Rice (Oryza sativa) belongs to the family of cereal grasses, along with wheat, corn, millet, oats, barley, rye, and numerous others. The grass family provides the world with over 60% of its caloric intake and over 75% of the protein for developing nations. The parts of the rice plant may be divided as follows: - roots, stem and leave, reproductive organs and the grain.
As the underground portion of the plant, the roots serve as support, draw food and water from the soil, and store food.
III Stem and Leaves
The role of the stem (or culm) is to support the leaves and reproductive structures, and to transfer essential nutrients between the roots, the leaves, and the reproductive structures. The stem is made up of a series of nodes and internodes in alternating order, and a mature internode is hollow and finely grooved.
The leaves function as the principal organs of photosynthesis and respiration.
IV Reproductive Organs
The panicle, or flower cluster, contains the reproductive organs of the rice plant. The panicle stands erect at blooming, but it usually drops as the spikelet’s fill, mature, and develop into grains. Varieties differ greatly in the length, shape, and angle of the primary branches, as well as in the weight of the overall panicle.
Each individual spikelet contains a set of floral parts. The flower consists of six stamens and a pistil. The stamens (which contain pollen or "sperm") are composed of two-celled anthers borne on slender filaments. The pistil consists of the ovary (containing the ovule, or "egg"), the style, and the stigma. During reproduction, the stigma catches pollen from the stamens and conducts it down to the ovary, where it comes into contact with the ovule and fertilization occurs.
The grain is the seed of the rice plant, a fertilized and ripened ovule containing a live embryo capable of germinating to produce a new plant.
Step 2: The growth stages of rice
The stages vary depending on the variety, ripening phase takes about 30 days, reproductive phase (40-45 days) and vegetative phase varies with each variety.
Step 3: Variety selection
3.1 Why suitable varieties?
A suitable variety gives good yields, taste good, and have a high market value. It’s important to select suitable varieties for each field due to their differences in soil quality and the risk of flooding or drought. This minimizes the risk of crop loss or failure and ensures good yields.
3.2 What is the criterion of selecting suitable hybrid varieties?
The most important decision relating to seed is the choice between hybrid seed and Open pollinated (OP) varietal seed. Rice hybrids are new to the market in East Africa, and offer farmers an additional choice when deciding what to plant. When choosing any variety to plant, it is important to choose one whose value has been demonstrated in your area, through tests, farmer’s demos or other means. Some of the differences between hybrids and OPVs are as follows:
Table 1; Differences between hybrids and OPVS
|Replant||Cannot be replanted; new seed each season||Should not be replanted|
|Disease||Generally better in disease||Resistance Normal (as expected)|
|Maturity||Often earlier, always more yield per day||Often longer maturity|
|Quality||Quality is average of two parents||Depends on the variety|
|Cost||Seed cost is higher, often 2-3 times||Cheaper|
|Profitability||Higher profits due to much higher yields||Less profitable|
Step 4: Seed selection
After the decision is made to buy hybrid or OP varietal seed, the next consideration is the quality of the seed. Good seeds are clean and pure (contains only grains from one variety) and healthy (full big grains, same color and no cracks). They have no stones, soil particles and weeds. Good seed reduces the necessary seed rate, provides healthy and strong seedlings, gives a uniform crop stand in the field, and results in higher yields. Every farmer should buy certified seed that is pure and labeled, or produce their own good seeds. Also, it’s important to remove unhealthy and insect damaged plants/panicles. Every time a farmer plans to plant, they should ask if the seed is certified. AFRITEC seeds will always have high germination, certified seed in their seed bags, and a way to verify the contents are as labelled. In Kenya, KEPHIS provides a system to check for authenticity but in other countries, AFRITEC will provide the same. After you identified a seed provider, the farmer needs to determine which variety (ies) will be suitable for the farm. Does the crop maturity fit the availability of water in the scheme, and does it have resistance to the diseases common to the area? It is very important to remember that farmers cannot replant hybrid seed. The next generation will have tall and short, late and early plants, and probably differences in grain shape as well. Hybrid seed MUST BE PURCHASED EACH SEASON. While most farmers currently replant their own OP Varietal seeds, even this practice is not advisable. Each generation this replanting practice will result in a 3-5% yield loss; if a farmer buys from a neighbor, she will have no idea about the true variety she is getting, diseases neither present nor how many generations old the seed might be.
Step 5: Field preparation and management of flooded soils and dry seeding
5.1 Steps for field preparation for direct seeding
Direct seeding field preparation is simple and cheap. It usually consists of; -
1. A light harrowing, no more than 10cm deep. DO NOT use a disk plow if it can be avoided.
2. Preplant fertilizer can be applied after the first pass, and a second pass can incorporate the fertilizer into the soil some 3-5cmdeep.
3. A pass with a smooting disk, even a heavy metal or wooden beam will smooth the surface, and make it suitable for planting.
4. String and digging sticks are all that is required to mark the field for planting. It can then be seeded as discussed above.
5.2 Steps for field preparation for Transplanting
The field preparation is more complicated and expensive. The following steps are followed; - 1. First, raised seed beds should be constructed, so that these beds will not flood. One meter sq for every 50g of seed used is recommended. The seed is spread on top of the raised beds, and lightly covered with soil or rice straw. 2. The beds are watered indirectly; the areas are flooded, but the raised beds are not covered with water. 3. In the time it takes for the seedlings to reach proper size, the fields can be prepared. 4. This is typically done by flooding the fields, then working the soil with a rotavator, or by hand with a Jembe. The latter is time consuming and laborious. 5. After some 20 days (this can vary from 10-21 days depending on other variables, the plants are pulled and transplanted. 6. Fertilizer can be incorporated into the mud, but this is not a common practice.
Step 6: Planting Rice Hybrids and varieties
The techniques for planting are either by direct seeding or transplanting as described below. However, the only difference between hybrids and varieties is the amount of seed normally used. Because of the increased vigor and tillering ability of hybrids, it is common to use 30% to 50% less seed for hybrids than varieties. The main objective of seeding rates is to generate 350 to 400 panicles per square meter. It is at this level of panicles that both OP varieties and hybrids reach their maximum yield potential. AFRITEC recommends 40kg/ha seed for our OP Variety AT058, but know most farmers plant as little as 20kg/ha. This is likely not enough seed to generate 400 panicles per M2. AFRITEC recommends 20kg/ha for hybrids, and we know this does generate sufficient panicles to maximize yields.
6.1 Direct seeding
Direct seeding as preferred by AFRITEC is the placement of seeds into rows in dry soil. It requires the digging of shallow trenches about 1-2cm deep, 20 cm between furrows. The seed is placed into these furrows about 2-5cm apart, and covered with a 1 cm of soil. The field is then watered and drained, and the seed germinates. Ideal plant spacing will be about 5cm x 20cm
Transplanting, of course, involves the use of seed beds to germinate and grow seedlings for 1021 days, then the uprooting of these seedlings and transplanting them into wet, puddled soil. Spacing’s for transplants varies widely, but a spacing of 15cm x 20cm is common.
Step 7: Early weeding versus herbicides
Like all crops, rice requires early weed management until the crop covers the rows, and shades out weeds. Weed control is important to prevent losses in yield and production costs, and to preserve good grain quality. Specifically, weeds decrease yields by direct competition for sunlight, nutrients, and water; increase production costs such as higher labor or input costs and reduce grain quality and price. Control of weeds during land preparation is crucial to reduce the amount of weed pressure in the field. The weeding regime is different for Direct Seeded and Transplanted, and the approaches are discussed below:
7.1 Direct Seeding in rows
It is very difficult to manually weed in a drill seeded rice crop, and as a result, herbicides are strongly recommended. Even in transplanted rice, herbicides are being used more frequently. Preplant weed control: Glyphosate can be used to clean fields before planting. This non-selective herbicide can be used for 2-3 days after the crop is planted and flushed. Post plant weed control should be done with selective herbicides. A number are available in Kenya, Including Satranil and others (see appendices). o The first application should be made approximately 14 days after the first flush, but should be judged by growth stage of the weeds. Herbicide effectiveness goes down dramatically if the weeds have more than 2-3 leaves. Generally, 2/3 of the total dosage is applied in the first application . The second application is made at 29 or 30 days, just a day before the application of the permanent flood, ensuring full absorption before the flood is applied. o If the flood is maintained, there should be few weed problems, as the water will prevent the germination of seeds which are under the soil. However, if the flood is allowed to go down and expose the soil, weed seeds will immediately germinate. This will result in weeds which will have to be controlled by hand labor, adding significant expenses to the enterprise.
Most weed control in transplanted rice has been done manually. If some places the planting pattern has more room between plants, and some mechanical weeding is done. However, in a standard planting pattern, much of the weed control is done by hand. Initial weed control is done during the tilling / rotavating stage of field preparation. The soil is kept saturated, and even slightly flooded to prevent more weed growth. Glyphosate is sometimes used on the field just prior to transplanting The recommended stem of a 2-3 day drying to allow for root repair and development, however, will also restart weed growth, and this will have to be dealt with either by manual weeding, or the application of selective herbicides. On again, weeds need to be controlled before they reach the 4 leaf stage. Water will have to be however to accomplish this, which can start a new flush of weed growth.
In both planting systems, weeds which start growing after the crop has covered the rows will have to be ignored, or removed by hand. Every weed which is ignored and matures will contribute thousands of seeds to the next crop, and this should be avoided if possible.Herbicides could be used where applicable to control weeds, but ensure they are safe to the receiving environment, humans and livestock. ALWAYS READ and FOLLOW the instructions on the product label. It’s important to use herbicides early (before or short after transplanting), at the recommended rate, and use the right herbicide for the right weed. Remember, Herbicides are poisonous; if they are not used properly they can cause health and environment problems. Label them clearly and keep them out of children’s reach after and before use.
Step 8: Rice nutrition (Fertilization)
Rice requires ammonium forming fertilizers to ensure the nitrogen levels remain stable in the soils. Mavuno rice is a balanced nutrient rich formulation specific to Kenyan rice fields as it provides the correct nutrient balance to the rice crop (Mavuno Rice Formulation -NPK 20.10.20+Calcium + Magnesium + Sulphur + Zinc + Copper + Boron + Molybdenum). The application of Mavuno rice is at time of planting the seed beds, where 50KG of Mavuno is evenly spread for one acre of rice seedlings. When Mavuno is deep-placed into the soil, the majority of nutrients remain in the form of ammonium, which is much less mobile than nitrates. More Nitrogen is available to the crop throughout its growth cycle. Therefore, losses to the atmosphere, groundwater are drastically reduced. Only about 4 percent of the N is lost to the environment, compared with about 35 percent when N is applied via broadcasting. When you transplant the seedlings in the paddy fields you need a top dressing fertilizer. Mavuno super granules is used to top dress the rice in the paddy fields, and is in round ‘ball’ shaped granules that are placed deep in the soil, 7cm deep in the paddy field. This increases yields by 30% whilst decreasing the amount of fertilizer required. This method replaces the typical topdressing application of broadcasting urea in rice paddy fields (which is currently the most common practice in Kenya).
Step 9: Water Management
Water management is different in direct seeded and transplanted crops for the first 30 days after planting. After 30 days, it is the same. For direct seeded crops, the first 30 days are managed as follows:
• After planting, the field should be filled with water to about 8-10cm. This water should be allowed to soak in for 24 hours. Thereafter, extra water must be drained off. Rice seeds will not germinate under both water and soil, so water left standing after a day will result in poor germination in that spot. Farmers can wait a few days to flush the fields, if rain is expected or irrigation water is not immediately available, but every day is a risk for loss of seed due to birds, rodents or insects.
• For the next 30 days, the direct seeded crop needs to be kept wet enough to avoid moisture stress in the plants. If it rains, additional irrigation may not be necessary. If it is dry, a flushing (irrigation) may be required every 5-10 days, depending on the soil type.
• At 30 days, the permanent flood is applied, after the second herbicide application and a topdressing of N (we recommend Mavuno Rice fertilizer)
• The field should be kept flooded until about 2 weeks before harvest, and allowed to dry before the crop is ready for harvest.
Transplanting requires much different water management;
• The field should be kept wet from the beginning of field preparation, until a few days after transplanting.
• The field should be allowed to dry for a day or two to allow the newly transplanted plants to heal the damaged roots, and establish themselves.
• After 2-3 dry days, water should be reintroduced, and the field kept wed until 2 weeks before harvest. The field should be allowed to dry in time for harvest.