor for the good use of water, being almost mandatory the use of drip irrigation systems, which avoids waste and ensures a homogeneous distribution of water, ensuring that each tree receives the right amount. The use of probes (tensiometers) that measure the humidity of the soil is becoming more and more frequent. These probes indicate exactly when irrigation should start and when it should stop, so each tree receives exactly the amount it needs. Both farmers and the public administration are making great efforts in this regard to promote increasingly efficient agriculture through irrigation technology and control. There are specialized research centers (e.g. IFAPA³) that transfer knowledge to farmers on how to manage farms to save as much water as possible. 

There are other factors related to crop management that can provide important water savings, such as keeping the soil always covered by organic matter such as leaf litter or plant debris and/or proper pruning of the tree to provide shade to the soil, both techniques tend to prevent the sun and the warm summer wind from drying out the soil. 

The water resources used by farmers can come from 3 main sources: reservoirs, wells and rainwater. Where farmers have water from reservoirs, these are organised in an irrigation community which ensures that water is distributed fairly on the basis of existing reserves, which usually vary between 5 000 and 8 000 cubic metres per hectare⁴.

The extraction of water from the subsoil is controlled by the administration and each farmer has a water meter in his well that controls the amount extracted. This amount is also limited according to the reserves of the subsoil. Farmers are increasingly aware that the recharge capacity of the aquifers should not be over-exploited, since on the coast they often become saline due to the penetration of sea water, thus cancelling out the irrigation capacity of the well permanently. If seawater enters a well, it cancels out its usefulness for irrigation because the salt burns the plant’s roots.

A large number of tropical fruit farms are located on mountain slopes and many farmers take advantage of the rainwater by cultivating terraces which, being at the same level, favour the infiltration of water, replenishing the aquifers and reducing the runoff.

The water consumption of each crop varies depending on the area and is adjusted to its availability, generally increasing the efficiency of its use as the shortage increases. The sustainability of the avocado crop is questioned because it is a plant of tropical origin, however, the efficiency of water consumption of this crop is similar to that of other fruits (960L/Kg) and is below other crops such as cereals (1,600L/kg), legumes (4000L/Kg) or nuts (9,000L/Kg), moving away from values as high as those needed for cattle production (15,000L/Kg)⁵. 

Globally, it is estimated that to produce 1 kg of avocado, about 1000 liters of water are needed; in the specific case of cultivation in Malaga and Granada, due to the effort of farmers and technological innovation, most farmers consume less than 700 liters to produce one kg of avocado⁶. IFAPA researchers estimate that in the near future consumption can be reduced to 500 L/kg⁷. If we add this to other advantages such as organic production, positive social impact or reduced carbon footprint due to their proximity to the European consumer, this makes avocado and other tropical fruits sustainable crops in these geographical areas. 



Statements on water use by some of the CrowdFarming farmers:

La Salada Farm: “We take care of the sustainability of the farm and its production in an integral way, and especially the water consumption of our avocados. We apply “microring” that guarantees a consumption of 280-380 liters of water for each kilo of avocado. This management of the irrigation system, together with the reuse and collection of rainwater, and the selection of both varieties and patterns that we have carried out, make the water footprint of our production one of the lowest that can be found”.

El Rinconcillo Farm: “We get our water from our own wells and by storing rainwater. An adult tree consumes about 32.5m3 per year. For irrigation we use drippers that make the water supply more efficient. We check the drippers weekly to prevent water leaks and use tensiometers to determine the water needs of each area. […] Trunks and branches are crushed and thrown onto the plantation pathways, together with the leaves to create a mulching that improves water retention and increases organic matter in the soil”.

The Atalaya Farm: “Our farm water comes from wells that are tested quarterly to ensure they are not saline. The whole farm has installed drippers and we have a pond to accumulate water”.

References
• Union Européenne [Online] at <Agricultura | Unión Europe> [Accessed in March 2019]
• IFAPA [Online] at <CENTRO IFAPA DE MÁLAGA | Instituto de Investigación y Formación Agraria y Pesquera (IFAPA)> [Accessed in March 2019]
• El cultivo del Aguacate [Online] at <El Cultivo del Aguacate en la Costa de Granada> [Accessed in March 2019]
• Water Footprint Network [Online] at <Water footprint of crop and animal products: a comparison> [Accessed in March 2019]
• SUR [Online] at <700 litros el agua para producir 1 kilo de aguacate> [Accessed in March 2019]
• Agricultural Water Management [Online] at <Yield and fruit quality of avocado trees under different regimes of water supply in the subtropical coast of Spain> [Accessed in March 2019]