|Low-external Input Rice Production (IIRR)|
Seeds used for planning require more careful handling than those used for grains (i.e., food or feed). Good quality seed spells good field emergence, seedling stand, crop growth, yields and healthy vigorous seeds. To obtain and maintain good quality seed, the following should be done:
Harvesting: As much as possible, harvest only during sunny days. Do not allow seeds to become too mature. Generally, it is best to harvest seeds 3040 days after heading in the wet season or 25-35 days after heading in the dry season (depending on earliness of cultivar). Grains in, panicles are yellowish brown at this stage. This allows enough time for the seeds to complete development but not too long that significant deterioration in the field occurs.
Seed Collection: Collect seeds only from healthy and vigorous plants (health of mother plants largely determines health of seeds produced). These mother plants may have already been identified long before maturity and have been given special care. Avoid plants along borders. Harvest seeds from the main, primary and secondary tillers together (seeds from the different tillers were found to have generally similar yields). If many cultivars are grown together in an area, make sure the seeds from each cultivar are well-identified and separated.
Seed Threshing and Winnowing: The germ or the embryo of the seeds must be protected from mechanical damage especially during threshing. Damaged seeds could result in non-germination or in seedlings which are abnormal. To minimize damage, sundry panicles for a few days before feeding them into mechanical threshers (if used). Clean threshed seeds by blowing or winnowing at least twice using native flat trays (bilao) to separate heavier seeds from light ones and from dust panicles and straw which may contain or attract insects.
Seed Threshing and Winnowing
Seed Storing and Invigorating: A panicle captains seeds which are premature (at the base), mature (at the middle) and over-mature (at the tip). When all the seeds in the panicle are collected, further upgrading is necessary to obtain only high density grains which are known to perform better in the field and in storage than those with lower grain density. Immerse and stir seeds thoroughly in water (1 kg seed/10 liter water). If available, use 6.5% ordinary salt solution (6.5 parts salt to 10 parts clean water, by weight). Alternatively, use 22% ammonium sulfate solution (2.2 parts salt-to 10 parts clean water). Ordinary soil/mud may also be used to increase the density of water. A good approximation of the right mixture (1.08 specific gravity for traditional tropical varieties) is when the blunt end of a fresh chicken egg sticks out by half inch above the surface of the solution. Most modern varieties require only water for effective sorting. Remove all floating seeds and debris and scoop out seeds that sink to the bottom. The solution may be re-used a few times. When seeds are meant to be stored, rinse the seeds with clean water. Dry-soaked seeds back to original moisture content before planting or storing.
For seeds that have been for quite some time (4-8 months) under ordinary room conditions, treatments may be-done to revitalize already partially deteriorated seeds to extend their storability or to improve performance of seeds to be planted immediately (seeds will germinate faster and more uniformly; plant growth and even yields are also perceptibly improved by approximately 10-20% with invigoration). Soak seeds for 2-8 hours in water (Or in the same salt solution used for storing, then rinse). Dry seeds properly (back to original moisture) before further storage or planting. Fresh seeds or heavily deteriorated ones (less than 60% germination) will not show improvements.
Seed Drying: Spread seeds thinly over a mat, sack or light-colored sheets laid on concrete floors or elevated surfaces. Airdry seeds for a day if moisture is relatively high (e.g., seeds wet from soaking or seeds from early harvest). Dry seeds under the sun for 3-5 days (avoid the 10 am - 2 pm heat) and stir constantly. Well-dried seeds (8-10% moisture) split with a cracking sound when bitten between teeth.
Seed Storage: The three common enemies of a seed in storage are high moisture (or humidity), high temperature and insect pests. For short-term storage (i.e., seeds kept for next planting season), keep dry, clean, healthy seeds in paper or plastic bags and store in a cool shady, dry place in the house or yard away from rodents and birds. Seeds may be kept in the panicles and hung on top of the kitchen stove. For longer keeping, use sealed tin cans or air-tight containers, one-third full of dry charcoal, ash or lime (1 part material/2 parts seeds to completely fill the container). For insect protection, coat seeds with ash, lime, vegetable oil (1 tsp/kg seed) or incorporate some botanicals, e.g., Gliricidia (kakawate) or other protectants like napthalene balls into the container. If sacks are used for storage, they may be treated with Makabuhay (Tinospora rumphii) or red pepper extract (prepared by cutting fresh material into small pieces then soaking and thoroughly mixing these in water). Sacks are then soaked in this for 4-6 hours, then dried. Do not use the seeds with protectants as food.
1. In flooded soil where oxygen is often inadequate for germination, soaking seeds with 40% calcium peroxide could increase germination, seedling survival and even yield.
2. In zinc deficient soil, coating of seeds with zinc oxide (or other forms of zinc) or soaking 2% suspension improves grain yield by 10-20%. Seedlings may also be dipped in the same solution before transplanting.
3. For treatments to break dormancy, see appropriate section. Soaking seeds in 50-56°C for 10-15 mins could break dormancy and at the same time control common pests and diseases.