The following article will guide you about how to enhance the quality of vegetables under protected cultivation.
Although India is second largest producer of vegetables next only to China with an annual production of 94 million tonnes from an area of 6.3 million hectares, but still the technology used and practices followed are predominantly traditional, resulting in low productivity and inconsistent quality and quantity of produce.
Since vegetables are highly perishable commodity therefore, the ultimate quality and shelf life of the produce depends on pre and post-harvest management. Mostly, yield and quality of vegetables are influenced by several pre harvest factors viz., genetic (i.e. variety), cultural and environmental components.
In open field vegetable cultivation genetic and cultural components are generally managed by growers but there is no control over environmental components. Protected cultivation is one way which has check over environmental components partially or fully, but this entirely depends upon the kind of protected structures being used vis-a-vis prevailing environmental conditions in that area.
Now a days, guarantee of fruit quality in vegetables has become one of the most important strategic weapons in the national and international competition for the favour of consumers. In many countries where climate serves as limiting factor for year round vegetable production, protected cultivation has become a boon.
Generally, the quality and yield potential of vegetables are high under controlled environment. Since there are various factors responsible for regulation of quality and yield of vegetables under such environment, therefore it is essential that the growers must be educated about their management and also equipped and guided about value addition thus harnessing them maximum benefit from their produce.
Actually ‘Quality of vegetables’ is an illusive concept which is difficult to define, although it can be discussed in terms of four basic characteristic of food, namely:
(i) Eye appeal or colour
(ii) Odour or flavour
(iii) Texture or feel
(iv) Nutritive value
Besides, the parameters like size, type and shape of the fruit attained importance in quality measurement in high value vegetables, especially slicing tomatoes, cherry tomatoes, coloured peppers, slicing cucumbers etc. grown under protected conditions. It is, therefore essential that the growers are aware of the following steps involved in management of quality of vegetables during their protected and off-season cultivation.
A. Quality Management in Vegetables under Protected Condition:
1. Selection of Variety:
It is pre-requisite to select a suitable variety to be grown under greenhouse or other protection for fetching high price of the produce. Although consumer’s choice is region and location specific, yet the quality standards can be managed by selecting suitable varieties of vegetable crops preferred in high markets.
For instance, in case of slicing tomato the average weight of the fruit should be 120 to 140 g with TSS above 5.0 per cent, oblate shape, deep colour, firm, green shoulders along with a very long shelf life like the Israeli variety R-144 (Daniela), a variety popular world over. In case of cherry tomato, however, the average weight of the fruit should be up to 15.0 g with a TSS more than 6.8 per cent and deep globe shaped fruits, green shoulders coupled with long shelf-life like the Israeli variety HA-818.
Similarly in sweet pepper the size, shape, weight and colour of the fruit also play an important role in the market. Mostly four lobbed fruits, attractive in colour (i.e. red, yellow or orange) along with average fruit weight of 180 to 250 g and fruit size of 10 × 8 cm (length x diameter) are mostly preferred in super markets in Europe, USA, Japan and other countries as well in Indian markets in Metro polies.
The exotic varieties like Fiesta (yellow fruits), Mazurka (red fruits), HA-1195 etc. and Indian varieties like Nun-3020, Nun-3019, Bomby, Orobellee, Indira, Bharat, Tanvi which are suitable for protected cultivation meet the prescribed quality standards.
In case of slicing cucumber, the fruits should be dark green in colour, 14- 16 cm in length, slightly ribbed thin skin, no bitterness, no seed formation and varieties with crisp fruits are preferred for protected cultivation. For this purpose the suitable parthenocarpic varieties are Hasan and Muhasan from Europe and Sarig and Dinar from Israel. The varieties which are available in India are Satis, Kian, Alamir, Nun-3019 and Nun-9729.
In case of muskmelon, the yellow-orange good netted varieties having flattened globe shape and 1.0-1.5 kg fruit weight, good firmness with green flesh colour are usually preferred by the elite markets in various countries including India.
In summer squash or Zucchini, the fruit quality preference of the consumer is region specific. In European market, long cylindrical, oblong and short tapered fruits are preferred. The length of the fruits should be 20-25 cm with attractive golden yellow, orange or mottled light green colour of fruits. In some markets round tap shaped and coloured fruits are preferred by the consumers. The important varieties suitable for this purpose are Goldy, Australian Green, Chandrika, Patty Pan, and Pusa Alankar.
Similarly in other vegetables, selection of suitable varieties for protected cultivation plays an important role in management of the required quality standards.
2. Cultural Practices:
There are several cultural practices viz., planting density, fertigation, training, pruning, pollination, plant protection and harvesting of fruits also influence the quality and nutritional status of different vegetables. But under protected cultivation of vegetables like slicing tomatoes, cherry tomatoes, coloured peppers, slicing cucumbers, netted melons and summer squash or Zucchini the quality of vegetables can be managed up to a required limit.
(i) Tomato:
Optimum spacing for getting required size of fruits in slicing tomato is 50 cm from plant to plant and 60 cm from row to row in single stemmed tomato plants, whereas the cherry tomato crop can be planted at a spacing of 30 × 60 cm. By allowing only one single branch by removing all side and by maintaining 5-6 fruits per truss the optimum size and quality of fruits can be attained in big size slicing tomatoes.
Aided pollination in greenhouse not only increase the fruit yield but it also increases the fruit quality, particularly during the period of low temperature during winter season. Similarly, by applying two secondary nutrients, along with recommended dose of N: P: K supplemented with micro-nutrients like Zn and Mg, the quality of fruits can be enhanced in greenhouse tomatoes as the disorders like blossom end rot (BER) and fruit cracking will be taken care of.
(ii) Sweet Pepper:
The sweet pepper crops can be transplanted at plant to plant spacing of 30 cm with row to rows spaced at 60 cm and by allowing two main branching on one plant by removing all other branches through regular training and pruning for getting optimum size and quality of fruits. Proper time of fruit harvesting also plays an important role in management of fruit quality in sweet pepper.
Employing honey bees for pollination, the fruit quality in sweet pepper can be further upgraded. Application of secondary nutrients (Ca and sulphur) along with the recommended dose of N: P: K supplemented with and application of micro-nutrients like Zn and Mg, the fruit quality in sweet pepper can be managed up to a certain level by checking BER and deformed fruit disorders.
(iii) Cucumber:
Optimum quality of fruits can be achieved in cucumber by proper fertigation, timely harvesting of fruits and by planting the crop at a spacing of 30 × 60 cm. Constant water supply is essential for optimum growth and fruit quality during flowering and fruiting period. Removal of excess fruits from the vines also help in maintaining the fruit quality in slicing cucumber and more specifically in parthenocarpic varieties of cucumber.
Proper adjustment of fertigation according to season and soil conditions increases the fruit quality and reduces the “mis-shapen fruits” disorder in cucumber under greenhouse conditions. Regular pruning and plant balance can also reduce the chances of black fruit in cucumber.
(v) Muskmelon:
The muskmelon crop should be transplanted on a plant spacing of 50 cm from plant to plant with single rows planting on each bed for getting optimum size and quality of fruits. Growth stage specific fertigation scheduling in muskmelon is best for increasing the TSS of fruits. Several other factors like ripening stage, fruit load and leaf area also influence the fruit quality in muskmelon.
B. Managing Environmental Factors for Quality Enhancement:
Climatic factors have been shown to have an important influence on the yield, quality and nutritional value of vegetables.
Mainly the light intensity, temperature, water availability and relative humidity are the determinants of yield and quality in vegetables under controlled environment:
1. Light:
Light intensity and light quality can have profound effects upon crop yield and quality over the course of time. In general, lower the light intensity, the lower the content of ascorbic acid in plant tissues. Ascorbic acid content also generally increases with increased exposure to light; particularly in green leafy vegetables.
Light has also been shown to be required for the formation of a carotene in tomatoes. Various studies performed with tomato produced in full light versus shade have shown that tomatoes produced in full light contained more yield, sugar and dry matter than grown in shade. Greenhouse crop of tomato, cucumber and pepper are normally grown in rows or double rows oriented N-S and have a mature height of 2 meter or more.
With this system of growing the plants get sufficient light intensity for their required growth, yield and quality. Low light intensity caused flower bud abscission of pepper. The low light intensity problem under protected conditions is more pronounced during winter months as compared to other seasons. It cannot be regulated on commercial scale.
2. Temperature:
The atmospheric environmental conditions, which include carbon dioxide concentration, relative humidity and temperature, are unmanageable in open field production of crops, but they have strong implications on yield and quality of crops. These factors can be managed partially or fully under protected cultivation of vegetable crops. In case of tomato and pepper, the optimum temperature for fruit setting is highly essential for round the year production of these crops under protected conditions.
In sweet pepper, under low temperature the fruits become conical and deformed with less seed content. In tomato high temperature changed the ratio of ABA: IAA and GA3 which is un-favourable for fruit setting. High temperature causes abscission of flowers in pepper plants and, thus, reduces yield and quality of fruits. Under protected cultivation of vegetables, the temperature can be modified accordingly.
Mean daily temperatures have been found to affect the growth rate of greenhouse gown tomatoes. In young tomato plants, maximum rate of bio-mass accumulation occurred at a temperature close to 25°C. Tomato fruit set and fruit weight per plant decreased as the mean daily temperatures do not have the same effect on tomato. Day temperature is more important than night temperature in determining the fresh and dry weights, plant length, leaf area, leaf and truss numbers of young tomato plants.
In sweet pepper, vegetative growth and development depends mainly on the 24 hour mean temperature, while the effect of the day/night amplitude is of minor importance. Temperature also affect pepper flowering. The formation of well-shaped, elongated fruits in sweet pepper requires that night temperatures be high (18°C to 20°C) during flower development and low (8-10°C) thereafter. Temperature plays a significant role in greenhouse cultivation of sweet pepper. It affects the mean fruit weight as well as the yield of high quality fruits.
Cucumber requires higher temperatures than tomato and sweet pepper for optimum plant growth. The maximum rate of bio-mass production is normally achieved at a constant air temperature of 30 to 35°C, whereas the optimum temperature for rapid expansion of leaves is 25°C. The difference between the day and night temperature had no effect on cucumber fruit yield but it improved the fruit quality.
Temperature is a major regulator of developmental processes, yield and quality in vegetable cultivation under protected conditions. The temperature can be regulated according to the vegetable crops to be grown under greenhouse conditions, but it needs lot of energy.
3. Humidity:
Normally, the humidity between 55-80% did not affect the growth and development of greenhouse vegetable crops. The pollination process is also less affected under this range of relative humidity under protected conditions. Extremely low humidity can lead to high transpiration and reduce photosynthesis rates.
High humidity is considered more important than low humidity in greenhouse cultivation of vegetables and it has a significant impact on the energy balance of the crops. Water availability and relative humidity also plays an important role in determining the yield and quality of vegetables under greenhouse conditions.
Low relative humidity can cause differential partitioning of calcium and boron in vegetables, resulting in nutritional disorders such as BER in tomato and sweet pepper and tip burn in lettuce. The extent of these disorders depends upon the environment, water availability and cultivar under cultivation.
Cucumber yield has been reported to increase by high humidity during day time, but was unaffected by humidity at night or by 24 hour mean humidity. In tomato, final yield reduced by high humidity at night, but in sweet pepper day and night humidity did not affect the yield.
Although the effect of the final yield differed between these three vegetable crops, but the fruit quality was reduced by high humidity at harvest in all the three vegetable crops. In greenhouse cultivation of vegetables, high humidity is a major concern in connection with fungal and bacterial diseases.
Incidence of Botrytis on greenhouse tomatoes can be reduced considerably by reducing the relative humidity to 75 per cent as compared to 90 per cent. Similarly, the incidence of other fungal diseases can be reduced by decreasing the relative humidity in the greenhouses.
4. Carbon Dioxide:
CO2 enrichment in the greenhouse is a recommended practice in cold climates like that of north-eastern United States and northern and western Europe during winter cultivation of vegetable crops. The positive effects of CO2 in greenhouse vegetable crops are increased plant height, number of leaves and lateral branching, advanced flowering, high fruit numbers, high fruit yield and better quality of fruits.
It also affects flavour and quality of vegetables and its enrichment in greenhouse affects photosynthesis, growth and yield by decreasing the oxygen inhibition of photosynthesis in plants. The optimal CO2 concentration for growth and yield appears to be between 700 to 900 u/1-1.
Enrichment of the greenhouse with carbon dioxide at 1000 u/1-1 increase vitamin A content with lack of ventilation, but did not affect vitamin C content in tomato. The enrichment also increased the ascorbic acid content in tomato but this practice is limited up to United States and European countries and limited farmers in Israel are also following this practice.
If the environmental factors are modified or changed according to the vegetable crop requirement then the quality of vegetables can be increased manifold.
C. On Farm Value Addition:
Quality in high value vegetables can be measured by harvesting the vegetables on an appropriate stage of maturity separately looking to the available local and export markets. Harvesting of individual slicing tomato fruit is mostly done with attached calyx by using sharp knife or scissors, whereas cherry tomato fruits can be harvested in clusters as per the requirement of the market.
Sweet pepper fruits are also harvested with attached calyx after getting proper fruit colour on the plant itself. Similarly, slicing cucumbers are harvested by using harvesting knives or scissors to avoid damage to the plants and fruits. Summer squash fruits are also harvested on an appropriate stage of maturity as per the demand of the available market.
After harvesting, proper grading of the produce or fruits is done according to the standards specified by the Indian Standard Institution (ISI). Sorting and grading of produce can be done manually or also by using machines looking to the high cost and unreliability of manual sorting, especially in tomato.
Computer vision based sorting system is being used in several advanced countries, where tomato is classified according to shape, size, colour and surface defects. However, manually the grading is done according to size, shape, weight and colour of the fruits and three to four grades are made viz., A+, A, B and C.
After sorting and grading of the vegetables, packing must be classified widely depending upon the commodity to be packed, nature of the product and whether it is to be taken to the local market or transported to a distant market and the means of transportation available.
Now a day there is greater demand for the pre-packed vegetables in super markets and other elite markets like in European countries, USA, Japan etc. It reduces the labour and increase the disposal. Mostly the produce is pre-packed at the place of destination. The quality and appearance must be carefully and critically controlled to agreed standards to the market.
Slicing tomatoes can packed in packing of 1.0 kg by weight or 6-8 fruits by number but cherry tomatoes are packed in the boxes or containers in which mostly strawberries are packed and the packing is usually in 250 grams pack. Coloured peppers are also packed by numbers or by weight and generally there are four fruits in a pack. Slicing cucumber and summer squash fruits are also packed by numbers or by weight as per the demand of the super markets.
But supply to the five star hotels is done in open containers like plastic crates or boxes after grading of the vegetables and only A+ grade fruits are supplied to the hotels on a very high premium. So, this is the most essential step or operation required for maintaining quality in vegetables grown under controlled conditions adding value to the produce, thus, carving more prices to the growers.