Rainwater management for increased productivity among small-holder farmers in drought prone environments

https://doi.org/10.1016/S1474-7065(02)00098-0Get rights and content

Abstract

A critical analysis of conventional water resources assessments and re-visiting the on-farm water balance suggests large scopes for water productivity improvements in small-holder rainfed farming systems in drought prone environments of Eastern and Southern Africa. The paper addresses key management challenges in trying to upgrade rainfed agriculture, and presents a set of field experiences on system options for increased water productivity in small-holder farming. Implications for watershed management are discussed, and the links between water productivity for food and securing of water flow to sustain ecosystem services are briefly analysed. Focus is on sub-Saharan Africa hosting the largest food deficit and water scarcity challenges.

The paper shows that there are no agro-hydrological limitations to doubling on-farm staple food yields even in drought prone environments, by producing more “crop per drop” of rain. Field evidence is presented suggesting that meteorological dry spells are an important cause for low yield levels and it is hypothesised that this may constitute a core driver behind farmers risk aversion strategies. The dry spell induced risk perceptions contribute amongst others to soil nutrient mining due to insignificant investments in fertilisation. For many small-holder farmers in the semi-arid tropics it is simply not worth investing in fertilisation (and other external inputs) as long as the risk for crop failure remains a reality every fifth year with risk of yield reductions every second year, due to periodic water scarcity during the growing season (i.e., not necessarily cumulative water scarcity).

Results are presented from field research on small-holder system innovations in the field of water harvesting and conservation tillage. Upgrading rainfed production systems through supplemental irrigation during short dry-spells is shown to dramatically increase water productivity. Downstream implications of increased upstream withdrawals of water for upgrading of rainfed food production are discussed.

Finally it is argued that some of the most exciting opportunities for water productivity enhancements in rainfed agriculture are found in the realm of integrating components of irrigation management within the context of rainfed farming, e.g., supplemental or micro irrigation for dry spell mitigation. Combining such practices with management strategies that enhance soil infiltration, improve water holding capacity and plant water uptake potential, can have strong impact on agricultural water productivity. This suggests that it is probably time to abandon the largely obsolete distinction between irrigated and rainfed agriculture, and instead focus on integrated rainwater management.

Introduction

Water productivity in rainfed agriculture will have to increase dramatically over the next generation if food production is to keep pace with population growth. Almost the total population growth (95%) and the bulk of present under-nutrition occur in tropical developing countries, of which a large proportion depends on rainfed agriculture for their livelihoods. In sub-Saharan Africa, e.g., over 60% of the population depend on rain-based rural economies, generating in the range of 30–40% of country GDP (World Bank, 1997). Rainfed agriculture in sub-Saharan Africa is practised on approximately 95% of the agricultural land (the remaining is under irrigated agriculture) and will remain the dominant source of food production during the foreseeable future (Parr et al., 1990). In general yields from rainfed agriculture are low, in many parts of the water-scarce tropical world oscillating around 1 t ha−1 (Rockström, 2001). There is ample evidence to suggest that the low productivity in rainfed agriculture is more due to sub-optimal performance related to management aspects than to low physical potential (Agarwal and Narain, 1997; Benites et al., 1998; Rockström and Falkenmark, 2000; SIWI, 2001). This means that in the developing countries experiencing the most rapid population growth, dependence on rainfed agriculture operating at a sub-optimal level is high. Furthermore, it has been estimated that there is limited new land to put under agriculture (McCalla, 1994; Young, 1999), contrary to the last three decades in sub-Saharan Africa when the bulk of increased food production originated from expansion of agricultural land. There is thus a growing pressure to increase agricultural productivity through raised yields per unit soil and unit water.

This paper presents the agro-hydrological rationale to focus on water productivity in rainfed agriculture, identifies key management challenges in the attempt to upgrade rainfed agriculture, and presents some field experiences on system options for increased water productivity in small-holder farming in drought prone environments. Implications for watershed management are discussed, and the links between water productivity for food and securing of water flow to sustain ecosystem services are briefly analysed. The focus is on semi-arid and dry-sub-humid tropical agro-ecosystems where the importance of increase in water productivity is highest.

Section snippets

Rainwater management––the rationale

A broad approach to water productivity in land management that covers both irrigated and rainfed agriculture has implications on water resource management. Conventionally, focus on global, regional and national freshwater resources and withdrawals has been on the stable and accessible surface and sub-surface flow of water in rivers, lakes and groundwater, the so-called blue water branch in the hydrological cycle (UN, 1997; Cosgrove and Rijsberman, 2000). Blue water is withdrawn for direct blue

Hydroclimatic challenges

Water related problems in rainfed agriculture in water scarcity prone tropics are often related to high intensity and large spatial and temporal variability of rainfall, rather than low cumulative volumes of rainfall (Mahoo et al., 1999; Rockström et al., 1998; Sivakumar and Wallace, 1991). Rainfall is highly erratic, and rain often falls as convective storms, with high rainfall intensity and extreme spatial and temporal variability. Coefficients of variation range from 20–40%, increasing with

Supplemental irrigation

Bridging dry spells through supplemental irrigation of rainfed crops can be an interesting option to increase water productivity at production system level (Oweis et al., 1999; SIWI, 2001). Supplemental irrigation in small-holder farming systems can be achieved with water harvesting systems that collect local surface runoff (sheet, rill and gully flow) in small storage structures (100–1000 m3). Water harvesting, broadly defined as the concentration of surface runoff for productive purposes, has

System implications––balancing water for food and nature

Increasing withdrawals of water in rainfed and irrigated agriculture may have negative implications on water availability to sustain direct human withdrawals and indirect withdrawals to sustain ecosystem services. As shown by Rockström et al. (1999) almost the totality of global green water flow (88%) is already at present used to sustain biomass growth in the World’s biomes. While agriculture (rainfed and irrigated) annually accounts for an estimated 7000 Gm3 yr−1, forests and woodlands require

Conclusions and discussion

There is no doubt that the immense challenge of doubling food production over the next 25 years in order to keep pace with population growth, requires increased attention to water productivity and rainwater management, simply by making the best use of the local water balance. As shown in this paper, even in water scarcity prone tropical agro-ecosystems, there is seemingly no hydrological limitation to double staple food crop yields in rainfed small-holder agriculture. Furthermore, evidence

References (38)

  • Hobbs, P.R., Dhillon, S., Singh, Y., Malik, R., 2000. New reduced and zero tillage options for increasing the...
  • IWMI, 2000. Water supply and demand in 2025. International Water Management Institute,...
  • F. Li et al.

    Rainwater harvesting agriculture: An integrated system for water management on rainfed land in China’s semiarid areas

    AMBIO

    (2000)
  • H.F. Mahoo et al.

    Rainfall variability and its implications for the transerability of experimental results in semi-arid areas of Tanzania

    Tanzania J. Agric. Sci.

    (1999)
  • McCalla, A.F., 1994. Agriculture and food needs to 2025: why we should be concerned. Washington, D.C.: Consultative...
  • Ngigi, S.N., Thome, J.N., Waweru, D.W., Blank, H.G., 2000. Technical evaluation of low-head drip irrigation...
  • Oldreive, B., 1993. Conservation farming for communal, small-scale, resettlement and co-operative farmers of Zimbabwe....
  • Oweis, T., Hachum, A., Kijne, J., 1999. Water harvesting and supplemental irrigation for improved water use efficiency...
  • J.F. Parr et al.

    Improving the sustainability of dryland farming systems: A global perspective

  • Cited by (0)

    View full text