Evaluating irrigation scheme performance in a tropical environment: The Guanacaste scheme, Costa Rica*

Abstract

Irrigation is expanding in the tropics and could make an important contribution to the intensification of production in those tropical areas where a dry season limits productivity. A study was carried out to characterize irrigation performance and the yield gaps of a tropical irrigation scheme that covers more than 41 000 ha in northern Costa Rica. The study covered a 5-year period, from 2014 to 2018. The performance indicator relative irrigation supply (RIS) ranged between 2.48 and 3.78, values higher than those typically observed in schemes of temperate areas, but in the low range of those documented in the tropics. Despite the excess of water usage, it was found that there were farms with water shortages, especially in the canal tails during the dry season, but there was also damage caused by excess of water in the rainy season. The potential yield of the two main crops (rice and sugar cane) was determined with the AquaCrop simulation model. Actual yields were determined via a farmers' survey that also inquired about irrigation management issues. Yield gaps were determined for each of the two sectors that make up the irrigation scheme (South and West canals). The mean yield gap of rice in the South Canal sector (3.34 t ha À1 ) was smaller than that of the West Canal sector (4.84 t ha À1 ). The highest yield gap of rice occurred in the rainy season in the West canal sector. The yield gap of sugar cane in the West canal sector was significantly larger than that in the South canal sector (170 and 148 t ha À1 , respectively). A farmers' survey, combined with an examination of soil maps, revealed that poor drainage through the heavy soils that predominate in the West canal sector is one of the main causes of the large yield gap, in both rice and sugar cane. While users are relatively satisfied with the provision of irrigation water and its cost, several opportunities (e.g. water delivery, amount of fertilizer in sugar cane, water supply and irrigation system on farms) for improving scheme performance and for closing the yield gaps are discussed.