Study of vertical water flows contribution to the crop water consumption in suka kollus using a mixed drainage system

Abstract

The suka kollus, considered among the most important hydraulic structures of ancestral Andean technology, are used as a technique for crop production in flood-prone soils, enabling subsurface irrigation of crops by means of drainage channels. They also generate a thermoregulatory effect depending on the channel/ridge ratio and the total size of the infrastructure. They could be a valuable way of making use of marginal soils if some of the drainage channels are replaced by underground drains to increase the area of cultivation. This work was therefore undertaken to study the flow of water under a “mixed” drainage system (surface and subsurface drainage) adapted to the suka kollus system.The work was carried out in marginals in the Kallutaca area, La Paz, Bolivia. The potato cultivar ‘Imilla negra’ (Solanum tuberosum ssp. andigena) was used in four treatments with different platform widths: T1 (control), the traditional system in which all drainage was via open channels; and T2, T3 and T4, where one, two and three channels were, respectively, replaced by drains. The study describes the comparison between T1 treatment, with open drains at a depth of 1 m and platform width of 6.5 m (T1) with the other treatments, i.e. subsurface pipe drains at a depth of 1.2 m and a platform widths of respectively 12 m (T2, where one channel was replaced by a drain), 18 m (T3, where two channels were replaced by drains) and 25 m (T4, where three channels were replaced by drains)The results showed that the distance of 6.5 m between drainage channels, commonly used in traditional suka kollus, was less than the calculated distances. As such, it was possible to expand the area of the platforms by setting the drainage channels between 10 and 14 m apart. Crops yield in the T2 and T3 treatments (10.67–11.35 Mg/ha, respectively) are significantly higher compared to the traditional open drainage system, T1 (8.33 Mg/ha) and the wider platform width of 25 m, T4 (7.3 Mg/ha) due to the higher height of plants and the greater number of tubers per plant, compared to the control. Likewise, the high clay percentage of the second stratum of the T3 treatment could be beneficial in terms of greater retention of water at the root level, mainly for periods of water deficit. The crop water requirements were covered by the upward flows from the water table and by precipitation, demonstrating that the suka kollus system is sustainable under current climatic conditions.