Participatory Planning of Appropriate Rainwater Harvesting and Management Techniques in the Central Rift Valley Dry Lands of Ethiopia

Despite the extensive efforts of rainwater harvesting and management (RWHM) interventions for moisture-stressed areas in Ethiopia, the adoption and wider dissemination of the newly introduced techniques have been generally meager. The objective of this study was, therefore, to develop appropriate RWHM techniques through a participatory planning process in the Central Rift Valley (CRV) dry lands of Ethiopia. To achieve this objective, a combination of literature reviews, focus group discussions, questionnaire surveys, agro-meteorological analyses and field experimentations were undertaken. Perceived agro-meteorological challenges were determined through the questionnaire survey and validated through meteorological data analyses. Potential in situ RWHM techniques were selected in a participatory process and field-tested for two consecutive growing seasons to evaluate their performances. Those techniques which were selected in a participatory process showed statistically higher crop yields than the existing practices under both low and normal rainfall years. The result of this study implied that the introduction of new RWHM techniques can be successful when they are adjusted and modified in accordance with the existing tillage, hoeing and related land management practices. It was concluded that participatory planning of in situ RWHM techniques allows both the utilization of existing knowledge and opportunities while empowering the farmers to select and introduce new practices as per the existing socioeconomic and environmental settings. The new participatory planning approach will augment the recent efforts of promoting various types of RWHM techniques for improved rainfed agriculture in the vast dry lands of Ethiopia.


Introduction
Rainwater harvesting and management (RWHM) techniques hold a promising significance to exploit the full potential of the smallholder-based rain-fed agriculture in dry land regions (Biazin, 2012;Rockstrom et al., 2010;Rosegrant, 1997;Sachs et al., 2004).There are a range of RWHM techniques being practiced in sub-Saharan Africa (Biazin et al., 2012;WOCAT, 2010).The commonly applied RWHM techniques are either indigenous or modified from indigenous techniques (Critchley et al., 1994;Liniger et al., 2011;Reij et al., 1996).A review of the RWHM practices in sub-Saharan Africa revealed promising biophysical and socioeconomic performances (Biazin et al., 2012).As an example, micro-catchment and in situ rainwater harvesting techniques could improve the root zone's soil water content by up to 30% thus mitigating the adverse effects of dry spells during critical crop growing seasons (Abdulkadir & Schultz, 2005;Araya & Stroosnijder, 2010;Makurira et al., 2009;Motsi et al., 2004).Because dry land soils are mostly degraded and poor in fertility, the combined applications of rainwater harvesting and soil fertility improvements could improve the crop yields by up to 6 times as compared to traditional systems (Fatondij et al., 2006;Jensen et al., 2003;Zougmore et al., 2003).Socioeconomic assessments in Ethiopia and Tanzania revealed that economic circumstances were better for the users of rainwater harvesting techniques than the non-users (Awulachew et al., 2008;Hatibu et al., 2006).decades.However, the adoption and wider dissemination of the externally introduced techniques has been generally meager.The introduction and myopic implementations of several micro-dams for runoff harvesting and small-scale irrigation were not successful in Northern Ethiopia (Abera, 2004).About 340,000 underground rainwater tanks (cisterns) were constructed in the four administrative regions of Ethiopia (Tigray, Amhara, Oromia and Southern Region) between 2003 and 2004 to promote supplemental irrigation of crops (Bekele et al., 2006).However, only 37% of these cisterns were operational by the end of 2004.In central and northern Ethiopia, where there has been continuous efforts of soil conservation and rainwater harvesting, many farmers have developed negative attitudes towards introduced measures (Abera, 2004;Amsalu & de Graaff, 2006).The introduced RWHM technologies were found to be: complex and unfit to the existing farming systems, labor demanding, difficult to construct and require high initial investments (Biazin et al., 2012;Bewket, 2006;Bewket & Sterk, 2002).There has been a lack of farmers' involvement at different levels of project planning and implementations.
On the other hand, although farmers are endowed with vast indigenous knowledge of RWHM, they have perceptible gaps in technical know-how (Critchley, 1996;Rajabu, 2005).They need to enhance their technical skills through supports from local institutions and scientific communities.Integrating indigenous knowledge with scientific approaches was found important for the successful planning and development of appropriate RWHM techniques in northern Ethiopia (Nyssen et al., 2000).Stone bunds could be effectively implemented and widely applied by the farmers of Tigray region only after integrating the bunds with the traditional knowledge of lynchets, locally called 'daget' (Nyssen et al., 2000).
Like other parts of the vast dry land areas of Ethiopia, agricultural production in the Central Rift Valley (CRV) is limited primarily by water scarcity.The annual rainfall variability and the non-productive loss of rainfall through soil evaporation and surface runoff are more limiting factors than the total annual amount in the CRV of Ethiopia (Biazin & Stroosnijder, 2012;Tilahun, 2006).Therefore, the objective of this study was to develop appropriate RWHM technologies in the CRV of Ethiopia through a participatory process.A participatory RWHM planning approach has been developed and validated.This approach can be aptly used in the future planning and development of RWHM techniques in other dry land parts of Ethiopia or elsewhere in sub-Saharan Africa, where rainfed agriculture continues to be the main source of livelihood.

Description of the Study Area
This study was undertaken in the Central Rift Valley (CRV) of Ethiopia.The study area is geographically located around 7 o 33′ N latitude and 38 o 40′ E longitude.It is situated at about 190 km south of the capital, Addis Ababa.It has an altitudinal range of 1580-1660 m above sea level and an average slope of 2%.The area has a semi-arid climate with an aridity index (the ratio of mean annual precipitation to mean annual reference evapotranspiration) of 0.37, according to the UNCCD classification of dry lands (MEA, 2005;UNCCD, 2000).The annual rainfall varies between 270 and 960 mm (CV = 30%) with a mean value of 650 mm for the past 30 years.Agricultural water scarcity in the predominantly rain-fed agricultural system of the CRV is caused by annual rainfall variability and non-productive losses of precipitation in the form of evaporation and surface runoff.The soils of the study area are predominantly sandy loam soils (Biazin & Stroosnijder, 2012).These soils are liable to surface crusting after every wetting and drying cycle.The soils have poor fertility and are shallow with an impermeable calcite layer between 0.55 and 0.70 m (Biazin & Stroosnijder, 2012).
Although the area was previously covered with dense acacia woodlands, which was historically used by the pastoral Oromo people coming from the nearby highland areas, a significant proportion of the area is now subjected to cultivation and year-round grazing (Eshete, 1999).Major crops are maize (Zea mays L.) and haricot bean (Phaseolus vulgaris L.).Livestock mainly includes cattle and goats.Following each crop harvest, livestock freely graze on the crop residues.Although cattle manure is abundant around homesteads where the households corral their livestock, most of the local households did not apply any manure to their cultivated fields.

Participatory Processes
A combination of socioeconomic and biophysical data collection and analysis techniques were employed in this study during 2008 -2010.Semi-structured interviews with key informants, focus-group discussions and questionnaire surveys were undertaken from March to September, 2008.Upon a participatory selection of potential in situ RWHM techniques, field experimentation and evaluation of the selected techniques was undertaken for two growing seasons during 2009 and 2010.The participatory processes of data collection and analyses that were followed in this study are summarized in 6 steps as follows (Figure 1).The perception of the local community to agro-meteorological determinants was assessed through key informant interviews, focus group discussions and a questionnaire survey.Four focus group discussions were conducted with both rich and poor household groups of 8-10 people each.Based on the outcome of the focus group discussions, a well thought out survey questionnaire was developed.The survey questionnaire was distributed to 66 households.Accordingly, the main causes of droughts and perceived frequencies of either moderate or severe droughts affecting crop production were examined.The lists of agro-meteorological factors that limit crop production were identified.

Identification of Indigenous RWHM Practices and Opportunities (Step 2)
Many of the rainwater harvesting techniques in sub-Saharan Africa are indigenous or modified from indigenous practices (Critchley et al., 1994;Lininger et al., 2011;Reij et al., 1996).Any attempt to improve water productivity and water-use efficiency of a given agricultural system should, therefore, start with an inventory of current land management and rainwater harvesting practices (FAO, 2005).As a follow up of the previous survey (step 1), key informants interviews, focus group discussions and survey questionnaire were undertaken.The number and types of households used in the second step of the survey were similar to the first survey.The second survey was applied to obtain the list of indigenous RWHM practices and related opportunities in the CRV of Ethiopia.All practices associated with tillage, land management, soil improvements and existing opportunities for improved crop productivity (possibility of using mulch, compost, manure, etc.) were assessed.

Identification of New (Potential) RWHM Techniques (Step 3)
The most commonly applied rainwater harvesting and management (RWHM) techniques and their performances in sub-Saharan Africa (SSA), Western Asia and Northern Africa were previously documented (Biazin et al., 2012;Oweis & Hachum, 2006;Oweis et al., 2004;Oweis et al., 2001).Therefore, the most applicable in situ RWHM techniques for the CRV of Ethiopia were identified from the aforementioned sources.Moreover, important toolkits like WOCAT (http://www.wocat.net), the works of Soil and Water management network (SWMnet), and International Water Management Institute (http://www.iwmi.cgiar.org)were explored.The performance of the techniques, the similarities with the indigenous practices in the CRV of Ethiopia, agro-ecological similarity, and affordability with the existing farming systems were important considerations during the identification of potentially applicable new techniques.
Step 1: Identification of perceived agro-meteorological determinants Step 2: Identification of indigenous RWHM practices and opportunities Step 4: Illustration of the new RWHM techniques and possible merging with indigenous practices Step 6: Field evaluation of the selected RWHM techniques Step 3: Identification of new (potential) RWHM techniques Step The identified techniques (Step 3) and their expected benefits were illustrated to the local farmers and representatives of potential stakeholder groups.A day-long workshop was held with 19 key informants (15 men and 4 women) including farmers from different wealth classes, village leaders, representatives from the offices of agriculture and local non-governmental organizations.Some of the new techniques were demonstrated and explained for better understanding of the implementation processes.The key informants suggested possible modification of the new practices and merging of them with the indigenous practices.The possibility of using local opportunities for RWHM development and possible combinations of RWHM techniques with soil improvement techniques was also discussed.Finally, the participants suggested appropriate procedure and mode of impelementations in accordance with their existing biophysical and socioeconomic settings.
2.2.1.5Selection of the Most Appropriate RWHM Techniques (Step 5) The selection of the most appropriate RWHM techniques was done by the key informants who attended the demonstration (Step 4).The key informants set their own selection criteria (constraints, advantages and opportunities) for each of the new RWHM techniques.The facilitator made sure that all the partcipants had equal chance of suggesting the selection criteria and voting for the ranking.Those techniques which were rated as more important than the existing traditional system were considered as accepted.

Field Evaluation of the Selected RWHM Techniques (Step 6)
Before attempting a wider dissemination of the agreed upon techniques, a field trial was carried out to evaluate the benefits of the selected techniques on crop yields and their implementation challenges.The trial was conducted for two consecutive years on plots provided by 4 volunteer (pilot) farmers.Farmer-driven experimentation allows farmers to systematically assess the value of the innovations they choose (Sturdy et al., 2008;WOCAT, 2007).It also provides researchers with a venue for learning about socioeconomic and biophysical influences of farmers' decisions.Crop yields from each of the RWHM techniques were measured at the end of each growing season and compared to the traditional system (control).Finally, the farmers rated the performances of the RWHM techniques as 'not good', 'good' and 'very good' based on the maize yields.

Biophysical Data Collection and Analyses for Validation
Precipitation and reference evapotranspiration data were obtained from the Langano Meteorological site (during 1981-2006) and an automatic weather station (during 2009-2010) that was installed during this study period.
Onset of the rainfall season, dry-spells of different lengths, mean dekadal precipitation, coefficient of variability of the dekadal rainfall and crop water stress (CWS) were used to characterize the extent of drought in the CRV of Ethiopia.The onset of the rainfall season was calculated based on the definition stated previously (Biazin & Sterk, 2012).Hence, when the onset of the rainfall season was later than June 15, the year was considered as severe drought for Maize which is the staple crop in the CRV of Ethiopia.Dry-spells of length m are defined as a sequence of m-dry days preceded and followed by dry days whereby the lengths of successive spells are readily seen to be independent (Biazin & Sterk, 2012).The probabilities of dry spell lengths of 5, 7, 9, and 19 were determined for the months between March and September.The onset and dry spell analyses were done using INSTAT version 3.36 based on the method described by Stern et al. (2006).The CWS was estimated from the ratio of dekadal precipitation (RF) to dekadal reference evapotranspiration (RET) as described in the equation below.
The selected in situ RWHM techniques were evaluated in the field for two growing seasons (2009 and 2010) on maize.The field experiment was done in a split plot design where tied-ridges, sub-soiling and traditional tillage with the traditional Dirdaro were considered as the main plots.These main plots were further divided in to two sub-plots, with one unit treated with farmyard manure (4.5 Mgha -1 ) and the other without manure.Surface runoff, soil water content of the maize rooting zone and root length density (RLD) were measured continuously throughout the maize growing seasons.The amount of surface runoff was measured after each rainfall event during the maize growing seasons in 2009 and 2010.Soil water content was determined using a Time Domain Reflectometer (TDR) instrument.The overall maize yields were determined at the end of each growing seasons.Finally, statistical analyses were done to examine the effects of the in situ RWHM techniques on hydrological and plant parameters mentioned earlier.Analysis of variance (ANOVA) was done using SPSS version 17 (Julie, 2007).Tukey's honestly significant difference test for equal variances and Dunnett's T3 test for unequal variances were used for mean separations.
Although it may be possible to introduce new potential RWHM techniques in to a given area, the expected benefits of each technique within a given agro-meteorological and soil conditions need to be simulated.Hence, the simulation of the different new RWHM techniques was done using the FAO's AquaCrop model.It was reported that there was a good fit between the simulated and observed values of maize yield in the CRV of Ethiopia (Biazin & Stroosnijder, 2012).Hence, the effect of tied-ridges on maize yield in response to different rainfall patterns (onset, amount and distribution) and fertility levels was simulated for validation of the farmers' qualitative evaluations and scientific explanations.

Agro-Meteorological Determinants, Opportunities and Indigenous Practices (Steps 1 and 2)
According to the farmers' accounts, maize production in the CRV of Ethiopia is limited due to agricultural drought (100% of the respondents, N = 66), poor access to chemical fertilizers (72% of the respondents), and poor access to better seeds (55% of the respondents).There was a difference in the perception of rich and poor households regarding the occurrence of drought in the CRV.While rich households perceived the occurrence of drought every 7-10 years, the poor households perceived it within a range of 3-5 years.Long dry spells during the growing season and late onset of the rains were perceived as the major agro-meteorological determinants for crop production.Table 1 presents the perceived (N = 66) mean lengths of dry-spells that are critical to the growth of the local maize variety (Awassa BH540) at the crop's different developmental stages.Flowering and grain filling (61-90 DAS) 7 Maturation stage and drying (91-120 DAS) 9 † DAS, days after sowing.
Indigenous land management practices that are used as in situ RWHM were identified in the CRV (Table 2).Most of these techniques are associated with tillage, hoeing and soil management.Tillage during planting is carried out carefully in such a way that moisture conservation is possible.Before the introduction of line sowing of maize, tillage during sowing was entirely made using the old Malibes technique, which is flat and without furrows.Recently, many farmers (67% of the respondents, N = 66) adopted a new type of tillage, Dirdaro furrow, in association with line sowing.The Dirdaro furrows are made with the traditional Maresha plough after every two planting rows with an average interval of 50-54 cm across the slope just after sowing.The furrows help to reduce runoff and enhance infiltration.Furthermore, the soils are inverted from the ridges to both sides of the planting rows, thus reducing soil evaporation from around the rooting zone.This practice is widely applied in northern Ethiopia (Nyssen et al., 2011).Removal of the surface soil crusts either by manual hoeing or Maresha plowing is necessary following wetting and drying cycles during the maize growing season.Because of this, the local farmers apply one or two hoeing operations.However, manual hoeing loosens only the thin soil surface.Therefore, about 35-45 days after planting, Shilshalo ridging is commonly practiced using the traditional Maresha plow on the furrows that were made for Dirdaro.It is normally practiced following rain events which otherwise is believed to dry up the crop.Despite the abundance of farmyard manure, the local farmers do not distribute it on their farmlands for soil improvements as they fear that it may dry up the crops.Few farmers (26% of the respondents) shift the location of corralling so that they can use the fertilized land for maize cultivation.

Identification and Illustration of Potential New Techniques and Their Expected Benefits (Steps 3&4)
Table 3 presents the most commonly applied in situ RWHM techniques in sub-Saharan Africa (SSA).The performances of these in situ RWHM techniques were found to be very effective when they were combined with soil improvement techniques such as addition of manure and compost (Jensen et al., 2003;Zougmore et al., 2003).Ridges can be left open, or closed (tied-ridges) at regular intervals for holding water and facilitating infiltration (Lal, 1990;Wiyo et al., 1999).Mulching can be done either with crop residues or stones and rock fragments.Sub-soiling, reduced tillage, zero tillage, and other conservation agriculture practices are done making use of different implements in different regions of Africa (Rockstrom et al., 2009;Walker et al., 2005).With the new Maresha-modified ridger, it is possible to make wider ridges than the Dirdaro furrows; tying of the ridges will also help to reduce runoff.
It is difficult to apply shilshalo with the new ridger.Dry farmyard manure 2 It improves crop yields; unlike other parts of Ethiopia, dry farmyard manure is not used as a source of household energy due to better access for firewood and charcoal from the woodlands.
It may initiate drying up of the maize crop when applied either in fresh or damped particularly during dry seasons.

Sub-soiling 3
It enables to loosen the soil deeper than the traditional tillage and enhance infiltration of rainfall.
It is difficult to apply crossplowing during consecutive tillage operations; purchase of the sub-soiler incurs additional cost.
Compost 4 It improves crop yields; the ingredients (leaves and crop residues, manure, soil) are easily available.
Difficulty of getting water for the preparation of compost during the dry season; bad smelling may not be good for health.

Traditional tillage 5
It is easy to practice as they have already experienced it; There is no extra expense required.
It is not good enough to conserve moisture.
Mulching 6 Enhance infiltration of rainfall and cover the soil from the sun Mulch is desperately needed as source of feed for livestock during the dry seasons.Reduced tillage 7 It may be applied when onset is late Without repeated tillage crop yields can be very low.

Zero tillage 8
No suggested advantage Without tillage crop yields can be very low

Field Performances of the Selected RWHM Techniques (Step 6)
The farmers perceived that tied-ridges in combination with manure showed the largest maize yield (Table 6).However, tied-ridges and sub-soiling without soil fertility improvements were not good enough to improve crop yields during the very dry year in 2009.The use of farmyard manure has shown promising benefits under both very low and normalrainfall conditionswhen it was used in combinations with either the traditional tillage or the in situ RWHM techniques.Good Not good 0.5 0.4 "-" implies the reference (control).

Agro-Meteorological Challenges and Opportunities (Steps 1 and 2)
Figure 5 depicts the probability of dry spells that are perceived as critical to maize during the different developmental stages.Particularly, dry spell lengths of 5 to 7 days are generally common during the maize growing season.Long-term meteorological analyses revealed that late onset of the rains caused 5 severe drought years for maize during the last 28 years, while long dry spells caused 6 moderate and 2 severe drought years (Biazin & Sterk, 2012).Moreover, there is a reasonable gap between the long-term mean dekadal (ten days) precipitation and Reference evapo-transpiration (RET), particularly during the months of May and June (Table 7).These months are either in the first or second developmental stages of maize in the CRV.According to Doorenbos and Kassam (1979), crop water stress becomes severe when the available water from the rainfall is less than half of the crop water demand.Based on long-term mean values, the first dekad of May, third dekad of May and first dekad of June have crop water stress (Table 7).The inter-annual variability of decadal rainfall is painfully high during the maize growing season implying unreliability of the rainfall (Table 7).All these support the perception of the farmers on drought.Apart from this, field experiments during 2009 and 2010 growing seasons revealed that runoff is triggered when there is rainfall amount of at least 12 mm per day (Figure 6).The total rainfall during the growing season is more correlated (r = 0.89) with the number of days with a rainfall of greater than 12mm than with the total number of rainfall days (r = 0.4).Despite the severe agricultural water scarcity, the higher probability of different lengths of dry spells and the intensive nature of the rainfall infers that there is an opportunity to develop water conservation techniques associated with runoff harvesting.An extensive review of the most commonly applied in situ and micro-catchment RWHM techniques along with their performances was made (Biazin et al., 2012).It was revealed that spectacular gains in crop yields could be obtained from appropriate combinations of RWHM and soil improvements.Simulation in response to planting of maize during differentmonths in the CRV of Ethiopia revealed that tied-ridges are more effective when applied forsowing in April than for sowing in May and June (Table 8).Simulations based on long-term meteorological data revealed that combining tied-ridges and soil improvements can increase maize yields by more than double.
Although tied-ridges caused water logging effects during above normal rainfall years elsewhere in sub-Saharan Africa (Jensen et al., 2003), it is less likely to occur in the CRV of Ethiopia where consecutive wet days are least likely to occur and the soil is dominantly sandy loam.During the 2010 growing season (rainfall amount = 420 mm; 46 % probability of exceedance), maize yield was significantly (α < 0.05) higher in plots treated with either farmyard manure or tied-ridges than the control with traditional tillage (Table 9).The interaction effect of manure application and tied-ridges on maize yield was also significant (α < 0.05).During the very dry season of 2009 (rainfall amount = 230 mm; 96% probability of exceedance), the use of the Maresha-modified tied-ridges and sub-soiling did not improve maize productivity (α > 0.05), while incorporating dry farmyard manure improved the maize productivity significantly (α < 0.05).This implies that as long as the dry farmyard manure is evenly distributed during the offseason, the local perception that manure causes maize drying is unfounded.Standard error of the mean in parentheses and mean values followed by similar letters a-c along a column of a given year or x-y across a row are not significantly (α = 0.05) different.Benefits were computed as [(yield from introduced technique -yield from the control) / yield from the control] × 100

Conclusions
The participatory RWHM planning approach enabled to examine the major challenges and utilize existing knowledge and opportunities thus empowering the farmers to introduce new RWHM techniques as per the socioeconomic and environmental settings.The application of this new approach in the CRV of Ethiopia showed that the introduction of in situ rainwater harvesting techniques needs to include an assessment of the major agro-meteorological challenges, existing tillage, hoeing and associated land management practices.In the CRV dry lands of Ethiopia, agricultural water scarcity is mainly caused by the long dry spells and associated non-productive losses via soil evaporation and surface runoff.This was confirmed by both the local people's accounts and agro-meteorological analyses.For an effective implementation of the new approach, the FAO's AquaCrop model, upon proper calibration and validation for different crops and regions of Ethiopia, could create a database explaining the expected benefits of the various rainwater harvesting techniques in response to different rainfall patterns and fertility levels.The RWHM techniques that were selected and modified as per the existing land management practices in a participatory process showed significantly higher maize yields than the traditional practices under both low and normal rainfall years.The new approach may augment the recent efforts of promoting various types of RWHM techniques for improved rainfed agriculture in the vast dry lands of Ethiopia.

Figure 1 .
Figure 1.Schematic steps of the participatory rainwater harvesting and management planning process employed in this study

Figure 6 .
Figure 6.Runoff (mm) observed under Tied-ridges (TR), Sub-soiling (SS) and Traditional tillage with Dirdaro (T) from a maize field in 2010 in the CRV of Ethiopia.Standard error of the mean indicated as error bars for mean runoff.During the 2009 growing season, only three rainfall events could produce runoff.Hence, runoff amounts of 2.5 mm from rainfall of 14 mm (July 7), 4.5mm from rainfall of 27.1mm (July 14), and 2.3 mm from rainfall of 15mm (July 20) were measured from the traditional Dirdaro tillage

Table 1 .
Perceived mean lengths of critical dry spells during the different developmental stages of maize in the CRV, Ethiopia

Table 2 .
Indigenous land management used as in situ rainwater harvesting techniques and level of application by the local households in the CRV of Ethiopia It breaks the surface crusts and loosens the soils; it helps to pile soil around the root zone where soil evaporation can be reduced.

Table 3 .
The new in situ RWHM techniques, their features and performances elsewhere as illustrated for the farmers in the CRV, Ethiopia Yield increment = (mean crop yield obtained when RWH is applied -mean yield with the control without any technology)*100/ mean yield with the control without any technology. ¥

Table 5 .
Farmers' ranking of the in situ RWHM techniques and their possible constraints and advantages in the

Table 6 .
Qualitative farmers' evaluation and measured maize yield according to the different in situ RWHM techniques during 2009 and 2010 growing seasons in the CRV, Ethiopia

Table 7 .
Long-term mean dekadal (ten days) rainfall (RF), dekadal Reference Evapotranspiration (RET) and crop water stress (CWS) index during the maize growing season in the CRV of Ethiopia Values in parenthesis are meant for the ratio of dekadal precipitation to reference evapo-transpiration. €

Table 8 .
Simulated maize yield with tied-ridges and traditional tillage systems according to different planting months in the CRV, Ethiopia

Table 9 .
Statistical analyses on maize grain yield determined according to different in situ RWHM techniques during 2009 and 2010 growing seasons in the CRV, Ethiopia *Values parentheses refer to total rainfall during the growing season of maize from sowing to harvest.