An assessment of soil and water management techniques towards improved rainwater productivity in Semi-Arid Gwanda District, Limpopo Basin.

Transcription

1 UNIVERSITY OF ZIMBABWE An assessment of soil and water management techniques towards improved rainwater productivity in Semi-Arid Gwanda District, Limpopo Basin. By Liberty Gilbert Moyo (R985255L) A thesis submitted in partial fulfillment of the requirements of the Master of Science degree in Water Resources Engineering and Management (WREM) Department of Civil Engineering Faculty of Engineering July 2006

2 Declaration I Liberty Gilbert Moyo hereby declare that the work contained in this thesis is the result of my work and has not been produced anywhere with the exception of such quotations or references that have been attributed to the authors or sources that I have acknowledged. I also declare that the interpretation of results from the collected data is entirely mine and based on the period that I collected the data. Further data collection and analysis by a different person may result in different interpretations. Signed by The Author L.G.Moyo Date ii

3 ABSTRACT Soil and water management is viewed as key to improving water productivity in rain fed agriculture in the semi arid climates. Water is viewed as the major limiting factor in agricultural production. As a result, technologies to manage soil water to survive against agricultural droughts are being promoted by agricultural research institutions and nongovernmental organizations. A major challenge is to seek if these advanced technologies really result in the perceived benefits in smallholder agriculture, particularly in semi arid regions that are most hardly hit by the effects of dry spells. This thesis reports on work done to evaluate if there are any significant yield benefits and water productivity improvements derived from in situ and off-field rainwater harvesting techniques for rain fed agriculture in semi arid areas of Gwanda, Zimbabwe. Field experiments on soil water management techniques were analyzed. In situ techniques studied include double spring ploughing, basin tillage, ripper tillage and conventional tillage and the off-field techniques in practice include dead level contours with infiltration pits, fanya juus and conventional contour ridges. The results show that the double spring ploughing results in higher yields (but no significant difference) from the other soil and water management techniques and what the farmers are currently practicing. Maize yields varied from 950 kg ha -1 to 1400 kg ha -1 in the experimental plots with different soil and water management techniques giving an insignificant yield difference (p> 0.05). Field results suggest an increase in rain water use efficiency giving an average of 6.5 kg ha -1 mm -1 with micro dosing with ammonium nitrate at a rate of 10 kg ha -1 and an average of 6.1 kg ha -1 mm -1 without micro dosing during the assessment period in rain fed agriculture. The concept of micro dosing results in insignificant yield benefits in a good rainy season in the semi arid environments. It is concluded that deep winter ploughing and basin tillage can bridge short mid season dry spells though they are labour intensive. Labour requirements to implement the soil and water management techniques evaluated do not match the yield benefits in rain fed agricultural production. Key words: soil water management, water productivity, rainwater use efficiency; rainwater harvesting i

4 Acknowledgements I am thankful to Eng H. Makurira and Dr A. Senzanje of the University of Zimbabwe for the tireless supervision of this work. Special thanks go to Mr W. Mupangwa of ICRISAT. This work falls under Mr Mupangwa s broader PhD work under the Challenge Programme research in the Mzingwane catchment. Once again, thank you Mr Mupangwa for identifying the farmers to work with, preparing the experimental plots and organizing our field logistics. I am also grateful to the Challenge Programme for Water and Food for funding this work. I wish to also thank Chinhoyi University for appointing me a staff development fellow. Many thanks also go to the Moyo, Mutero and Garawaziva families for their support and encouragement. Above all, immeasurable thanks to our Almighty God. ii

5 Dedication This work is dedicated to my late father Dominic who did not live to see the output of this study. Earth is not place for angels. iii

6 TABLE OF CONTENTS ABSTRACT.i ACKNOWLEDGEMENTS.ii DEDICATION iii TABLE OF CONTENTS...iv LIST OF TABLES..vi LIST OF FIGURES... vii LIST OF ACRONYMS...viii 1.0 INTRODUCTION Background Problem statement Justification Main objective Hypotheses General research questions Sub questions... 3 CHAPTER LITERATURE REVIEW Semi arid areas and their characteristics Definition of water use efficiency (WUE) Seasonal Rain Water Use Efficiency (RWUE) Definition of Effective Rainfall Water Productivity Other factors affecting water productivity Soil and water management strategies Factors affecting adoption of soil and water management technologies Water partitioning Rainfall Partitioning in farming systems sub-saharan dry land Rainwater Harvesting In-situ rainwater harvesting methods External (Macro) Catchments rainwater harvesting CHAPTER STUDY AREA AND METHODOLOGY Description of Study Area Methodology Baseline survey (Focus group discussions) Experimental setup Determination of Effective Rainfall Determination of seasonal Rain Water Use Efficiency (RWUE) Data Processing and statistical analysis CHAPTER RESULTS AND DISCUSSION Focus group discussions iv

7 4.1.1 Farming and cropping practices Soil water management practices in ward Soil water management practices in ward Soil water management practices in ward Rainfall Data Yield results observed from the replicates without fertilizer Yield results observed from the fertiliser and tillage treatment Biomass yields and rainwater use efficiency estimates Discussion of Results Soil water management techniques in the study area Farmers view on the soil water management techniques Rainfall Biomass production Biomass rainwater use efficiency Crop Yields Grain rainwater use efficiency CHAPTER CONCLUSION AND RECOMMENDATIONS Conclusion Recommendations REFERENCES APPENDICES v

8 List of tables Table 1. Factors influencing evapotranspiration... 4 Table 2. Socio- economic and biophysical factors considered by smallholder farmers... 8 Table 3. ANOVA table for yield from different tillage treatments Table 4.Standard error of difference of mean for tillage treatments Table 5.ANOVA table for yield from fertilizer and tillage treatments Table 6.Average grain yields and above ground biomass yield (kg/ha) and rainwater use efficiency (RWUE) (kg/ha/mm) from experimental plots ( ) Table 7.ANOVA table for rainwater use efficiency of grain yield for fertilizer and tillage treatments Table 8.Standard error of difference of mean for fertiliser and tillage treatments vi

9 List of figures Figure 1. Evapotranspiration against yield... 6 Figure 2. Water productivity against yield Adapted from Molden et al (2003)... 6 Figure 3. Interactions between crop, soil and water management... 8 Figure 4. General overview of rainfall partitioning in farming systems in the semi-arid tropics of sub-saharan Africa Figure 5. Planting basins that have collected the early rains in Gwanda district (Zimbabwe) Figure 6.A fanya juu with cross ties in Gwanda district (Zimbabwe) Figure 7.Dead level contour with infiltration pits in Gwanda district (Zimbabwe) Figure 8. Location of the study area in Zimbabwe Figure 9.Seasonal rainfall graph for Beitbridge station (source: Meteorological Department) Figure 10.Decadal rainfall distribution in replicate 1 for 2005/06 season Figure 11.Decadal rainfall distribution in replicate 2 for 2005/06 season Figure 12.Decadal rainfall distribution in replicate 3 for 2005/06 season Figure 13.Yield for the tillage treatment in replicate Figure 14.Yield for the tillage treatment in replicate Figure 15.Yield for the tillage treatment in replicate Figure 16.Average yield for all the tillage treatment Figure 17.Comparison of yield from the fertilizer and tillage treatments in replicate Figure 18.Comparison of yield from fertilizer and tillage treatments in replicate Figure 19.Comparison of yield from fertilizer and tillage treatments in replicate Figure 20.Comparison of average yield for the fertilizer and tillage treatments Figure 21. Spatial variation of rainfall in ward Figure 22.Daily rainfall distribution for the growing season in replicate Figure 23. Daily rainfall for the growing season in replicate vii

10 ANOVA AREX ICRISAT ITDG FAO NGO WVI List of acronyms Analysis of variance Agricultural Research and Extension International Crops Research Institute for the Semi-Arid Tropics Intermediate Technology Development Group Food and Agriculture Organization Non Governmental organization World Vision International viii

11 1.0 INTRODUCTION CHAPTER Background The Zimbabwean agricultural industry comprises of large scale and small-scale communal sectors with about 70% of the population living in the communal areas. About 74% of the communal farmland is located in the semi arid region (Shumba, 1984). The semi-arid environments fall in Natural Farming regions III, IV and V (Norton, 1995) and 70-80% of the Zimbabwean population earn their living from rain fed agriculture (UNDP/UNSO, 1997). The Zimbabwean natural farming regions have been divided based on annual rainfall amounts and variability. Rainfall onset and length of the growing season are unpredictable and highly variable making smallholder crop production in the semi- arid region risky and unstable. Rainfall is considered the major limiting factor to crop production in Zimbabwe (Hussein, 1987; Hulme, 1996). The recurrent droughts that are being experienced in the sub Saharan region have resulted in low crop production that, in turn, threatens food security in the communities. The first millennium development goal target to halve the people who suffer from extreme poverty and hunger between 1990 and 2015 in Southern Africa where food security has become increasingly problematic over the last 20 years. In addressing food security the millennium project major concerns for agriculture include water resource management, soil fertility and improved access to improved varieties of crops and livestock and agricultural extension services (United Nations, 2005b). Poor yields together with a large population growth have often led to severe food shortage in the region. Crop production by smallholder farmers in these regions continues to depend on the limited rainfall and the success of crop production depends on soil water management practices that increase total soil water available to crops. Soil water is the major resource upon which sustainable cropping depends on. It is thus key element in the management of cropping systems. The climatic conditions in the semi arid regions demands more efficient on farm water management techniques. Utilization of rainfall to enhance soil water availability and productivity can be improved through agricultural practices that minimize runoff, increase infiltration, improve water holding capacity, plant water uptake potential and reduce direct soil surface evaporation. Integrating irrigation management practices such as micro irrigation with rain fed farming can increase water productivity through dry spell mitigation. Soil water management is viewed as one of the means that farmers can employ to increase water productivity and survive the climatic risks. Gwanda district is generally too dry for successful crop production without employing supplemental irrigation. Unfortunately, communal farmers have no other choice but to grow crops under rain fed agriculture. Millet, sorghum and maize are the major crops grown in the district. Livestock production is extensively practiced in Gwanda district with cattle, donkeys, and goats kept at almost every household. The long term average annual rainfall for the Gwanda district is 350mm/annum and this is generally insufficient to support the preferred crop, which is usually maize. Non 1

12 governmental organizations and government departments related to agriculture are encouraging farmers to implement different soil and water management techniques so as to increase water productivity under the prevailing climatic conditions in the semi arid district. The yield benefits from the implemented soil and water management techniques have not been evaluated despite the work being strenuous and lots of money being put into them. This study focuses on evaluating the water productivity of different soil and water management techniques that can be employed by farmers in a bid to survive against agricultural drought. The research points towards getting the best option that can be employed by smallholder farmers to enhance food security. 1.2 Problem statement Smallholder farmers in the semi arid part of Zimbabwe depending on rain fed crop production are practicing different soil water management strategies but there is still low crop production. A survey by ICRISAT survey, 2004/05 showed that maize yields generally oscillate around 0.2 t/ha in the dry areas of Natural Regions V. The potential maize yield in smallholder agriculture is at least 1.2 t/ha in the semi arid part of Zimbabwe. The rainwater use efficiencies of the soil and water management technologies such as dead level contours, basin planting, ripper tillage and deep winter ploughing remains unknown. 1.3 Justification The low productivity in rain fed agriculture is due to sub-optimal performance related to management aspects than to low physical potential (Agarwal and Narian, 1997). Advising farmers on suitable sowing dates, crop varieties have become difficult due to uncertainties associated with the growing season parameters. The rainfall is seasonal and it occurs in the period from mid November to mid March with periodic mid season dry spells occurring in late January. Irrigation costs are prohibitive to the average farmer leaving the farmers with the option of rain fed agriculture only. Soil water management in the semi arid climates has remained the tool that can help farmers realize better yields by reducing the effects of terminal drought, which is common in arid and semi arid areas. While farmers are being encouraged to adopt different soil water management techniques by non-governmental and agricultural research organizations in an effort to survive agricultural droughts, yields have remained low and there is insufficient understanding of the effectiveness of the soil water management techniques. An understanding of the water productivity from in situ rainwater harvesting techniques such as planting basins, ripper tillage, deep winter ploughing and conventional tillage would help in recommending more efficient methods to the smallholder rain fed subsistence farmers. 1.4 Main objective To investigate the effectiveness of soil and water management techniques and their water productivity in semi arid area of Gwanda District in Zimbabwe. 2

13 1.4.1 Specific objectives To assess the current soil and water management techniques which are being employed by smallholder farmers. To compare the crop yields that are obtained from different soil and water management techniques. To determine the seasonal rainwater productivity of the different soil and water management techniques. To investigate other factors that affect seasonal rainwater productivity in smallholder agriculture. 1.5 Hypotheses Soil and water management practices employed by farmers have low water productivities. There exist more efficient soil and water management techniques which, if adopted, can lead to improved crop productivity 1.6 General research questions. How effective are the promoted soil and water conservation practices in cushioning farmers against dry spells? What are the ways and means farmers are employing to survive against agricultural droughts? Sub questions What are the current soil and water technologies being employed by farmers in the fields? What is the water productivity of the different soil and water management technologies? What is the relationship between the soil and water management technologies and the yield? 3

14 CHAPTER LITERATURE REVIEW 2.1 Semi arid areas and their characteristics The average annual rainfall for semi-arid areas varies from mm/annum and it ranges from mm/annum in dry semi arid to dry sub humid zones (Rockstrom et al., 2000). The length of the of the growing period ranges and days in the semi- arid zone and dry sub-humid zone respectively. Potential evaporation levels are high ranging from 5-8 mm/day (FAO, 1986) giving cumulative evapotranspiration of mm over the growing period. Poor rainfall partitioning aggravated by poor resource base could cause low crop production. An increase in food production in the semi-arid regions could be achieved through increase in biomass produced per unit land and unit water (Rockstrom et al., 2002). 2.2 Definition of water use efficiency (WUE) The definition is not strictly standardized as it varies according to the purpose for which it is used. It can be defined on different spatial and temporal (daily, weekly, seasonal, yearly scales). On a spatial scale it can be defined, for instance on: The field scale, as the ratio of the amount of biomass produced (total dry matter of grain or tuber, etc) to the amount of water evapotranspired (i.e., transpiration by crop and evaporation from soil). Evapotranspiration is affected by a number of factors as shown in table 1. On a watershed scale water use efficiency is defined as the ratio of the amount of biomass produced to the amount of water flowing into this water shed (precipitation) minus the amount of water flowing out. Table 1. Factors influencing evapotranspiration Factor Relevant Characteristics Rainfall Amount, intensity, frequency, distribution over an area Meteorological Temperature, relative humidity, radiation, wind velocity parameters Land Topography, slope, type of use Soil Depth, texture, structure, bulk density, organic matter content Soil water Turbidity due to clay colloids, temperature, nature of dissolved salts Management Type of tillage, degree of leveling, type of layout (terracing, ridging) Crops Nature of crops, depth of root system, crop rotation stage of growth, degree of land cover Source: (FAO, 1978) 4

15 Where possible water use efficiency should be replaced with more specific definitions such as precipitation-use efficiency (PUE), irrigation use efficiency, transpiration use efficiency. This is particularly important if WUE is not equal to yield over evapotranspiration. The difficulty in using WUE is that quite often incorrect assumptions are made in the calculations of evapotranspiration leading to erroneous and misleading values of WUE (van Duivenbooden et al., 1999) 2.3 Seasonal Rain Water Use Efficiency (RWUE) It is the ratio of grain yield to the seasonal effective precipitation (kg /ha/mm). This is a more specific definition that does not use evapotranspiration Definition of Effective Rainfall Effective rainfall is that rainfall which can be used for crop growth including rainfall intercepted by plant foliage, rainfall that can enter and be stored in the root zone.it is generally the only water source for rainfed crops. It can be increased through rainfall harvesting (Rosegrant et al, 2002). This is a narrow definition because water is also required to meet non-consumptive needs such as land preparation and leaching of salts. (FAO, 1978) interpret effective rainfall as that portion of seasonal rainfall, which is useful directly or indirectly for crop production at the site it falls. It includes water intercepted by living and dry vegetation, lost as evaporation from the soil surface and precipitation lost by evapotranspiration during growth. It also includes that fraction that contributes to leaching, percolation or facilitates other cultural operations either before or after sowing without any harm to yield or quality of principal crops. 2.4 Water Productivity Water productivity is defined by the following equation [ Y ] WP = / Equation 1 W c Where WP is Water productivity in (kg/ha/m 3 ) Y is Yield in (kg/ha) W c is Water Consumption in (m 3 ) Water consumed includes effective rainfall for rain fed areas and both green and blue water diverted water from water systems for irrigated areas (Molden, 1997). Water productivity can therefore be expressed as the relationship between the plant biomass and the water supplied or consumed. The crop growth is directly governed by evapotranspiration (Fig 1). Water productivity (Molden et a.,l 2003) means raising crop yields per unit of water consumed. (Fig 2). It is a vital parameter to assess the performance of irrigated and rain fed agriculture. 5

16 ET(m 3 ) ET Vs Yield Yield (t/ha) Figure 1. Evapotranspiration against yield Water Productivity (m 3 /t) Water productivity Yield (t/ha) Figure 2. Water productivity against yield Adapted from Molden et al (2003) Crop water productivity will vary greatly according to the specific conditions under which the crop is grown. Mitigating dry spells results in improved water productivity in rain fed agriculture in semi arid and dry sub- humid tropics. This can be achieved through: Maximizing plant water availability through maximizing infiltration of rainfall, minimizing evaporation, increase soil water holding capacity and maximize root growth. Maximize plant water uptake capacity through timely of operations, crop management and soil fertility management. Bridge crop water deficits during dry spells through supplemental irrigation. 6

17 Other factors affecting water productivity Soil fertility Smallholder farmers generally farm on poor quality sandy or sandy loam soils (Twomlow and Bruneau, 2000). Frequently, such soils are infertile, deficient in nitrates, phosphates and sulphur (Burt et al., 2001). In Zimbabwe smallholder farmers were generally confined to poorer soils during the colonial imbalances in land distribution. Fertiliser usage is low in southern Africa with use averaging 28 kg/ha compared to India which uses about 62 kg/ha (Twomlow et al., 1999). In southern Africa farmers opt to increase their cropping area to cope with declining yields as a result of declining fertility rather than investing in fertiliser. This is a short-term solution as the land resource is also limited. As soil fertility declined, farmers have maintained household food requirements by increasing the cropped area to compensate for lower yield. In southern Zimbabwe less than 5 % of farmers commonly use fertilizer (Ahmed et al., 1997). Sixty percent of households owning cattle did not even use cattle manure as to improve soil fertility. In Natural region III, IV and V of Zimbabwe, on farm trials results confirmed that farmers could increase their yields by between % by applying approximately 10 kg of nitrogen per hectare which is about a bottle cap per plant (Twomlow et al., 2006). Farmer resources Water productivity varies from field to field depending on the resources such as drought power, labour, access to machinery and seed varieties. These factors affect the planting time and crop management practices such as weeding which affect crop performance. Access to improved varieties for smallholder farmers is often limited and many classic "green revolution" improved varieties are not drought resistant. They produce the expected high yields only when free of water stress. 2.5 Soil and water management strategies Soil and water management strategies encompass a wide range of activities that minimize runoff and increase soil water. Soil water is defined as the suspended water in the uppermost belt of soil or zone of aeration lying near enough to the surface so that it can be discharged into the atmosphere by evaporation and transpiration. Soil water is very important for crop growth. Figure 3 shows a number of components, which might be present in an improved smallholder farm. 7

18 Better plant growth Higher production Increased ground Improved Crop management Improved Rainwater Management Better land husbandry improved rooting conditions. Maintenance of soil fertility Reduction of soil loss Increased infiltration Reduction in drought risk Decrease in runoff Improved soil Management Adapted from Douglas (1990) Figure 3. Interactions between crop, soil and water management Factors affecting adoption of soil and water management technologies In considering new technologies households consider socio economic and biophysical resources at their disposal (Table 2) Table 2. Socio- economic and biophysical factors considered by smallholder farmers Socio-economic Labour availability Draught power availability Implement availability and condition Timeliness and risk considerations Profitability of farming systems Biophysical Rainfall Soil fertility and soil type Soil moisture Crop establishment methods weeding methods Source: (Twomlow et al., 1999) 8

19 Labour and draught animal powers are the key resources. Household composition, labour productivity and other off farm work influence labour availability. Labour productivity is influenced by sex, age, nutritional status, and health and food availability. It is estimated that labour for food production is contributed by women (FAO, 1995) Water partitioning Soil water management seeks to enhance infiltration and reduce the amount of runoff. Pathways through which water is gained or lost from a defined system is known as the water balance. The main components making up the soil water balance include inputs through rainfall, soil water storage in the soil matrix and output through evapotranspiration, drainage and runoff. Determination of the soil water balance involves quantification of these components by direct or indirect measurements. The generalized on field water balance per unit time step can be described as follows (Rockstrom et al., 1997) P + R = R + E + E + D s Equation 2 Where on off s c + P is rainfall (mm) R on R off E s E c D S is runon from upstream zones (mm) is runoff (mm) is soil evaporation (mm) is crop transipiration (mm) is deep percolation (mm) is change in soil water storage (mm) Some of the components of the water balance can be managed on the farm and thus improving water productivity. Mulching can reduce soil evaporation or increasing crop nutrition to enhance growth can increase shading while transpiration. Transpiration can only occur if there is water available in the root zone; high evapotranspiration component of the water balance reflects high water productivity Rainfall Partitioning in farming systems sub-saharan dry land Figure 4 gives the indication of partitioning of rainfall into different water flow components in rain fed agriculture in sub-sahara dry lands. The characteristics of dry lands are frequent large and intensive rainfall, which results in significant deep drainage amounting to 10-30% of the rainfall (Klaij and Vachaud, 1992). Productive green water flow transpiration in general is reported to account for merely 15-30% of the rainfall and 9

20 this is the important component in crop production. Evaporation from the soil and interception ranges between 30-50% however this value can be exceeded in sparsely cropped farming systems in the semi arid regions (Allen, 1990). Run off accounts for % of the rainfall in the dry lands. The rainfall partitioning shows that there is a high risk of soil water scarcity in crop production in the semi arid tropics of sub Saharan Africa, irrespective of the spatial and temporal variability of rainfall. Source: Adapted from Rockstrom (1999) Figure 4. General overview of rainfall partitioning in farming systems in the semi-arid tropics of sub-saharan Africa:R= seasonal rainfall,es=(evaporation from soil and interception),ec=plant transpiration,roff=surface runoff,d= deep percolation 2.6 Rainwater Harvesting It is broadly defined as the collection and concentration of runoff for productive purposes (crop, fodder, pasture, livestock and domestic water supply) (Evanari et al., 1971). It includes all methods of concentrating, diverting, storing and utilizing and managing runoff for productive purpose. Storage of the water can be short term or long term. Short term storage is storage in or just above the soil profile for crops, fodder, pasture and tree production whereas long storage is for domestic and livestock water supplies. On farmland systems it is practiced to enhance soil infiltration and improve water-holding capacity while storage systems to enhance supplemental irrigation are less common, especially in sub-saharan Africa (SIWI, 2001). The potential of water harvesting for improved crop production in sub- Saharan Africa received great attention in the 1970s and 1980s. This was due to the widespread droughts in Africa, which left a trail of crop failures and a serious threat to human, and livestock life. Consequently a number of water harvesting projects was set up in sub-sahara Africa. The main objectives were to combat the effects of drought by improving plant production and in some areas rehabilitating abandoned and degraded land (Critchley et al., 1994). However, few of the projects have succeeded in combining technical efficiency with low cost and acceptability to the local farmers. Common rainwater harvesting technologies found in sub-saharan Africa include conservation tillage that incorporates a number of cultural 10

21 practices such as mulching and ridging. Small field structures such as tied ridges and buds within cropped area are also common (Ngigi, 2003) In-situ rainwater harvesting methods In situ rainwater harvesting involves methods to increase the amount of water stored in the soil profile or holding the rain where it falls. This may involve small movements of rainwater as surface runoff in order to concentrate the water where it is wanted most. Cultural practices to harvest rainwater and prolong periods of soil moisture availability include tied-ridges, mulch ripping, no-till-tied-ridges, off-season weeding, and deep winter ploughing. World Vision International (WVI) and ICRISAT are promoting basin tillage in Gwanda. Other in situ rainwater harvesting techniques being promoted by WVI are pot holing and tied ridges between planting rows (Mupangwa et al., 2005). Modified tied ridges in conjunction with either basal or manure is also being practised in the district. Retention of crop residues in fields under cultivation decreases run-off, but is unpopular, as farmers prefer to feed livestock with the residues. Conservation Agriculture and water productivity Conservation agriculture is generally defined as any tillage system with the objective to minimize the loss of soil and water or tillage and planting combination which leaves at least 30 % or more mulch or crop residue cover on the surface (SSSA, 1987). In Zimbabwe in particular and the region in general, this term has been loosely used to refer to any tillage system whose objective is to conserve or reduce soil, water and nutrient loss or which reduces draught power input requirements for crop production (Nyagumbo, 2002). Traditionally conservation agriculture has focused on soil conservation with the aim of reducing soil erosion. Conservation tillage, which covers a spectrum of noninversion practices from zero tillage to reduced tillage, is part of conservation agriculture. Conservation tillage systems have resulted in significant increase in yields in sub-saharan Africa e.g., Ghana, Nigeria, Zimbabwe, Tanzania, South Africa and Zambia (Elwell, 1993; Oldreive, 1993). Conservation tillage practices as zero tillage has resulted in water productivity improvements in rain fed farming in Pakistan (Hobbs et al. 2000) and in Semi arid Babati district, Tanzania rain water use efficiency improved from 1.5 kg/ mm/ha in the mid 80s under conventional disc plough to between 2 to 4 kg/ mm/ha during the 1990s after introduction of mechanized sub soiling (Rockstrom and Jonsson, 1999). No till tied ridging This is a conservation tillage technique involving the use of semi-permanent ridges with cross ties, which reduce water flow along the furrows thus increasing percolation time (Elwell and Norton, 1988). The ridges are intended to remain in place for several years before being ploughed out to incorporate manure and to accommodate crop rotations by the farmer. Planting is done on top of the ridges. In subsequent seasons land preparation simply involves planting on top of the ridges once the soil has become moist for good emergence. Crossties are put every 1.5 m. In drier areas planting may also be carried out 11

22 in the furrows where most of the run-off water collects, however these have access problems. Mulch ripping This system of tillage involves the retention of previous season s residues and the land is ripped between the crops rows. The tillage equipment is a ripper tine attached to the body of a medal plough with the mould board and share removed. The crop is planted in the ripped line. The major constraint to ripping is the availability of rippers and draught power. Deep winter ploughing This involves conventional ploughing during the winter period to a depth of about 23 cm. The field s is ploughed again in summer and planting is done into a clean seedbed. This tillage system buries the last season s crop residues and enhances water infiltration when the rains come through increased porosity and reducing surface runoff by providing rough surface which helps in temporary storage of rainwater. Deep tillage requires high draught power, which is normally in short supply in many parts of the semi-arid areas especially in winter when there is little or no vegetation for grazing livestock. Contour ridging and farming Historically soil conservation in Zimbabwe focused on the construction of contour ridges, which were introduced in 1926 (Alvord, 1936) aimed at redirecting and dissipating overland flow from farmers fields. To many farmers soil conservation is still synonymous with contour ridging. The soil conservation measures were enforced into law by the Natural resources act of 1941 and the Land Husbandry act of The way the construction of these conservation works resulted in them being seen as a tool of oppression despite their perceived advantages hence freedom fighters discouraged them. After independence enforcement of the laws became very weak resulting in almost complete failure to maintain established contours or to construct new ones. As a result these no longer exist in the smallholder farms especially in Gwanda district (Nyagumbo, 2001). Contour farming is important where cultivation is done on slopes ranging from 3% and above. All farm husbandry practices such as tilling and weeding are done along the contours so as to form cross-shape barrier to the flow of water and encourage infiltration. The non-use of contour farming/ridging in some other semi-arid parts of the country is attributed to lack of power and equipment to till the land. Basin tillage in southern Zimbabwe The basins can be dug with hand hoes without having to plough the field and seeds are planted in the small holes. The majority of smallholder farmers in southern Africa struggle to cultivate their fields in a timely manner because they lack draft animals (Twomlow et al. 1999) so basin tillage ensures timeliness of planting to the farmer. The 12

23 recommended dimensions of each basin for southern Zimbabwe are 15 cm (length) by 15 cm (width) by 15 cm (depth) and the basins are spaced at 90 cm by 60 cm (Twomlow et al. 2006). In southern Zimbabwe it is recommended that the planting basins are dug from early August through to October in the same positions annually. Planting basins are a type of conservation agriculture because they reduce loss of soil and water. Rainwater is collected into the basins during the early season rainfall events (October and November) as shown in figure 5. The use of planting basins can leave more than 30% of the crop residues on the soil surface. Figure 5. Planting basins that have collected the early rains in Gwanda district (Zimbabwe). Fanya juu This is a Kiswahili phrase for make up slope. A fanya juu terrace is a variant of a conventional contour ridge. It is formed by digging a ditch and throwing the soil up slope to make an embankment, which forms a runoff barrier, leaving a trench that may be graded to drain excess runoff in the humid areas or graded to retain runoff in the semi arid areas. Channel depth is cm with cross ties as in Figure 6. The technique has been applied locally in Zaka (Dreyer, 1997). It has also been widely used in Ethiopia, Tanzania, Kenya and Rwanda (Hagmann, 1994, Critchley 1991). The terrace bank is usually stabilized by growing grass on it, often as fodder. High value crops can be grown on the base of the ditch. Critchley (1991) reports that at a spacing of 20 m they require approximately person-days per hectare. This equates to about 3.3 m per person- 13

24 day, which is a lot more labour intensive than standard contours. Community groups in a reciprocal form of labour often carry out construction. Figure 6.A fanya juu with cross ties in Gwanda district (Zimbabwe). Dead level contours with infiltration pits These are trenches, which are constructed at zero percent slopes so that they retain runoff that gets into them. Pits are dug along the contour ridge to trap runoff and increase infiltration (Figure 7). The pits are filled with grass or stover that is covered by a thin layer of soil so that the organic material can decompose to form compost. The pits trap rain as it falls and then the water infiltrates down slope thereby providing moisture to the crops in the field. The dead level contour ridges vary in sizes having cross-sectional dimension of m width and m depth. 14

25 Figure 7.Dead level contour with infiltration pits in Gwanda district (Zimbabwe) External (Macro) Catchments rainwater harvesting This system involves harvesting of water from catchments of areas ranging from 0.1 ha to thousands of hectares either located near the cropped area or long distances away. It involves transfer of runoff from external land such as area not cropped and grazing land to supplement rainfall received directly on the area where crops are grown. Run off is directed to cultivated fields where temporary storage structures can be dug in the ground and can be applied later as supplementary irrigation. In Gwanda practices such as rock water harvesting are being implemented in some parts of the catchment especially the north, but are still uncommon (Mupangwa et al. 2005). 15

26 CHAPTER STUDY AREA AND METHODOLOGY 3.1 Description of Study Area Location The study was conducted in Gwanda district in Ward 17, 18 and 20 in Matabeleland South Province (Grid Ref.29 0 E 21 0 S) Mzingwane sub-catchment of Limpopo basin in Zimbabwe (Figure 8). Experimental sites were in ward 17. Figure 8. Location of the study area in Zimbabwe Climate The study area lies in Natural Region V (Vincent and Thomas, 1960). The rainfall in the study area is normally received in one season from mid October to end of March. Natural Farming Region V receive rainfall that is normally less than 500 mm/annum year with an average annual rainfall of less than 350 mm/annum and is very erratic with mean annual 16

27 temperatures of 30 0 C (Unganani, 1996). The historical rainfall data from the nearest weather station is shown on figure 9. The historical data shows that 13 years out of 34 years had rainfall slightly above the long term average of 350 mm /annum. Sixteen years had rainfall below the long term average. Rainfall (mm) Total rainfall(mm) Long term mean rainfall Season Figure 9.Seasonal rainfall graph for Beitbridge station (source: Meteorological Department) Soils and Topography The major soil type is sandy loam (Inhlabathi) and minor soil type is black clay (Sidaka) with effective soil depth of 50 cm -70 cm. Drainage varies from being well drained in clay to excessively well drain in the sand loam soils. Topography is almost flat to gently sloping with slope percentage ranging from 0.1%-2.5% slope. Vegetation is mainly Mopani and the Acacia species Agricultural practices Region V covers 30% of the total land area of Zimbabwe and is classified as being suitable for extensive livestock production and wildlife; 27% of the smallholder farming area falls in this region. Communal farmers occupy 46% of the area of Natural Region V (Morse, 1996). Gwanda district is too dry for successful crop production without irrigation, but communal farmers have no other choice but to grow crops in these areas even without access to irrigation. Millet, sorghum and maize are the major crops grown in the area. Livestock production is extensively practiced in Gwanda district. The majority of the smallholder farmers in the districts keep livestock that includes cattle, goats, sheep and donkeys. The success rate of rain fed agriculture in Natural Region V has been known to be in the order of one good harvest in every four to five years (Shumba, 1994). 17

28 3.2 Methodology The research was done in two parallel stages. A baseline survey was conducted in the form of focus group discussions. The focus group discussions were conducted to characterize the traditional soil water management technologies in the study area and to provide a basis for comparison. The other stage was the experimental set up to evaluate other soil water management techniques, which are being promoted by non-governmental and agricultural research organizations. Maize (Zea mays) is the most preferred crop hence it was used in the experiments Baseline survey (Focus group discussions). The study wards were recommended by the Gwanda district Chief Executive Officer who introduced the researcher to the ward councillors of ward 17, 18 and 20. The villages in which focus group discussions were held were randomly selected in the three wards. In ward 17 discussions were conducted in Humbane village, in ward 18 discussions were conducted in two villages namely Buvuma and Meja. In Ward 20 discussions were conducted in two villages namely Mkhalipe and John Dip East (Ngoma). There were at least 20 participants in each focus group discussion. The guiding questions for the focus group discussions are given in the appendix Experimental setup and treatments The experimental set up was in ward 17 in three different farmers fields. The farmers and researchers jointly managed the plots. The study was designed consisting of 20m by 10m plots with three replicates to ensure statistical validity. Two of the replicates were on sandy loam soils and the other on clay loam soils and they were located in different villages so as to average the results. Two factors were analyzed which are fertilizer with two levels and tillage with five levels. Fertilizer levels were top dressing and no top dressing. Cattle manure was applied at a rate of 3 t/ha to all the plots. Maize variety (Zea mays) SC 401 was planted in all the plots on the 20 th of December. Two weeding sessions were done to all the plots. Micro dosing with ammonium nitrate (34.5%) was done to half of the plot on the first week of February when the maize was at knee height at a rate of 10 kg/ha (equivalent to half coca cola bottle cap per plant) as recommended by (ICRISAT, 2006) for semi arid regions. The tillage levels were planting basins, deep winter ploughing, ripper ploughing, conventional ploughing and the farmer practice. Plots were randomly arranged in the sense that no tillage technique had a fixed position.the techniques were (i) Planting basins: Planting basins were dug with dimensions of 15cm length by 15cm width by 15cm depth and spaced at 90 cm by 60 cm. Three maize seeds were planted in each basin and thinned to two at two weeks after emergence and resulting in a plant spacing of 90 cm by 30 cm. Thinning was done to the weakest plant. 18

29 (ii) (iii) Deep winter ploughing: The plot was first ploughed in winter by the research partner at ICRISAT to a depth of cm. The plot was ploughed again in summer and planting was done with a single maize seed per planting position. Planting was done with one maize seed per planting position at spacing of 90cm by 30 cm. Ripper ploughing: The plot was ploughed with a ripper that opens planting lines only leaving the other part of the plot undisturbed. Planting was done with one maize seed per planting position at spacing of 90cm by 30 cm. (iv) (v) Conventional ploughing plot: The ploughing was done with a conventional plough with the planting furrow opened by the plough. One maize seed per planting position at spacing of 90 cm by 30 cm. Farmer practice plot: This was the control plot. The ploughing was done with the conventional plough. The plot was measured from the farmers field were management was done by the farmer only. This plot was used for comparison with the plots that were managed by the researcher and the farmer. 3.3 Determination of Effective Rainfall Effective rainfall was determined by adding the cumulative rainfall recorded throughout the cropping season. The daily rainfall records were made using a plastic rain gauge, graduated conical flask installed in the plots. Effective rainfall was calculated from planting date to harvesting date using the equations 4 and 5 (Brouwer and Heibloem, 1986) considering that not all the received rainfall is available to the crops. Effective rainfall = 0.8* (rain-25) if rain >75mm/month Equation 4 Effective rainfall =0.6* (rain-10) if rain <75mm/month Equation Determination of seasonal Rain Water Use Efficiency (RWUE) Maize was harvested from the whole plot and the total cob and above ground stover was measured in the field using a pocket balance for each plot. Maize was shelled from the cobs and a sample was oven dried to bring the moisture content to 12.5 %, which is the recommended storage and marketing moisture content. The grain weight was measured and expressed in kilogrammes per hectare. The water productivity was calculated using the equation (6) according to (Boutfirass et al., 2002) [ Y ] RWUE = / P e Equation 6 Where RWUE is Rain Water Use Efficiency in Kg ha -1 mm -1 Y is yield in Kg ha -1 P e is Effective Rainfall in mm 19

30 3.5 Data Processing and statistical analysis Data handling and processing was done with Excel and statistical analysis was done by Analysis of Variance (ANOVA) using GenStat Release 6.1 statistical program for Windows to find whether there was any significant differences between the yield and water productivity means of the tillage and fertilizer treatments. 20

31 CHAPTER RESULTS AND DISCUSSION 4.1 Focus group discussions Farming and cropping practices The major crops grown in Gwanda South are pearl millet, sorghum and maize. The main legume is cowpea with groundnuts and bambaranuts being grown to a lesser extent. Crops, which are intercropped with the cereals, are pumpkins and watermelons. A few farmers grow sunflower and sweet potatoes. The major soil type is sandy loam (inhlabathi), which is good for all the crops grown in the district. Minor soils include black clay (isidaka) and red clay (isibomvu), which are also good for cereals. Some areas have sodic soils (isikwakwa), which are not suitable for cropping. Low rainfall is the major problem faced by the farmers in Gwanda South. Dry spells are experienced during the growing season especially in January and the length of the growing seasons is highly variable. Seed is also a major problem to the farmers who cannot afford it. Other problems faced by farmers in the district are striga weed in maize and sorghum and pests like crickets, caterpillars and stalk borer, which are a problem in cereals. Some farmers are aware that early planting and applying manure can lower the striga attack. Crop rotation practices are not very popular in the district as management tactic to control pets and diseases on crops Soil water management practices in ward 17. There are no in situ soil and water management techniques in the ward. All the focus group discussion participants have dead level contours with infiltration pits which border their fields. Farmers took up the dead level contours in 2004 because they were provided with tools to use by Practical Action Southern Africa, which is a non governmental organization. The NGO encouraged farmers to form groups of 20 farmers as a reciprocal form of labour. Farmers report that crops look good in the fields with the dead level contours during short mid season dry spells but the yield benefits from the technology are not yet known. The disadvantage of applying the dead level contour with infiltration pits is that it is labour intensive Soil water management practices in ward 18. There are off field soil and water management techniques in the form of dead level contours with infiltration pits and the conventional contour ridges that were introduced by the former AGRITEX. Some few farmers do not have any soil water management practices on their fields and there are no in-situ practices to manage soil water in the 21