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Dry spell mitigation to upgrade semi-arid rainfed agriculture: Water harvesting and soil nutrient management for smallholder maize cultivation in Machakos, Kenya
Stockholm University, Faculty of Science, Department of Systems Ecology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Improvements in on-farm water and soil fertility management through water harvesting may prove key to up-grade smallholder farming systems in dry sub-humid and semi-arid sub-Sahara Africa (SSA). The currently experienced yield levels are usually less than 1 t ha-1, i.e., 3-5 times lower than potential levels obtained by commercial farmers and researchers for similar agro-hydrological conditions. The low yield levels are ascribed to the poor crop water availability due to variable rainfall, losses in on-farm water balance and inherently low soil nutrient levels. To meet an increased food demand with less use of water and land in the region, requires farming systems that provide more yields per water unit and/or land area in the future. This thesis presents the results of a project on water harvesting system aiming to upgrade currently practised water management for maize (Zea mays, L.) in semi-arid SSA. The objectives were to a) quantify dry spell occurrence and potential impact in currently practised small-holder grain production systems, b) test agro-hydrological viability and compare maize yields in an on-farm experiment using combinations supplemental irrigation (SI) and fertilizers for maize, and c) estimate long-term changes in water balance and grain yields of a system with SI compared to farmers currently practised in-situ water harvesting. Water balance changes and crop growth were simulated in a 20-year perspective with models MAIZE1&2.

Dry spell analyses showed that potentially yield-limiting dry spells occur at least 75% of seasons for 2 locations in semi-arid East Africa during a 20-year period. Dry spell occurrence was more frequent for crop cultivated on soil with low water-holding capacity than on high water-holding capacity. The analysis indicated large on-farm water losses as deep percolation and run-off during seasons despite seasonal crop water deficits. An on-farm experiment was set up during 1998-2001 in Machakos district, semi-arid Kenya. Surface run-off was collected and stored in a 300m3 earth dam. Gravity-fed supplemental irrigation was carried out to a maize field downstream of the dam. Combinations of no irrigation (NI), SI and 3 levels of N fertilizers (0, 30, 80 kg N ha-1) were applied. Over 5 seasons with rainfall ranging from 200 to 550 mm, the crop with SI and low nitrogen fertilizer gave 40% higher yields (**) than the farmers’ conventional in-situ water harvesting system. Adding only SI or only low nitrogen did not result in significantly different yields. Accounting for actual ability of a storage system and SI to mitigate dry spells, it was estimated that a farmer would make economic returns (after deduction of household consumption) between year 2-7 after investment in dam construction depending on dam sealant and labour cost used.

Simulating maize growth and site water balance in a system of maize with SI increased annual grain yield with 35 % as a result of timely applications of SI. Field water balance changes in actual evapotranspiration (ETa) and deep percolation were insignificant with SI, although the absolute amount of ETa increased with 30 mm y-1 for crop with SI compared to NI. The dam water balance showed 30% productive outtake as SI of harvested water. Large losses due to seepage and spill-flow occurred from the dam. Water productivity (WP, of ETa) for maize with SI was on average 1 796 m3 per ton grain, and for maize without SI 2 254 m3 per ton grain, i.e, a decerase of WP with 25%. The water harvesting system for supplemental irrigation of maize was shown to be both biophysically and economically viable. However, adoption by farmers will depend on other factors, including investment capacity, know-how and legislative possibilities. Viability of increased water harvesting implementation in a catchment scale needs to be assessed so that other down-stream uses of water remains uncompromised.

Place, publisher, year, edition, pages
Stockholm: Institutionen för systemekologi , 2004. , 38 p.
Identifiers
URN: urn:nbn:se:su:diva-98ISBN: 91-7265-843-6 (print)OAI: oai:DiVA.org:su-98DiVA: diva2:200763
Public defence
2004-04-23, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 8 C, Stockholm, 13:00
Opponent
Supervisors
Available from: 2004-04-01 Created: 2004-04-01Bibliographically approved
List of papers
1. Dry spell analysis and maize yields for two semi-arid locations in East Africa
Open this publication in new window or tab >>Dry spell analysis and maize yields for two semi-arid locations in East Africa
2003 In: Agricultural and Forest Meteorology, ISSN 0168-1923, Vol. 117, no 1-2, 23-37 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25889 (URN)
Note
Part of urn:nbn:se:su:diva-98Available from: 2004-04-01 Created: 2004-04-01Bibliographically approved
2. Rainwater management for dry spell mitigation in semi-arid Kenya
Open this publication in new window or tab >>Rainwater management for dry spell mitigation in semi-arid Kenya
1999 In: East African Agriculture and Forestry Journal, Vol. 65, no 1, 57-69 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:su:diva-25890 (URN)
Note
Part of urn:nbn:se:su:diva-98Available from: 2004-04-01 Created: 2004-04-01Bibliographically approved
3. Run-off water harvesting for dry spell mitigation in maize (Zea mays L.): results from on-farm research in semi-arid Kenya
Open this publication in new window or tab >>Run-off water harvesting for dry spell mitigation in maize (Zea mays L.): results from on-farm research in semi-arid Kenya
2005 (English)In: Agricultural Water Management, ISSN 0378-3774, E-ISSN 1873-2283, Vol. 74, no 1, 1-21 p.Article in journal (Refereed) Published
Abstract [en]

Maize (Zea mays L.) yields obtained by small-holder farmers in semi-arid zones in sub-Sahara Africa (SSA) are often less than half of potential yields. Water deficit during critical crop growth stages together with low nutrient input interacts to reduce yields. Collection of surface run-off, which could be used as supplemental irrigation may prove beneficial in improving current small-holder farming system in SSA. This paper presents the results of an on-farm study of the effects of supplemental irrigation (SI) on maize yield in semi-arid Kenya. Surface run-off from a catchment of 2.7 ha was harvested in a hand-dug earth dam of 300 m2. The water was supplied by gravity to mitigate dry spells in fertilized (SI30, SI80 kg N ha−1) and non-fertilized (SI0 kg N ha−1) maize. Treatments of SI were compared to non-irrigated treatments (NI80, NI30, NI0 kg N ha−1). Rainfall varied, during the five seasons of study, from 196 to 564 mm. The volume of water harvested in the dam ranged between 1% and 4% of seasonal rainfall. The outtake for supplemental irrigation varied between 20 and 240 mm per season. Seepage losses accounted for 11 to 74% of harvested dam water. Lowest maize yields were in NI0, representing farmers’ current practise. SI with fertilizer increased yields compared to non-irrigated and fertilised treatments (NI30, NI80) for low rainfall seasons (<300 mm). High rainfall seasons (>300 mm) resulted in no yield increase for SI compared to NI. Mean seasonal grain yield for SI and fertilizer (30 or 80 kg N ha−1) of 1796 kg ha−1 was significantly higher (P < 0.001) than NI0 kg N ha−1 of 1319 kg ha−1, and higher than SI0 kg N ha−1 and NI30 kg N ha−1 (P < 0.01). Lowest average rain and irrigation water use efficiency (RUE, kg grain mm−1 ha−1) was for NI0 with RUE = 2.1, and highest for SI30 with RUE = 4.1. Water harvesting of surface run-off added as SI resulted in improved maize yields as a result of dry spell mitigation, but only in combination with N fertilizer. To upgrade on-farm water management in semi-arid SSA, the results suggest that supplemental irrigation combined with fertilizer may reduce the currently existing yield gap in small-holder farming systems.

Keyword
Dry spell mitigation; Supplemental irrigation; Maize yield; Water harvesting; Semi-arid; Kenya; Water use efficiency
Identifiers
urn:nbn:se:su:diva-25891 (URN)10.1016/j.agwat.2004.11.002 (DOI)
Note
Part of urn:nbn:se:su:diva-98Available from: 2004-04-01 Created: 2004-04-01 Last updated: 2010-08-11Bibliographically approved
4. Risk analysis and economic viability of water harvesting for supplemental irrigation in the Semi-arids
Open this publication in new window or tab >>Risk analysis and economic viability of water harvesting for supplemental irrigation in the Semi-arids
2005 (English)In: Agricultural Systems, ISSN 0308-521X, E-ISSN 1873-2267, Vol. 83, no 3, 231-250 p.Article in journal (Refereed) Published
Abstract [en]

Food insecurity affects a large portion of the population in sub-Saharan Africa (SSA). To meet future food requirements current rainfed farming systems need to upgrade yield output. One way is to improve water and fertiliser management in crop production. But adaptation among farmers will depend on perceived risk reduction of harvest failure as well as economic benefit for the household. Here, we present risk analysis and economical benefit estimates of a water harvesting (WH) system for supplemental irrigation (SI). Focus of the analysis is on reducing investment risk to improve self-sufficiency in staple food production. The analysis is based on data from two on-farm experimental sites with SI for cereals in currently practised smallholder farming system in semi-arid Burkina Faso and Kenya, respectively. The WH system enables for both SI of staple crop (sorghum and maize) and a fully irrigated off-season cash crop (tomatoes). Different investment scenarios are presented in a matrix of four reservoir sealants combined with three labour opportunity costs. It is shown that the WH system is labour intensive but risk-reducing investment at the two locations. The current cultivation practices do not attain food self-sufficiency in farm households. WH with SI resulted in a net profit of 151–626 USD year−1 ha−1 for the Burkina case and 109–477 USD year−1 ha−1 for the Kenya case depending on labour opportunity cost, compared to −83 to 15 USD year−1 ha−1 for the Burkina case and 40–130 USD year−1 ha−1 for the Kenyan case for current farming practices. Opportunity cost represents 0–66% of the investment cost in an SI system depending on type of sealant. The most economical strategy under local labour conditions was obtained using thin plastic sheeting as reservoir sealant. This resulted in a net profit of 390 and 73 USD year−1 ha−1 for the Burkina Faso and Kenyan respective site after household consumption was deducted. The analysis suggests a strong mutual dependence between investment in WH for SI and input of fertiliser. The WH system is only economically viable if combined with improved soil fertility management, but the investment in fertiliser inputs may only be viable in the long term when combined with SI.

Keyword
Water harvesting; Supplemental irrigation; Semi-arid; Labour cost; Cost–benefit
National Category
Biological Sciences
Identifiers
urn:nbn:se:su:diva-25892 (URN)10.1016/j.agsy.2004.04.002 (DOI)
Note
Part of urn:nbn:se:su:diva-98Available from: 2004-04-01 Created: 2004-04-01 Last updated: 2010-07-12Bibliographically approved
5. Modelling on-farm water balance effects of water harvesting system for Zea mays in semi-arid Kenya
Open this publication in new window or tab >>Modelling on-farm water balance effects of water harvesting system for Zea mays in semi-arid Kenya
Manuscript (Other academic)
Identifiers
urn:nbn:se:su:diva-25893 (URN)
Note
Part of urn:nbn:se:su:diva-98Available from: 2004-04-01 Created: 2004-04-01 Last updated: 2010-01-13Bibliographically approved

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