System of rice intensification (SRI)
SRI involves the use of certain management practices, which together provide better growing conditions for rice plants, particularly in the root zone, than those plants grown under traditional practices. SRI was developed in Madagascar in the early 1980s by Father Henri de Lauhanie, a Jesuit priest. In 1990, Association Tefy Saina (ATS) was formed as a Malagasy NGO to promote SRI. It has since been tested in China, India, Indonesia, Philippines, Sri Lanka and Bangladesh with positive results.
Most rice farmers plant fairly mature seedlings (20-30 days old), in clumps, fairly close together with standing water maintained in the field for as much of the season as possible. These practices seem to reduce the risk of crop failure. It seems logical that more mature plants should survive better, that planting in clumps will ensure, that some seedlings should result in more yield; and that planting in standing water means the plants will never lack water and weeds will have little opportunity to grow.
There are six practices in SRI.
1. Young seedlings: Seedlings are transplanted early. Rice seedlings are transplanted when only the first two leaves have emerged from the initial tiller or stalk, usually when they are between 8 and 15 days old. Seedlings should be grown in a nursery in which the soil is kept moist but not flooded. The seed sac should be kept attached to the infant root, because it is an important energy source for the young seedlings. The young seedlings should be planted so carefully that the root tip is not left pointing upward.
2. Single seedling: Seedlings are planted singly rather than clumps of two or three or more. This means that individual plants have room to spread and to send down roots. They do not compete as much with other rice plants for space, light and nutrients in the soil.
3. Wider spacing: Seedlings are planted in a square pattern with plenty of space between them in all directions. Usually, they are spaced at least 22.5 cm × 22.5 cm. It helps for vigorous root growth and more tillering. The square pattern facilitates in situ incorporation of weeds by Conoweeder.
4. Lesser seed rate: SRI method requires much lower seed rate (5–8 kg/ha) than traditional methods (75–100 kg/ha).
5. Moist but unflooded soil conditions: Rice has traditionally been grown in water under submerged condition. In SRI method, soil is kept moist but not flooded during the vegetative period, ensuring that more oxygen is available in the soil for the roots, occasionally the soil should be allowed to dry to a point of cracking except in saline soils.
This will allow oxygen to enter the soil and also induce the roots to grow and search for water. In SRI method, unflooded condition is only maintained during vegetative period and from flowering to harvest, 1-3 cm of water is kept in the field as is done in the traditional method.
6. Conoweeding: Weeding can be done by conoweeder. The cost of conoweeder will be around Rs. 800–1500/- depending upon the type and materials used. First weeding should be done on 14 DAT and this should be continued up to 40 days at 7–10 days interval. At least two or three weeding is recommended.
This practice seems to improve the soil structure and increases the soil aeration. Thus, the incorporation of weed biomass into the soil results in enrichment of CO2 near to root zone, increases the biological activities, increases soil microbes population and activities, results in better nutrient availability in soil and uptake by plants. If conoweeder is not available, rotary weeder can be used.
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