This document provides an overview of the System of Rice Intensification (SRI), which is a methodology for growing rice that can produce higher yields with fewer inputs. SRI involves transplanting young seedlings with wide spacing, maintaining moist soil rather than continuous flooding, and incorporating other practices. Key findings from SRI include larger and more extensive root systems, increased numbers of tillers per plant, and higher yields compared to conventional rice growing. While promising, SRI is still being studied scientifically to better understand the mechanisms producing its effects. The document discusses several potential explanations for SRI's results and calls for further research collaboration.

1. A Review of the System of Rice Intensification (SRI) Norman Uphoff Cornell International Institute for Food, Agriculture and Development for presentation in Mymensingh, September 25, 2002

2. SRI IS A “WORK IN PROGRESS” Something new , but only in part; much still to be demonstrated scientifically While SRI appears ‘too good to be true’ there is much evidence it is ‘for real’ SRI is being used successfully by a growing number of farmers in a growing number of countries (15+)

3. SRI IS A METHODOLOGY rather than a “TECHNOLOGY” Different paradigm for rice growing Management produces a different phenotype SRI is a set of PRINCIPLES that are applied through a set of PRACTICES that farmers are expected to adapt to suit their local conditions

4. The basic idea of SRI is that RICE PLANTS GROW BEST (A) When plant ROOTS can grow very large and deep because they have been transplanted carefully , i.e., without trauma, with optimally wide spacing between plants (B) And when rice is grown SOIL that is: well aerated with abundant and diverse soil microbial populations

5. “ Starting Points” for SRI Transplant young seedlings , 8-15 days, quickly and very carefully Single plants per hill with wide spacing in a square pattern, 25x25 cm or wider No continuous flooding of field during the vegetative growth phase (AWD ok) Use rotating hoe early and often (2-4x) Recommend application of compost Practices produce a different PHENOTYPE

12. OBSERVABLE RESULTS Average yields about 8 t/ha -- twice the present world average of 3.8 t/ha Maximum yields can be twice this; about 16 t/ha, with some over 20 t/ha Water requirements reducible by 50% Increased factor productivity for land, labor, capital and water -- MORE IMPORTANT THAN YIELD Lower costs of production per/kg MOST IMPORTANT FOR FARMERS

13. LESS OR NO NEED FOR: Different varieties , though best yields from high-yielding varieties and hybrids; traditional varieties can yield very well Chemical fertilizers -- while these give positive yield response with SRI, we find that compost gives best results Agrochemicals – plants more resistant to pests and diseases with SRI methods so pesticides, etc. not often needed

14. FURTHER BENEFITS Seeding rate reduced as much as 90%, 5-10 kg/ha yields more than 50-100 kg; smaller nursery area, less water needed No lodging because of stronger roots Environmentally friendly production due to water saving, no/fewer chemicals More accessible to poor households because few capital requirements

15. DISADVANTAGES / COSTS SRI is more labor-intensive , at least initially -- but can become labor-saving ? SRI requires greater knowledge/skill from farmers to become better decision-makers and managers -- but this is good for human resource development! SRI requires good water control to get best results, making regular applications of smaller amounts of water -- but this can be obtained through investments ? Maybe not possible in monsoon climate

16. SRI is COUNTERINTUITIVE LESS BECOMES MORE -- by utilizing the potentials and dynamics of biology Smaller, younger seedlings will give larger, more productive mature plants Fewer plants per hill and per m 2 can give more yield Half the water can give higher yield Fewer or no external inputs are associated with greater output New phenotypes from existing genotypes

17. These are remarkable claims But they reflect experience on farms, more than on experiment stations They have some, if not yet complete, support in the scientific literature Note: I am not the originator of SRI , just a proponent for its being evaluated and used where appropriate, now working with many colleagues around the world SRI is the due entirely to the work of Fr. Henri de Laulanié, S.J . (1920-1995)

20. BACKGROUND CIIFAD involvement with Tefy Saina began in 1994 around Ranomafana National Park in Madagascar, where yields averaged 2 t/ha Previous work by NC State University got average yield up to 3 t/ha, maximum of 5 t/ha During 1994-99, Tefy Saina helped farmers average 8 t/ha , with best yields up to 16 t/ha Over same period, farmers in French project improving small-scale irrigation on the high plateau had the same results

22. Spread beyond Madagascar Nanjing Agricultural University - 1999 Agency for Agricultural Research and Development, Indonesia - 1999-2000 Philippines, Cambodia, Bangladesh etc. China Hybrid Rice Center - 2000-2001 International conference, Sanya, China, April 2001 -- 15 countries represented

23. Participants at the SRI Conference in Sanya, China

24. Reports from Sanya Conference

25. SIX PROPOSED EXPLANATIONS (1) Rice is not an aquatic plant, or even hydrophilic Although rice can survive under continuous flooding, It does not thrive under these [suboptimal] conditions.

30. Evidence on Root System Development/Degeneration Evaluated by ‘pull’ test of root resistance (O’Toole and Soemartono 1981) Three plants [3-week seedlings, 3/hill, close planting, continuous flooding] averaged 28 kg/hill (Joelibarison 1998) Single SRI plants [12-day seedlings, 1/hill, 25x25 cm, aerated soil] averaged 53 kg/hill -- resistance/plant > 5 times

31. Dry Matter Distribution of Roots in SRI and Conventionally-Grown Plants at Heading Stage (CNRRI research: Tao et al. 2002) Root dry weight (g)

32. Root Activity in SRI and Conventionally-Grown Rice (Nanjing Agr. Univ. research: Wang et al. 2002) (Wuxianggeng 9 variety)

34. (2) Tillering in rice is regulated by structural pattern of growth Understood in terms of PHYLLOCHRONS -- related to leaf age or degree-days , but more precise and illuminating than ref. to “early, active, or maximum tillering...” Discovered by Katayama (1920s-30s), further developed by de Laulanié (1993) Under good growing conditions and if the root system is intact, the number of tillers per plant can exceed 100

38. What speeds up the biological clock? (adapted from Nemoto et al. 1995) Shorter phyllochrons Longer phyllochrons Higher temperatures > cold temperatures Wider spacing > crowding of roots/canopy More illumination > shading of plants Nutrient supply in soil > nutrient deficits Soil penetrability > compaction of soil Sufficient moisture > drought conditions Sufficient oxygen > hypoxic soil conditions

41. (3) Profuse tillering should not be considered unproductive An negative relationship has been reported in the literature between the number of tillers/plant and the number of grains/panicle This, however, reflects conventional hypoxic growing environments of rice plants, with root degeneration

43. With a large and intact root system and profuse tillering this relationship is positive. Increased grain filling results from a positive-sum dynamic between the growth and vigor of roots X tillers and leaves

45. This is what makes it possible to go from 2 t/ha to 8 t/ha A synergistic relationship between root development and tillering with each supporting the other’s growth Then both together can support increased grain filling With good root development , 80% or more effective tillering, more filled grains and higher grain weight

46. (4) Positive benefits are seen from soil aeration during the vegetative growth period

47. (5) SRI capitalizes on the fact that the uptake of N is a demand-led process

48. Paths for Increased Grain Yield in Relation to N Uptake, using QUEFTS Analytical Model (Barison, 2002)

49. Rapid tillering and root growth Creates demand for nutrients -- accelerating plant growth after first 5-6 weeks Where does supply come from? Probably attributable to biological processes and sources ; cannot be explained by “chemical” analyses

50. (6) The contributions of soil microbial activity are likely the foundation for SRI success “ The microbial flora causes a large number of biochemical changes in the soil that largely determine the fertility of the soil.” (DeDatta, 1981, p. 60, emphasis added)

51. Biological Nitrogen Fixation? BNF can occur with all gramineae species, including rice (Döbereiner 1987, and others) In flooded paddies, BNF is limited to anaerobic processes; SRI provides aerobic conditions as well; BNF must be occurring Mixing aerobic and anaerobic soil conditions increases BNF (Magdoff and Bouldin 1970) Nitrogenase production is suppressed by the use of chemical fertilizers (van Berkum and Sloger 1983)

52. P SOLUBILIZATION? P solubilization is increased under alternating aerobic and anaerobic soil conditions; Turner and Haygarth (2001) measured large increases in soluble organic P with alternate wetting/drying “ Microbiological weathering” is probably more important than are the geochemical forms of weathering Biological weathering processes are probably also increasing the availability of other nutrients such as S, Zn, etc.

53. MYCORRHIZAL Contributions? Fungi cannot grow in anaerobic soil so flooded rice has forfeited the benefits of mycorrhizae for centuries Mycorrhizal fungi can increase volume of soil accessed by root up to 100x Plants with mycorrhizal associations can grow well with just a fraction of the P supply that “uninfected” plants need

54. Benefits from Rhizobia in rice now being explored Studied where rice and clover grown in rotation in Egypt, for many centuries These endophytic bacteria induce more efficient acquisition of N, P, K, Mg, Ca, Zn, etc. in rice (Yanni et al. 2001) Rhizobia increase yield and total protein quantity/ha , by producing auxins and other plant-growth promoting hormones -- however, no BNF demonstrated

55. ROOT EXUDATION Farmers report that SRI practices “improve their soil quality” over time -- yields go up rather than down just by adding compost -- hard to explain The soils around Ranomafana were evaluated in chemical terms as some of the poorest in the world (Johnson 1994) e.g., 3-4 ppm P, low CEC all horizons

56. Larger canopies and root systems increase exudation and rhizodeposition 30-60% of C fixed in canopy is sent to the roots, and 20-40% of this exuded or deposited in rhizosphere (Neumann and Römheld 2001, in Pinton et al. 2001) Also 20% of plant N is transferred (Brimecombe et al. 2001) Roots and shoots are “ two-way streets ” However, little is known about exudation in rice (Wassmann and Aulakh 2000)

57. SRI Raises More Questions than It Gives ANSWERS This is a PRACTICE-LED innovation Scientists have a challenge/opportunity to develop explanations for observed phenotypical changes : Greater root growth Greater tillering Less senescence of roots and canopy Positive correlation: tillering x grain filling

58. Plant Physical Structure and Light Intensity Distribution at Heading Stage (CNRRI Research: Tao et al. 2002)

59. Suggested Focuses for Explanation of SRI Effects Root development  different transplanting, wider spacing & soil aeration; roots ignored Soil microbial abundance and activity  plant, soil, water & nutrient management, mixing aerobic / anaerobic conditions

60. MANY OPPORTUNITIES SRI is a still “work in progress” invite interest & collaboration -- no IPR SRI puts a presumed “ biological ceiling ” for rice in a different perspective Fr. De Laulanié speculated that rice yields could even reach 30 t/ha when we fully utilize phyllochron dynamics Exciting time to be a rice scientist!

61. THANK YOU More information is available on the SRI WEB PAGE : http://ciifad.cornell.edu/sri/ including Sanya conference proceedings E-MAIL ADDRESSES : [email_address] [email_address] [email_address]