Soilless Cultivation to Secure the Vegetable Demand of Urban and Peri-Urban Population

Abstract

Globally, more people live in urban areas than in rural areas, with 54% of the world’s population residing in urban areas in 2014. It is estimated that by the year 2050, the world’s population would increase to 10 billion, and close to 80% of human settlements would be concentrated in and around urban locations. This growing urban population will need access to healthy and nutritious food. To provide food to these urban-based inhabitants, vast areas of cultivable land might be required. But then again due to competition from sectors other than agriculture, researchers, experts, and planners are skeptical about the accessibility of such spread-out land parcels, particularly those around the prevailing and futuristic metropolitan agglomerations. This strong worldwide urbanization also puts a demand for producing vegetables in close proximity to the consumers. This gives us one of today’s major challenges. Land, water, chemical fertilizers, and energy are vital resources for food production. Only 1% of freshwater found on the earth is accessible or available for human usage. Nearly 70% of that water is used in agriculture mainly for irrigation. Reserves of fertilizers, that are crucial for the production of food, are running out. With agricultural land becoming scarcer and the need for producing closer to or even in the cities to shorten the supply chain, not always the best soil can be chosen for producing crops. In this critical condition, we have to identify some alternatives to produce the vegetable crops without using soil medium in urban and peri-urban areas where rooftop/terrace space is available abundantly. When grown on the substrate, the quality of underlying soil is not a consideration, since plants do not root in the underlying soil; water and nutrients are delivered directly to the crop via the substrate. Substrate cultures can even take place without soil, for example, on concrete floors in buildings.

1. Introduction

Soil is usually the most available growing medium for all kinds of plants. Almost all of the vegetables we find on grocery store shelves are produced either directly or indirectly in open field soils. In general, soil serves two basic purposes—it acts as a reservoir to retain nutrients and water, and it provides physical support for the plant through its root system [1]. A well-drained, pathogen-free field soil of uniform texture is the least-expensive medium for plant growth, but the soil does not always occur in this perfect package [2]. Existing levels of abiotic and biotic stresses in soil severely affects agricultural and horticultural production. Some soils are poorly textured or shallow and provide an unsatisfactory root environment because of limited aeration and slow drainage. Pathogenic organisms are a common problem in field soils. On the other side, the shrinking of agricultural land due to continuous urbanization and industrialization also affects the total agriculture and horticulture production [1]. Strong worldwide urbanization also puts a demand for producing vegetables in close proximity to the consumers. When adverse conditions are found in soil and reclamation is impractical, some form of an alternate method of cultivation without soil may be justified. Soilless cultivation is another way of growing agricultural and horticultural crops. The recent scientific invention proved that it is also possible to produce crop plants without soil, i.e., soilless culture [3, 4, 5].

Presently, many countries are focusing special attention towards soilless cultivation, i.e., hydroponics, aeroponics, and other substrates medium, such as cocopeat and compost [6]. Subtropical countries, such as India, aeroponics or cocopeat substrate-based cultivation is ideal as water is precise input for us. Besides cocopeat, several other substrates viz., sand, rockwool, vermiculite, expanded clay granules, perlite, zeolite, and pumice could be used alone or by mixing with other organic or inorganic substrates as a medium for growing crops. Among all available organic substrates, peat moss mined from the earth is the highly used growing medium in horticulture, particularly in the nursery sector. However, peat moss is a limited resource with great demand, and the extraction of peat causes negative impacts on the environment. Most of the soilless substrates have superior hydraulic and physical features than those of soil and also permit synchronized optimization of oxygen and water availabilities for plant growth. Nutrient availability to plants can be better managed in the soilless system of cultivation than in most soils. With the help of the soilless system of cultivation, it is possible to minimize or reduce the discharge of dissolved ions, pesticide residues, etc., to the freshwater bodies which in turn prevent environmental pollution. Further, the carbon and water footprint can be reduced by practicing the soilless system of cultivation in limited available land on the earth. Soilless substrate-based cultivation improves water and nutrient use efficiencies when compared to the soil which ultimately minimizes carbon and water footprint.

Soilless culture is rapidly gaining momentum and popularity and is one of the fastest-growing sectors of agriculture. There has already been a great deal of buzz throughout the scientific community for the potential to use soilless culture in future food production. Soilless culture could well dominate food production in the future. The application of these systems is likely to increase close to existing cities as well as in mega-cities worldwide in the near future. To meet the growing demand for soilless culture technology, ICAR-Indian Institute of Horticultural Research, Bengaluru has standardized a simple and low-cost production technology, including nutrient formulations for open and polyhouse soilless cultivation of most commonly consumed vegetables viz., tomato, chilli, cabbage, cucumber, French bean, garden peas, ridge gourd and leafy vegetables and few exotic vegetables, such as zucchini and colour cabbage using Arka Fermented Cocopeat (AFC) as substrate. Therefore, the production of vegetables under soilless culture using Arka Fermented Cocopeat and IIHR standardized nutrient solution namely Arka Sasya Poshak Ras may be practiced for meeting the demand of the urban population. Using this technology, urban and peri-urban people can grow their choice of vegetables to meet their daily vegetable requirements [7]. This chapter provides the reader with an understanding of the availability of various soilless media, specifications of the ideal substrate, suitable vegetable crops for soilless culture, how to grow vegetables under soilless culture, and nutrient and water management. This chapter is ideal for agronomists, horticulturalists, greenhouse and nursery managers, extension specialists, and people involved with the production of plants particularly vegetable crops under soilless culture.

2. Soilless culture

Soilless culture is a method of growing plants without soil. In this method of cultivation, plants are grown by providing nutrients, water, and physical support in a container. Soilless culture is normally called water or solution culture, the technique was firstly termed by W.F. Gericke as hydroponics (water working) in the 1930s [8]. Several workers use the term hydroponics to mention the systems that include some kind of organic or inorganic substrates to support the plant physically and to hold water in its inert matrix. The hydroponics method of cultivation has been used every now and then in the world as a profitable business of growing vegetable, flower, ornamental and medicinal plants. Because of the availability of various types of substrates along with scientific advancements, soilless culture has entered into the viable commercial stage. It supplies fresh vegetables in countries with limited arable land as well as in small countries with dense populations. Plants grown in hydroponics or soilless culture had consistently superior quality, high yield, rapid harvest, and high nutrient content.

3. Container growing of vegetable crops

Soilless culture in bags, pots, or troughs with a lightweight medium, i.e., cocopeat is the simplest, most economical, and easiest to manage of all soilless systems. There are different types of containers are available, i.e., long wooden troughs in which one or two rows of plants are grown, polyethylene bags, or rigid plastic pots containing one to three plants. In the bag or pot system, the solution is not recirculated. The most common types of media used in containerized systems of soilless culture are peat-lite, or a mixture of bark and wood chips. Bag or pot systems using bark chips or peat-lite are in common use [9]. Drain holes should be provided in the base of the containers to drain out any excess water or flush out any excess nutrient solution from the container.

4. Vegetable crops suitable for cultivation under soilless culture

The existence of a diverse climate in India ensures the availability of all types of fresh vegetables. India stands second in vegetable production in the world, after China. As per National Horticulture Database (Second Advance Estimates) published by National Horticulture Board, during 2019–2020, India produced 191.77 million metric tonnes of vegetables. The area under vegetable cultivation is 10.35 million hectares. The global area under soilless cultivation of vegetables is 95,000 ha only. This is a very meagre area at the world level when compared to an area under soil-based cultivation of vegetables. There is a range of limitless options in soilless culture regarding the type of vegetable crops to be grown. The list of suitable vegetable crops under different groups for growing in both open-field and polyhouse soilless culture conditions is given in Table 1.

Type of vegetable crops	Name of the vegetable crops
Transplanted vegetables	Tomato, brinjal, chilli, onion, cabbage, cauliflower, and broccoli
Direct sown vegetables	Okra, zucchini, cucumber, ridge gourd, bottle gourd, spine gourd, radish, beetroot
Perennial vegetables	Drumstick, curry leaf, chekkurmanis and agathi
Leafy vegetables	Amaranthus, palak, and lettuce
Spice crops	Coriander and fenugreek
Legume vegetables	French bean, garden peas, Dolichos, cowpea, and yard long bean

Table 1.

List of vegetable crops that can be grown successfully under soilless culture.

Source: Kalaivanan et al. [10].

5. Home garden structures

Based on the space available in terrace or rooftop of home two types of gardens can be adopted viz., 1. terrace garden and 2. vertical garden. If a terrace or back yard or front yard space is available the vegetables and medicinal herbs can be grown in the accessible area. In the recent past, urban areas have become thickly populated and society prefers to live in apartment-type living places owing to its many advantages. For apartment dwellers, space is the limiting factor to grow their vegetables and medicinal herbs. However, every apartment has a utility area, where vegetables and medicinal herbs can be grown by adopting the vertical garden structures. In both types of gardens, vegetable and medicinal herbs are grown in pots or grow bags or rectangular trays.

6. Terrace garden structure

Terrace garden can be two models i. open garden and ii. shade net garden. In an open garden, containers are placed on the terrace, and vegetables and medicinal herbs are grown. Hence, the investment is only on containers, growing media, seeds, crop production and protection chemicals, and home garden tools. In the case of a shade net garden, a shade net is installed and crops are grown inside the shade net. The investment is Rs 100/square feet in addition to the above-mentioned investment. However, the shade net garden protects the plants from pests and diseases to a greater extent, reduces the use of crop protection measures, and the crops and produce are much healthier as they are grown under protected conditions.

7. Shade net garden

Installation of shade net is very simple and can be done by any local artisans (Figure 1). It requires galvanized pipes (G.I.) of 60 mm diameter (“B” Class), fasteners, and an agro shade net (50%). The length and width of the shade net can be any size based on the area available and the height will be 8½ feet. The G.I pipes are grouted to the terrace if it is to be on a terrace or can be fixed on the ground with proper concrete foundation if it is to be on an open yard. The space between two adjacent G.I. columns is 10 feet. A simple door is required to be provided at any one convenient place of the structure. The dimension of the door is 1.2 × 1.8 m (W × H). The entire G.I structure is covered with a 50% agro shade net with fasteners. The containers, such as grow bags, pots, and rectangular trays, can be placed inside the shade net.

Figure 1.

Shade net garden.

8. Vertical garden structure

The vertical home structure is designed considering (i) size suitable for terrace/utility area, (ii) to grow vegetables consumed by a family on daily basis, (iii) pots suitable for respective vegetables/leafy vegetables/flowers/medicinal plants, (iv) structure suitable for handling in terms of the height of reach, mobility, the requirement of light available to all the pots, and (v) effective utilization of maximum area for growing plants. The vertical garden structure has three major substructures viz., (i) base frame, (ii) main central support and (iii) supports for pots/grow bags (Figure 2). Main centre support is a rectangular shape frame/tube anchored to the base frame with necessary supports. Support for pots/grow bags are fabricated suitable for different pot sizes and shapes and fitted at four different height levels. Heavy-duty nylon caster wheels are fitted at the bottom of the base frame for the mobility of the vertical garden structure. The selection of pot size is based on the growing media requirement to facilitate proper growth during the crop period.

Figure 2.

Vertical garden.

The vertical garden has four height levels and the topmost level was decided based on the maximum reach of a normal human being hand reach. Vegetable crops that grow a height of higher than 2 feet (tomato, chilli, brinjal, peas, etc.,) are placed in the bottom-most level of the vertical garden structure. Leafy vegetables (palak, amaranthus, coriander, etc.) that grow to a height of about one foot are placed above the bottom layer. Medicinal crops or again leafy vegetables are placed above the second bottom layer. Flowers are placed at the topmost level of the structure which would give aesthetic look.

9. Characteristics of growth medium (substrates) used in soilless cultures

9.1 Technical specifications for substrates

According to [11, 12, 13] substrates must have the following properties:

• Inert (no reaction with the nutrients)

• pH neutral

• Porous

• Low density

• Hydrophilic

• There should not be any radioactive pollutants and heavy metals in substrates

• As much as possible the substrate should be usable in natural form without any additional processing

• The substrate can either be obtained by mining from nature or otherwise produced in the industry

• It should have constant quality without much change particularly in physical properties during use

• Substrate should have a lifetime of a minimum of 3 years

• The substrate should be easy to handle and use

• The cost of the substrate should be low

• The nature of the substrate should be either biodegradable or destroyed without causing any environmental risk

• It should not undergo any structural change during repeated sterilization

• The substrate must be free from pest and disease-causing agents/pathogens.

Substrates, such as rockwool, cocopeat, clay granulates, pumice, sand, Irish peat, and perlite, are able to meet the above specifications [14, 15].

9.2 Substrate categories

Ideal substrate should fulfil four important roles viz., (i) should act as a reservoir for plant nutrients, (ii) should hold enough water, (iii) provide good aeration, and (iv) physical support for good plant growth and development. Only a few substrates that are available in the market generally support all the four functions as mentioned above but at a very limited level. However, some of the soilless media may not support all the functions, i.e., sand gives good physical support and aeration but is very poor in nutrient and water supplying capacity. Various growing media and crops grown in different countries are given in Table 2. Based on the source or origin of substrates, soilless growing media may be classified into two groups namely organic and inorganic medium. Peat moss, wood residues, sawdust, barks, and cocopeat are some of the widely used organic substrates in soilless cultivation. Other substrates, such as perlite, sand, vermiculite, calcined clays, pumice, and rockwool are most commonly used inorganic substrates in hydroponics or soilless cultivation.

Authors reference	Country	Area in ha	Media/ system	Key crops grown
Hassall et al. [16]	Spain	4000	Rockwool, sand, perlite	Cucumber, capsicum, tomato, lettuce
Hassall et al. [16]	Netherlands	10,000	Rockwool	Strawberry, tomato, cucumber, lettuce, cauliflower, muskmelons, gerbera, chrysanthemum, carnation
Jiang et al. [17]	China	1250	Rockwool, NFT, DFT	Carnation, roses, chrysanthemum, tomato, cucumber, lettuce
Donnan [18]	France	1000	Rockwool	Capsicum, tomato, cucumber, cut flowers
Bradley et al. [19]	Canada	2000	Rockwool and perlite	Cucumber, capsicum, tomato,

Table 2.

Various soilless culture media and crops grown.

10. Arka Fermented Cocopeat substrate

An ideal potting medium for vegetable crops must be well aerated and porous, hold sufficient moisture, have adequate drainage, and must provide adequate nutrients to the plants. Among all substrates, cocopeat is the one that retains moisture, stores, and releases nutrients to roots over an extended period of time for enhancing plant growth. Therefore, it is considered an ideal soilless growing media for vegetable crops. In this connection, the technology for conversion of raw coir pith into fermented cocopeat has been standardized at ICAR-Indian Institute of Horticultural Research, Bengaluru and released as a product called Arka Fermented Cocopeat (AFC). Arka Fermented Cocopeat is developed by the solid-state fermentation of raw coir pith, by employing a fungal consortium and enriched with the Arka Microbial Consortium comprising of N fixing, P and Zn solubilizing, and plant growth-promoting microbes could be a potential substrate for soilless cultivation of vegetables, flowers, and medicinal crops, etc. Arka Fermented Cocopeat is very popular and used as a growing media in the nursery for raising seedlings of various vegetable crops and rootstocks of different fruit crops. However, it has not been evaluated as a growing media for the cultivation of vegetables under soilless conditions. Therefore, a series of experiments on soilless cultivation of different vegetables were conducted at ICAR-IIHR to study the suitability of Arka Fermented Cocopeat (AFC) as substrate along with commercial cocopeat and soil. The results revealed that the substrate AFC recorded better yield and quality in vegetable crops compared to commercial cocopeat and soil. Arka Fermented cocopeat (AFC) alone or AFC + vermicompost or AFC + vermicompost/FYM/compost are also the best substrate combination for growing vegetable crops under soilless cultivation.

Raw coir pith fermented cocopeat

11. Nutrient management in soilless vegetable cultivation

Seventeen nutrient elements are considered essential for the growth and development of any living plant on the earth. The absence of anyone essential nutrient will make it difficult for the growth of plants and will not allow the plant to complete its life cycle. Further, the role of essential nutrients cannot be played or replaced by any other nutrients. In soilless culture or hydroponics, the nutrients which are considered essential should be supplied in the form of nutrient solution. Mostly C, H, and O are taken by the plants from water and CO₂ in the air. Remaining essential nutrients viz., P, K, Ca, Mg, S, Fe, B, Cu, Zn, Mn, Mo, and Cl need to be supplied to the plants by the growers in the form of the nutrient solution prepared from soluble inorganic salts. Most of the growing media used to have a smaller quantity of these mineral nutrients but they should not be taken into account while formulating fertilizer schedule because they are either very little when compared to the requirement of plants or they may not be readily available form to plants. The main route to attain success in the soilless culture of vegetables depends on the ideal management of plant nutrients through the supply of nutrient solutions prepared from soluble inorganic salts. It is also possible to prepare a nutrient solution by buying a ready mix of all essential nutrients. There are several formulations of nutrient solutions available in the literatures. Nevertheless, most of them are empirically based. Table 3 comprises some of them.

Nutrient	Cooper [20]	Steiner [21]	Hewitt [22]	Hoagland & Arnon [23]
	mg L^−1
N	200–236	168	168	210
P	60	31	41	31
K	300	273	156	234
Ca	170–185	180	160	160
Mg	50	48	36	34
S	68	336	48	64
Fe	12	2–4	2.8	2.5
Cu	0.1	0.02	0.064	0.02
Zn	0.1	0.11	0.065	0.05
Mn	2.0	0.62	0.54	0.5
B	0.3	0.44	0.54	0.5
Mo	0.04	Not considered	0.04	0.01

Table 3.

Concentration ranges of essential mineral elements according to various authors.

Proper nutrition factors, such as pH level, electrical conductivity (EC), the types of nutrition, the composition of nutrients irrigated, and so on are the key factors to improve the quality and yield of vegetables. Vegetable crops can be grown organically by mixing organic manures, such as FYM, compost (kitchen waste compost, city compost), and vermicompost, with substrate cocopeat @ 1:1:1 ratio which will take care of the nutrient requirement of the plants. Vermicompost @100 g/plant should be applied at monthly intervals. Decomposed kitchen waste can also be applied. ICAR-IIHR standardized nutrient solution (Arka Sasya Poshak Ras) may be practiced for meeting the nutrient requirement of the plants under cocopeat-based soilless cultivation. Arka Sasya Poshak Ras is a liquid nutrient formulation (comprising solutions A and B) is a unique blend of the macro and micronutrients which are well balanced to support the growth of vegetables.

12. How to use Arka Sasya Poshak Ras

• It is suitable for most commonly used vegetables (tomato, chilli, cabbage, zucchini, cucumber, ridge gourd, French bean, peas, cowpea, Dolichos, etc.) and leafy vegetables (amaranthus, coriander, palak, etc.)

• One litre each of nutrient solution viz., A and B can be diluted with 200 litres of water (5 ml/litre) and applied @ 200 ml per plant (tomato, chilli, brinjal, cabbage, cucumber, ridge gourd, and zucchini).

• For leafy vegetables, 3.5 ml of each nutrient solution A and B may be diluted in 1 litre of water and applied @ 600 ml per bag of size 4 × 1 × 1 feet.

• For peas, beans, Dolichos, and cowpea, 4.0 ml of each nutrient solution A and B may be diluted and applied @ 600 ml per bag of size 4 × 1 × 1 feet.

• The frequency of nutrient solution application is two times per week starting from the 10th day of transplantation up to 30 days from the date of sowing or transplanting and three times per week thereafter.

13. Optimum pH of the nutrient solution

pH regulates/controls the availability of most of the essential plant elements in a nutrient solution. The nutrient solution pH between 5.8 and 6.5 is considered as most optimal. Higher or lower nutrient solution pH than the suggested range for individual crops, the nutrient deficiencies will become apparent or toxicity symptoms will grow.

14. Electrical conductivity of the nutrient solution

Similar to pH, electrical conductivity (EC) is one of the most important properties of nutrient solutions. The EC level between 1.5 and 2.5 dS/m is considered ideal for hydroponics/soilless culture. The strength of the nutrient solution strictly depends on the EC level of the solution. The total concentration of the solution is only indicated by the EC and not the specific nutrient components. Too high or too low EC level in nutrient solution may create salinity problems or the supply of some nutrients to the crop may be insufficient. Higher EC will not allow nutrient absorption to take place due to osmotic pressure and lower EC severely affects plant health and yield. However, among different species, the yield response of the plants may vary widely with respect to the EC level of the nutrient solution. So, the terms “too low” and “too high” need to be quantitatively defined for each cultivated plant species based on experimental results. When plants take up nutrients and water from the solution, the total salt concentration, i.e., the EC of the solution changes. Freshwater must be added If the EC is higher than the recommended range. Add nutrients if the EC is lower in the nutrient solution.

15. Production technology for soilless cultivation of vegetables

The production technology for soilless cultivation of zucchini, colour cabbage, chilli, coriander, cucumber, French bean, peas, and tomato on Arka Fermented Cocopeat under open as well as in protected conditions has been standardized at ICAR-Indian Institute of Horticultural Research, Bengaluru. The results of most of the experiments conducted with different vegetable crops in grow bags under open-field and polyhouse soilless culture indicated that the plants grown in soilless culture recorded higher yield and better quality, particularly in mineral nutrient content compared to soil-grown plants. This technology would be highly suited for urban and peri-urban vegetable cultivation for meeting the food security in cities. This particular technology has already been popularized through various training programmes, exhibitions, magazines, and media. Many growers have already started adopting IIHR soilless culture technology in the cultivation of vegetables using AFC as a substrate.

16. Open-field vs polyhouse soilless cultivation of vegetables

Between open and polyhouse soilless cultivation, the highest yield and better fruit quality were recorded with zucchini, chilli, coriander, cucumber, French bean, peas, and tomato with open conditions. However, colour cabbage recorded maximum head weight and highest yield in polyhouse soilless cultivation. Similarly, brinjal also recorded higher yield in polyhouse than in open-field soilless culture because of better control of pests, particularly brinjal shoot and fruit borer. Pest and disease management was easier in polyhouse than in open-field soilless culture [24].

16.1 Zucchini

Between open and polyhouse soilless cultivation of zucchini, the highest stem diameter (35.2 mm), maximum fruit length (23.2 cm), fruit girth (42.9 mm), fruit weight (315.4 g), and yield (5.27 kg/plant and 65.8 t/ha) were recorded with open conditions [25, 26]. However, the maximum plant height (80.6 cm), number of leaves (47.4), number of fruits (22.3), and total plant dry biomass (144.7 g/plant) were recorded with polyhouse conditions.

16.2 Red cabbage

When open and polyhouse soilless cultivation of red cabbage were compared, the maximum plant height (25.71 cm), head diameter (33.7 cm), head length (12.9 cm), average head weight (817.8 g/plant), and yield (45.43 t/ha) was recorded with polyhouse conditions [27].

16.3 Chilli

Open field soilless cultivation outperformed polyhouse cultivation in almost all the parameters (number of fruits (228), fruit length (11.8 cm), fruit girth (10.3 cm), average fruit weight (5.68 g), and yield (1.29 kg/plant)) recorded during the course of the experiment except plant height [28].

16.4 Coriander

The performance of coriander under open-field soilless culture was found to be better than polyhouse soilless culture [28].

16.5 French bean

In French bean, open field soilless cultivation outclassed polyhouse in stem diameter (11.2 mm), number of branches (6.14), number of pods (42.74), pod length (15.04 cm), pod girth (7.23 mm), and pod yield (286.4 g/plant)) recorded during the course of the experiment except for plant height [29].

16.6 Garden peas

Best nutrient scheduling found in open-field conditions recorded better growth and yield in garden peas under polyhouse also. Between soil and cocopeat, soil recorded maximum growth and better yield compared to cocopeat [30].

17. Substrate effects on growth, yield, and quality of vegetables

With respect to different substrates studied, zucchini, chilli, coriander, cucumber, and tomato raised on Arka Fermented Cocopeat registered better growth and yield than soil. However, colour cabbage and peas recorded better growth and yield with soil. French bean plants recorded on par yield with both soil and soilless substrate.

17.1 Zucchini

Zucchini plants recorded maximum plant height (54.7 cm), stem diameter (35.2 mm), number of leaves (39.3), total plant dry biomass (139.8 g/plant), number of fruits (16.8), fruit length (23.2 cm), fruit girth (42.9 mm), fruit weight (315.4 g) and yield (5.27 kg/plant and 65.8 t/ha) when the plants raised on Arka Fermented Cocopeat compared to soil (3.70 kg/plant and 46.3 t/ha) [25, 26].

17.2 Colour/red cabbage

Among the substrates, soil registered maximum stem diameter (24.9 mm), number of leaves (28.3), head diameter (36.8 cm), head length (13.7 cm), average head weight (977.8 g), and yield (54.32 t/ha) in red cabbage compared to Arka Fermented Cocopeat (817.8 g and 45.43 t/ha, respectively). Nevertheless, AFC recorded maximum plant height (25.7 cm) than soil (24.5 cm) [27].

17.3 Chilli

In grow bags, chilli raised on Arka Fermented Cocopeat registered maximum number of fruits (232), fruit length (11.8 cm), fruit girth (10.3 mm), average fruit weight (5.68 g), and yield (1.29 kg/plant) compared to soil (1.02 kg/plant) [28].

17.4 French bean

Plants grown in AFC and soil (41 pods, 6.83 g pod weight, 283 g/plant, and 19.97 t/ha) were recorded on par yield with each other. Most of the macro and micronutrient concentrations in French bean pods were found to be higher in soilless plants than in those grown in soil [29].

17.5 Garden peas

Between soil and cocopeat, soil recorded maximum growth and better yield compared to cocopeat. The results showed or indicated that the soil is found to be more suitable for peas followed by cocopeat. However, most of the mineral nutrient contents in pods were found higher in soilless plants than in those grown in soil. In peas, root growth was better in plants grown on cocopeat than the plants grown under soil. However, when it comes to nodule formation, a good number of nodules was observed in the roots of plants grown on soil but no nodulation in the roots of the pea plants grown on cocopeat [30].

17.6 Cucumber

Arka Fermented Cocopeat recorded better growth and the highest yield of cucumber compared to soil [31]. Alifar et al. [32] also recorded higher biomass and cucumber fruit yield in cocopeat.

17.7 Tomato

Among the substrates studied, tomato plants raised on Arka Fermented Cocopeat registered maximum growth and yield (87.6 t/ha) compared to commercial cocopeat (76.7 t/ha) and soil (58.2 t/ha). The fruit quality was better when tomato plants were grown on Arka Fermented Cocopeat compared to commercial cocopeat and soil [33]. Plants grown in cocopeat substrate produced a higher fruit number (5.2%) and total yield (0.7%) than that of rockwool substrate. Fruit size and fruit quality characters showed no significant differences within growing substrates [34].

18. Standardized NPK levels for soilless vegetable production

Liquid nutrient formulations for growing zucchini, colour cabbage, chilli, coriander, cucumber, French bean, peas, and tomato on Arka Fermented Cocopeat under open and polyhouse soilless culture have also been developed. Best nutrient scheduling under open conditions was found to register maximum growth and yield in polyhouse conditions as well.

18.1 Zucchini

Nutrient scheduling of 168 ppm N-NO₃, 16 ppm P, and 189 ppm K recorded maximum fruit length (24.12 cm), fruit girth (44.4 mm), fruit weight (335.6 g), and yield (5.71 kg/plant and 71.39 t/ha) under open conditions. The above-mentioned nutrient scheduling recorded maximum growth and zucchini fruit yield in protected conditions also [25, 26].

18.2 Colour/red cabbage

Nutrient scheduling of 185 ppm N-NO₃, 41 ppm P, and 210 ppm K recorded maximum stem diameter (25.71 mm), a number of leaves (24.82), head diameter (36.79 cm), head length (14.64 cm), average head weight (972.25 g/plant), and yield (54.01 t/ha). The best nutrient scheduling under protected conditions is also found to register maximum growth and red cabbage yield in open conditions [27].

18.3 Chilli

In Chilli hybrid Arka Meghana, the highest number of fruits (248.2) and yield per plant (1.43 kg) was recorded with scheduling of 176 ppm N-NO₃, 29 ppm P, and 200 ppm K per plant and found to be on par with 194 ppm N-NO₃, 32 ppm P, and 228 ppm K (218.6 fruits and 1.30 kg yield per plant). However, the maximum fruit length (12.22 cm), fruit girth (10.98 mm), average fruit weight (5.96 g per fruit), and dry chilli yield (287 g per plant) was recorded with 194 ppm N-NO₃, 32 ppm P, and 228 ppm K nutrient scheduling [28].

18.4 Coriander

The production technology for soilless cultivation of coriander var. Arka Isha under open as well as in protected conditions has been standardized. The highest leaf yield of 4.79 t/ha was recorded with scheduling of 132 ppm N, 21 ppm P, and 150 ppm K under an open-field system of soilless cultivation. The performance of coriander under open field soilless culture was found to be better than polyhouse soilless culture [28].

18.5 Cucumber

Supplying of 166 ppm N-NO₃, 33 ppm P, and 207 ppm K recorded the maximum stem girth (18.43 mm), highest fresh (1690 g/plant), and dry plant biomass (540.8 g/plant), highest average fruit weight (212.9 g) and yield (2.11 kg/plant and 32.51 t/ha) under open-field conditions [31].

18.6 French bean

Scheduling 141 ppm N-NO₃, 29 ppm P, and 179 ppm K recorded maximum plant height (47.11 cm), stem diameter (11.22 mm), number of branches (6.14), highest total fresh (205.8 g/plant), and dry biomass (35.89 g/plant), highest number of pods (42.74), pod length (15.04 cm), pod girth (7.31 mm), average pod weight (6.69 g), and yield (286.4 g/plant and 20.18 t/ha) [29].

18.7 Garden peas

Nutrient scheduling of 133 ppm N-NO₃, 27 ppm P, and 168 ppm K recorded maximum plant height (65.66 cm), stem diameter (6.51 mm), number of branches (3.14), highest plant biomass (24.04 g/plant), number of pods (15.14), pod length (7.07 cm), pod girth (9.67 mm), average pod yield (83.25 g/plant and 1.17 kg/bag) under open-field soilless cultivation. The best nutrient scheduling found in open-field conditions recorded better growth and yield under polyhouse also [30].

18.8 Tomato

The highest number of fruits (80.14) and yield (93.9 t/ha) of tomato hybrid Arka Rakshak was recorded with the split application of 15:35:15 percent of the recommended NPK (180:120:180 kg NPK/ha), during establishment to early flowering, followed by 12.5:12.5:12.5 percent application during fruit development and 72.5:52.5:72.5 percent application during harvest. Nutrient scheduling significantly improved the TSS while other quality parameters were not significantly enhanced [33].

Tomato, colour cabbage, zucchini, and peas in soilless cultivation

19. Analysis of solution, tissue, and media

Knowledge of the nutritional status of all components (nutrient solution, substrate/media, and plant tissues) of a soilless cultivation system is very much required to judge the success of fertilizer schedules with respect to plant nutrients availability and the plant tissue nutrient content and it also helps to identify the reasons of any deficiency and toxicity symptoms that may appear in plants. The costs of the information with respect to the nutritional status of all components are a form of assurance towards success. The nutrient solution in a recirculated hydroponics system of cultivation may be utilized for a few days (short use) to a few weeks (extended use). To extend the life of nutrient solution to a few weeks in recirculated soilless culture/hydroponics system, it is always better to analyse the solution periodically for pH, EC, and individual nutrient concentration. Based on the nutrient analysis, periodic replenishment or adjustment in nutrient solutions can be made using nutrient stock solutions. By doing so, the longevity of nutrient solutions can be extended and the cost required for buying nutrient solutions or soluble salts can be reduced. Total salt content estimation on daily basis will also give the status of the nutrient content in the solution even though this cannot substitute for comprehensive analysis [2].

To avoid toxicity and deficiencies of nutrients in recirculated solutions due to continuous variation in nutrient status, it is necessary to do solution analysis for complete control over nutrient management in liquid soilless culture. The frequent requirement of solution analysis in water-based soilless culture gives a reason for switching over to solid substrate-based soilless culture. In solid substrate-based soilless culture systems, the evenly balanced nutrient solution is given to plants at the time of irrigation. In this way, the problem of nutrient solution management in solid substrate-based soilless cultivation systems can be minimized. Also, by accurately weighing the soluble salts at the time of nutrient solution preparation, it is possible to make a very properly working solution.

Like nutrient solution and substrate analysis, tissue analysis (leaf petioles or blades and whole leaves) is also warranted for successful nutrient management in plants. Tissue analysis during the crop growth period provides the current status of nutrient content in plants. Based on the nutrient content in plants, the fertilizer program may be adjusted or modified for better plant growth and productivity in soilless cultivation. Nutrient data obtained through tissue analysis may also help in interpreting nutrient deficiency or toxicity symptoms. Depending on plant parts sampled, location of sampling, and method used for analysis, the critical nutrient levels may vary. Critical nutrient concentrations for tomatoes, cucumbers, and different vegetables have been reported by various researchers [2, 35, 36, 37].

20. Water management in soilless vegetable cultivation

Substrate texture, porosity, and surface area to be wetted are vital considerations in making the right choice of irrigation in soilless vegetable cultivation [15]. While selecting an irrigation system for container or bag culture, one should keep in mind that the main purpose of irrigation is to apply nutrient solution homogeneously by making wet of entire growing media. A dry substrate or medium will make it very difficult for the plant root system to function properly [38]. Therefore, proper water management in soilless culture is very much important not only for meeting the water requirement of the plants but also for distributing the nutrients uniformly in the media. During summer, plants need extra water and hence the plants should preferably be irrigated twice a day. For soilless media, watering needs to be done only when the surface/subsurface of the media/substrate is dried and excess watering may be avoided.

21. Nutritional quality of vegetables grown in soilless culture

The results of most of the experiments conducted with different vegetable crops under open-field and polyhouse soilless culture indicated that the fruits of plants grown in soilless culture recorded better quality, particularly in mineral nutrient content compared to soil-grown plants [7, 33]. Most of the nutrient concentrations in zucchini fruits were found to be higher in soilless plants than in those grown in soil [7]. The fruit quality was better when tomato plants were grown on Arka Fermented Cocopeat compared to commercial cocopeat and soil. Calcium content in tomato fruit samples was found to vary significantly among soilless media viz, cocopeat, rice hull, perlite, zeolite, and mica, and no significant variation was recorded with a phosphorus content of the fruits [39, 40]. Another study conducted by Borji et al. [41] revealed that there was no significant variation in Ca and Mg concentrations in tomato fruits obtained from the plants grown in different substrates.

The substrate combinations, viz., volcanic tuff, peat + volcanic tuff (1:1), volcanic tuff + spent mushroom compost (1:1), peat + volcanic tuff + spent mushroom compost (1:1:1), and soil, were compared for fruit ascorbic acid content in tomato and found no significant difference among growing media and soil [42]. Higher total soluble solid in tomato fruit produced from the tuff or sand-growing medium in two seasons was recorded as compared to fruit growing in soil [43]. A comparison, between rockwool (R), perlites plus carbonized rice hull (PCRH), cypress bark (CB), and coconut coir (CD) was carried out in a greenhouse using a small type of tomato (Lycopersicon esculentum Mill. cv. T-148) in a summer experiment. The high total soluble solids content (°Brix) was represented by coconut coir (CD) treatment [44]. Most of the macro and micronutrient concentrations in cucumber fruits were found to be higher in soilless plants than in those grown in soil. The highest K, Ca, and Cu were recorded in cucumber fruits harvested from the plants grown on soil. Most of the macro and micronutrient concentrations in French bean pods were found to be higher in soilless plants than in those grown in soil. However, the highest K was recorded in the pods harvested from the plants grown on soil compared to Arka Fermented Cocopeat.

22. Nematode infection and nodulation under soilless cultivation

In polyhouse French bean cultivation, nematode infection was found to be almost nil in plants grown on cocopeat but nearly half of the plants grown in soil were affected with a nematode [29]. In peas, root growth was better in plants grown on cocopeat than the plants grown under soil. However, when it comes to nodule formation, a good number of nodules was observed in the roots of plants grown on soil but no nodulation in the roots of the pea plants grown on cocopeat [30].

23. Net profit from soilless vegetable cultivation

The results of most of the experiments conducted at ICAR-IIHR, Bengaluru with different vegetable crops in grow bags under open-field and polyhouse soilless culture indicated that the plants grown in soilless culture recorded higher yield and better quality, particularly in mineral nutrient content compared to soil-grown plants. The yield of different vegetables grown under soilless culture in an area of 100 m² is as follows; 1260 kg for tomato, 803.6 kg for zucchini, 204 kg for colour cabbage, 300 kg for chilli, 441 kg for cucumber 280 kg for French bean, and 81.9 kg for garden peas. Net profit from the vegetables grown in an area of 100 m² varied from Rs 7140 for cucumber to Rs 35,960 for zucchini and the net profits of the rest of the crops found to fit in between. This technology would be highly suited for urban and peri-urban vegetable cultivation for meeting the food security in cities. The production technology developed at ICAR-Indian Institute of Horticultural Research for soilless cultivation of most commonly consumed vegetables in India has generated a lot of interest among the soilless growers for the cultivation of vegetables on AFC. This particular technology is being popularized through various training programmes, exhibitions, magazines, and media. Many growers have already started adopting this particular technology in the cultivation of vegetables using AFC as a substrate.

24. Advantages and constraints of soilless cultivation

A substantial quantum of research work carried out in recent past stating the advantages and disadvantages of soilless cultivation of vegetables.

24.1 Advantages

Compared to a conventional soil-based cultivation system, soilless cultivation provides several advantages than disadvantages. Soilless cultivation provides ideal conditions for the growth of plants which in turn helps in getting a higher yield. With little effort, time and cost, it is possible to do very relaxed and clean vegetable cultivation under soilless culture. The majority of soil-born pests and diseases can be controlled just by shifting over to soilless cultivation from the traditional way of farming. Degraded and poor fertile soils can be easily brought into soilless cultivation. It affords an unsoiled working environment and thus labour engagement is easy. List of other advantages of soilless culture is control of plant nutrition, ability to control pH and EC, water economy and control, reduction of labour requirement, sterilization practices, control of root environment, multiple crops per year and unsuitable soil can be used, etc.

24.2 Limitations

In spite of several merits offered by soilless culture, it has few demerits as well. Technical know-how and high initial cost are the two important things required for scaling up of soilless culture at the commercial level. The requirement of investment and technical knowledge will go up further when combining soilless culture with protected cultivation. Experts with precision management skills are needed for nutrient solution preparation, pH and EC maintenance, identification and correction of mineral nutrient deficiency, aeration; upkeeping all the weather parameters in support of ideal plant growth in protected structures, etc. Above all, much attention is important for plant health management. The requirement of energy inputs is very high to run the soilless culture system, particularly in hydroponics. Because of higher initial cost, technical knowledge on crop agronomy and physiology limits the soilless culture to high-value crops cultivation. Growing low-value crops in hydroponics may not be so economical.

25. Conclusion

In urban and peri-urban agriculture, no doubt that the soilless culture is rapidly gaining impetus and acceptance among growers. In advanced countries, the system of soilless cultivation is so popular and well-received mainly for commercial cultivation of high-value vegetable crops, medicinal and ornamental crops but now it is spreading very rapidly in rest of the world. With this speed, the soilless culture is certainly going to dominate in future food production. Growers are presently turning towards alternate technologies, such as soilless culture due to the decline in the availability of arable lands and the problem of soil-borne diseases in soil-based cultivation. Due to better water use efficiency in soilless culture, this particular system of cultivation can also be taken to places where water availability is limited. Presently the hydroponics unit setting up cost is too high because of limited adoption but by acceptance and adoption of more and more growers, the cost of the unit can be brought to affordable levels. Further, this technology is not getting popularity as expected in some of the developing and underdeveloped countries due to various reasons, such as high initial investment and the requirement of skilled manpower. Standardized soilless production technology by the public and private research institutions is very important to popularize and create mass awareness among urban and peri-urban growers. In this direction, ICAR-IIHR is not stopping after standardizing the soilless production technology for vegetables but also putting more and more effort into the spread of this particular technology at the national level. ICAR-IIHR soilless culture production technology has already been popularized through various training programmes, exhibitions, magazines, and media. Many growers have already started adopting IIHR soilless culture technology in the cultivation of vegetables, flowers, and medicinal crops.