The System of Crop Intensification

The System of Rice Intensification (SRI; see EDN 70, and http://sri.ciifad.cornell.edu/) has changed the way millions of farmers plant rice. The management practices used with SRI have also now been tried with many other crops. Here we present an update about crops that have demonstrated increased yields using similar management practices.

System of Rice Intensification– A Recap

To recap, SRI includes several main cultivation practices that stem from broad principles (more information is available in EDN 70):

1. Seedlings are transplanted early and carefully. With 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. Careful transplanting of seedlings when they are very young reduces shock and increases the plants’ ability to produce numerous tillers and roots during their vegetative growth stage. Grains of rice are eventually produced on the panicles (i.e. the “ears” of grain above the stalk, produced by fertile tillers). More tillers result in more panicles, and with SRI methods, more grains are produced on each panicle.
2. Seedlings are transplanted singly rather than in 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, for light, or for nutrients in the soil. Root systems become altogether different when plants are set out singly, and when the next practice is followed:
3. Wide spacing. Rather than in tight rows, seedlings are planted in a square pattern with plenty of space between them in all directions. Usually they are spaced at least 25 x 25 cm apart. The optimum spacing (producing the highest number of fertile tillers per square meter) depends on soil structure, soil nutrients, temperature, moisture and other conditions. The general principle is that plants should have plenty of room to grow. If you also use the other practices mentioned here, seldom will the best spacing be closer than 20 x 20 cm. The maximum yields for rice have been obtained on good soil with 50 x 50 cm spacing, just four plants per square meter.

Because of the wider spacing and single transplanting, SRI uses a much lower seeding rate than do traditional methods, saving up to 100 kg of seed per hectare. Yet yields generally increase greatly, because each plant produces so much more grain.

1. Moist but non-flooded soil conditions. Rice has traditionally been grown submerged in water. Clearly rice is able to tolerate standing water. However, standing water creates hypoxic soil conditions (lacking in oxygen) for the roots and hardly seems to be ideal! Rice roots have been shown to degenerate under flooded conditions, losing ¾ of their roots by the time the plants reach the flowering stage. This die-back of roots under flooded conditions has been called “senescence,” implying that it is a natural process. But it actually represents suffocation, which impedes plant functioning and growth.

With SRI, farmers use less than half of the water they would use if they kept their paddies constantly flooded. Soil is kept moist but not saturated during the vegetative growth period, ensuring that more oxygen is available in the soil for the roots. Occasionally (perhaps once a week) the soil should be allowed to dry (e.g. to the point of cracking, if your soil is clay and prone to cracking). This will allow oxygen to enter the soil and will also induce the roots to grow and “search” for water. After all, when the soil is flooded, roots have no need to grow and spread in search of water, and they will lack enough oxygen to grow vigorously. EDN 70 includes a more thorough explanation of water management with SRI, including its benefits for plants.

1. Weeding. This can be done by hand or with a simple mechanical tool. Farmers in Madagascar find it advantageous, both in terms of reducing labor and of increasing yield, to use a mechanical hand weeder developed by the International Rice Research Institute in the Philippines in the 1960s. It has vertical rotating toothed wheels that churn up the soil as the weeder is pushed down and across the alleys formed by the square formation of planting. Many other weeder designs are also available. A manual published by WASSAN (Watershed Support Services and Activities Network), available on the SRI website from CIIFAD at Cornell, outlines what to look for in a good weeder, and shares information about a number of innovative designs for weeders: http://sri.ciifad.cornell.edu/countries/india/extmats/SRIWeederManual06.pdf

Weeding is labor-intensive—it may take up to 25 days of labor to weed one hectare— but the increase in yield means that the work will more than pay for itself. The first weeding should be done ten to twelve days after transplanting, and the second weeding within the next two weeks. At least two or three weedings are recommended, but another one or two can significantly increase the yield, adding one to two tonnes per hectare. Probably more important than removing weeds, this practice of churning the soil seems to improve soil structure and increase aeration of the soil.

1. Organic inputs. Organic matter enriches the soil with plant-essential nutrients and creates an aerated environment conducive to microbial life and root growth. Compost can be made from any biomass (e.g. rice straw, plant trimmings and other plant material), with some animal manure added if available. The source of plant biomass can be selected to optimize levels of certain nutrients in compost. Banana leaves, for instance, are high in potassium. Leguminous plants add nitrogen, and other plants such as Lantana camara, Afromomum angustifolium and Tithonia are good sources of phosphorous. Compost adds nutrients to the soil slowly and can also contribute to a better soil structure. It seems fairly intuitive that some form of nutrient input is necessary on poor soils if chemical fertilizer is not added. With huge yields of rice being harvested, something needs to be returned to the soil! Targeted application of compost (in the planting holes, for example) will make the most of a valuable but limited nutrient supply.

Together, these crop management practices can result in plants that are stronger, larger and more resilient, and in soil that teems with diverse microorganisms.

The System of Crop Intensification

The System of Crop Intensification (SCI) is the term being used to describe the principles of SRI when applied to other crops. In India, the term System of Root Intensification (another SRI) is sometimes used. These principles are:

1. Early establishment of healthy plants, with care taken to protect the root growth potential of seedlings.
2. Sufficient space between crops, as influenced by planting densities, to allow for optimal capture of soil nutrients and sunlight.
3. Enrichment of soil with organic matter, which slowly releases nutrients to crop plants and provides aerated conditions conducive to root growth and soil microbial life.
4. Controlled water management to avoid anaerobic conditions in the soil, a principle especially relevant to irrigated crop production.

These principles are the basis for the above-mentioned SRI practices, which can be adapted for other crops, local conditions and available resources.

Why do these crop management principles and practices work? It seems that setting up the proper environmental conditions helps plants reach their genetic potential. An organism’s genotype is the actual genetic information of that particular species and variety of plant. With plant breeding, changes are made to the genotype, so that the resulting plants will have desirable characteristics (such as increased yield). Plant breeding is important, but is a slow and often expensive process. And if plants are grown under suboptimal conditions, they will not reach their full growth and yield potential.

Many farmers and scientists have been surprised at the extent to which a combination of improved management practices can alter a plant’s growth and development, regardless of the variety that is used. This is an extremely important and encouraging idea, which seems to be holding true for many crops in addition to rice!

Table 1 in this article gives examples of crops now being grown using SCI, condensing information from a report by Norman Uphoff called “Raising Smallholder Food Crop Yields with Climate-Smart Agroecological Practices.” (The report is available online at http://sri.ciifad.cornell.edu/aboutsri/othercrops/OtherCropsBrochure_Uphoff101012.pdf.)

The comparisons listed in the table are not from a single carefully controlled scientific experiment. Despite that, the substantial and multiple instances of yield increases illustrate the powerful effect that management practices can have on production levels. The column on the far right of the table includes links to manuals (or, in some cases, presentations) with more detailed information, where available.

Conclusion

SRI surprised farmers and scientists. It seemed counter intuitive that fewer inputs (of seed, water, etc.) could result in vastly larger yields. Now we are perhaps surprised that the phenomenon goes beyond just rice. Careful, controlled management can have a dramatic impact on the development and growth of many different crop plants, ultimately resulting in much higher yields. That is good news for all, but perhaps especially for resource-poor farmers.