Introduction
Because better seed results in healthier seedlings which may lead to higher yields, the importance of planting only the highest quality seed cannot be overemphasized. Seedlingvitality in the early growth stages is largely the result of careful seed selection and preparation. Furthermore, since seed cost and availability are often two major economic constraints to small farmers, it is important that they know how to calculate the precise amount of seed needed to plant their farms. One of the most effective ways to improve a farmer's yield and to help derive maximum utility from his limited resources is by teaching him to select only the best available seed, to calculate precisely the quantity he will need, and to prepare a good seed sample for sowing.
I. Selecting Rice Seed
Only the best seed should be selected for planting for the following reasons:
- good seed results in healthier, heavier, and potentially higher-yielding seedlings.
- good seed results in seedlings which recover quickly from transplanting shock.
- good seed results in rapid root growth, enabling seedlings to draw nutrients from the soil quickly and effectively.
- good seed results in uniform germination and growth of seedlings, making it easier for the farmer to time crop management practices (e.g. transplanting, irrigation, fertilization, weeding).
- good seed has a high germination rate, facilitating exact calculation of seed requirements and thus preventing wastage d´," to nursing of too few or too many seedlings.
A good sample of rice seed should be:
- genetically pure (Genetic purity cannot always be determined by visual inspection; the best way to ensure genetic purity is by obtaining seed from a reliable source - e.g. the Ministry of Agriculture, an international agricultural organization - or by encouraging farmers to produce their own seed.)
- dried to less than 14% moisture content (since improperly dried seed often rots during storage.)
- capable of germinating at a rate of at least 80% (since it is usually uneconomical to plant seed if a considerable portion will not germinate.)
- free of weed seeds - free of diseases - free of Pest infestation
- free of inert matter (e.g. chaff, empty grains, grit, broken grains.)
Important: When dealing with seed of unknown origin, always remember that it is often impossible to evaluate a seed sample merely by looking at it. Genetic impurities, improper dryness, disease contamination, and pest infestation often do not manifest themselves until the seed is sown and has started to grow. Be sure to test a small portion of the sample (by actually growing an experimental plot) to ensure that the seed is acceptable. Never commit a farmer to growing seed which may turn out to be of poor quality.
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| Seeds preparation |
II. Testing the Germination Rate
When the time comes to calculate how much seed rice will be needed to plant a particular area, it will be important to know what percentage of the available seed will actually germinate. Seed may not germinate for several reasons: it may be dormant (incapable of germinating until a minimum interval has elapsed after the seed matured), or it may no longer be viable (the embryo may no longer be alive). When dealing with a seed of unknown age and quality, it is always a safe bet to test the germination rate to avoid wasting money, time, and effort in replanting if the sample fails to germinate well.
Various germination tests can be performed to determine germination rates. One of the simplest and most inexpensive tests - and one that many farmers can learn to do themselves - is the Rag Doll Test.
(Materials required: several teaspoonful of the seed to be tested, 3-5 handkerchief-sized rags, 3-5 small sticks, several short lengths of string.)
1) Soak the rags in clean water and spread them out on a flat surface.
2) From the seed sample, count out exactly 100 grains for each rag and distribute the grains evenly around the cloth (ten rows of ten grains facilitates counting.)
3) Carefully roll each rag around a separate stick, leaving the seeds undisturbed inside
Figure
4) Fasten the rags to the sticks with string and store the finished Rag Dolls in a warm moist place for five (5) days.
5) Moisten the cloth several times every day (this is very important; if the Rag Dolls are allowed to dry out, the seeds will die.)
6) After five (5) days, unroll the rags and count the number of seeds with roots. If each Rag Doll contains exactly 100 seeds, the number of sprouted seeds will equal the germination rate of the sample (e.g. if 85 seeds out of 100 sprouted, the germination rate equals 85%)
7) Average out the germination rates indicated by the 3-5 separate Rag Dolls to derive a more reliable overall germination rate.
Note: A germination rate of at least 80% is generally considered acceptable. If the germination rate is 60-80%, remember when procuring seed that more than usual will have to be nursed to compensate for non-germinating seeds. If the germination rate is lower than 60%, the rice should probably not be used for seed (unless there is no other seed available, or unless it is of an uncommon variety which the farmer especially wants to multiply).
Caution: If a seed sample has an unacceptable germination rate, do not encourage a farmer to eat it unless you and s/he are certain that the seed has not been treated with pesticide.
III. Soaking and Incubating Seed
Rice seed should be soaked in clean water and then incubated prior to sowing on seedbeds or directly into tilled soil. Soaking and incubation ensure that by the time the seeds come into contact with the soil they will already have germinated. Pre-germination encourages rapid, even growth and minimizes the danger of seed being washed away (since the emerging radicle quickly burrows down into the soil to anchor the seed in place).
a) Soaking
When the seed is ready to be pre-germinated (approximately 3-4 days prior to sowing), a specific-gravity cleaning method should be used to extract all empty and partially-filled grains. Pour the seed into a bucket containing clean water and stir gently. Discard all grains which float to the surface; they contain less endosperm than those which sink and will tend to give rise to weak seedlings. (Note' many farmers will be reluctant to discard what will seem to them to be perfectly good seed. As a demonstration, encourage the farmer to sow the floating seed separately from the rest. The two stands of seedling should show a marked difference in terms of germination rate and seedling vitality.) When the floating grains have been removed, soak the remaining seed in clean water for 24 hours. Soaking ensures that enough water will penetrate through the husk to cause germination in the embryo.
b) Incubation
After the seed has soaked 24 hours, drain off the standing water and transfer the wet seed into a burlap sack (if a sack is unavailable, use a basket lined with leaves Make sure the sack (or basket) is filled only very loosely, to permit expansion of the seeds during incubation. Incubate the seed in a warm, shady place for approximately three days, making sure to moisten the sack several times each day. Mix the seed periodically by hand, since toward the center of the sack the germination process will generate considerable heat. Turn the sack daily to discourage the emerging radicles from growing down (they'll try to). When the radicles have attained a length of approximately 1/2" sow the seeds. Avoid letting the radicles grow longer, as they will penetrate the walls of the sack and/or intertwine. When handling germinated seed, always remember that the newly-emerged radicles are extremely sensitive and succomb easily to drought stress, extreme temperature, and/or rough handling.
Figure
IV. Calculating Seed Requirements
There exists no exact formula applicable to all situations for calculating the amount of seed needed to plant a given area. Several important variables affect seed rice calculations, and they should be taken into account in the case of each individual farmer.
The most significant variables includes
- size of the individual grains The size of the individual seed grains can vary enormously from one variety of rice to the next. Thus, a 10-lb. sample of a small-grained variety may contain twice as many actual grains as a 10-lb. sample of a large-grained variety (so that a farmer will have to sow only half as much seed by weight of a small-grained variety to produce the same number of seedlings).
- germination rate of the seed sample The germination rate must be taken into account whenever seed requirements are calculated, since even the most careful calculations will yield an incorrect figure if only a portion of the seed ends up germinating. (To cite an extreme example, if the Rag Doll Test indicates a germination rate of only 50%, then the farmer must nurse twice as much rice as usual to compensate for half the seed not germinating.)
- farmer's planting practices Differences in planting practices cannot be overlooked airing seed requirement calculations. A farmer who plants 2-3 seedlings/hill at a wide spacing will make a small number of seedlings go a long way, whereas a farmer who plants 8-10 seedlings/hill at a close spacing will require more rice. Remember also that different varieties may require different spacings - this, too, will affect seed requirements.
- presence of inert matter in the seed Since farmers sometimes work with seed produced locally under less than ideal conditions, they occasionally must use seed containing large amounts of empty grains, chaff, weed seeds, and grit. Extraneous substances such as these must be taken into account whenever seed requirements are calculated. A farmer accustomed to sowing 20 lbs. of high-quality seed will experience a seedling shortage if he fails to recognize that the 20 lbs. of inferior seed he nursed this year in fact contained 2 lbs. of chaff and grit (hence only 18 lbs. of actual seed).
Because of these and other variables, there exists no universal formula for calculating seed rice requirements. Perhaps the simplest and most effective approach to the problem of calculating seed requirements is to conduct a small experiment with each farmer to determine requirements on an individual basis. Begin by encouraging each farmer to sow a small amount of seed - perhaps 5-15 lbs. Assist the farmer in all stages of seed selection and preparation, and at the time of transplanting offer advice about proper spacing of the seedlings. Then measure the area the farmer was able to plant with a known quantity of seedlings. By extrapolating, you should be able to determine the seed requirements for the entire farm. Record the information for future reference.
Note: Sometimes it will be necessary to calculate seed rice requirements far in advance of actual planting - for example, if seed for an entire farming region is being ordered in bulk months in advance. Under those circumstances, a useful "ball-park" figure to work with is 1 bushel seed/acre of swamp (for transplanted rice). This rate will tend to be a bit generous, bit it is always best to play it safe when estimating seed requirements. Leftover seed can usually- be put to good use, whereas a shortage of seed could prove disastrous should additional supplies be unavailable.
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| Ready for sowing |