PRE2018 3 Group16

Group members

Edwin Steenkamer	1006712
Sjir Schielen	1024154
Thijs Conner	1011148
Tobin van den Hurk	1009573
Tom Verberk	1016472

Introduction

The environmental challenges in Africa, which are only increasing in difficulty due to, among other factors, the consequences of global warming, are a real concern for the food production in this area. As a consequence, independent and poor small-scale farmers and small villages living of agriculture across Africa may struggle to sustain themselves. The agricultural sector in Sub-Saharan Africa is dealt a bad hand, considering the suboptimal conditions they have to deal with in this arid and drought-prone land. Since the agricultral sector makes up a large part of the Sub-Saharan labor market, every improvement made in this area will benefit a substantial part of the African population. However, the lack of proper education and the misuse of technology in these agricultural areas hinders the development of efficient food production. This problem knows many sides and solving all of these in one solution is virtually impossible.

While researching the exact problems, it has become apparent that the lack of water is a clear limiting factor in agriculture. Even though this does not come completely out of the blue, only after some research it became apparent that there is still a lot of room for improvement regarding water usage. Therefore, we want to make a system that collects, stores and distributes water in a smart and efficient way. Since the climate varies heavily across the enormous continent which is Africa, the solution presented on this wiki focuses primarily on Southern Africa, where both the dry season and rainy season are lengthy and significant. This allows for collecting water when rain is abundant, and storing it untill it is needed in the more dry parts of the year. This in turn would decrease the amount of failed harvest caused by drought, allow for a greater variety in crops, and shift the farmers' focus from trying to survive even if a harvest fails to maximizing harvest all year long instead.

Approach

For this project, an initial literature study is required. By exploring the subject in a top-down fashion, the main focus of the project can be adjusted. In other words, gathering information on the broad topic of farming in sub-optimal conditions in general, allows for the project to delve deeper into the aspects of farming deemed most important. Using this method instead of starting with a focus on a specific problem regarding farming, eliminates the threat of discovering this specific problem is not as interesting or important as expected. Another benefit of starting with an extensive research on the state-of-the-art, is that the amount of assumptions is expected to be limited. This allows for more grounded arguments and reasoning as to why certain aspects are deemed more important.

This led to the opinion that the most effective way of improving agricultural gains is by conquering extended periods of drought. Transporting water from more humid areas is a possibility, but unfavorable due to transportation costs and limited availlability of water even in those more humid parts. Therefore, a means to improve the usage of the already availlable water during the rain seasons is more desirable.

The process of increasing water efficiency has 3 distinctive steps, which all need to be looked at individually first: collection, storage and distribution. Then, these parts need to be combined into one construction, centered around the user.

Deliverables

This project will ultimately consist of 3 deliverables, a literature study, a system design and a model. The project’s literature study will focus on the following topics: Sub-Saharan african agriculture, agriculture in Botswana, farmers in Botswana, existing alternative solutions to our problem and the individual components of our system.

Furthermore, a system will be designed to solve the problem given in our approach. This system will consist of three parts: a water catchment part, a water storage part and an irrigation part. Finally, a model will be made to verify the effectiveness of our system.

State-of-the-art

Agriculture is one of the biggest sectors we have in this world. Without food, we would not be able to live on this planet. Since this project focuses on small-scale farmers, the research is divided into different subjects deemed most important in getting a better picture of how small-scale farmers could be assisted. The first section will briefly touch on some of the core aspects of Sub-Saharan agriculture, after which a more in-depth state of the art will be presented on drought prevention techniques such as water collection, irrigation, and water storage.

Sub-Saharan African agriculture

The best ways to provide energy to systems implemented on a farm.

Energy production is vital to the development of Africa. Currently only an estimated 31% of the whole population in Sub-Saharan Africa has access to electricity, whereas about 80% of the energy consumption is still accounted for by traditional biomass energy. An increase in energy consumption is needed for Sub-Saharan Africa to develop. Climate changes poses a threat to the already vulnerable agricultural sector of Sub-Saharan Africa. Energy sources other than biomass with low carbon emissions are needed to improve the agriculture in these fragile environments. The lack of funding is the major problem and as the globe warms, time is of the essence [15]. Sub-Saharan Africa offers conditions that may be beneficial for energy production. The area receives solar radiation with an intensity that is among the highest on the planet. The now commercially available technology concentrating solar power (CSP) is a candidate technology which, with the right investments, can generate a lot of power in North Africa [32]. There are possibilities for large scale energy production in this area, which may benefit other parts of the world as well, but the main problem remains funding.

How does livestock and vegetation affect (and benefit) each other.

There are theoretical benefits to the interaction between crops and livestock. Livestock can be used for physical labour on the land and manure can fertilize the soil. In Sub-Saharan Africa, however, this concept is not well integrated. The concept is not applied through the availability of information, but through environmental differences [25]. Another theory suggests that households in Sub-Saharan Africa use livestock as a buffer stock to insulate their consumption from income fluctuations. As the problems of engaging in rainfed agriculture are inevitable in a drought-prone area, it is often assumed that livestock form a buffer for the dry season. Results indicate that livestock transactions play less of a consumption smoothing role than often assumed. One can conclude that there are better ways to manage agriculture [13]. Another problem is that most livestock was introduced to Africa through trade with Europe and the Middle-East, hence the animals are less adapted to the extreme conditions [19]. The use of different animals as livestock may benefit the harsh areas. It is, however, important to analyze how effective species are with water. A way to do this is by the concept of livestock water productivity (LWP) [10]. LWP is defined as the ratio between the sum of all net livestock products and services and the sum of all depleted/ degraded water. It assigns a numerical value with the unit dollar per cubic meter of water. By using this concept a numerical problem can be formulated that allows optimization. This approach does, however, rely on available information and it is estimate based.

Methods of Soil sampling and analysis.

Soil consists of many different kind of elements which can have an effect on the crop growth. To measure these elements soil sampling and analysis has to be done. Different analysis methods are needed for different elements such as chemical, biological, organic matter, physical and water analyses [6] [17] [24]. The effectiveness of these tests, for a low budget and uneducated farmer, are dependant on the ease of use and low-cost equipment. Investigating new and improved ideas of how to measure specific elements may help in choosing the right tests [33] [35] [20]. In case of putting these sensors on a robot an assessment also has to be made about the effectiveness of different kind of agricultural robots [26].

Soil analysis and degradation.

Not just the drought, but rather soil degradation combined with the rapid increase in population in developing areas such as Sub-Saharan Africa, will pose a major threat for food production in the near future[31]. To combat this degradation, adequate measures should be applied. Measuring the soil composition at different locations in a single field, will give more insight in the so-called micro-variabilities[5]. These measurements can be used to more efficiently water, manure, and weed crops, which has proven to be more effective than simply introducing new techniques or machinery[4].

Obstacles for small scale farmers in poor countries.

The demand for food products for export markets is increasing severely in developing countries . But most of the small-scale farmers in those countries have difficulties profiting from this increasing demand. This article[12] gives a few problems small-scale farmers are having including pesticide use and poor storage facilities. To improve these farmers need technology, but to choose which technology is needed and then actually integrate this technology is easier said than done[14]. The conclusion is that a combination of lack of knowledge, resources, and technology is the reason small-scale farmers are having trouble to increase their production and make their farm more efficient[9].

Technology that is used in agriculture in industrialized countries.

Nowadays technology is having a massive impact on agriculture, especially in industrialized countries. A great example of this is precision farming. This type of farming uses wireless network systems (WNSs) to make sure every plant or animal gets a very precise treatment[7]. Other examples of smart farming is given in these articles[16][18]. The first article describes a system that can measure physical parameters of the soil that play a vital role in farming activities and the second article describes a system that can reduce the amount of water used by implementing a soil moisture sensor to automate the water sprinkler.

Drought

Drought is considered to be one of the most complex natural hazards, as it affects more people than any other natural hazard, yet for all the damage it causes it receives relatively little attention. Of all natural hazards, it is the most difficult to predict and it can last longer than any other. Currently, there are many factors that cause a lack in preparedness by people living in drought-prone areas. One of these factors is the lack of a universally accepted definition of the word drought. Various scientific disciplines, such as meteorology, agriculture, hydrology and socio-economy, have different definitions. Here, the focus lies on the agricultural definition and the meteorological definition. The agricultural definition refers to a period of time in which the amount of water in the soil no longer meets the requirements of the crop. Meteorological drought is defined as the amount of precipitation being a certain percentage lower than usual for a prolonged period of time[9].

The Botswanan situation

Precipitation

Rainfal, PET and day length in Gaborone[42]

Botswana is a typical semi-arid country: average annual evapotranspiration (sum of evaporation and transpiration by vegetation) exceeds the annual rainfall by a factor 3-4 in the north-east to 8-10 in the south-west. Seasonal rainfall and its distribution are very irregular and dry periods of more than one month are common. The country’s agricultural sector is built around the rainy season. The figure below shows the average rainfall from recorded data between 1925 and 1984, the average Penman potential evapotranspiration (PET) and theoretical day length for Gaborone[42].

What stands out is that rainfall is less than PET all year round. This means that the shortage of water is a problem not only in the dry season but also in the wet season. Keep in mind that the figure shows average data. The fluctuations in precipitation are unpredictable and it is not uncommon for a dry month to appear in the rainy season.

To manage agriculture, the rainy season is divided in three periods which roughly coincide the farming cycle. The early rainy season spans from October to December and is meant for soil preparation, planting and the first stages of crop development. The mid rainy season lasts from January to February. This period contains fast vegetative growth and has the highest water requirements. The late rainy season concludes the rainy season in the months March and April. In the late rainy season, the final stages of crop development occur and the water requirement declines[42] [43].

In practice, the farmers face challenges. First of all, the PET is higher than the amount of rainfall all year round. This means that even in the rainy season there is not enough water to support all biomass. Second, the fluctuations in arbitrary dry periods in the rainy season cause unpredictable risks in the cycle. The farmer needs enough time for his crops to grow while there is water available. Yet, if a dry month occurs it can cause the harvest to fail without enough time left in the rainy season for the farmer to replant. Even if the crops survive, the lack of water will cause less biomass to be produced.

A system that collects, stores and smartly irrigates water can be a solution. Since annual evapotranspiration exceeds annual rainfall, a smart way of collecting, storing and using the water is necessary. By collecting more water, a part of the water that would otherwise evaporate can be used. By improved storage, the farmer has a water supply that can act as a buffer in potential arbitrary dry months. If the water is used in a more effective way, which is aimed to be optimized by the use of technology, less water is lost in watering crops.

Farmer's current efforts of dealing with existing drought

Drought can be divided into two parts: predictable drought and unpredictable drought. As described in the section ‘The Botswanan situation’, there is a rainy season and a dry season. Predictable drought is the dry season. Unpredictable droughts are droughts that occur in the rainy season or predictable droughts that last longer than usual. Predictable droughts that last longer than usual can be specified as prolonged dry seasons.

Farmers in Botswana use the farming cycle and the division of the rainy season into the early, mid and late sections as a way of dealing with the predictable droughts. These droughts are still a problem, as it pressures the agricultural sector into a critical period in which it must produce. Predictable droughts, however, form less of a problem than unpredictable droughts, as data shows that years, in which there was no unpredictable drought in the rainy season, produce a decent harvest. Data published by Botswana’s Ministry of Agriculture Department of Research, Statistics and Policy Development [45] show the crop yield in kilogram per hectare per year as can be seen in the figure below.

Yield per hectare planted trends (kg/ha) per crop[45]

The Seven Year-Drought consisted of a prolonged dry season and dry months in the rainy season[46]. The Seven Year-Drought started in 1981 and ended in 1987. As the data below shows, there is a steady decline in crop yields after 1981 as it reaches an all time low in 1984. After the drought, in 1988, the food production is back to average. Normal years, or years with a predictable drought, have an average food production, hence the problem lies in unpredictable droughts.

Unpredictable droughts, such as the Seven Year-Drought, are the major problem. As the figure shows, after 1981 crop yields steadily decreased. Due to government effort and water reserves that are used in case of drought, the crop yields did not plummet in one year, but they decreased steadily. The water reserves are used for large scale farmers to assure a maximum crop yield given the circumstances. This means that small scale independent farmers are the real victims of a drought. It rarely is the case that a small scale independent farmer has access to water reserves or is supplied with water by the government. As of now, their best efforts are in managing the water they have as effective as they can. Though, if there is not enough, there is nothing they can do.

Opportunities in Botswana

Botswana is in many ways seen as a success story in Africa. As a developing country it has had the highest economic growth in the world. Now, the country is ranked fifth in the list of GDP per capita of African countries. In 2013, Fosu argued that after gaining independence from the British Empire in 1966, it was one of the poorest countries in the world (pp. 187-189)[12]. The country found great economic growth due to the following reasons. The country has known free and fair democratic elections ever since its independence. “Botswana has had no coups, no political instability, no civil wars, no threats of secession and excellent, dedicated, uncorrupt leadership” (pp. 188). Another driver of the economy is the country’s mining activities. Approximately 90 percent of Botswana’s export products are categorized under gems and precious metals. Botswana also invested in tourism as a sustainable source of income.

Although it may seem like Botswana is a country that does not need help, the country still faces the same problems as other poor Sub-Saharan African countries. “There is a great deal of poverty in rural areas, inequality is high (though falling), the economy has been unable to diversify, and more important there is a huge rate of HIV infection that the government is now fighting” (pp. 188)[47]. Small scale independent farmers are still struggling to make a living. When harvests fail, Botswana has the money to import food from other countries (mainly South Africa), but small scale independent farmers in poor rural areas are left with nothing.

There may lie an opportunity here, as the country still faces the problem of food production in droughts and poverty still exists in rural areas. If an automated system can improve the country’s food production, it will yield great benefits for Botswana. Through investing in a system that collects, stores and irrigates water automatically, small scale farmers have more certainty in their food production. This ultimately leads to a decrease in the inequality between the poor and the rich and it makes Botswana less dependable on food imports.

Users

The users of the technology can be divided into primary, secondary and tertiary users. The primary users are small based farmers that live in conditions which are suboptimal for agriculture. These conditions are mainly found in drought-prone areas of Africa, such as the areas in or around deserts. As primary users, the artifact or technology is directly aimed to be of use to this group.

Secondary users are the people in nearby villages that benefit from a more consistent food supply. They benefit from the available food through the farmer's use of the artifact. Bigger farmer organizations (or collectives/unions) are also considered secondary users, as they benefit from higher production caused by the farmer's use of the artifact. Larger scale farmers may also use the technology, although it was intended for small scale farmers. Larger scale farmers are therefore considered secondary users.

The tertiary user is society as a whole. If food production increases it will benefit society. Society as a whole is not using the artifact, but it benefits from a more efficient use in water for agriculture through the increased production. As the artifact is aimed to increase the efficiency in the use of water, it is projected that more food becomes available. This is likely to cause economic growth in these developing areas, which makes it attractive to investors. Therefore, investors can also be seen as a tertiary user.

User Requirements

The technology requires a source of energy. As the energy infrastructure in Africa is underdeveloped to non-existent in certain areas, this forms a problem. In, for example, Sub-Saharan Africa, only an estimated 31% of all inhabitants have access to electricity [15]. Access to electricity is usually in towns or cities, which is not where the farmer has his piece of land. This means that the users require the technology to generate its own needed energy or to work on fuel.

The scarcity of water is the main reason behind this artifact. Water is very valuable in areas prone to drought and the sad reality is that it literally is a matter of life and death. Therefore the artifact must be efficient with water. This means that it should catch as much water as possible and store it while keeping losses at a minimum.

Although the technology is primarily aimed to be used for crops, it is unlikely that it will be the only use. If drought strikes and there is water available in the storage tank, people will use it for consumption. Even if it is explicitly clarified that it is no drinking water, to the people it is still better than no water at all. Therefore it is required that the storage tank keeps the water clean to a certain degree. This induces more difficulty in the design of the artifact which was not projected at first, but it does make the artifact more user oriented.

Former automation solutions have failed due to the weak state of the economy in these developing countries. Farmers live off the harvest rather than the profit they receive from selling their crops. This means that no jobs should be replaced by the artifact, which is vital for it to be adopted in the first place. The farmers will not use technology that replaces their jobs, therefore it is important that the artifact performs a task that no farmer can do. The system collects, stores and irrigates water, which are tasks that farmers cannot do themselves.

The artifact is aimed to help the farmer with water management. It is projected to perform this task autonomously, but in the end the farmer should have full control. In the case of a severe drought, if the water is required for drinking, the farmer should have access to the storage tank. Therefore the farmer should be able to intervene with the autonomous way of operation on request. The farmer should be able to understand how to interact with the artifact in the desired way. Therefore, it should be understandable. When specifying the system requirements, it should be taken into account that illiteracy rates are globally the highest in the underdeveloped parts of Africa, which is the same area in which the artifact is projected to operate.

A requirement that is applicable to all users and non-users of the artifact, is that the artifact’s greenhouse gas emissions should be as low as possible. This requirement becomes more and more important as the effects of climate change begin to show. It is especially important for the farmers in drought-prone areas as they live in areas which are expected to be heavily affected by climate change.

System requirements

Assesment of possible design choices

Water collection

There are multiple possible way to gather water, some of these are better suited for the situation than others. Below the possible solutions are listed, the solutions are graded based on:

• Feasibility
  
• costs
  
• Revenue
  
• Space needed
  
• weather dependency

Below are the different criteria explained.

Feasibility
When looking at the feasibility of a solution we look at the practical and technical feasibility, in this technology invented yet and how do you transport all the needed material with bad infrastructure are questions asked when looking at the feasibility.

Cost
The costs can be seperated into two mayor categories short term costs and long term cost. Short time costs are the cost needed to buy the required materials to build the artifact, long term costs are the fixed costs that comes with the artifact.

Revenue
Revenue is measured by how much water the artifact will collect on average.

Space needed
Small based farmers often don’t have a lot of free space which is not used for farming or living. Our artifact therefore has to be space effective.

weather dependency
As the weather is not something that can be regulated some artifacts might not work with negative weather.

Criteria assessment

Dig a Well

The first proposed solution is the simple solution of digging a well. If you have a well present at your farm, you are close to water everytime.

• Feasibility
  

As has been shown before LINK a well can be dug in Africa and is a good way to get some water, Wells are however highly greographicly dependent, Wells only work when there is a reservoir in the ground. These reservoir however are very rare. Meaning that a well cannot be build at any place.

• costs
  

The cost of digging a well are only short term, the only costs is building the well, besides the material for the well the digging of the hole has to be financed as well. digging a hole will have a cost ranging from 2.000 to 500.000 usd depending on the depth of the well. [57]

• Revenue
  

The revenue of the well in depth dependent. With an average bucket of 10 liter and after installing a system which gets the water up at a speed of 1 m/s. The well will get at max capacity a yield of 36.000 liters / meter per hour. However one must be careful not to dry the well.

• Space needed
  

The well itself doesn’t take up a lot of space, only problem is that there has to be a suited space to dig the well. Meaning there has to be a reservoir present and the location has to be somewhat level.

• Weather dependency
  

The well is only weather dependent if there are long droughts which will make the well empty.

• Conclusion
  

If we look at the above mentioned advantages and disadvantages we clearly see that the main advantages are that it is obvious, it has been done before and it will get enough revenue too water the farm. However the main disadvantage is that a well cannot be build at any place, it has to be build above a reservoir. Also a well cannot be improved a lot. Given these two disadvantages we think that a well is not the best solution.

Automated pump

Instead of building a well we can also dig an automated pump, the pump will be smaller than a well, but more efficient.

• Feasibility
  

As stated by the well, an automated pump will be geographically dependent. Another disadvantage with regards to the will is that a automated well needs more sophisticated equipments, which means that getting the right machines there might be a problem.

• Cost
  

The average cost of building a automated well will lie around 8000 usd. Which is way less than the average well costs. [58]

• Revenue
  

The average revenue is about 5 gallons per minute for 2 hours. This to make sure the well doesn’t dry [59]

• Space Needed
  

A pump doesn’t need any space, but the position the pump will be places must depend on the terrain.

• Weather Dependency
  

The pump is only weather dependent during long droughts.

• Conclusion
  

The main advantages of a automated pump are the relative cheap building and the relative big revenue. Big disadvantages however are that there is not a lot of technical advancement possible and that a automated pump cannot be build anywhere. Since our group of users is every small based farmer. We think this is not the best solution.

Rooftop water harvesting systems

The general idea of a rooftop water harvesting system is that all the water that falls on your rooftop will be collected and transported via pipes to water tanks. This method has reseanably low effort since most of the things needed for this system are already present.

• Feasability
  

This method is reasonably feasable, the farmers already have houses and there are no technical solutions needed. The only problem would be the material of the houses (the house has to have a good roof).

• Costs
  

The only things that would cost money with this idea is a huge tank, pipes to transport the water to the tank and some sort of material to improve the roof if needed. The overal cost would therefore highly depend on the amount of water that can fit into the tank. Prices can vary from 100 euro (100 liter) till 360 euro (1000 liter).

• Revenue
  

The revenue of the system is primarily based on the surface of the roof. Therefore we don’t expect this solution to have the revenue to support an entire farm, given the small amount of rainfall.

• Space needed
  

For this artifact is only space needed for the watering tank.

• Weather dependency
  

This artifact is highly weather dependent, if the weather is bad, this artifact will have a lower revenue than expected, when the weather is good the revenue will increase.

• Conclusion
  

The main advantages of this system is that it relatively low cost. Since the only extra things needed are some pipes and a tank. Another benefit is that it is easy to setup. However the main advantage is that the revenue most likely will not be enough for the entire farm. Therefore we don't think this is the best solution.

Government-built water infrastructure

Another possibility would be for the government of the country to make a countrywide water network. This would not solve the water problem for one single farmer, but for farmers across the country.

• Feasibility
  

Although this solution seems by far like the best one. The project is not really feasible. Some farms are a long distance separated from each other. Besides that, the land is not always suited to lay pipelines and most countries lack the technical support and knowledge to pull of such a big project.

• Costs
  

the costs of this project would quickly go up into the billions. Although precise calculations have never been made, many expect the costs to far outweigh the benefits that will be gained from such a system.

• Revenue
  

The revenue of this project would be better than all the other artifacts. This project would solve all the watering problems as water can get easily transported from areas where there is water.

• Space needed
  

The space needed at the farm is close to none, since all the pipes would most likely be beneath the ground. If this is not the case than the pipes will take up quite a lot of space.

• Weather Dependent
  

This artifact is no weather dependent as water can get shipped from other places.

• Conclusion
  

The main advantage of this system is it's revenue, when such a system is in place there will most likely never be any water problems anymore. Huge disadvantage however is the huge costs that come with this project. Therefore we don't think this is the solution.

Water gatering robots

As the normal way for farmers at this moment is to walk to a well and get water, we could automate this process by making a robot who gets water out of a well on its own.

• Feasibility
  

Technically speaking there are already robots who can travel a certain route. There is also enough ways for the robot to get the certain energy and the robot wouldn't be big. So getting the robot there also wouldn't be a big problem.

• costs
  

The cost of this would only be the installation the robot, after that the costs would be the power the robot uses, but this can be helped if the robot would get a solar power supply.

• Revenue
  

The revenue of this artifact would be the same as it is now for a human to get water. It would therefore not increase the revenue, it would however relieve the farmer of this hazardous job.

• Space needed
  

The only space needed for this artifact is space to store the robot.

• Weather dependency
  

This artifact doesn't have a lot of weather dependency. However when wells are dried this artifact might need reprogramming.

• Conclusion
  

The main advantage of a water gathering robot is that it does the work cheap and good. However we plan to increase the amount of water of the farmer, not the way he gets his water, therefore this artifact is not suited for our idea.

Collection canvas

• Feasibility
  

A construction to keep the sheet in place is required. This is easily achieved by connecting the sheet to wooden poles, where the height of these poles is variable

• Cost
  

A 10m x 12m sheet costs between 60 and 80 euros, depending on the thickness of the sheet chosen. If the sheet is placed over the crops as described in the ‘space needed’ section, a mechanism should be created to roll the sheet in and out. When decided that the farmer can make use of a semi-automatic, manual mechanism, costs are expected to remain low when using a pulley system. An automated sheet, however, can become rather expensive. As an example, fully automatic pool covers for small pools cost around 2500USD. A benefit of the fully automatic method is the option to add a rain sensor for opening and closing based on weather conditions.

• Revenue
  

The revenue of this method depends heavily on precipitation. If the construction of the sheet is sufficiently stable, it would be able to collect most if not all rainfall in the area covered by the sheet. No water should remain on the sheet, as this water would evaporate and go to waste.

• Space needed
  

2 different methods of placing the sheet are possible. The first method is placing the sheet on unused areas, allowing for the sheet to be close to the ground. The second, more efficient method would be to place the sail over the crops, and create a mechanism that can roll out the sheet when it rains and roll it back in as it clears up.

• Weather dependency
  

The sheet collects water only when it precipitates, which varies heavily across Africa
> Northern Africa remains dry for most of the year, except for the coastal areas which see the most rain between November and March.
Southern Africa has half a year of drought, from April to October, and half a year of rain, November to March. In particular, Botswana seems to have these clear distinctions.

• Conclusion
  

Although this solution seems to have it's disadvantages at the start, it looks like this is the best solution for your everyday smallbased farmer in botswana

Water storage: stagnant VS. moving

It has been shown that mismanagement of irrigation resulting in the formation of stagnant pools lead to the transmission of water-related diseases such as schistosomiasis, malaria and typhoid fever [36]. Moreover, under the condition of stagnant water, cyanotoxins can reach high concentrations in water and might represent health and ecological risks [37]. Furthermore, stagnant water has a decreased oxygen content which is disadvantageous for crop growth. It has been found that aeration of crops can increase the yield by up to 96% [38] [39] [40]

Irrigation

(Subsurface) drip irrigation can reliably provide an increased yield and water use efficiency. Some difficulties in adopting this technology have been expressed by the few farmers who adopted it. The main recommendations for being able to have a successful adoption of this technology is. (1) Redesign drip system to help prevent common problems (2) Invest in clear education for adopter, focusing on maintenance and repairs. (3) Encourage the adoption of complementary technologies to support the function of drip systems, such as water storage, purification and delivery systems[41].

Soil measurement devices

There are many different techniques to measure the soil moisture levels. To make a better choice which one to pick, the different techniques will be compared to each other with regard to the user requirements. This is listed in the table below.

As can be seen in the table, devices may differ quite dramatically per category. To ultimately decide which device will be put in our system, these devices will be compared to our system and user requirements. The first requirement which will be looked at, is that the system should be cost effective. Some of these devices with a high capital cost (>$1000) or high annual cost ($>100) will therefore not be taken into consideration. Furthermore, the measurement device has to be able to interface to a computer, since this is necessary to make an automated system. Additionally, the measurement device should require as little maintenance as possible, since maintenance of the sensor may be difficult for the farmers. Since most of the farmland in Botswana consists of a lighter sandy soil, measurement devices that only work on medium/heavy soil are also unwanted. This list of requirements only leaves three measurement devices from the table, namely the cut-off sensor, the Gro-point and the Campbell 615.

To assess which one of these sensors would be best for our system, these sensors will be compared.

Cut-off sensor: “The cut-off sensor is a rectangular plastic card 20 x 10 cm that is covered in geotextile. Two parallel copper rods are glued to the face of the card and are connected by cables to an electronic controller. The controller is fitted in the power line to the solenoid valve. When the wetting front arrives at the cut-off sensor, the geotextile becomes wet and the electrical resistance between the two rods decreases. This change is detected by the electronics, and the power to the valve is turned off. As the soil dries the resistance increases and the sensor is reset [56].” The soil sensing volume of this sensor will thus be around the size of the sensor itself [34]. Furthermore, no calibration is necessary for this type of sensor.

Campbell 615: “The campbell 615 consists of a 30-cm wave guide with the measurement electronics built into the probe head. the signal return from the guides causes a circuit (a bistable multivibrator) to change states between two discrete values. The output of the sensor is a frequency that reflects the number of state changes per second (or Hz). A wetter soil will cause a longer signal-return time, and will cause the 615 circuit to vibrate at a lower frequency. The wave guides can be buried for in situ readings or used as a portable probe [56].”

Furthermore, “calibration relates the output signal frequency to the volumetric water content. A calibration equation has been developed for a loamy fine sand. It has an accuracy of ± 2%. The product literature states that the same equation has been used with a range of mineral soils with an accuracy of ± 2.5%. The 615 has the disadvantage of being affected by salinity in soils of salinity > 2 dS/m. Custom re-calibration is required to optimise accuracy[56].”

This type of sensor has a soil sensing volume radius around the sensor of about 1.2 inch [34].

Gro-Point: “The Gro-Point uses the time-delay transmission concept to measure the soil dielectric. it measures a larger soil volume (4 - 5 ft3 ). and is designed for greater accuracy in both high clay and high sand soils. The Gro-Point is buried at the required position in the root zone. Furthermore, no calibration is necessary for this type of sensor [56].” [34]

From this information it seems that the Gro-point will be the best choice for our system. It may be more expensive then the cut-off sensor but makes up for it since it has a large measurement volume, which means less of these sensors will have to be placed. It also has the advantage that it is not a discrete sensor. The Gro-Point can give a precise value for the amount of water in the soil and not just say if there is too much or too little.

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Scientific papers

The summaries of the scientific papers which have been read can be found here