RICE is grown here under diverse climatic and edaphic conditions. Basmati predominates in traditional rice tracts of Punjab. Temperate Japonica rice is grown in Swat at high altitude in the mountainous valleys. IRRI type long grain heat-tolerant variety of tropical rice is grown in the south of NWFP, Sindh and Balochistan.
Transplanting is the major method of growing rice. In this method rice is grown in a nursery, pulled and transplanted into well puddle and prepared field. Rice seedlings can either be transplanted manually or by mechanically. In transplanted rice, spacing between hills varies with variety and seedling age. A spacing of 20 x 20 cm is recommended. A hill should be transplanted with two healthy seedlings.
For transplanted seedlings, age is a major factor in determining yield. Transplanting shock, this is a setback to growth due to uprooting and replanting of seedling, increases with increased age of seedling. In general, the effect of transplanting on yield increases with the decreasing age. Seedling age also varies with environmental conditions and the type of nursery. The physical and bio-chemical factors set a minimum and maximum age for a particular nursery. Minimum age of a seedling for transplanting is about 15-20 days. However, ideal seedling age is about 30 days; tilling capacity is reduced if older seedlings are transplanted.
Nursery seedlings: Rice which is to be transplanted into puddle soil must first be nursed on seed beds. The main reason for rising nursery is to provide seedlings a substantial head-start on weeds. Rice nursery is raised by four methods in world, viz. the wet-bed nursery, the dry-bed nursery, the dapog and mat type in trays. Each has its advantages and disadvantages. Dapog method originated in the Philippines and is now fairly common in South East Asia, but not practised in Pakistan. Mat type is being introduced in the country. Wet-bed and dry-bed methods are common here depending on the soil and water availability.
The wet-bed method is popular worldwide. It is used in areas where water is adequate. In our country, it is commonly followed in Punjab and the NWFP. The area selected for nursery is watered for about 30 days before sowing. It helps in eradication weeds. When weeds germinate after a week, the field is thoroughly puddled and levelled. Clean seed is shifted into gunny bags and soaked in water for 24 hours. After soaking it is placed under shade and covered with gunny bags. Water is sprinkled over seed after intervals and turned with hands about three times in a day for proper aeration and avoiding damage by heat due to suffocation. After about 36-48 hours, the seed sprouts and is ready for sowing. Pre-germinated seeds are then broadcast in seedbed. Once the seedlings are established, the nursery is impounded with water. Water level is then raised gradually. Some decomposed organic manures and small amount of inorganic fertiliser as basal dose may also be added in the nursery. Remember to flood the beds while uprooting. Uproot seedlings by holding at a few times between thumb and forefinger at the base of culms and pulling sideway.
The dry-bed method of nursery is practised in dry soil conditions. The fields are prepared under dry conditions. Seeds beds of convenient dimensions are prepared by raising soil to a height of about 5-10 cm. A thin layer of farmyard manure or half burnt paddy husk could be spread over nursery bed mainly to facilitate uprooting. In this method, soaked seed are spread over seedbed and then irrigated. In some areas of Punjab rab method of nursery raising is also practised.
Nursery raised by soaking seeds and then broadcasting pre-germinated seeds may be ready for transplanting within 40-45 days under both system of nursery growing. For decades, our farmers are using pre-germinated seeds for rice nursery raising that result in poor and delayed germination. Not only it is very difficult to handle the pre-germinated seeds but it also makes the nursery sowing a tedious job. Nursery seedlings thus raised can be transplanted when they are 40-45 days old, while, 30-day-old seedlings are considered ideal for transplanting. Older seedlings result in lower tilling capacity thus reducing the final yield. Sub-optimum plant population and uneven crop stand resulting from poor nursery seedlings are the most important yield limiting factors in the traditional rice production system which ultimately results in low paddy yield. Success in raising healthy rice seedlings depends mainly on planting high quality seeds with increased vigour. Seeds with enhanced vigour have high percentages for germination and vigorous seedling growth than seeds low in vigour generally produce weak seedlings that are susceptible to environmental stresses. Seeds high in vigour generally provide for early and uniform stands that give seedlings a competitive advantage against environmental stresses. Improved seed invigoration techniques like seed priming are being used to reduce the germination time, to get synchronised germination, improve germination rate, and better seedling stand in many field crops like wheat, maize including rice.
These seed priming techniques including hydro priming, osmo-conditioning, osmo-hardening and hardening has been successfully employed for earlier and better nursery stand establishment, which result in improved performance of traditional rice production system.
Recently, after a series of trials at farmer’s field of districts of Sialkot, Sheikhupura and Faisalabad, researchers at the Department of Crop Physiology, University of Agriculture, Faisalabad, have successfully established an improved method of nursery raising by using primed seeds instead of pre-germinated seeds as in case of traditional method of nursery raising. The seed priming techniques like osmo-hardening with CaCl2, followed by hardening and osmo-hardening KCl are found the most effective and promising seed priming techniques in both coarse and fine rice varieties for raising healthy and vigorous nursery seedlings growth.
These seed priming techniques not only improve nursery seedlings and performance of improved nursery seedlings, increased growth, yield and quality of transplanted rice production system are also reported. Rapid and more uniform germination and seedling growth, younger seedlings are able to be transplanted after 25-30 days which result in higher tilling that ultimately lead to improved kernel yield of the transplanted rice.
Transplanted rice raised by improved nursery method is also resistant to lodging due to natural calamities such as windstorm having healthy and vigorous seedling growth of main culms and secondary branches and deeper, more vigorous and fibrous root system development.
It should always be kept in mind that it is really very easy to raise healthy seedlings by primed seeds if one is prepared to take enough time to do the job properly. Success in raising healthy rice seedlings depends mainly on the constant supervision and proper management.
Authors: Dr Shahzad M. A. Basra, Dr M. Farooq & Hafeez ur Rehman