Physics and Chemistry of the Earth 29 (2004) 1069–1073 www.elsevier.com/locate/pce

Rainwater harvesting for sustainable agriculture in communal lands of Zimbabwe Kudakwashe E. Motsi a

a,*

, Edward Chuma a, Billy B. Mukamuri

b

Department of Soil Science and Agricultural Engineering, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe b Centre for Applied Social Sciences, University of Zimbabwe, P.O. Box MP 167, Mount Pleasant, Harare, Zimbabwe

Abstract The study was carried out at three sites in Communal Lands of Zimbabwe namely, Mudzi (Natural Region V), Gutu (Natural Region IV) and Chivi (Natural Region V). These areas have marginal rainfall in terms of quantities (below 500 mm per year) and distribution with a normal rainfall year coming once in every five years. Four tillage treatments were experimented on in the three sites. These were tied ridges, infiltration pits, fanya juus and the conventional ploughing on the flat. The tillage treatments were paired at farm level for easy management considering that farmers were participating in the research trials. The conventional tillage technique was used as control. The objective of the study was to evaluate and recommend rainwater harvesting techniques that ensure effective capture and utilization of rainfall for sustainable crop production. This was achieved through monitoring residual moisture, after every rainfall shower, in the different tillage treatments. Monitoring of residual moisture was done, up to a depth of 30 cm, using a h-probe. Yields of maize from the different tillage treatments were determined. Farmers also carried out their own evaluation of the treatments at mid-season and at the end of the season. In addition the researchers tested dissemination techniques that ensured maximum adoption of rainwater harvesting techniques. Tied ridges were ranked best by both the stakeholdersÕ evaluation and the theta (h)-probe in retaining moisture compared to all the other treatments in the season under consideration. The farmers who practiced tied ridges realized yields of about 3 t/ha compared to conventional tillage treatments whose yields were about 1.5 t/ha. Yields were statistically significantly different for the different treatments. The recommendation was for the farmers to adopt the tied ridges in areas that receive marginal rainfall and experience mid-season droughts. Lead farmers should educate others on the advantages of the tillage treatments. Ó 2004 Published by Elsevier Ltd. Keywords: Moisture retention; Rainwater harvesting; Sustainable agriculture; Participation

1. Introduction Zimbabwe is generally poor in terms of water resources given the conditions of unpredictable rainfall, very high evaporation losses and high conversion of rainfall to runoff. The mean annual rainfall of the country is 650 mm, the main part of which occurs from November through March with the rest of the year vir*

Corresponding author. E-mail address: [email protected] (K.E. Motsi).

1474-7065/$ - see front matter Ó 2004 Published by Elsevier Ltd. doi:10.1016/j.pce.2004.08.008

tually dry. The coefficient of variation of the rainfall is above 20% and in worst cases may be as high as 40% for most Communal Lands and this has implications on the crop growing season. Lineham (1978) analyzed the crop growing season by defining the start and end of the season according to the first and last rainy pentads. The length of the rainy season, according to the rainy pentad analysis, ranges from 160 days in the Eastern Highlands to less than 50 days in the extreme south of Zimbabwe. In addition to the short season about 90% of the total rainfall in Zimbabwe is associated with

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thunderstorm activity producing falls of short duration and high intensity. Rainfall intensities greater than 13 mm/h are likely to lead to runoff in all but the sandiest soils with high infiltration rates. With 50% or more of the rainfall having intensities above this level, a high proportion of rain is therefore likely to be lost as runoff, particularly at sites where the natural vegetation has been excessively disturbed or where cultivation practices exacerbate this process. Communal Lands have been cleared of vegetation and most of the arable fields are not protected by conservation structure. Interventions are required, especially in the Communal Lands, which maximize the retention of the thunderstorm rain on the soil surface thereby increasing the soil-water contact time. Rainwater harvesting (RWH) is the method of inducing, collecting, storing and conserving local surface runoff for agricultural production. In Africa the different RWH techniques were introduced long back and are still in use today. Countries in Africa like Zimbabwe, Kenya, Swaziland and Ethiopia have since introduced some of the techniques of RWH such as fanya juu, infiltration pits and tied ridges in communal areas (Reij et al., 1996). According to Bainbridge (1998), the infiltration pits improve water infiltration rate, water retention, reduces evaporation, increase surface storage and the time available for infiltration to occur. Stern et al. (1992) at Roodeplaant showed that pitting was beneficial in reducing surface run-off, maintained higher plant evapotranspiration rates and yields than control treatments. Macartney et al. (1971) reported that tied ridging in Tanzania gave higher maize yields in high rainfall areas although this was an exceptional case. According to ElSwaify et al. (1985)Õs summaries, the system in Africa has been beneficial not only for reducing run-off and soil loss, but also for increasing crop yields. Fanya juus were also introduced between 1983–84 at And-tid area in Ethiopia as a moisture and soil conservation measure. In some parts of Sudan (Red sea Hills) sorghum was planted where the mean annual rainfall was 100 mm or less and the yields were as high as 4 t/ha. In some countries such as Kenya, the method failed because poor people did not have resources like tools, money and the labour force to do the work (Critchley, 1991). Although the farmers realized the benefits of RWH they seem discouraged from practicing in them maybe due to lack of knowledge that benefits far outweigh the resources constraints. Thus, considering the climatic conditions in the country and the benefits derived from RWH, there was need to investigate different tillage treatments with the full participation of farmers so that they could realize the benefits. It was hoped that the research would enable those participating in the research to inspire others to take up the rainwater harvesting techniques

(RWH). The general objective of the study was to evaluate rainwater-harvesting techniques and recommend ones that ensure effective capture and utilization of rainfall for sustainable crop production. The specific objectives were to investigate different tillage systems as rainwater harvesting techniques that effectively minimize water loss, to determine the yields and benefits derived from the different tillage treatments and to develop and test dissemination techniques that would promote maximum adoption of rainwater harvesting technologies.

2. Methodology The study was carried out at three sites in Communal Lands of Zimbabwe namely, Mudzi district in Mashonaland east province, Gutu and Chivi districts in Masvingo Province. The study was carried out at farmersÕ fields with their full participation in the selection of the treatments that were to be tried on their fields. The fields where trials were carried out have sandy loams to sandy soils derived from the granite parent material. These soils have inherent low water holding capacities and are susceptible to erosion given the bare vegetation conditions and the high intensity of the rainfall showers. The areas surrounding the fields used to have savanna woodlands but now are almost bare. Rich and poor farmers participated in the research trials. Farmers volunteered into the project during stakeholder workshops that were held to introduce the project to the communities. After explaining what the project was all about participants were asked to volunteer into the project. The response was overwhelming such that only ten farmers were selected. In Chivi all selected farmers participated in the research but six and four farmers in Mudzi and Gutu respectively finally took part in the research in the first year. Farmers who participated in the research were assisted in carrying out field operations especially the construction of water harvesting structures. Four tillage treatments were under observation for one season with respect to moisture retention and crop yields. Field treatments were as outlined below: 2.1. Treatment 1—Tied ridges Tied ridging consisted of ploughing and ridging at a 0.75 m row spacing, followed by an operation to tie the ridges before planting, using hand hoes, with small mounds along each furrow so as to impede the runoff of the rainwater. The mounds were at intervals between 2 and 3 m and care being taken to leave them at a height that was less than that of the main ridge to be used for planting. Hire cost for the animal powered system were about US$ 0.90/h.

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2.2. Treatment 2—Fanya juus This technique, which originated in Kenya, involved throwing of soil excavated from the drainage channel to the upper side of the channel. The channel depth was usually 50–60 cm with cross-ties at 10 m intervals. The channels were graded on a dead level contour (level fanya juu). Grass was planted on the embankment to stabilize it while trees or bananas were planted in the trenches to utilize some of the excess retained water (Hagmann, 1994). 2.3. Treatment 3—Infiltration pits These are deep trenches dug along the contour ridge to trap run-off and increase infiltration. The pits were filled with grass or stover that was covered by a thin layer of soil so that the organic material could decompose to form compost. The pits would trap rain as it fell and then the water would infiltrate downslope thereby providing moisture to the crops in the field.

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least four farmers in the same ward. Moisture readings were taken at a grid of nine different points in each plot using a moisture meter ML2X connected to a theta (h) probe moisture sensor. Residual moisture readings were measured in % volume and this was done on daily basis. The soils were analyzed in the laboratory to determine the soil types and to confirm water holding capacities. Each of the farmers had a rain gauge to measure the actual rainfall received in his/her fields. A mid season evaluation of the experimental techniques was also carried out. This was done through field days and use of survey questionnaires. This was to enable farmers to objectively evaluate the rainwater harvesting techniques. The yields were measured after randomly sampling cobs from each plot (Arnon, 1972). Statistical analysis, ANOVA, of the residual moisture and yield results was also done to determine whether there were any statistical significant differences between treatments.

3. Results and discussion 2.4. Treatment 4—Conventional farmer practice This is farmer practice of maize planting on the flat and this treatment acted as the control against which the other four treatments were compared. For animal traction, the simplest equipment consisted of a mouldboard plough with about 8 in. (0.20 m) working width. Hire costs for the same implement and the animal amounted to US$ 0.96/h. Using a tractor, the hire costs for a wheeled tractor with a plough varied between US$ 12 and 15/h. Maize is the most commonly grown crop in all Communal Lands so its yield levels from the different tillage treatments were compared. On each of the four tillage treatments under study there was mechanical weeding by hoe, plough or cultivator (as conditions allowed). Treatments were replicated by experimenting with at

18

Infiltration pits

Tied ridges

The soils that were investigated were sandy loams. On average the soils had 16% clay, 70% sand and 14% silt. The water holding capacities ranged from 6 mm/m to 10 mm/m in the areas under study compared to the standard 9 mm/m to 13 mm/m (FAO, 2002). This could be due to poor soil structure and low organic matter. Soil residual moisture was monitored continuously for nineteen (19) weeks with readings being taken every day. The weekly average residual moisture for different tillage treatments are as shown in Fig. 1. It was observed that tied ridges, on average, retained moisture better than all the other treatments. This was so especially during times of mid-season droughts in the three sites where the research was conducted. When the amount of rainfall increased it was observed that tied ridges, except for fanya juus, consistently retained soil moisture better

Fanya juus

Conventional tillage

Soil moisture %vol basis

16 14 12 10 8 6 4 2 0 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 Time in weeks

Fig. 1. Average residual soil moisture.

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than other treatments. After the soils had about 14% vol. residual moisture fanya juus were better than all the other treatments. May be the fanya juus were in this case able to consistently retain moisture better both in the field and in the drainage channel. Statistically the moisture retention capacities of the different tillage treatments were significantly different. Maize yields from the different tillage treatments were measured. Generally the yield depended on the water retention capacity of the technique. As shown in Fig. 2 the average yield of maize from tied ridges was 3.4 t/ha compared to 1.5 t/ha for conventional tillage. The yields for the other treatments were better than the conventional tillage treatment. The statistical analysis showed that the yield levels for the different treatments were significantly different. This could be attributed to the fact that crops were less stressed by moisture shortage in the rainwater harvesting techniques. In all the field days held the average distribution of farmersÕ preferences of the different tillage system was as shown in Fig. 3. Farmers selected the tillage system they thought retained moisture better than others based on crop conditions in the field and the yield. As shown in Fig. 3, 45% of the farmers indicated that they preferred tied ridges as the system were to practice and only 5% of the farmers opted to continue with conventional

tillage. About 95% of farmers indicated that they were going to adopt rainwater techniques in future. Those who did not want to adopt any of the treatments sighted shortage of labour, draught power and equipment as the main drawbacks.

4. Conclusions Generally the soils in the areas under study had poor water holding capacities. This could be due to poor structure and low organic matter. Water harvesting techniques had statistically significant better residual moisture retention capacities than the conventional tillage treatment. The moisture retention capacities of tied ridges, infiltration pits and fanya juus were significantly higher compared to conventional tillage. Tied-ridges were observed to be the best in terms of moisture retention. This was more so during times of mid-season droughts. The yields under tied ridges, infiltration pits, fanya juus were significantly higher compared to yields under conventional tillage. Tied ridges had the highest yields per unit area followed by fanya juus.

5. Recommendations

Yield per hectare (kg)

4000 3500 3000 2500 2000 1500 1000 500 0

Tied ridges

Infiltration pits Fanya juu Treatment

Conventional

Percentage of farmers prefering system

Fig. 2. Average maize yields per treatment.

50 45 40

There is need to improve the water holding capacities by practising tillage options that improve retention of organic matter in the soil so that soil structure is improved. Most farmers in the low rainfall areas should adopt the sustainable RWH techniques to make sure that each raindrop that fall in their fields is used to enhance crop productivity by minimizing moisture stress in the field. Thus it is recommended that farmers should construct semi-permanent or permanent structures that ensure minimum seasonal labour in the construction of the rainwater harvesting tillage techniques. The RWH techniques must also be evaluated in areas with other soil types and also using other crops to enable concrete conclusions to be drawn with regard to their effectiveness in retaining soil moisture and improving crop productivity.

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References

25 20 15 10 5 0

Fanya juu

Tied ridges

Infiltration pits

Conventional

Treatment

Fig. 3. FarmersÕ preferred rainwater harvesting tillage system.

Arnon, I., 1972. Crop production in dry regions. Oxfarm, London. Bainbridge, D.A., 1998. A handbook for erosion control and watershed rehabilitation, Hungry Valley. SERG/USIS ESP for State Parks OHMVRA, San Diego, CA, p. 120. Critchley, W., 1991. Looking after our land, Soil and water in Dry land Africa. Oxfam publishers, Oxford, U.K. El-Swaify, E.S., Pathak, P., Rego, T.J., Singh, S., 1985. Soil management for optimized productivity under rainfed conditions in the

K.E. Motsi et al. / Physics and Chemistry of the Earth 29 (2004) 1069–1073 semi-arid tropics. In: Stewart, B.A. (Ed.), Advances in Soil Science, 1. Springer-Verlag, New York, pp. 1–64. FAO, 2002. Irrigation Manual- Planning, Development, Monitoring and Evaluation of Irrigated Agriculture with Farmer Participation. Hagmann, J., 1994. The Fanya Juu System; An option for soil and Water conservation in Semi-Arid Zimbabwe. Paper published as Project Report of the AGRITEX/GTZ Conservation Tillage Project, IAE, Harare/Masvingo. Lineham, S., 1978. The onset and end of the rains in Zimbabwe. Notes on Agricultural Meteorology No. 24. Zimbabwe: Department of Meteological Services, Ministry of Transport.

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Macartney, J.C., Northwood, P.J., Dagg, M., Lawson, R., 1971. The effect of different cultivation techniques on soil moisture conservation and the establishment and yield of maize at Kongwa, Central Tanzania. Trop. Agric. Trinidad 48, 9–23. Reij, C., Scoones, I., Toulmin, C., 1996. Sustaining the Soil: Indigenous soil and water conservation in Africa. In: Reij, C., Scoones, I., Toulmin, C. (Eds.), Sustaining the Soil: Indigenous soil and water conservation in Africa. Earthscan, London, pp. 1–27. Stern, R., Vander Marwe, A.J., Laker, M.C., Shainberg, I., 1992. Effects of soil surface treatment on runoff and wheat yield under irrigation. Agron. J. 84 (1), 114–119.