Protected farming is associated with uniform, healthy and disease-free plant material. This planting material presents better hardening and enhanced germination percentages. That is because disease-free, clean and inert substrate is used all through the world to produce greenhouse cucumbers and tomatoes. You can be completely assured of genetically better transplants that are free of diseases. Fact to know: the frame of the structure used in protected cultivation safeguards the different crops from several damaging factors.
These include chemical and physical deterioration, climate moisture, soil, snow, rain and wind. There is nothing called off season in protected cultivation. Thus, that means that this farming method is a lot more rewarding economically. You can grow veggies and fruits even in the off season. Net-houses, walk-in tunnels and shade have made possible year-round production of veggies. Fact to know: Are you worried that about not getting tomatoes, summer squash or cucumbers in the winters?
It is time to stop worrying and start filling your big shoppers. That is because, everything from tomatoes to okras are now available with protected cultivation.
Techniques of protected cultivation increase the crop yield. Do you know how? Higher density of plants by close planting increases yields of veggies and fruits tremendously. Like for instance, if you use low plastic tunnels early nurseries of flowering annuals and veggies can be increased.
With protected cultivation you can always expect high value horticultural produce of cherries, capsicum and muskmelons.
If you are wondering how then the credit goes to the net houses. These houses make help in reducing the adverse effects of rains, and scorching sun in herbs, ornamentals and veggies. Fact to know: If you are a fan of colored capsicums then there is nothing like protective cultivation for growing the cool season crop. In just months you can get tons of colored bell peppers.
The insect-free net houses ensure virus-free cultivation. Protected cultivation encompasses a sustainable approach. The poly house helps in changing the micro climate hence certain insects cannot enter. Fact to know: Insects that get attracted because of UV light cannot enter because of the opaque UV covering. Consequently, there is minimum use of pesticides and insecticides.
With perfect plant environment control and appropriate structures like glasshouse, you can expect year-round cultivation. Fact to know: with protected cultivation you can have percent productivity. And, in some cases, even more. Protected cultivation prevents the growth of weeds as you control the temperature conditions by using several structures. These can be low tunnels, shade net house, polyhouse and a greenhouse.
With no weed growth there is higher uptake of micro-nutrients by the active zone of the roots. This process conserves soil moisture and thereby reduces the requirement of irrigation water. Fact to know: protected cultivation acts a smart barrier to soil pathogens thus you can never find any weed growth in your crops. As you may know, plants are sessile. Under arid climates, cultivation of tomato in greenhouses covered by polyethylene films would be limited by high temperature problems for most of the year Fig.
In areas with arid climates, the use of insect proof nets, although they reduce the impact of covers on temperature, would induce high temperature issues during periods ranging from 4 months in Keetmanshop Fig.
The favorable period for tomato cultivation under net covers would be shorter under an equatorial climate, ranging from 1 month in Libreville Fig. It is worth noting that the use of covers would allow off season tomato production in Gaborne Fig. This first effort to determine the suitability of tomato greenhouse cultivation with climatic conditions in SSA provided evidence that temperature is a serious issue in closed shelters with no cooling system, i.
Even if the use of insect proof nets mitigates the detrimental impacts of covers on temperature and air moisture, greenhouse cultivation is restricted to cooler months and would offer during this period the opportunity to produce out season vegetables.
It thus appears that, because of the climatic conditions, low-tech greenhouses are not suitable for use all year round in most of areas in SSA and this restriction of the cultivation period should be taken into considered in cost benefit analyses. Many smallholders consider the use of chemical inputs as a strategy to ensure their production and their livelihood. However, the use of pesticides can no longer be considered as a solution to control insect pests because of the development of resistance Martin et al.
Research has been underway for more than 10 years on the use of insect proof nets over vegetable crops as a generic protection to control insect pests while ensuring sufficient natural ventilation.
Insect proof nets are believed to be a suitable solution to reduce the use of insecticides and to protect vegetable crops from the emergence of new devastating insect pests for which chemical treatments are not effective Martin et al. Several studies on cabbage Brassica oleracea L. Gogo et al. However, contradictory studies on hot pepper Capsicum chinense Jacq. Several studies have been dedicated to optimizing mesh size to ensure sufficient ventilation to limit heat load and efficient physical protection against insect pests Saidi et al.
This task is not easy since the optimum size varies with the crop, the pressure from insect pests, and climatic conditions. The capacity of nets to exclude insect pests has been widely studied in net screens used for greenhouse ventilation Bell and Baker ; Bethke et al.
Results showed that there is no clear relationship between mesh size and the pest exclusion efficiency Bethke and Pain Berlinger et al. Similarly contrasted results of field trials have been reported on the efficiency of nets to exclude insect pests.
It is difficult to compare insect proof nets since several mesh features including size, geometry and blending, i. Depending on the authors, mesh size is given either as the number of holes per inch or as the size of the hole, but this does not apply if the mesh is not square or is woven.
In addition, the difference in nets efficiency could also be due to slipping of unevenly woven yarn. With certain exceptions, large pests Lepidoptera, Diptera are well controlled whereas small pests Hemiptera, Thysanoptera, Mite are not. In most field experiments, fruit worms were well controlled by a large mesh regardless of the crop and the mesh size tested Martin et al. Some bigger insect pests such as Spodoptera littoralis and Tuta absoluta can also circumvent physical protection by laying their eggs on the nets and their very small prenatal larvae then pass through the mesh Biondi et al.
Our overview of the literature indicates that nets, whatever their mesh size, cannot completely exclude small insects pests such as aphids, thrips, white flies and mites, but they can reduce and delay infestation of the crop Gogo et al. Experiments on tomato in Kenya showed that nets with mesh size of 0.
Contradictory results were obtained on cabbage in Benin since similar nets promoted the development of aphids and the finest mesh size did not improve protection against insect pests Simon et al. Similarly, modeling approaches used by Holt et al. It is worth noting that the physical protection provided by insect proof nets is not specific. Use of covers on crops is therefore a suitable alternative to face changes in pest pressure related to the emergence of new insect pests.
However the side effect of the lack of specificity of net exclusion concerns natural enemies. It is believed that nets can favor the development of some insect pests because of the exclusion of natural enemies and more favorable climatic conditions, including an increase in air moisture and shade. Results on cabbage in Benin suggested that removing nets during the day would favor natural predation and avoid bursts in populations of insect pests Licciardi et al.
Actually, the use of biological control is an effective and environmentally friendly alternative to complete protection against insect pests provided by covers. Biological pest management is facilitated in closed shelters since it reduces the dispersion of parasitoids and predators and increases their development because of favorable climatic conditions Yang et al.
However biological control in SSA is limited by the affordability of auxiliary insects that are adapted to tropical climatic conditions. There is thus a need to identify indigenous natural enemies in SSA to extend biological control. In parallel to biological control, in the case of entomophilous crops, such as tomato, cantaloupe or eggplant, excluding pollinators could also be an issue.
A study on cantaloupe Cucumis melo L. These authors reported that the best results were obtained by maintaining covers throughout crop development and by introducing pollinators inside the shelters.
The use of parthenocarpic varieties or mechanical vibrations of plants are alternative ways to avoid the problem of pollination in closed shelters.
Several studies have been conducted to improve the capacity of nets to exclude insect pests by increasing their repellent effects including irritancy, odor masking, and visual masking.
The use of treated nets was found to be an effective alternative to increase irritancy of nets and to control aphids on cabbage Martin et al. Martin et al. However, it is worth noting that treated nets may also have a negative impact on auxiliary populations Martin et al.
To avoid the impacts of insecticides on the environment and on human heath, use of treated nets with repellent plant extracts may be a viable alternative Deletre et al. Research has also been conducted to increase the visual masking capacity of covers by changing their color. Lower levels of infestation by aphids and whiteflies on tomato and bell pepper Capsicum annuum L. These differences in infestation were explained by changes in the spectrum of light transmitted by the nets.
These results are in line with the results of a study by Kumar and Poehling who reported lower rates of infestation of tomato crops by sucking insects in a greenhouse covered with UV blocking covers. However, the impact of optical features of covering materials should be considered with caution since changes in light composition are also known to affect plant physiology, including fruit and vegetable quality Singh et al. It was recently reported that a combination of physical protection with a push—pull strategy using aromatic basil Ocimum basilicum L.
This study suggested that the effect of aromatic plants on whiteflies may be enhanced by nets because of higher concentration of volatile compounds. In conclusion, there is a consensus that PCT is not a silver bullet against insect pests and they have to be included in Integrated Pest Management IPM combining several control techniques such as i biological control, ii chemical treatments of the net, or iii the use of companion plants.
The use of covers does not only require changes in cultural practices to control insects, but modifies the entire cropping system since it also affects the functioning of crops and the soil Table 1. The modification of climatic conditions by covers requires adaptation of the cultivars used, since they perform differently in these specific environments Cheema et al.
Use of varieties with high resistance to cryptogrammic diseases is particularly recommended in the case of cultivation in closed shelters because of the increase in air moisture. The physical support provided by high shelters encourages producers to use trellising systems to cultivate indeterminate or climbing varieties since it facilitates crop handling, increases the yield and extends the production period.
In the case of tomato Lycopersicon esculentum Mill. To control the soil water balance, fertility, and sanitary quality, PCTs also require changes in soil management practices. Irrigation management has to be adapted to PCTs since they decrease crop evapotranspiration and rain feed. The sanitary quality of soil and its fertility are also affected by vegetable cultivation in non-moveable shelters as a result of unbalanced crop rotations limited to high value vegetable species such as tomato, sweet pepper Capsicum annuum L.
Similarly, it is more challenging to integrate agro-ecological practices aimed at increasing soil sanitary quality and fertility, such as intercropping and fallow, in protected cultivation cropping systems because of profitability issues. To overcome soil-borne disease and fertility issues, large producers often switch to soilless cultivation, which increases investments and production costs. Grafting is an alternative environmentally friendly and effective way to improve water and nutriment uptakes and reduce the impacts of soil borne diseases and pathogens when genetic resistances are available Lee and Oda ; Schwarz et al.
This requires identifying a suitable combination of scion and rootstock with higher yield and resistances to abiotic and biotic stress while preserving the quality requirements of the fruit or vegetable. Although grafting is widely used in Asia, it is not widespread in Africa Keatinge et al. To introduce grafting systems in Africa, a vibrant and effective seedling system is needed, which is currently only the case in Ethiopia. In conclusion, PCT considerably modifies the management of cropping systems in terms of i crop rotations and ii cultural practices, i.
Side impacts of PCT, i. As a result, PCT seems to be an ongoing process to better control plant environment causing new agronomic and economic constraints. This raises the question of the profitability and the suitability for smallholders of such practices which disrupt open field cultivation and require higher investment. Protected cultivation tends to artificialize cropping systems to create optimum conditions for plant development, and improve yields and the quality of the products.
Better control of the crop environment requires investments in more sophisticated equipment that increase the fixed cost of production. The profitability of protected cultivation relies on the capacity to obtain sufficiently higher yields and sales prices to offset the increase in fixed costs. Higher sales prices can be obtained with PCT by exploiting niche markets that are not accessible with open field production.
Consequently, the economic interest of PCT depends on its ability to better respond to market requirements than open field production. Since PCT requires higher investments and specific skills, this raises the questions of the accessibility of these techniques to small-scale producers, and of the technical support and policies required to promote these technologies. First we discuss the capacity of PTC to improve crop productions, then we focus on the profitability of these techniques and finally we identify limitations to the adoption of PCT by smallholders.
Concerning yield, the advantages of protected cultivation vary with the crop and with local agronomic constraints. Saidi et al. Kiptoo et al. In Benin, the use of insect-proof nets on cabbage crops that were removed during the day was reported to increase yields 3.
It is worth noting that the effects of nets vary greatly with the climatic conditions and pest pressure since the last mentioned authors revealed that the use of permanent insect proofs nets during the hot season could reduce the yield of the cabbage crop because of excessive temperatures and poor insect pest control Simon et al.
Similar results were obtained with row covers on tomato since yields increased in Kenya Gogo et al. Performances of PCT vary also considerably depending on the level of technology used to control the crop environment. In addition to yield, PCTs have an impact on the quality of crop products. For several crops, including green beans Gogo et al. The impact of PCT on vegetable quality is linked to the covering materials used. Studies on tomato Tinyane et al.
Studies on lettuce provide evidence that the impact of covers on vegetable quality depended on the cultivar Ntsoane et al. Another component of quality that can be improved with PCT is a reduction in pesticide residues in vegetables, as the result of reduced use of insecticides.
In addition to increasing the yield and the quality of the products, one of the main advantages of PTC is being able to exploit opportunities for off-season vegetable production.
A study of markets in seven African countries revealed that fruits and vegetables were the commodities with the highest seasonality Gilbert et al. Market trends are explained by the seasonality of vegetable crops which are greatly dependent on climate conditions and shifts in crop pest pressure. Moreover, the marked fluctuations in the sales price of vegetables are strengthened by their perishability and by the lack of appropriate infrastructures for processing and postharvest preservation.
A recent meta-analysis showed that average postharvest losses in SSA ranged between Mitigation of the impacts of climate hazards and crops pests by PCT enables the production of off-season vegetables and the fulfillment of market requirements that cannot be met with open field cultivation.
Studies in Ghana Attoh et al. PCT also makes it possible to produce in more challenging agronomic contexts such as urban areas thanks to more efficient use of land and resources. The capacity of PCT to meet urban agricultural challenges is worth noting since this form of farming is expected to play a major role in the supply of food and the creation of jobs in cities in developing countries De Bon et al.
In conclusion, PCT has several agronomic advantages that enable the production of high quality vegetables and off-season products, which can be profitable if producers succeed in exploiting market opportunities.
The economic performances of PCT rely on the balance between costs and benefits and the profit that can be made with PCT compared to open field cultivation. The first difficulty encountered in trying to establish the profitability of PCT is the marked difference in increases in yield obtained in PCT systems compared to open field cultivation. A cost-benefit analysis was conducted in Kenya to compare the profitability of tomato Lycopersicon esculentum Mill.
As a result, the authors reported that net profits per square meter were 13 times higher for tomato cultivation in greenhouse than in the open field even though fixed costs, i.
It is worth noting that even bigger differences in net profits of tomato cultivation in greenhouse are reported, i. These results are evidence that the higher profits that can be obtained with greenhouse cultivation are related to more risky speculation because of higher fixed costs and such variable yields.
Another cost-benefit analysis in Benin showed that the use of basic low tunnels for cabbage Brassica oleracea L. One important finding of this study was that insect nets ensured both more stable costs and more stable yields than non-netted crops in the open field, generating more stable cash flows for producers. The same study revealed that for a 3-year period, i.
A study conducted in the northern plains in India revealed that, contrary to in greenhouses, cultivation of cucurbits under plastic row covers and in walk in tunnels is only profitable off season i.
In contrast to the previously mentioned studies, several authors did not recommend the use of PCT because of insufficient return on investment, for example for the cultivation of okra Abelmoschus esculentus using row covers in Alabama Gordon et al.
These contrasted results suggest that the profitability of PCT depends on the answer to the following question, how does PCT allow producers to better respond to market requirements and to get higher prices for their products? PCT can be a good way to produce high quality vegetables that respect the quality standards of export markets and stringent limits on maximum residue levels of pesticides in foodstuffs. In a review article Maertens et al.
These authors underlined that smallholder access to exports market depends on their production capacity and on local competition with large commercial farms. For local and regional markets, the opportunity represented by PCT to reduce the use of pesticides remains under-valued.
In most cases, there is no difference in farm gate prices between insecticide free and treated crops because of the lack of labeling and regulations Gogo et al. Although efforts have been underway for decades to transfer and develop low tech PCT adapted to SSA climatic conditions and that smallholders can afford, adoption of these techniques by producers remain limited.
The development of PCT in Tanzania is an interesting example that reveals the potential impediments to upscaling these technologies to smallholders. Since the beginning of the s, Tanzania has seen the rapid appearance of greenhouses owned by foreign investors for flower cultivation and seed production, following the already more-advanced and well-established Kenyan greenhouse cultivation sector.
This drove the development of the horticultural sector through the development of private associations and the growth of agribusinesses. These technologies have been the subject of growing interest by local producers, especially after several major pest outbreaks and under the impulse of greenhouses companies.
Unfortunately, producers faced an wide range of difficulties, from the unsuitability of the greenhouse design for local climatic conditions, the lack of technical support, to the absence of remunerative markets. These issues led some of them to simply abandon protected cultivation and return to open-field farming. There are many examples in Africa and elsewhere of failed projects in which technologies were transferred to unsuitable areas Deininger and Byerlee Low-tech PCTs are particularly concerned by this issue since, as underlined in section I.
A, the sustainability of such technologies is restricted to specific climatic conditions, i. Several authors reported that investment capacity is still one of the main limiting factors of protected cultivation, although low-tech PCTs have been designed to be affordable by smallholders, Bhatnagar ; Chatterjee et al.
As is true for other technologies, the upscaling of PCT to smallholders is hindered by the marked heterogeneity of farms in terms of income, production objectives and access to inputs Chikowo et al. The promotion of PCT should preferentially target resource-endowed producers rather than resource-constrained households since resource-endowed producers already have access to priority technologies to increase crop productions including fertilizers, improved cultivars and irrigation system.
Nevertheless, spraying pesticides appears to producers to be less risky since it is a well-known practice and, in contrast to nets, it is a curative method that can be readily used and adjusted at any stage of crop development. Skills and knowledge and are also main limits to the adoption of PCT, which requires considerable changes in cropping systems see section I. This is consistent with the results of studies conducted in Kenya revealing that i greenhouse producers had a higher education level than open field producers Wachira et al.
The success of the vegetable basket plan launched at the end of the s in China is an inspiring example of the success of a policy to promote protected cultivation technologies by providing technical support, access to capital, and to organized marketing. The Chinese plan aimed to improve the supply of food to cities notably by subsidizing the construction of greenhouses and developing networks of demonstration farms to promote new modes of production Gale Since imported greenhouses were too large and expensive for smallholder producers, efforts were made to propose low tech and effective greenhouses Gu As a result, the area dedicated to greenhouses cultivation in China increased from 0.
From the late s to , Chinese exports of vegetables have more than tripled Gale et al. Little is known about the environmental impacts of protected horticulture in SSA, and especially about the low-cost protected cultivation techniques for smallholders analyzed in this paper. Like open-field vegetable cropping systems, protected vegetable cropping systems use fertilizers, pesticides, energy and water. Production, transport, use and end-of-life of these agricultural inputs have impacts on the environment through the consumption of abiotic resources and the release of chemical compounds into the soil, air and water.
The introduction of supplementary inputs in vegetable cropping systems, including plastics for covers, iron or wood for the frames, and energy based equipment that consumes energy, raise concerns in relation to their production and transport but also to their low biodegradability and their potential impacts on terrestrial and marine ecosystems Jambeck et al.
A recent study by Steinmetz et al. They also discussed the difficulty involved in recycling plastic mulches used for only a period of a few months because of the cost of collecting and sorting and the technical problems involved in treating plastic contaminated with soil and agrochemicals. These reviews underlined the need for an overview of all the environmental impacts associated with cropping systems, from cradle-to-grave.
An evaluation and comparison of the environmental impacts of protected and open field cropping systems with a tool such as life cycle assessment is greatly needed. Life cycle assessment is an internationally standardized methodology ISO and ISO that accounts for the entire life cycle of a product, from resource extraction for inputs to waste disposal, in the assessment of the environmental impacts of production methods and systems.
Yet, using such a method in the SSA context is a huge challenge because of the variability of existing systems and the scarcity of data. Results revealed potential impacts for the environment and for human health from 4 to 23 fold—expressed per kilogram of fresh tomato—higher than the impacts of tomatoes grown in European cropping systems even in heated greenhouses.
These very high impacts were explained by the low and variable yields of crops, the low performance of irrigation systems in terms of fuel consumption, the high emissions of nutrients and the excessive use of insecticides. In this context, can the use of plastic covers help farmers reduce their impacts per kg of product? It is argued that the higher yields obtained with protected cultivation as well as the reduced use of pesticides and the higher water efficiency can mitigate the environmental impacts of these technologies based on the use of plastic Van Lenteren Life cycle assessment has most often been used for protected and open-field horticulture in European and Mediterranean countries.
As an illustration, Table 2 presents the global warming potential and several input rates per kg of tomato obtained from some of these studies on tomato production. Marked differences in environmental impacts were found depending on the levels of technology used for tomato cultivation, the production period, and the location.
Tomatoes produced all year round in soilless heated greenhouses had the highest impacts. For instance, the global warming potential of these systems listed in Table 2 was on average more than ten times higher than the one of open field cultivation. Not surprisingly, the authors of these studies concluded that the use of artificial methods to produce out-of-season vegetables in winter in temperate regions was not to be recommended from an environmental perspective.
The studies reviewed in Table 2 indicate that the impact of tomatoes produced in unheated greenhouses is comparable with that of tomatoes grown in the open field. The studies agree that for tomato cultivation, water use efficiency is higher in the greenhouse than in the open field. This is consistent with a study on lettuce showing that hydroponic techniques reduce water use more than ten times in comparison with open field systems Barbosa et al.
In the Netherlands, where tomato yield is more than five times higher than in Almeria, the quantity of active pesticide ingredients used per kilogram of tomato produced was estimated to be about 20 times lower Peet and Welles The construction of low tech polyethylene greenhouse with a wooden framework was reported to have a lower environmental impact than glasshouses with zinc coated steel, with respect to global warming, human toxicity and terrestrial ecotoxicity indicators Russo and Scarascia Mugnozza This is mostly explained by the fact that emissions of zinc due to the corrosion of the galvanized steel frame of the greenhouse contaminates water and ultimately affect human health.
The importance of this contribution to the human health impact was also demonstrated in a case study of tomato in Rwanda produced in the open field and greenhouses Basset-Mens The lifespan of the greenhouse materials depends on intrinsic factors, including its polymers, on the additives used, and on its thickness, and on extrinsic factors including climate conditions and use of agrochemicals. Management of wastes also has a major influence on the environmental burden of protected cultivation methods.
The management of plastic wastes differed considerably from that in the LCA of tomato cultivation reviewed in Table 2 , since they were considered to be totally re-used or recycled Payen et al. These differences between authors reflect the variations in waste management between locations. The presence of impurities, including soil and pesticides, cause technical problems and increases the cost of recycling of agricultural plastic wastes Briassoulis et al. An alternative to recycling is energy recovery from plastic waste that takes advantage of the high calorific value of these materials and could be used as a replacement for regular fuel.
It is estimated that the calorific value of polyethylene, which is used in the vast majority of agricultural plastic wastes, is similar to that of diesel fuel and higher than that of natural gas Scarascia-Mugnozza et al. In LCA, particular attention should be paid to waste management processes especially to estimate terrestrial ecotoxicity.
Perrin et al. The results of this review converge with the above conclusions identifying heated greenhouses as the system with the most impact. For this type of cropping system, the sources of energy used to heat the greenhouse represent the key lever for reducing the impacts.
Overall, the key sources of variations in the LCA results across all cropping system types were the yield, the use of inputs energy, infrastructure, auxiliary equipment, fertilizers, and pesticides but also the assumptions made concerning allocation and substitution procedures. As already mentioned, this study also confirmed that, except for heated greenhouses, the differences between types of cropping system open-field versus unheated greenhouses were generally less than the intra-type differences due to the diversity of cropping practices.
From a methodological point of view, Perrin et al. Field fluxes of phosphorous, pesticides and water and associated impacts: eutrophication, toxicity and water deprivation, although very important for horticultural cropping systems, were often not evaluated in the studies reviewed. The non-evaluation of the impacts of pesticide use was often justified by the lack of consensual, reliable and user-friendly methods.
In brief, existing LCA studies on protected compared to open-field horticulture revealed that although protected horticulture can yield more and better quality produce, the extra costs for the environment due to the materials used for protection manufacturing, transport, recycling and final disposal and possible energy use for heating or cooling can hinder their expected better eco-efficiency mostly if the technology is not properly managed.
The actual impacts per kg of produce will therefore depend on the efficiency of the use of key inputs per kg of produce, which is closely linked to both the production conditions of the producers and the quality of management.
In Rwanda, Basset-Mens reported that the environmental impacts of two low tech greenhouses producing tomatoes were highly contrasted. In contrast to the first greenhouse, the second greenhouse was found to have less impact than open field systems, except for human toxicity impacts.
The marked difference in the performances of the two greenhouses was attributed to poor farmer practices in the first greenhouse leading to a lower yield despite a higher use of pesticide, fertilizer, and the use of fuel for irrigation. A combination of optimum techniques mesh size and shape, repellent, biological control , appropriate regions for reducing insect pressure and improving yield, and also training producers in the optimal use of these techniques, should improve the eco-efficiency of vegetable production in SSA.
However, these potential benefits will need to be validated through complete and reliable LCA studies using real farm data. From the point of view of environmental evaluation, many challenges face the proper evaluation of these systems in SSA.
In the context of data scarcity, they include optimal accounting for the diversity of practices, reliable estimation of field fluxes and related impacts due to organic fertilizers, pesticide applications and water use for irrigation and a proper evaluation of the effect of plastic on soil fertility. The success of protected cultivation techniques PCT worldwide have encouraged research and projects to transfer these technologies to sub Saharan Africa to overcome agronomic constraints and ensure vegetable production all year round.
Efforts have been made to develop low-tech PCT affordable to smallholders and to adapt them to climatic conditions. Contrasted agronomic performances have been reported for low-tech PCT because of poor control of insect pests and climatic conditions.
The side effects of covers on climate as well as the lack of equipment to control temperature and air moisture, limit the use of closed shelter to a restricted period of the year. Studies revealed that PCT is not a silver bullet to control insect pests and must be combined with other practices, including biological control, push-pull methods, and chemical treatments.
In this review, we underlined that PCT requires considerable changes in cropping system management since cultural practices have to be adapted to exploit the opportunities offered by this technologies, i.
The break with existing cropping systems requires providing technical and economic support to small producers for whom investment capacity is a major limitation to the adoption of these technologies. Policies have a major role to play in supporting the development of PCT by organizing the market, providing technical support and enabling access to finance. The higher fixed costs of PCT increase the economic risk and they have to be offset by increased yield or the opportunity to exploit niche productions to profit from higher sales prices.
The identification of niche productions is a main challenge for PCT, particularly in local markets since trends in off-season production opportunities are difficult to predict and because quality is poorly reattributed. Ultimately, PCTs are promising technologies to improve the supply of vegetables in SSA all year round, but their upscaling requires making sure the level of technology used makes it possible to overcome agronomic constraints and suits the socio-economic context of producers.
To this end, further research is needed i to understand impacts of low-PCT on climatic conditions and on insect pest populations in order to improve their design and combine them with other methods of pest control and ii to estimate the profitability of these techniques for smallholders so as to design suitable and affordable cropping systems. Further research is also required to determine whether the increased use of low biodegradable materials such as plastics in PCT does not imply agronomic benefits are obtained at the expense of the environment.
If studies conducted in northern countries suggest that the impact of low tech PCTs on the environment is comparable to that of open field cultivation if properly managed, whether these results can be extrapolated to SSA is still not known, given the diversity of cultural practices and the management of wastes.
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