Growing crops without soil | The Daily Star
12:00 AM, January 12, 2010 / LAST MODIFIED: 12:00 AM, January 12, 2010


Growing crops without soil

Cucumbers growing on rooftop using hydroponics technology

HYDROPONICS is a modern method of crop production. In this method, crop is grown not on soil, but artificially in a protective environment using mineral nutrient solutions in water. In the 19th century, scientists discovered that plants absorb essential mineral nutrients as inorganic ion in water. Soil acts as a mineral nutrient reservoir. When water is added to the soil, it dissolves the mineral nutrients. Those are absorbed by plant roots. Soil is no longer required for plant growth when mineral nutrients are properly introduced into plant's water supply artificially.
Hydroponics is used to grow high value crops like fruits, vegetables and flowers commercially in Europe, USA, Japan, Taiwan, China, Thailand, Singapore, Malaysia and the Middle East.
As no soil is necessary, this method can be profitably applied to grow crops in window-boxes or on rooftops in a crowded city where there are no gardens to grow fresh vegetables and fruits.
Deserts, rocky and stony ground in mountainous areas or barren and sterile lands may be made productive at a relatively low cost through the adaptation of hydroponics. As the plants are not susceptible to soil-borne diseases, the quality of the produce is excellent. The plants are not affected by weeds, which are a source of serious problem in the traditional method of crop production.
For raising seedlings, 25 mm by 25 mm size sponge blocks are used. In the middle of each block, one seed is placed. Seeds are treated before putting in the blocks. The blocks are then put in a tray having 50 to 80 mm water so that sponges can easily float in water. Seedlings of appropriate age are later placed in holes made on cork sheets to grow plants.
There are usually two systems of hydroponics. In the circulating system, nutrient solution is made to flow past the roots of plants in trays for at least seven to eight hours by pump through pipes. In the non-circulating system, plants are grown in containers of nutrient solution, such as glass jars, plastic buckets, tubs or tanks. No pumps or water circulation is required. A gap of 50 to 70 mm is maintained between solution and cork sheet placed above it in such a way that roots are above the solution to get oxygen. Holes are made in cork sheets so that plants can get required oxygen through it. It has been estimated that water requirement in hydroponics is as little as 1/20th, or 5% of the amount used in a regular farm to produce the same amount of food.
Nutrient solutions are made of potassium nitrate, calcium nitrate, potassium hydrogen phosphate and magnesium sulphate. Various micronutrients like iron, manganese, copper, zinc, boron, molybdenum etc., are typically added to the hydroponics solutions. Solutions are added in trays after every 12 to 15 days.
Proper maintenance of pH and electrical conductivity (EC) is very important in hydroponics. pH and EC should be checked in the morning and afternoon to maintain them between 5.8 to 6.5 and 1.5 to 2.5 ds/m, respectively.
In recent years, the scientists of Bangladesh Agricultural Research Institute (BARI)) have successfully produced cucumber, tomato, lettuce, capsicum, strawberry and marigold in both circulating and non-circulating systems. It is expected that this modern method of high value crop production will be adopted in the near future as entrepreneurs are coming forward to invest in agriculture on a commercial.

The writer is an Agricultural Engineer and former DG, BARI.

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