The dynamics between irrigation frequency and soil nutrient management: transitioning smallholder irrigation towards more profitable and sustainable systems in Zimbabwe

Abstract

Successful irrigated agriculture is underpinned by answering two critical questions: when and how much to irrigate. This article quantifies the role of the Chameleon and the Wetting Front Detector, monitoring tools facilitating decision-making and learning about soilwater-nutrient dynamics. Farmers retained nutrients in the root zone by reducing irrigation frequency, number of siphons, and event duration. Water productivity increased by more than 100% for farmers both with and without monitoring tools. Transitioning smallholder irrigation systems into profitable and sustainable schemes requires investment in technology, farmers and institutions. Importantly, technologies need embedding in a learning environment that fosters critical feedback mechanisms, such as market constraints.

The importance of learning processes in transitioning small-scale irrigation schemes

“…Incentives for action are important, and we propose that the reduced need for irrigation labour and improved yields and income were critical in driving individual learning and the spread of change beyond those who had the tools. The emergence of improved collective action (preparedness to participate in scheme maintenance and pay for water) represents another outcome of aggregate change in behaviour (Chilundo et al, 2020;Mdemu et al, 2020;Moyo et al, 2020). These findings align with another characteristic of complex adaptive systems, whereby the aggregation of changes in the strategies of adaptive actors leads to the emergence of large-scale behaviour (Holland, 1995).…”

“…The importance of this initial learning should not be underestimated: as farmers developed trust in the tools, they began to skip irrigation events, and gained confidence and experience in managing the system. They also maximized the contribution of rainwater to minimize the use of irrigation water (see Moyo et al, 2020, for a discussion). When discussing reductions in irrigation frequency with farmers, they were adamant that such changes would never have been accepted if they were externally enforced: 'a big no!'…”

“…said Senzeleni Mpofu of Silalatshani (van Rooyen, personal communication). Similarly, farmers learnt about nutrient leaching from their use of the tools and integrated this knowledge with irrigation frequency and rainfall events to determine the required frequency and amount of irrigation (Moyo et al, 2020). Farmers experimented by reducing the frequency of irrigation, which was expected but not advocated by TISA, and when they continued to see high moisture levels, they reduced the number of siphons and eventually irrigation duration.…”

“…A highly adaptive knowledge system has emerged, in which farmers their adapt water use in response to crop type, growth stage and rainfall. Mental models have shifted, with many farmers and extension staff in Silalatshani now managing irrigation as supplementary to rainfall, which was the original intended role of the schemes (Moyo et al, 2020). Table 6.…”

“…Adoption is influenced by many factors, including socio-economic, cultural and institutional factors, and the cost and complexity of technologies (Stevens, 2006). While formal training may impart knowledge regarding irrigation scheduling, farmers are often unable to act alone: for example, the rigid irrigation schedules often enforced by irrigation management committees mean irrigation happens at fixed frequencies, regardless of a crop's water requirements (Moyo et al, 2020). Hence, inflexible scheduling prevents farmers from practising with the knowledge gained from monitoring.…”