Crop Establishment Techniques

Establishment of medicinal plants in field may be grouped into direct sowing and transplanting. Many of the field crops are sown directly in the well-prepared field. However, some of the crops like rice, tobacco, etc. are first sown in the small seed-bed (nursery) and then the seedlings are transplanted in the field. Transplanting of rice seedlings in the puddled field is followed in the South East Asia mainly for better weed control. The seedlings are large enough to compete with weeds that emerge later. Rather, weeds emerge about the same time as the seedlings from direct sowing and thus compete with the crop during the growing season. Tobacco seeds are small (0.08-0.09 mg) and the emerging seedlings are tiny and delicate. Hence, the seeds are unsuitable for sowing directly in the field and are sown in the nursery and tended carefully till the seedlings attain a particular size before transplanting in the main field.

Nursery Techniques

Adequate care is needed for successful raising of nursery. Choice of nursery field, land preparation, manuring, adequate facilities for irrigation and timely control of pests and diseases are required for the production of healthy seedlings.

Nursery Site

Nursery area should be a good fertile piece of land nearer to the water source. It should have good drainage facility and located at an elevated place. The field should be fully exposed to sunlight. It should be devoid of any perennial weed infestation. Nursery site may be regularly changed so as to minimize the incidence of pests and diseases and weed infestation. This will also eliminate contamination of other varieties.

Nursery Methods

Depending upon the method of preparation of land, nursery can be grouped as wet or dry nursery. In the wet nursery, land is puddled, leveled and pre-germinated seeds are sown. Land is ploughed to fine tilth and raised nursery beds are formed under dry condition. Dry nursery is also followed for rice in some of the situations.

Ideal Seedling

An ideal seedling should be healthy and free from pest and diseases. It should be robust and sturdy having shallow root system. Seedlings should be dark green in colour with high content of carbon and nitrogen.

Seeds and Sowing

Seed rate depends on test grain weight, germination percentage, spacing to be adopted and number of seedlings to be planted. Seed rate for rice can be calculated using the following formula:

Seed rate (kg/ha) = 1000 grain weight (g) x Number of seedlings per hill / Spacing (cm²) x 100

Corrections are made for germination percentage and another 20% seed rate is added to cover the risk.

After Care

Irrigation is regulated until proper germination and establishment of the seedlings. The beds are allowed to saturate till the sprouts are about 5 cm in height and thereafter, a constant level of 2.5 cm or water may be maintained. Pre- emergence herbicide, butachlor or thiobencarb @ 1.0 kg a.i/ha is applied 8 days after sowing to control weeds in the nursery. A thin film of water is maintained at the time of herbicide application and then allowed to disappear. Adequate plant protection measures are required to guard against pests.

Nursery is manured with organic manure, FYM or compost @ one ton per 1000 rrf. At the time of nursery preparation, diammonium phosphate (DAP) @ 2 kg MO m is applied. If the seedlings show symptoms of N deficiency and the growth is not satisfactory, urea is top dressed at the rate of 500 g per 40 m2, 7-10 days prior to uprooting seedlings.

Optimum Age and Pulling out of Seedlings

Optimum age of seedlings is important, especially for the short duration rice varieties having a very short vegetative period. Seedlings are ready for transplanting at four leaf stage. Normally one week period of nursery for one month rice duration is the thumb rule. The duration of nursery is 21-25 days for short duration, 25-30 days for medium and 35-40 days for long duration varieties.

Dapog Nursery

The dapog method of raising seedlings was developed in the Philippines. This involves growing seedlings on a concrete floor or on a raised bed of soil covered with polythene sheets. A small nursery area of 30-40 m2 is required for one ha of main field. Raised seed-beds are prepared after final land leveling and are covered with polythene sheets. Banana leaves with the midribs removed can also be used instead of polythene sheets. The polythene sheets prevent entry of roots into the soil. The dapog beds should be about 1.5 m wide and its length depends on the area to be planted. Pre- germinated seeds are sown on the top of the sheets at the rate of 2.0 kg/rrf of nursery. Water is sprinkled and the seeds are pressed gently with hand or with a wooden flat board twice a day for the first 3-6 days. This helps the roots to remain in contact with water retained on the surface and prevents drying. After six days, the seed-beds are watered up to a depth of 1-2 cm. In about 14 days, seedlings are ready for transplanting. By this time, the roots are well developed and interwine with one another so that the nursery can be cut into stripes, rolled and transported easily to the planting site. One m2 of dapog nursery can be used to transplant about 200 m².

Dry Nursery

In places of water scarcity, raising of dry rice nursery is practiced. The nursery area is ploughed under dry condition and the field is brought to fine tilth. Light soils are preferred for dry nursery bed preparation. Farm yard manure or compost @ 12.5 t/ha is spread uniformly and incorporated into the soil, 2-3 weekk before sowing. Long beds of convenient length and 1.0-1.5 m width are formed. Channels of 30 cm width between the beds are formed for irrigation.

The seeds are sown dry, either broadcast or in lines and covered with a thin layer of soil or compost. In some places, water is impounded into the bed and soil is stirred to form mud. After the clay particles settle, sprouted seeds are broadcast sown. Nursery beds are irrigated periodically. In dry areas and in calcareous and saline alkaline soils, chlorosis is the major problem in dry nurseries. Seed treatment with FeSO4 and flooding the soil may give some relief. The seedlings obtained from the dry nurseries are generally hardy and establish very fast in the main field.

Nursery Techniques for Tobacco

1. Nursery Preparation: Sandy or sandy loam soils are preferable for raising nursery. Seedlings rained in heavy soils with poor drainage are predisposed for damping- off disease. Raised beds are prepared with one m width and convenient length, not exceeding 10 in. All around the beds, channels are formed to a width of 50 cm and depth of 10 cm. The soil is removed from the channel and evenly spread over the bed and leveled. In heavy soils, sand is mixed in the bed to improve drainage.
2. Manuring: Proper manuring is important to obtain healthy and sturdy seedlings in a short time. Nitrogen, phosphorus and potash are essential. In sandy soils, magnesium should also be added. Nitrogen deficiency causes stunting and yellowing of seedlings resulting in poor growth. Excess nitrogen produces seedlings which are lanky and succulent and interferes with proper estuuhshnient in the main Held. High dose of organic manures gives better results. However, under unfavorable seasonal conditions, it pre-disposes the seedlings to damping- off disease which is difficult to control. A combination of organic and inorganic manuring is normally practiced.
3. Seeds and sowing: Tobacco seeds are tiny. One g of seed contains about 10,000 seeds and hence a low seed rate of 3 kg/ha of nursery is sufficient. Normally 40-60 m2 nursery area is required to plant one ha of main field. Seeds are broadcast- sown over the beds. Since the quantity is very low, the seeds are normally mixed with sand and sown in the beds. After sowing, the beds are raked with fingers to ensure proper covering of seeds with the soil. Shallow sowing to a depth of about 0.25-0.50 cm. is practiced.
4. Care of nursery: It is necessary to keep the surface of the bed moist till germination is completed. For the first ten days after sowing the bed is kept moist. Especially in the hot moons, even missing one watering can cause severe damage to the germinating seeds. Provision of covers and mulches over the seed beds is beneficial as they conserve moisture during germination. They also protect the tender seedlings from strong sunlight and beating rains. When the seedlings emerge, the cover can be removed. Otherwise, the seedlings may become etiolated and lanky for want of adequate sunlight. It is also necessary to harden the seedlings by withholding water a week to ten days before planting. This practice helps the seedlings to withstand the shock of transplanting.
5. Age of nursery: Normally seedlings of pencil thickness and with 10-15 cm height are preferred. Short seedlings may establish well under optimum 'conditions in heavy soils. However, in light soils lengthy seedlings are preferred. The seedlings are ready for planting in 7-8 weeks after sowing.