The Intensive Rice System (IRS) is a rice cultivation method that produces significantly higher yields with far fewer seedlings planted and fewer inputs than traditional methods (i.e. flooding) or more “modern” methods (using mineral or agrochemical fertilizers). This approach involves the use of various plant, soil, water and nutrient management practices. SRI has been successfully used in a number of countries and has been widely promoted by Dr Norman Uphoff with Cornel University.
What is SRI?
SRI involves the use of a combination of management practices that optimize the growing conditions of rice plants, particularly in the root zone. It was developed in Madagascar in the early 1980s by Father Henri de Laulanie, a Jesuit priest who spent more than 30 years working with farmers in the country. In 1990, the Tefy Saina Association (ATS) was formed as a Malagasy NGO to promote the SRI. Four years later, the Cornell International Institute for Food, Agriculture and Development (CIIFAD) began working with Tefy Saina to introduce the SRI around Ranomafana National Park in eastern Madagascar, supported by the US Agency for International Development. It has since been tested in China, India, Indonesia, the Philippines, Sri Lanka and Bangladesh with positive results.
The results obtained with SRI methods are remarkable (see Table 1 and Ryan Haden’s thoughts below for the added perspective on returns). In Madagascar, on some of the poorest soils found and where yields were generally 2 t/ha, farmers using SRI now average more than 8 t/ha, with some obtaining 10-15 t/ha. Some farmers have even obtained more than 20 t/ha. In other parts of the country, over a five-year period, hundreds of farmers harvested an average of 8-9 t/ha.
|Methodology Classical||Methodology SRI|
|Tuft / m2||56||42-65||16||10-25|
|Plants / tuft||3||2-5||1||1|
|Talles / tuft||8,6||8-9||55||44-74|
|Panicles / tuft||7,8||7,8||32||23-49|
|Grains / panicle||114||101-130||181||166-212|
|Grains / tuft||824||707-992||5.858||3.956-10.388|
|Yields (t / ha)||2,0||1,0-3,0||7,6||6,5-8,8|
|Root strength (kg)||28||25-32||53||43-69|
Rice growth and yield with SRI compared to traditional methods.
Data for traditional methods were calculated from measurements on five adjacent fields. The data for the SRI methods are averages and ranges of 22 experimental plots. The data are taken from a Master’s thesis by Joelibarison, 1998.
With most, if not all, varieties grown using SRI, rice yields have at least doubled. There are no external inputs required for a farmer to benefit from it. The methods should work with all the seeds used. However, it is necessary to have an open mind about new methods and a willingness to experiment. With SRI, plants are treated as the living organisms they are, not as handling machines. The yield potential of rice plants is maximized by ensuring optimal growing conditions.
At first, SRI practices seem somewhat counterintuitive, challenging assumptions and practices that have been in place for hundreds or even thousands of years. Most farmers plant fairly mature young rice plants (20-30 days old) in fairly tight tufts with standing water kept in the field as much as possible for most of the season. Why? Why? These practices seem to reduce the risk of crop failure. It seems logical that more mature plants should survive better, that planting in beds will allow some plants to survive transplanting; that planting more seedlings should result in higher yields, and that planting in standing water means that plants will never run out of water and that weeds will have little chance of developing.
Despite this reasoning, farmers found nothing in the use of SRI practices that put their crops at greater risk than traditional methods. Four “new” practices, in particular, play a key role in the SRI.
The plants are transplanted early.
Rice plants are transplanted when only the first two leaves have appeared from the initial talle or stem, usually when they are between 8 and 15 days old.
With SRI, young plants are planted when they are 8-15 days old, when there are only two leaves. The plants on the left are 8 days old. With traditional methods, young plants are planted when they are several weeks old. The seedlings on the right are 31 days old. Photos by Joshua Harber.
Seedlings must be grown in a nursery where the soil is kept moist but not flooded. When transplanting plants, remove them from the nursery with a trowel and keep them moist. Do not let them dry. The seed bag (the remains of the sprouted seed) must be kept attached to the infant root, as it is an important source of energy for the young seedling. Plants should be transplanted as soon as possible after being removed from the nursery within half an hour and preferably within 15 minutes. When placing seedlings in the field, carefully place the roots in the soil on their side with a horizontal movement, so that the tip of the root does not inadvertently point upwards (which happens when the seedlings are plunged directly downwards into the soil). The end of the root must be able to grow downwards. Careful transplanting of young plants when they are very young reduces shocks and increases the ability of plants to produce many tillers and roots during their vegetative growth phase. Rice grains are finally produced on the panicles (i.e., the “ears” above the stem, produced by fertile tillers). More tillers lead to more panicles, and with SRI methods, more cereals are produced on each panicle.
Young plants are planted separately rather than in tufts.
This means that individual plants have space to propagate and to lower the roots. They do not compete much with other rice plants for space, light, or nutrients in the soil. Root systems become quite different when plants are presented separately, and when the next practice is followed.
The plants are widely spaced.
The plants are planted in a square pattern with a lot of space between them in all directions rather than in tight rows. Usually, they are spaced at least 25 x 25 cm apart (Figure 2). Feel free to experiment because the optimal spacing (producing the greatest number of fertile tillers per square meter) depends on soil structure, soil fertility, temperature, humidity and other conditions. The general rule is that plants must have plenty of space to grow. If you also use the other practices mentioned here, the best spacing will rarely be closer to 20 x 20 cm. Maximum yields were obtained in good soil with a spacing of 50 x 50 cm, and only four plants per square metre.
To carefully space the plants (making weeding easier), you can place sticks at appropriate intervals (e. g. every 25 cm) on the edge of the field and then pull strings between them. The strings must be marked with the same intervals so that you can plant in a square pattern. Leaving large spaces between each plant ensures that the roots have enough space to grow, and plants will be exposed to more light, air and nutrients. This results in increased root growth (and therefore better nutrient absorption) and tillering. The grid also makes weeding easier.
The SRI seedlings (left diagram) are very widely spaced compared to those planted with traditional methods (right). These diagrams show the seedlings at about one month of age, when they are about the same size. However, the SRI seedlings, having been transplanted a few weeks earlier, at that time had already suffered the shock of transplanting and may have started tillering. Sketch by Christi Sobel.
When farmers are more experienced, they can save time by marking the hatched lines on the ground surface with rakes or other devices. Note that the SRI uses a much lower seeding rate than traditional methods. An evaluation of the SRI found that the seed application rate was only 7 kg / ha compared to the traditional seeding rate of 107 kg / ha -however, yields doubled due to the fact that each plant produced many more grains
Wet but not flooded soil.
Rice is traditionally grown immersed in water. It is clear that rice is able to tolerate standing water; however, standing water creates hypoxic soil conditions (lack of oxygen) for the roots and does not seem to be ideal. It has been shown that rice roots degenerate under flood conditions, causing 3/4 of their roots to be lost as the plants reach the flowering stage. This decline in flood conditions has been called “senescence”, which implies that it is a natural process. In reality, it represents choking, which prevents the plant from functioning and growing. With SRI, farmers use less than half the water they would use if they kept their rice fields permanently flooded. The soil is kept moist but not saturated during the vegetative growth period, ensuring that more oxygen is available for the roots. From time to time (perhaps once a week), the soil should be left to dry to the point of cracking. This will allow oxygen to enter the soil and will also induce the roots to grow and “seek” water. After all, when the soil is flooded, the roots do not need to grow and expand, and they lack enough oxygen to grow vigorously.
Non-flooding conditions, combined with mechanical weeding, allow for greater air availability in the soil, and greater root growth means that the rest of the plant will have access to more nutrients. When the soil is saturated, air pockets (known as aerenchymae) form in the roots of submerged plants to carry oxygen. These air pockets absorb 30% to 40% of the root cortex and probably impede the transport of nutrients through the roots for the rest of the plant. More water can be applied before weeding to make the weeding process easier. Otherwise it is preferable that the water be applied in the evening (if it has not rained during the day), and all the remaining water on the surface is drained in the morning. This leaves the field free for air and heat during the day and flooded fields will reflect much of the solar radiation that reaches them, and will absorb less of the heat that helps plants grow. With SRI, non-flooding conditions are maintained only during the vegetative growth period. Later, after flowering, 1-3 cm of water is retained in the field, as is done with traditional practices. The field is completely cleared 25 days before harvest.
In addition to these four main practices, two other practices are extremely beneficial when using SRI. These practices are not controversial and have long been recognized as valuable for crops.
This can be done by hand or with a simple mechanical tool. Farmers in Madagascar find it advantageous, both in terms of reducing labour force and increasing yield, to use a hand-held mechanical weeder developed by the International Rice Research Institute in the 1960s. It has vertically rotating gear wheels that shake the ground as the curry is pushed down and through the paths formed by the square planting pattern. Weeding is labour-intensive – weeding one hectare could take up to 25 working days – but increasing yields means that the work will be more than profitable.
An example of a mechanical weeder with vertical rotating gear wheels, often used with the SRI. Plans are available at ECHO for this weeder and for a larger one with five wheels. Sketch of the weeders by Paya deMarken, Peace Corps Volunteer in Madagascar
The first weeding should be done 10 to 12 days after transplanting, and the second weeding should be done within 14 days. At least two or three weedings are recommended, but one or two additional weedings can significantly increase yield by adding 1-2 t/ha. Probably more important than weed removal, this practice of churning the soil seems to improve its structure and increase soil aeration.
SRI was initially developed with the use of chemical fertilizers to increase yields on very poor soils in Madagascar. But when subsidies were abolished in the late 1980s, it was recommended to use compost, and even better results were observed. Compost can be made from any biomass (e.g. rice straw, plant residues or other plant material), with a little added manure if available. Banana leaves have a potassium intake. Cuttings from shrub legumes have a nitrogen supply. Other plants, such as Tithonia diversifolia and Afromomum angustifolium, may be rich in phosphorus. Compost slowly brings nutrients into the soil and can also contribute to a better soil structure. It seems quite intuitive that some form of nutrient input is required on poor soils if chemical fertilizer is not added. With huge amounts of rice harvested, the nutrients must be returned to the soil!