Plastic Low Tunnel Technology for Off-Season Cultivation of Cucurbits

Vegetable growers, for getting higher prices from their off-season produce, often try to send their produce to the market early in the season and also try to extend the growing season for selected vegetable crops for the purpose of obtaining marketing advantage of their off-season produce.  For example, crops like long melon, round melon, bottle gourd, bitter gourd, muskmelon summer squash etc. if grown early in spring or early summer often command a greater price on the market. Also producing crop when large quantities of the crop produce are not available (considered as “off-season”) can also command greater prices and increased demand.

Presently, river bed cultivation is in practice for production of cucurbitaceous vegetables in off-season in northern parts of our country, although area under river bed cultivation is very limited, which can not be extended further, but with the use of protective structures such as row covers or low tunnels vegetable crops like muskmelon, watermelon, long melon, round melon, bitter gourd, bottle gourd, summer squash etc. can be grown very early in the spring or summer season.  Important factors which are considered for off season cultivation are 1) increased costs of using season, extender production systems, 2) potential increase in sale prices of the crop if produced either earlier or later,  3) suitability of the crop to season extender production systems. The use of plastic low tunnels for off-season melons and summer squash production is a common practice in Israel for export of the produce to European countries.

Row covers or low tunnels are flexible transparent covering that are installed over the rows or individual beds of transplanted vegetables to enhance plant growth by warming the air around the plants in the open field during winter season. They can also warm the soil and protect the plants from hails, cold wind, injury, and advance the crop by 30 to 40 days than the normal season. This low cost technology for off season cultivation of cucurbits like muskmelon, round melon, long melon, bitter grand, bottle gourd and summer squash etc., is suitable and may be quite cost effective for the growers in northern parts of the country, where the night temperature during winter season goes below 8^oC for a period of 30-40 days. The major steps involved in this technology are as under:

Nursery raising for off-season cultivation of cucurbits

Seedlings of the desired cucurbits are raised in the nursery greenhouse in plastic pro-trays having 1.5" cell size in soil-less media in month of December or January and 28-32 days old seedlings at four leaf stage are transplanted under row covers or plastic low tunnels in the open field from mid January to mid February, when the night temperature is very low in northern parts of the country. Nursery of these crops can be also be raised even in polythene bags under very simple and low cost protected structures like walk-in tunnels or in locally available plastic trays in soil less media as per the need of the area. Crops like summer squash can be transplanted even in the month of December for complete off-season production and this crop will be ready for harvesting in the first week of February and can fetch very high price in the market.

Preparation of beds, fixing of hoops, transplanting of seedlings and covering of plastic

Transplanting of the seedlings is done in a single row on each bed at a planting distance of 50 cm on drip system of irrigation. Distance between the rows in usually kept 1.5 to 1.6 metre. Before transplanting of the seedlings on beds, flexible galvanized iron hoops are fixed manually on a distance of 1.5 m to 2.5 m. The width of two ends of hoop is kept 40-60 cm with a height of 40-60 cm above the levels of the beds for covering the plastic on the rows or beds for making low tunnels.Transparent, 30 micron, IR grade plastic is generally used for making low tunnels, which reflects infra-red radiation to keep the temperature of the low tunnels higher than outside field. Now-a-days with the introduction of biodegradable plastic for making low tunnels and for mulching purposes, it is not only eco-friendly but it may be sustainable technology for off season vegetable production.  This biodegradable plastic is available according to the requirement of the duration one want to cover the crop or use as mulch in the crop.  After that period the plastic after receiving sufficient sunlight, it becomes brittle. The film eventually breaks down into small flakes and finally completely composted in the soil. The plastic is usually covered in the afternoon after transplanting the desired vegetable like muskmelon, summer squash, bottle gourd, bitter gourd, round melon, cucumber etc. The plastic can be vented or slitted during the growing season as the temperature increase within the tunnels during the peak day time. Generally, 3-4 cm size vents are made on eastern side of the tunnels just below the top on a distance of 2.5 to 3.0 m after transplanting, and later on the size of the vents can be increased by reducing the distance between two vents with the increase in the temperature and ultimately the plastic is completely removed from the plants in month of February and March depending upon the date of transplanting growth of the crop and prevailing night temperature in the area.

Fig-1 : Low tunnels for off-season vegetable cultivation

Pollination under plastic low tunnel crops

Most of the cucurbits are monoecious in sex form and needs pollination, which is usually performed by honeybees (Apis melifera). When there is complete flowering bees can work in tunnels easily through the vents, made on the plastic. For effective pollination in crops like muskmelon, summer squash etc, one beehive, having 30000-50000 workers is sufficient for one-acre area. The beehive box is always kept on the northwest side of the field for effective working of the bees.

Fertigation and plant protection in low tunnel muskmelon crop

Fertilizers are applied through drip irrigation. During the first month (i.e. January or February) water can be applied @ 4.0 m³/1000m² at an interval of 6-7 days. After making fertilizer solution of N: P: K (5:3:5) is applied @ 80-100 ppm per cubic meter of water. During second month 4.0 m³ of water can be applied on duration of 4 days with fertilizer solution @ 120-150 ppm/m³ of water till beginning of flowering in the crop. Thereafter the fertilizer quantity is reduced to 20-30 ppm till the fruits are of lemon size after that the quantity is again increased to 120-150 ppm per cubic meter of water. Before the ripening of the fruits, the quantity of fertilizer solution is again reduced to 50-60 ppm for enhancing the quality of fruits in muskmelon. But in other cucurbits the quantity of fertigation is always in increasing order, starting from 50 ppm to 300 ppm at the peak fruiting period. The water and fertilizers requirement of crops is usually depends upon the growing season, crop and variety and soil conditions. If required systemic insecticide like confidor can be applied through drip irrigation water for control of insects at early stage of the crop when the crop is under plastic tunnels and no foliar spray is possible.

Harvesting and crop advancement

If the muskmelon crop has been transplanted in first week of February the fruits will be ready for harvesting in third week of April. Fruits from the mid January transplanted crop can be harvested in first week of April, which is normally 30-40 days early than the normal season. Similarly other cucurbitaceous crops can be advanced 40-60 days early than the normal season of growing under low tunnels in northern parts of the country. Crops like summer squash can be transplanted in first week of December, which are ready for harvesting in the first week of February, and can be treated as complete off-season crop. Different cucurbits can be transplanted from first week of December to first week of February and can be advanced 30-60 days over their normal season of cultivation (Table 1). Off-season fruits produced under low tunnels can fetch very high price in the market. This technology is quite economical for growing off-season vegetables in peri-urban areas of the northern plains of the country.

Table 1: Transplanting, crop advancement and expected cost benefit ratio in cucurbits.

S. No.	Crop	Transplanting time	Harvesting time	Crop advancement	Expected cost benefit ratio
1.	Summer squash	First week of December	First week of February	60 days	1:3 to 1:4
2.	Muskmelon	Third week of January to first week of February	Second week of April to Last week of April	30-40 days	1:2.5 to 1:3.5
3.	Bottle gourd	Third week of January to first week of February	Second week of April to Last week of April	30-40 days	1:2.5 to 1:3.5
4.	Bitter gourd	Third week of January to first week of February	Second week of April to Last week of april	30-40 days	1:3 to 1:4
5.	W. Melon	Third week of January to first week of February	Second week of April to Last week of April	30-40 days	1:2 to 1:2.5
6.	Cucumber	Third week of January to first week of February	First week of February	30 days	1:3 to 1:4

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Authors:
Rupesh Lawwa and Balraj Singh
Centre for Protected Cultivation Technology,
Indian Agricultural Research Institute, New Delhi-12
Ph. 011-25841063, 25842481 Email: rlawwa@gmail.com

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