Everything you need to learn about the cultivation, production and growth of cucurbits in off-season under plastic low tunnels.
Vegetable growers often try to advance the growing season for selected vegetables for obtaining early market advantage. If the crops like muskmelon, round melon, long melon, cucumber, bitter gourd, bottle ground, etc., are produced early by a month or so during summer, they fetch remunerative price in the market. River bed cultivation is an age old practice for production of certain cucurbits in off-season in our country, but area for river bed cultivation is very limited.
The growing season can be advanced by planting the crops early in the season, especially in case of some cucurbits which can be grown during January to mid-February in low cost protective structures such as plastic low tunnels or row covers. The use of plastic low tunnels (row covers) and plastic mulching for off-season muskmelon, watermelon and summer squash production is a common practice in USA, Israel and in some European countries for fetching high price of the produce.
Row cover or low tunnel is defined as a flexible, transparent covering which is installed over the rows or individual beds of transplanted vegetables to enhance plant growth and yield due to raised temperature around the plants in the open field during winter. These structures also raise the soil temperature and protect the plants from hails, cold wind injury besides advancing the crop by 30 to 45 days.
The cover may or may not be supported with hoops and is intended to be left over plants for a relatively short period of time (2-8 weeks) depending on the crop and weather conditions. Synonymous terms for row covers include cloches, tunnels and low tunnels. The tunnel was made possible by the introduction of polyethylene film after World War-II.
Low tunnels may be used for 4-8 weeks immediately after transplanting or seeding where the added cost could be recovered through increased early season prices. Covers should be removed when plants begin to flower to allow proper pollination. Low tunnels increase heat unit accumulation by 2 to 3 times over ambient temperature. Two to four degrees of frost protection may also be increased under low tunnels as early yields, and in many cases total yields.
This low cost technology for off-season cultivation of cucurbits like muskmelon, watermelon, long melon, bitter gourd, bottle gourd, summer squash, etc., is very simple and highly profitable for the growers in northern parts of the country. Muskmelon, though is highly suitable for off-season cultivation under plastic low tunnels as it is sensitive to low soil and air temperatures.
Various steps for off-season cultivation of cucurbits under plastic low tunnels are as follows:
1. Nursery Raising:
Seedlings of the desired cucurbits are raised in the nursery greenhouse in plastic pro-trays having 1.5 inch cell size in soil-less media in the month of December or January depending upon the crop. The seedlings of 30-32 days age, which have attained four leaf stages, are transplanted under row covers or plastic low tunnels in the open field from mid-January to first week of February, when the night temperature is very low in northern India. In northern plains, summer squash can be transplanted even in the first to second week of December, whereas muskmelon and watermelon are transplanted during end of January to first week of February.
2. Preparation of Beds, Fixing of Hoops, Transplanting 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. The distance between the rows is kept 1.5 to 1.6 meter. Before transplanting of the seedlings on beds, flexible galvanized iron hoops are fixed manually at a distance of 1.5 m to 2.0 m.
The width of two ends of hoops is kept 45-60 cm with a height of 45-60 cm above the surface of the beds depending upon the crop and its planting time. Generally, the tunnels are made in North to South direction to receive maximum sunlight. Transparent plastic of 30-50 micron (Infra-red grade) is commonly used for making low tunnels, which reflects infra-red radiation to keep the temperature of the low tunnels higher than outside.
The plastic is, usually, covered in the afternoon after transplanting the desired cucurbitaceous crops during morning time. The plastic can be vented or slitted during the growing season as the temperature increase within the tunnel during the peak day time.
Generally, 3-4 cm size vents are made on eastern side of the tunnels just below the top at 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. Finally, the plastic is completely removed from the plants during February or March depending upon the crop, its growth and prevailing night temperature at that time.
3. Pollination:
Most of the cucurbits are monoecious in sex form and needs pollination, which is usually performed by honeybees (Apis melifera L.). 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 workers is sufficient. The beehive box is always kept on the north-west side of the field for best activity of the bees.
4. Fertigation and Plant Protection:
Fertilizers are applied through drip irrigation. During the first month i.e. January or February irrigation can be applied @ 4.0 m3 per 1000m2 at an interval of 6-7 days. After making fertilizer solution of N: P: K (5: 3: 6) is applied @ 80-100 ppm per cubic metre of water.
During second month 4.0 m3 of water can be applied at a duration of 4 days with fertilizer solution @ 120-150 ppm/m3 of water till beginning of flowering in the crop, thereafter the quantity of fertilizer, in case of muskmelon, 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 metre 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. The water and fertilizer requirement of a crop depends upon the growing season, variety and type of soil. If required, systemic insecticide like confider can be applied through drip irrigation for control of insects at an early stage of the crop when it cannot be sprayed under plastic low tunnels.
5. Harvesting:
If the muskmelon crop has been transplanted during first week of February, the fruits will be ready for harvesting during third week of April. The fruits from the mid-January transplanted crop can be harvested during first week of April, which is normally 45 days early than the normal season crop.
Similarly, other cucurbitaceous crops can also be advanced by 40-60 days in northern parts of the country. Off-season fruits produced under low tunnels can fetch very high price in the market. In case of off-season summer squash the fruit yield is usually very high (i.e., 50-70 tonnes/ha), whereas the yield of other off-season cucurbits is normal or 5-10% more over their open field cultivation.