CAN INTEGRATED WATERSHED MANAGEMENT BRING GREATER FOOD SECURITY IN ETHIOPIA?

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1 CAN INTEGRATED WATERSHED MANAGEMENT BRING GREATER FOOD SECURITY IN ETHIOPIA? Oloro V. McHugh, Amy S. Collick, Benjamin M. Liu, Debele Bekele, Jim E. Haldeman and Tammo S. Steenhuis Department of Biological and Environment Engineering Cornell University, Ithaca NY USA Abebe Yitayew AMAREW Project, Bahir Dar, Ethiopia Gete Zeleke ARARI, Bahir Dar, Ethiopia Abstract: In the food insecure regions, short annual droughts of 2-4 weeks with a severe drought typically every 10 years are common. The moisture stress between rainfall is responsible for most crop yield reductions. Field are prepared for sowing with traditional animal drawn "Maresha" resulting in a root zone depth of less than 10 cm. In this paper, we show with the use of appropriate water balance models given the limited data available, that increasing shallow tillage depth moisture availability for the plant will increase. Experimental results confirm these finding and as a result of the greater water availability yields increase significantly. Strategies are discussed for implementation of these findings at a watershed scale in order to increase food security. Copyright IFAC Keywords: Agriculture, Computer Simulation, Knowledge Representation, Mathematical Models 1. INTRODUCTION Agriculture is the backbone of the Ethiopian economy. It is responsible for approximately 50% of the Gross Domestic Product, 90% of foreign exchange earnings, and 85% of the livelihoods of the population. Ethiopia's agricultural sector is driven by the subsistence strategies of smallholder farmers and their families. In the past due to insufficient knowledge base, some misguided agricultural policies, coupled with a rapidly growing population, chronic poverty, and capricious rainfall, have caused severe food security challenges for farm families and natural resource degradation. Drastic new approaches that lead to improvement of food security and a lessening of the dependence on food aid are needed. As part of a strategy to achieve food security while protecting the environment through sustainable land use development, integrated watershed management (IWM) approaches are being developed The major advantages of IWM approaches are involvement of those most affected by the decisions (i.e. the stakeholders) in all phases of the development of their watershed and holistic planning that addresses issues which extend across subject matter disciplines (biophysical, social, and economic sciences) and administrative boundaries (village, woreda etc.).

2 It has been estimated that 2 million ha of Ethiopia s highlands have been degraded beyond rehabilitation, and an additional 14 million ha severely degraded (UNEP, 2002). Removal of vegetation cover (through overgrazing and for charcoal production) exposes the soil to wind and water erosion. Soil compaction occurs in areas where there is excessive trampling by animals and, in cultivated areas, soil fertility is declining, as a result of the exhaustion of soils by mono-specific cropping and reduction of fallow periods. Soil degradation contributes to rising rural poverty and food insecurity, because productivity is reduced, and subsistence farmers are less and less able to accumulate reserves of grain (UNEP, 2002). The agro-pastoralists in Ethiopia living in semi arid watershed with degraded soils are among the poorest people in the world and depend totally on the renewable natural resources for their livelihoods. According to Hatibu (2003) of the Irrigation Water Management Institute, their poverty is mainly caused by inadequate availability of water for crop, livestock and other enterprises. He then argues that the shortage of water is not caused by low rainfall as normally perceived, but rather by a lack of capacity for sustainable management and use of the available rainwater on these degraded soils. Hatibu (2003) states "the most critical management challenge is how to deal with the poor distribution of rainwater leading to short periods of too much water and flooding, and long periods of too little water. The question is: can better management of the available rainwater help to reduce the occurrence and mitigate the impact of droughts during periods with low rainfall?" Hatibu's viewpoint divergences from the many traditional studies such as by Sonneveld and Keyzer (2003) that consider soil erosion and its effect on soil quality and water storage to be the main culprit in securing food security. However, in strong support of Hatibu's view, water scarcity was identified as the main problem in formal and informal stakeholders surveys in the one of the watersheds (McHugh et al., 2004). To examine if better water management of available rainfall in semi-arid climates can mitigate the impact of droughts and help to improve food security, this paper uses a simulation model. Model results are tested with number of experiments. The model selected has to be appropriate for the limited data, available in the developing world for watershed modeling. Two watersheds were selected for the testing phase: the Yeku and Lencha Dima watersheds. Both are located in semi-arid mountainous areas that are severely eroded and have unreliable rainfall. Mean annual rainfall amounts are sufficient for most types of agriculture provided appropriate water conservation measures are in place. A large percentage of the people use food aid to survive. The research in the watersheds is carried out under the watershed component of the USAID funded AMAREW project. This component is designed to demonstrate integrative approaches to research, extension, community development, and micro-enterprise development in two pilot watersheds in the eastern part of the Amhara region. One of the aspects of the program is to use food aid in a meaningful way in watershed development. 2. THE PROBLEM AND POTENTIAL Even in the semi-arid watersheds, rainwater is available in abundance during the rainy season and surpasses the evapotranspiration during a few months (July, August and September in most cases, and March and April for selected Ethiopian conditions). The main reason is the practical difficulty posed by the nature of rainfall. The rain is very poorly distributed in both spatial and temporal terms. Often there is too much water during a few days of the year, while water supply is insufficient during most of the year. It is estimated that in most Semi-Arid Tropics the time when it is actually raining is in total about 100 hours per year, out of the 8,760 hours of the year. As a consequence, the moisture stress between rainfall events (dry spells) is responsible for most crop yield reductions and sometimes even for total crop failures (Rockstrom et al., 2002). In their study, Rockstrom et al. (2002) reported that dry spells in rain fed agriculture of arid and semi-arid regions, which occur frequently, are responsible for a decrease in yield by about 70% or even sometimes a total crop failure. Hence, if one conserves the excess water during heavy rains in the rainy season so that plants can use it in the latter times during dry-spells, it may be possible to avert the majority of the production loss due to moisture stress. Although well known in principle, the technologies required overcoming the poor and extreme distribution of water resources through storage and transfer are usually not applied because of poor adaptation to the local conditions and unavailability of capital. As a consequence, there is critically low access to water for agriculture, drinking and sanitation. Poor access to water is, therefore, among the leading factors hindering sustainable development in semi-arid watersheds. Approaches to overcoming this problem include technologies for enhancing the productivity of water in rain-fed production, rainwater harvesting and precision irrigation. Rainwater harvesting is currently a high priority of the Ethiopian government and this program is well on its way. Precision irrigation is tried but often limited in the semi arid areas due to the lack of baseflow in the rivers. Therefore in this paper we are mainly concerned with enhancing the productivity of the rainfall (i.e., more crop per drop) by making more available to the plants and less to surface runoff. The benefits are three fold: less erosion because runoff is reduced; greater food

3 security by increased crop water availability and as a byproduct increased ground water recharge leading to higher baseflows and more precision irrigation during the dry season. Plowing depth, water retention and crop yield are inter-related. The traditional oxen drawn plow "Maresha" plows the soil only to a limited depth of 5-15 cm in the degraded soils and downward water movement of water is restricted because of the tight subsoil (Mwendera et al, 1997; Astatke and Saleem, 1998; Kaumbutho et al., 1999). Root depth is limited in these soils (Seghieri, 1995). In this paper, we will investigate if by increasing tillage depth water can be stored in the soil such that plants can survive the dry periods between rainstorms. We will use both computer simulation and field evidence. 3. THE MODEL Data requirements vary between models. In order for a model to be useful, its data requirements must be readily obtainable (Taylor et al., 2004). For example, runoff models require detailed information on soil type, moisture status, and vegetation characteristics. Often, and in the case of Ethiopia highlands, these data are extremely difficult to obtain. Lumped water balance models have less stringent data requirements. With just rainfall ) and potential evapotranspiration (ET p ) data, discharge can be calculated with the lumped Thornthwaite-Mather (TM) procedure for relatively large watersheds using generalized soil and aquifer characteristics (Thornthwaite and Mather, 1957; Steenhuis and van der Molen 1986). The TM procedure was developed in the early 1940s and has successfully been applied in basins with southern coordinates such as Mount Kilamanjaro in, Kenya (Dunne and Leopold, 1978), Luancheng County in Northern China (Kendy et al. 2003), Singkarark- Ombilin in Indonesia (Peranginangin et al., 2004), and northeastern Mexico (Mendoza et al. 2003). Applying the T-M procedure requires several assumptions. These are: The soil is divided in a root zone with a reasonable high saturated conductivity and zone below that is devoid of roots and has little or no connection with the plowed soil above Percolation through the plow pan and lateral subsurface flow is small and will be neglected. Overland flow is generated when the soil above the plow pan becomes saturated. In other words daily runoff is equal to the daily runoff minus the amount of open pore space at the beginning of that day in the soil above the plow layer. On days when the evaporation is greater than the rainfall, actual evaporation is a linear function of amount of water in the soil and the potential evaporation. On days when the rainfall is greater than the potential evaporation, the soil moisture content increases equal to the difference between precipitation and potential evaporation. These assumptions results a simple but powerful calculation method can be used to calculate daily fluxes and moisture contents in the soils without the need of arbitrary crop coefficients. 3.1 The Thornthwaite Mather Procedure The T-M procedure uses rainfall, potential evapotranspiration, and as soil physical parameters the available water capacity (AWC) of the root zone. With these input data and the assumption mentioned above the T-M model uses a spreadsheet to calculate the actual evaporation and the moisture content in the soil. The water balance for the root zone can be formulated as: (1) where S t is the soil moisture storage at time t, [L], R is the rate of rainfall input, [L/T]; ET is the actual evapotranspiration rate, [L/T]; ERF is the excess rainfall rate during which will become runoff with the assumptions made in the text [L]; is the soil moisture storage at time, t - t, [L]. The actual evapotranspiration (ET) is in turn calculated by using (2) Where, ET p is the daily potential evapotranspiration, [L/T]. The maximum soil moisture storage, S max, is calculated from: (3) Where, m s is the soil volumetric moisture content at saturation; m l is the limiting volumetric moisture content below which no evapotranspiration takes place, and D is the soil depth of the root zone, [L]. In other applications of the procedure, the upper moisture content is taken as field capacity but, here, because of the limited percolation in the subsoil, saturation is more appropriate. In case Eq. 1 calculates on a particular day a storage S t in excess of S max the rainfall in excess of saturation becomes runoff and S t is set back to S max. The model was run with a daily time step with daily precipitation and daily potential evaporation as input and then calculates the amount of water stored in the soil and actual evaporation as a function of the maximum amount of soil moisture stored in the soil.

4 3.2 Input data Among the major problems in hydrological studies inputs is daily precipitation data. These are not available for the Yeku and Lencha Dima watersheds. We resorted, therefore, to two meteorological sites within a 300 km radius. One climatological station is Maybar (Wollo) that has daily rainfall records and represents typical highland conditions with an average annual rainfall of 1156mm. The other station is Mekele (Tigray), which is located in a semi arid region with an average rainfall of 600mm per year. This station has only monthly records. Both stations report great variation in annual rainfall. Over the 12-year period of record the rainfall ranges for Maybar from approximately 800 mm to 1500 mm and for Mekele between 400 mm and 900 mm. Both stations have a non distinct bimodal rainfall pattern (Fig. 1): light rainfall from March to May (comprising about 24% of the annual rainfall distribution), and heavy rainfall from July to September comprising about 56% of the annual rainfall distribution. In running the model, rainfall a normal year, 1992 and a wet year, 1993 was chosen for both Mekele and Maybar. No daily rainfall data was available for Mekele. Consequently, the daily rainfalls were obtained by assuming that the ratios between monthly rainfall amounts at Maybar and Mekele was the same as the daily ratios. For example, if the ratio of the monthly rainfalls between Maybar and Mekele was 1.5 for the month of June, the daily rainfall amounts of Mekele would be the daily rainfall readings at Maybar divided by 1.5 for all the 30-days in June. For potential evaporation we took 4.5 mm/day for all the months except July and August for which 3mm/day was used. In order to calculate the maximum storage in the soil we multiplied the depth of the plow pan with the difference of soil water contents between saturation (0.45 cm 3 /cm 3 ) and wilting point (0.10 cm 3 /cm 3 ). Four depths of root zones are examined: 10, 15, 20 and 30 cm. The maximum water storages for these depths in the rootzone are respectively 35, 43, 70 and 105 mm. 3.3 Results Based on the Thornthwaite Mather method, the soil moisture storage was calculated for soils with a plow pan at 10, 15, 20 and 30 cm (Figs 2, 3 and 4). As stated above the roots did not extent below the rootzone Fig 2 is the simulation results for a normal year in Maybar (1992) and both years are given for Mekele (Figs 3 and 4). In these figures the rainfall is "hanging" from the top. As expected the amount of water stored at any time in the soil is greater when the plow pan is deeper. In these figures the storage for the 30 cm root zone is always larger that for the root zone of 20 cm and larger for 15 cm, etc. For the semi arid climate represented by Mekele the moisture content builds up for the relatively dry year is given (Fig 2). As soon as the potential evaporation exceeds the rainfall on day 180 in the beginning of July (Fig. 2). The maximum storage (i.e., the soil is saturated) is reached around day 210 at the end of July and then remains so until the end of August or beyond depending on the duration of the rains. This also means that during August most of the precipitation in excess of the potential evaporation becomes surface runoff and will cause erosion. For Maybar the annual rainfall is approximately twice that of Mekele (Fig. 1) and consequently the soil is much wetter throughout the year (Figs 3 and 4). This is especially true for the period of March through May. However the maximum soil water storage is only reached for short periods of time during because monthly average potential evaporation is higher than the monthly rainfall(fig. 2). The moisture storage during July and August is the same for Mekele and Maybar (compare Fig. 2 with Fig. 4). In both cases the soils become saturated. The soil remains wet longer in Maybar than for Mekele. Figure 2:Daily rainfall and soil moisture storage in the root zone for different root depths, Mekele, Tigray Figure 1:Average monthly rainfall (RF) and potential evapotranspiration (PET) at Maybar and Mekele. Figure 3: Daily rainfall and soil moisture storage in the root zone for different root depths, Maybar, Wollo

5 Table 1 provides another way to look at the impact root depth on soil moisture storage and plant growth. It is the same data as shown in Figs 3. Mainly for illustrative purposes, we decided that if on a particular day when there is less than 10 mm of plant available water in the soil, this is "insufficient". It is labeled as such in the tables. Moreover, if there are more than 4 days in the month with insufficient storage, we assume that the yield is impacted so that crop failure could occur. Only months that have sufficient rainfall are shaded gray (i.e., less than 4 days with insufficient rain). The trend is obviously more significant than the absolute numbers. It is evident from Table 1 that the deeper the root depth, the smaller the number of days that there is insufficient soil moisture. Especially the root depth of 30 cm seems to be most effective in reducing the stress days for the normal rainfall year depicted in Table 1. On the other hand, when the root depth is 10 cm, a crop with growth duration of 3 months will have difficulty surviving even under normal rainfall conditions (Table 1). During the wetter year, effect of root depth becomes less important because the rains are usually spaced more closely together Concluding Remarks Modeling Figure 4:Daily rainfall and soil moisture storage in the root zone for different root depths, Maybar, Wollo The T-M procedure demonstrated that integrated watershed management plans that include deep plowing or sub-soiling will likely increase food security. Deeper plowing, which is being advocated among others by GTZ, could make more water available to the crop by infiltrating more of the rainfall. However, the results are based on a model. In the next section, we will report on an experiment in which the outcome of model is checked. The model recommended practice of subsoiling (also called deep tillage) is compared with traditional plowing and other means of conserving water such as by open ridges and tied ridges. 4. LENCHE DIMA WATERSHED ON-FARM TRIALS On-farm tillage and water harvesting experiments were conducted during two years ( ) on a farmer's field in the Lenche Dima Watershed (N 11 o ', E 39 o ', 1540 m above sea level). The loamy clay soil is classified as a vertic luvisol and has a bulk density of 1.56 Mg m -3. Table 1: Number of days in a month with sufficient (shaded) and insufficient moisture (not shaded) status in the soil for different root depths (Mekele ). 4.1 Experimental design The experiment was setup as a randomized complete block design with four treatments and three replications. Each plot measures 6 m wide by 30 m long down slope and is enclosed by 50 cm wide (20 cm high) soil bunds on the top and two sides to prevent run-on water from entering the plot. The treatments are subsoiling with an ox-drawn subcultivator (DT), and in-situ rainwater harvesting using tied-ridges (TR) and open ridges (OR). These treatments are compared with the control tillage using the traditional single tined-plow called maresha (M). All plots were plowed twice during the dry season (first along the contour and second along the slope) with the oxen-drawn traditional plow (maresha). The week before sowing the open and tied-ridges were plowed along the contour with the ARARI- (Amhara Region Agricultural Research Institute) developed ox-drawn ridger. The open and tied ridges were 50 cm apart and with amplitude of cm and average ridge width of 27 cm. The tied ridges were tied manually at an average of 1m spacing. The traditional tillage (M) and subsoiled (DT) plots were plowed along the contour with maresha and the "tenkara kend" sub-cultivator, respectively, before planting. The tenkara kend sub-cultivator was developed by the German GTZ development organization in Ethiopia. Similar to the traditional maresha plow it turns the soil to a depth of about 8-15 cm but the sub-cultivator has an blade extension which cuts the soil an additional 6-12 cm without turning the soil. No external nutrients inputs were applied to the plots during experimentation or during the 10 preceding years. Seeds of a local variety of red sorghum (Djigourti) were manually sown at a rate of 10 kg per hectare in rows 50 cm apart on all plots. Five weeks

6 after sowing all sorghum plots were thinned to a spacing of 25 cm between plants and 50 cm between rows. Weeding was carried out manually twice at four and eight weeks respectively after sowing. Soil moisture was measured with TDR (time domain reflectometry) soil moisture probes and the gravimetric field technique. Ten measurements were taken with the 12-cm long soil moisture probes at each depth (0, 15, and 30 cm) in random locations on the top and bottom sides of each plot. The readings from the probes were calibrated for the soil type using results from the gravimetric measurements. Gravimetric measurements were taken with 6-cm diameter soil cores at each depth (0-15, 15-30, cm). Moist weight was measured immediately in the field. The samples were sun and air-dried for over two weeks before measuring dry weight. Plant height, total above-ground biomass, and root mass were measured on six randomly selected plants distributed throughout the plot. Root mass was determined from the below ground part of the plants. Grain yield was measured on 2 x 2 meter quadrats on the top and bottom of each plot. The number of plants within the quadrat was counted before harvesting. Plants and grain were sun and air-dried for over two weeks before taking dry weight Results Only the results of the 2003 cropping season are available. Table 2 presents the rainfall, evaporation, and temperature during the growing season. Rainfall during the cropping months totaled 516 mm and is comparable to 1992 rainfall amount for Mekele used in the T-M procedure. Evaporation rates exceed rainfall for all months except August which received 50 % of the total rainfall during the cropping season. Daily maximum temperatures are hot (above 30 o C for all months except December). Figure 5 shows the soil moisture for each treatment during the cropping season at 0-15 cm, cm, and cm depth. The ridges for the open ridge (OR) and tied-ridges (TR) plots remained dryer than the lower than the furrows affecting negatively germination and initial plant growth stages since the seeds were sown on the ridges. Below the ridges in the 0-15 cm soil depth the OR and TR treatments had consistently higher soil moisture than the other treatments. For the cm soil depth all treatments had similar soil moisture with slightly more for the subsoiling and water harvesting (open and tied-ridges) treatments. At the cm soil depth tied ridges had significantly more moisture than the other treatments. The OR and DT treatments also had more soil water content than M for most of the season. During the season rills developed in the OR plots reducing the capacity of ridges to store water. This could be the reason why the TR plot had considerably more moisture than the OR plots. The tied-ridges had some breaks but the effects on water retention were more localized due to the ties compared with the open ridges. The relatively steep slope (up to 9 %) of the plots and high intensity of the first major storm (56 mm in 50 minutes on July 31, 2 weeks after sowing) destroyed several of the ridges of the OR and TR plots creating in-plot rills and leveling some parts of ridges reducing their efficiency of water collection. This reduced the water harvesting function of the ridge treatments considerably. Table 2:Monthly rainfall, evaporation, and temperature for growing season in 2003 at Lenche Dima watershed, Hara Town, Gubalafto district, Amhara region. In accordance with the model results, sub-soiling improved the soil moisture for most of the season compared with the traditional tillage. The sub-cultivator cut the soil an additional 6-12 cm below the depth of soil turned by both the traditional plow and subcultivator (8-15 cm). This additional cutting appears to have increased the soil moisture below the 30 cm depth. Figure 6 presents sorghum root growth during crop development. During the first couple months (mid-july through mid September) after sowing root growth was similar for all treatments. After the initial phase of plant germination and plant establishment, root growth in the TR and OR plots excelled the DT and M plots. This could be due to the roots extending to the high moisture content deeper in the soil. During the second half of crop growth the DT treatment had better root growth than all other treatments. In the DT plots the soil is plowed to greater depth softening the soil for root growth. The final total root mass is higher for the water harvesting (TR and OR) and subsoiled (DT)plots compared with the traditional land preparation (M) plots. Table 3 shows the final sorghum biomass production and grain yields. As expected from the simulation, the DT plots produced the highest total above-ground biomass and grain yield. The TR and OR treatments produced similar grain yield. OR plots produced less root mass, but higher biomass compared with TR. The DT, TR, and OR produced higher grain yield than M. Germination and plant establishment rates for the TR plots was significantly less than the other plots (see Table 3) due to the low soil moisture content of the

7 Starting to manage rain water by sub soiling is only a beginning for better overall watershed management. Figure 6: Sorghum root growth during 2003 cropping season. Abbreviations are the same as in Figure 5. Soils need to further improved so that all the rainwater Table 3: Plant biomass, root mass, plant density and, grain yield from on-farm sorghum trials in Lenche Dima watershed during can be stored and not only a portion. Moreover by better understanding the hydrology, it might be possible to use interflow water for supplemental irrigation. Figure 5: Soil Moisture during 2003 cropping season sorghum trials in the Lenche Dima watershed for depths of 0-15 cm, cm and cm. M is traditional single tined plow called Maresha; TR is tied ridges; OR is open ridges and DT is deep tillage or sub-soiler. ridges where the seeds were sown and numerous breaks in the tied ridges washing the seeds and young plants away. Grain yield for the TR plots might have been higher if the plant density was not considerably less than for the other plots. 5. CONCLUDING REMARKS Both modeling and experimental evidence clearly showed that by providing more storage for water on the crop yield will increases and as a result there will be less dependance on food aid without increasing the risk to the farmer of crop failure. These improvements cannot be made without the input of the farmers, extension personnel and local researches. During the last two years, however, the integrated watershed management approach in the Lenche Dima watersheds has faced several difficulties. Although there is more than reason for this, all the conservation activities initially proposed were almost all related to stopping soil erosion and to not increased water storage. As clearly indicated by the farmers in the survey water had a higher priority than soil. It will be interesting to see if the farmers will more responsive to subsoiling than to the erosion related conservation measures. REFERENCES Astatke, A. and M. A. M. Saleem (1998). Effect of different cropping options on plant-available water of surface-drained Vertisols in the Ethiopian highlands. Agricultural Water Management, 36, Dunne, T. and L.B. Leopold (1978). Water in Environmental Planning. Freeman Company. New York.

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