Field level crop performance, farmer pressures and challenges in a large irrigation scheme

Irrigation is the largest consumer of freshwater and irrigated lands contribute a significant proportion of total food production. These statements are often accompanied by figures illustrating inefficient water use in agriculture. Policy decisions concerning water in agriculture tend to reference efficiency as the principal metric assessing performance. We see this reflected in documents such as the United Nations Social Development Goal 6 target 4 which aims to “substantially increase water-use efficiency across all sectors”. Optimising the output from a limited resource is necessary, however, the true measure of irrigation efficiency has been widely debated, creating different approaches and interpretations. The typical avenue is techno-centric and can lead to an offhand dismissal of so-called ‘old’ lower-technology irrigation systems as wasteful and inefficient. Irrigation efficiency has become a powerful tool both in political discourse as well as marketing campaigns for irrigation equipment.

A majority of farms are family-run enterprises and do not have at their disposal the capital and expertise of large agro-industrial companies. Challenges they face at field level may not be overcome by upgrading traditional irrigation methods with higher technology systems. The complexity of large irrigation schemes as hydrosocial systems cannot be overstated and compound the challenges individual farmers may be experiencing, such as problems related to their position in a scheme or along the supply network. The head-end/tail-end effect is one situation where farmers further from the head-end of water supply find a disadvantage compared to their head-end neighbours.

This work aims to follow recent research in irrigation efficiency which encourages employing a wider ranging and more comprehensive framework of indicators of irrigation performance, looking beyond the purely technical irrigation efficiency perspective and across scales. Working toward this, field level crop performance knowledge gaps were addressed. Using a set of phenology, crop stress and biomass productivity indicators derived from high-resolution optical and thermal satellite imagery, we were able to reveal important spatial patterns among farmers’ fields which may be linked to the performance of the irrigation scheme.

The study looks at the arid Northern Peruvian coast where the 110,000 ha Chancay-Lambayeque Irrigation System is supplied by water from the Andes. A substantial reservoir buffers discharge in the Chancay river on which an offtake supplies a 65 km main canal with an initial construction over 1000 years ago. The scheme is owned and operated by several Water Users’ Associations and small farmers share the supply with agro-industrial enterprises upstream. In this climate of almost negligible precipitation, crop stress and seasonal biomass production may be good performance indicators for irrigation. The resolutions are 30 m for crop stress using Landsat-8 surface temperature data and 20 m for biomass productivity using Sentinel-2 derived fAPAR. A spatial pattern analysis alongside the irrigation canal network was based on these indicators aiming to elucidate how a farmer may be affected by their location relative to the supply network, the crop type grown on their own or a (upstream/downstream) neighbour’s field and the condition of supply (abundance/scarcity).