Soilless culture technology to transform vegetable farming, reduce land pressure and degradation in drylands

Abstract Use of farmlands for food production is under pressure and providing food for a growing population is a global concern due to alternative land use and degradation, pest infestations, urbanization and industrialization which led to climate change and encroaches arable land; especially in drylands where water, fertilizer, land, and other farm input resources are scares and needs to be utilized efficiently to enhance crop yields. Soilless culture technology reduces the challenges facing in soil-based farming which could lower yields. Improving food production and access could be possible using soilless culture. However, limited and incomplete information is available to indicate the role of soilless culture in reducing land pressure and degradation in drylands. This review aimed to examine the role of soilless culture as climate change occurs to transform dryland vegetable farming, reduce land pressure and degradation. Data gathered from relevant and recently published peer-reviewed papers and converted into uniform measurement units, paraphrased, and discussed. Studies indicated that soilless culture efficiently uses water, fertilizer, and land by 90, 70 and 75%, respectively, with average yield advantage of 147.3 t. ha−1 over soil-based farming. Soilless culture avoids soil disturbance and reduces land pressure and degradation while promoting crop intensification through year-round production. It supports soil-based farming, minimizes the negative impacts of agrochemicals on the environment, mitigates climate change, and increases productivity in drylands. It is economically feasible, environmentally sound, and socially accepted.


Introduction
World population is increasing and by 2050, it is expected to reach 9.7 billion persons (Anonymous, 2022;Leridon, 2020).Providing food would need to be increased by 50% in 2030, and by 70% in the next 40 years to meet demand (Velazquez-Gonzalez et al., 2022).However, arable land for food production is being encroached by population growth, industry, and urbanization and it will decline by 1/3 of the amount currently available (Anonymous, 2018;Fedoroff, 2015).World dryland farming faces challenges of land degradation, desertification, pest infestation and variable weather that lead to lower crop production (Fedoroff, 2015;Huang et al., 2020).To supplement the degraded land with fertilizer and control devastating pests, a higher dose of chemical fertilizers and pesticides which have a negative effect on soil quality, and climate are frequently in use (Eigenbrod & Gruda, 2015).Expansion of urbanization and industrialization aggravates greenhouse gas emission which led to climate change.Dryland farming requires a climate smart technology that efficiently utilizes land, water, fertilizer, pesticides, and other farm inputs to enhance crop yields (Bello et al., 2019;Matthieu et al., 2018).
In modern farming, many technologies are designed which can work very fast, are highly effective, and optimize scare agricultural input resources (Kalantari et al., 2017;Matthieu et al., 2018).The development of new technology for food production is used to sustain the transformation of agriculture in response to population growth and resource demands (Sambo et al., 2019;Tzortzakis et al., 2020).One emerging and promising technique to overcome current threats facing in soilbased dryland vegetable farming is soilless culture.Soilless culture could be a solution to limited land area suitable for agriculture by optimizing agricultural inputs, reducing the environmental footprint including carbon, nitrogen, and water footprints which have adverse impact on the environment, worsen greenhouse gas emissions and climate change, and protecting against total crop failure to provide better opportunities for a sustainable supply of quality food in dryland areas (Matthieu et al., 2018;Pinstrup-Andersen, 2018).Shrinking and degrading of arable land and rapid increasing food demand might be dealt by soilless culture which enables crop production without soil (Arumugam et al., 2021;Waiba et al., 2020).Most studies on soilless culture have dealt with its applicability (Cicekli & Barlas, 2014), setup (Jayachandran et al., 2022;Pascual et al., 2018), production potential (Tzortzakis et al., 2020), challenges and opportunities (Fussy & Papenbrock, 2022;Kalantari et al., 2018), and affordability (Gibbons, 2020;Zaini et al., 2018).Limited or less organized information is available on its role in reducing land pressure and degradation (Muller et al., 2017), and crop protection from agricultural pests and climate-related risks (Eigenbrod & Gruda, 2015).This work is expected to disseminate organized information and knowledge about the effectiveness of soilless culture in combating arable land shortages and degradation and in reducing the impact of climate change and pest damage.This could support future research and practical application, transforming today's dryland vegetable farming and feeding the world's growing population.Therefore, the objective of this review was to examine the role of soilless culture as climate change occurs to transform dryland vegetable cultivation and reduce land pressure and degradation.

Review methodology
This work organized up-to-date works of various nutrient solution growing mediums collectively as soilless culture and contrasted with soil-based farming regarding land and other input resources use efficacy, productivity, environmental sustainability, and economic feasibility to transform dryland vegetable farming.The data presented and discussed in this paper were collected and synthesized from previously published journal articles, proceedings, and books relevant to this review.In choosing materials, the first priority was given to scientifically peer-reviewed and recently published sources of information.The second priority was given to the paper's relevance to issues related to the role of soilless culture in land, water, fertilizer, and pesticide use efficiency, protecting crops from climate and pest-related risks, improving yields, and its economic feasibility by contrasting it with soil-based farming and giving special focus to transform dryland vegetable farming.Data and information were taken after reading and understanding the research findings.For convenience of discussion, the collected data from literatures were converted into uniform measurement units, synthesized, interpreted, paraphrased, and discussed without losing the main concepts and meanings of the original findings.Finally, all the sources of information used in this review paper are cited and properly referenced.

Overview and concepts of soilless culture
Soilless culture started as early as the 1930s as an artificial means of crop production with mineral nutrient solutions in the absence of soil (Mushtaq, 2021), and has been used on a commercial basis for about 40 years (Benke & Tomkins, 2017).It replaces and complements soil-based farming with hydroponics, hydroponic aeroponics, aquaponics, urban farming, and vertical farming, i.e. high-rise farming in urban environments (Arumugam et al., 2021).In hydroponics, plants' roots are immersed in water, and nutrients are supplemented to the solution.In aeroponics, plants are suspended in a closed, or semi-closed, container and the plant's roots sprayed with nutrient-rich water solution.Aquaponics is the combination of aquaculture with hydroponics, which entails raising fish for consumption in a recirculating system and the soilless production of vegetables (Gibbons, 2020;Olubanjo & Alade, 2018).Dryland regions in Australia, Canada, China, England, France, Holland, India, Israel, Italy, Japan, Jordan, the Netherlands, Pakistan, Saudi Arabia, Singapore, South Korea, the United Arab Emirates, the United Kingdom, and the USA are experimenting with soilless culture technology (Arumugam et al., 2021) for growing vegetables, and their production potential, demand, and market prices are projected to grow in terms of their market share (Fussy & Papenbrock, 2022).

Overview and challenges in dryland agriculture
Dryland is characterized by arid, or semi-arid, regions and tropical, or sub-tropical, climates where rainfall is scarce, highly variable or confined to a short rain fall season (Akinyemi et al., 2021;Huang et al., 2016).About 40% of the world's arable land is located in drylands and 20% of it is degraded (Matthieu et al., 2018).Dryland farming has suffered from climatic variability, especially erratic rainfall, high temperature, high rates of evapotranspiration, saline and poor fertile soil as well as pest infestations.This leads to lower yields.About 32-38% of the world's population lives in dryland areas are the most populated with the highest unemployment, in which the farm land become pressured and degraded (Huang et al., 2016).This high dryland population needs land for crop production so they clear forest lands, and these activities alter climate that causes drought.

Soilless culture reduces land pressure and degradation
The fast population growth, increasing geographic extent of dryland, unwise use of agrochemicals, deforestation to expand arable land, free grazing, and land intensification are responsible for land degradation and declining arable land by 40% (Figure 1).By 2050, the world average arable land per person will reach 0.15 ha (Figure 1).This implies the planet is running short of farmland to feed a growing number of people, and this issue will increase in the future (Benke & Tomkins, 2017;Fedoroff, 2015).In Ethiopia, due to soil-based farming, arable land is declining and will be severely degraded by 27% (Agegnehu & Amede, 2017).
When human population increases, arable land degrades and declines in area.It is expected that people will turn to new technologies like soilless culture to create additional methods of crop production and to conserve land resources (Al-Chalabi, 2015;Goodman & Minner, 2019;Maye, 2019;Muller et al., 2017;Sharma et al., 2018;Vander Esch et al., 2017).With soilless culture, land use efficiency could be increased by 75% in drylands (Figure 2) and utilization of other organic waste materials by 28% (Pomoni et al., 2023).Soilless farmland is equivalent to 10-20 ha of soilbased farmland (Pascual et al., 2018), and may be able to support and complement soil-based farming in future agriculture (Lakhiar et al., 2020).
In the case of soilless culture, soil functions only to support infrastructures needed to install the soilless system and a hectare of land could be multiplied in to hundreds hectares of arable land through vertical farming (Benke & Tomkins, 2017;Pinstrup-Andersen, 2018).It does not use nutrients from the soil, so wide fragile dryland areas including rocks could be productive using soilless culture technology.Since soilless culture minimizes pressure on agricultural lands, it avoids soil disturbance and reducing land degradation while promoting crop intensification through yearround production.Generally, with the rise of soil erosion and loss of arable land, soilless culture is likely to be preferred and be synergetic with urbanization (Martin & Molin, 2019;Pradhan & Deo, 2019).With soilless culture, agriculture is possible everywhere (urban, rural, spaces, rock, and even in water bodies) with special focus to advance dryland farming.

Soilless culture as smart agriculture to optimize water, nutrient, and pesticides
Soil-based crop production in drylands face serious challenges with use of pesticides (fungicides, herbicides, viroids, and bactericides), synthetic fertilizers (urea, DAP, NPS (blended fertilizer), and Zn (zinc)), improved seed, and water resource use efficiency (Barbosa et al., 2015;Majeed, 2018).There is a need to minimize loss and optimize these farm inputs in vegetable production of soilbased agriculture (Pradhan & Deo, 2019), and reduce uncertainties in natural rainfall and soil nutrient status in drylands.
Agriculture uses 70% of the world's available fresh water (Matthieu et al., 2018).Nevertheless due to changing climate, the global amount and quality of water for dryland agriculture is expected to become scarcer by 2025 especially in drylands (Vander Esch et al., 2017).The problem is projected to cause deterioration of the farming sector (Matthieu et al., 2018;Sandi et al., 2020).It is necessary to advance agricultural technologies which optimize water resources.Soilless culture in closed system uses drylands' water efficiently due to lower evapotranspiration, none run-off and percolation (infiltration), lesser saline effect, and less crop-weed competition for growth factors.
With soilless culture, growing time, applied nutrients, arable land, and water can be optimized efficiently as comparing to soil-based farming (Figure 2).In soilless culture, water and nutrient solution from the reservoir is provided to single plant roots in right quantity, time, and site.Up to 5-10% of total water is enough with soilless culture compared to soil-based farming (Abdullah, 2016;Halbert-Howard et al., 2021;Nejatian et al., 2016) (Table 1).This may be due to no soil or no weeds to compete for water with crops and the system has a short growing period that demands less water and no water loss through evapotranspiration as of dehumidification techniques allow evaporated water to be reused instead; the water is recycled and used several times (Shang & Shen, 2018).Since soilless culture uses desalinized water it can reduce the toxic effects of salinity on crop growth and physiology (Pinstrup-Andersen, 2018; Sharma et al., 2018).It has been estimated that with soilless culture an average of 10.71 L of water is enough to cultivate one square meter and on soil-based farming depending on the type of crop, 200-600 L of water is needed to provide 1 kg of dry weight (Al-Chalabi, 2015;Shang & Shen, 2018).Findings from dryland countries indicated that vegetable dry weight reaches up to (40-48 kg•m −3 ) with soilless culture and (7-9 kg•m −3 ) in soil-based farming (Table 1).Soilless culture improves water use efficiency by 90% over soil-based farming (Figure 2).
Mineral nutrient deficiency is a global challenge to human health, especially in the developing world.This is mainly due to inherent poor soil fertility and applied chemical fertilizers lost by leaching and volatilization.The unwise use of chemical fertilizers can lead to leaching of NO 3 − to water bodies which contributes to eutrophication of surface water and destroys soil beneficial microorganisms.Soilless culture encourages precision nutrient application that minimizes nutrient depletion through leaching, maintaining nutrient sufficiency in plants root zones, and can improve fertilizer use efficiency by 368% (Thompson et al., 2020); soilless culture is saving up to 70% of fertilizers compared to soil-based farming (Figure 2).Besides, this culture converts the massive urban wastes into organic substrates (Gonnella & Renna, 2021), as it is more suited in urban areas.
As soilless culture is practiced in a controlled environment, the occurrence of pest is less.So it reduces the use of pesticides and in case infested with pest, it needs lesser pesticides with higher rates of efficiency by about 100% to control (Fussy & Papenbrock, 2022;Halbert-Howard et al., 2021;Sharma et al., 2018).In addition, it reduces the risk of pesticides on the beneficial and nontargeted organisms, pollution of the environment and water.With soilless culture, vegetable crops growth rate increases by more than 50% which enables about 8 harvests per year, under any weather condition and season (Abdullah, 2016).Soilless culture reduces the need for large size of arable land through constructing and expanding vertically and 1/3 times less than the amount needed by soil-based farming (Rai et al., 2022).

Soilless culture as climate change mitigation and crop protection strategy in dry lands
Drylands are the most sensitive areas to climate change, and El Nino that occurs when the surface water temperature rises in response to changes in trade winds over the pacific and results recurrent drought (Sandi et al., 2020).Due to rapid land degradation and soil disturbance via conventional farming, and greenhouse gas (GHG) emission, global warming is being environmental problem.Frequent soil tillage (soil disturbance) in soil-based farming increases the rate of CO 2 emission by 114% from soil to atmosphere (Zhang et al., 2020).Crops grown in one square meter area with soilless culture can decrease CO 2 emissions by 226,000 kg annually, which is equivalent to CO 2 emissions of 1155 people (Lee et al., 2015).Soilless culture addresses the rapid demand of food and mitigating climate change impacts in drylands (Abdullah, 2016).
Currently, soilless cultivation is a form of agriculture to mitigate the multidimensional appearances of climate change, drought, and safe crop production.Reduced tillage could reduce greenhouse gas (CO 2 ; CH 4 ; NO 2 ) emissions by up to 43% (Feng et al., 2020), and the more CO 2 emitted from cities may be absorbed and balanced by urban greeneries with soilless culture which reduces up to 205.1 kg CO 2 e/year (Puigdueta et al., 2021).On average, a single vegetable crop reduces about 2 kg greenhouse gas emissions (Cleveland et al., 2017).This indicates year-round crop cultivation with soilless culture can be a climate change mitigation strategy to change agriculture from CO 2 producer to CO 2 absorber.Short-duration crop production makes soilless culture the technology to address rapid demand of food and mitigating climate change impacts in dryland environments (Abdullah, 2016).
Little is known about GHG emissions from soilless culture.On average, about 0.13% (2 kg) N 2 O-N ha −1 yr −1 emitted from soilless culture (Karlowsky et al., 2021).A concern has been given to localized food production as climate change mitigation strategy.This reduces the GHG emitted via produce transportation to market by 28% (Newell et al., 2021).Soilless culture practiced in urban and peri-urbans where near to marketplaces.This shortens transport routes, reduces fuel consumption and greenhouse gas emissions.The CO 2 emitted with soilless culture could be reduced by 90% with CO 2 misting and enriching technologies, and this has been claimed to increases yield by up to 30% (Hidaka et al., 2022).Besides, if conditions like sufficient moisture, organic substrate in the root zone, minimal heat losses, and replace source of energy with solar energy, may minimize the probable GHG emissions and global warming impacts.
Plant pests are more troublesome under drought or moisture deficient conditions in dryland environments.Management of diseases, insects, and weeds are components of reduced production loss (Joyce et al., 2019).Soilless culture is undertaken in controlled growing environments, so there is less probability of epidemic disease occurrences and other pests from outside penetrating the farm.

Contrasting soilless culture with soil-based farming in crop productivity, food security, and sustainability
About 3.5% of the world's food is produced utilizing soilless culture (Joshi et al., 2022).Soilless culture promotes fast plant growth, sustainable and higher productivity compared to conventional farming.On average, crop yield exceeds by 11-23 fold and improved nutritional quality (Aires, 2018;Gashgari et al., 2018;Muller et al., 2017).
Soilless culture provides better nutritional quality (bioactive compounds, macro-and micronutrients), and antioxidant activities compared to soil-based farming (Aires, 2018;Cicekli & Barlas, 2014) with longer shelf-life which indicates consumers may prefer and pay more for soilless based produced food (Pinstrup-Andersen, 2018).This improvement in nutritional quality and shelf life is mainly due to its controlled system to amount and composition of nutrients and environmental conditions light and temperature (Aires, 2018;Barman et al., 2016;Sakamoto & Suzuki, 2020).
To promote economic feasibility of soilless culture, it is necessary to advance it in a way that uses cheap circular economy organic wastes (food wastes, crop residues, and animal wastes) as substrates, and maximizing productivity and optimizing operational costs (Mushtaq, 2021).

Economic feasibility of soilless culture over soil-based farming in vegetable production
Assessing economic feasibility for any agricultural technology is a reason for adoption by growers.Soilless culture has confirmed to be as economically sound due its high crop yield year-round, resource use efficiency, and reduces transport cost to sell the produce.It is typically established in urban and peri-urban areas, the route to market is short, and it may not be expensive to transport the items to customers and deliver products directly to surrounding homes within a neighborhood or through self-provisioning at the level of each individual household (Benke & Tomkins, 2017).Local food production reduces economic losses from imports that overheads the local economy.Although the initial cost and supply inputs of soilless culture are high, once established, its payback period is short, which is about 3.69 years (Souza et al., 2023), with average net profit of 700,796.26$ ha −1 (Table 3), and will give a double return with a small size of land; suggesting that soilless culture is profitable.Studies from world dryland countries show that soilless culture is sound for vegetable production (Table 3).Soilless culture is more profitable with 20% premium price of vegetables if it incorporates organic substrates.It is expected to fill the gap between population growth and arable land pressure as well as reduce land degradation and desertification sustainably (Akinyemi et al., 2021).Annually, soilless culture contributes about 25.2 billion USD to the global market (Mushtaq, 2021).The demand and customer preference of soilless culture grown vegetables is growing worldwide because of ability to meet unmet demands for produce grown conventionally (Sakamoto & Suzuki, 2020).

Opportunities and sustainability
Soilless culture has a numbers of opportunities to advance dryland farming.It optimizes dryland farm resources, reduces waste and loss of agricultural inputs, eliminates carbon emission (Thomaier et al., 2015), and reduces adverse impacts of soil-based farming (Kalantari et al., 2017).It's socially accepted.It creates employment opportunities for the landless and unemployed.It could serve a recreational purpose by creating an evergreen environment and enhancing  the quality of social life to increase well-being in a society (Kalantari et al., 2017).This may play substantial role to improve arable land-and economic-related problems in dryland areas (Eigenbrod & Gruda, 2015).It fits the current and future agricultural policy of reducing number of animals and come with few qualified through cut and carry feeding system.The cut-and-carry system, often referred to as "zero grazing," cuts forage or straws from soilless-grown crops and brings it to where the animals are kept for dairy or fattening.This minimizes land degradation by avoiding overgrazing, so that anyone can farm both parallel.Soilless culture is economically feasible, socially accepted, and environmentally sound (Figure 3) which is a sustainable technology to transform dryland agriculture.

Challenges for expansion of soilless culture in dryland agriculture
The primary challenge for this technology is low adoption rate due to its high cost of installation and maintence.Since it requires skilled man power, automated and computerized system of artificial light, water, nutrient, and pesticide application is a challenge to introduce to farmers living in substandard conditions.It is only suitable for a limited range of horticultural crops and requires a lot of energy for water pumps, supplemental artificial light, heating and cooling loads which has been reported to result in an overall estimate of energy use for the soilless culture production of 90,000 kJ/kg (Barbosa et al., 2015;Kalantari et al., 2018;Sarkar & Majumder, 2015).Plants in a soilless culture are supplied via the same nutrient solution, which indicates that plants within the system should have the same requirements.Unlike in soilbased farming, this limits the biodiversity of crops to be cultured at a time in same space.
Soilless culture demands advanced infrastructure, higher initial cost investment (Kalantari et al., 2018), and requires a good level of technical and scientific knowledge.As a result, low attention is given by growers in dryland environments.

Conclusion
The ever-facing biotic and abiotic challenges as well as arable land challenges in dryland farming may be transformed by introducing and popularizing soilless culture that optimizes resources for plant growth.It is a promising technology to scale up safe and sustainable crop productivity in marginal environments that creates jobs and contributes to food security for the growing world population by enabling agriculture to explore substandard space for agricultural production.

Figure
Figure 1.The world population (billion) is rapidly increasing and projected to grow for the future; total arable land (billion hectares) is slightly expanded by clearing forests while arable land (ha) per person is sharply declining over the periods (1900-2100) (Anonymous, 2018, 2022; Benke & Tomkins, 2017).

Figure
Figure 2. Role of soilless culture in reducing the large demand of field crops' growth resources (growing time, nutrient or fertilizer, arable land and water) and improving crop yields (t.ha _1 ) (Pomoni et al., 2023; Sarkar & Majumder, 2015).
Figure 3. Percentage of environmental, ecological and social sustainability dimensions of soilless culture (Kalantari et al., 2017).

Table 1 . Water use efficiency (L kg -1 ) dry matter production of vegetable crops in soilless and soil-based farming
SLC = with soilless culture, SBF = soil-based farming; Ad = advantage of soilless culture over soil-based farming, and L kg −1 =kilogram•L −1 of water

Table 2 . Estimated yield (t-ha -1 ) of soilless culture compared to soil-based agriculture of vegetable crops
SLC= with soilless culture; SBF = soil-based farming and YAd = yield advantage.