SRI -- The System of Rice Intensification: An Opportunity for Improving Food Security in Latin America? Presented at: 2nd International Rice Meeting, Havana Norman Uphoff Cornell International Institute for Food, Agriculture and Development (CIIFAD) in cooperation with Association Tefy Saina (ATS)
More tillers and more than 400 grains per panicle
The System of Rice Intensification (SIMA) developed in Madagascar almost 2 decades ago can:
Increase rice production -- double yield
Improve food security esp. for poor HHs,
Raise total factor productivity, and
Enhance the environment -- cut demand for water by half, no use of agrochemicals
The main objections against this methodology have been that:
SRI requires good water management
SRI is labor-intensive
SRI appears “ too good to be true”
(1) Water control is definitely necessary
(2) But SRI also gives higher returns to labor, and over time, it can become labor-saving
(3) Appearing “too good to be true” only means that SRI should be subjected to careful scrutiny
In Madagascar , where yields average 2-2.5 t/ha, 100s of farmers in 2 programs (USAID and French) have averaged 8-9 t/ha over a 5-year period -- on mostly very poor soils.
In China , the first SRI trials at Nanjing Agric. University gave 9.2 to 10.5 t/ha . While these levels can be achieved in China with the best varieties and best techniques, these take twice as much water as applied with SRI. SRI method used with hybrid rice varieties has given yields in the 12-15 t/ha range.
In Cambodia and Myanmar , where conventional yields are even lower than in Madagascar (2 t/ha), farmers using SRI have averaged 5-6 t/ha with NGO guidance.
In Sri Lanka , where the average yield is about 3.5 t/ha, farmers have averaged ~8 t/ha with SRI, with some farmers achieving much higher yields.
In Sri Lanka and Madagascar , some farmers are getting yields in the range of 15 to 20 t/ha once they have mastered the techniques and improved their soil quality. The maximum potential of SRI methodology remains to be fully realized.
OBSERVABLE PHENOTYPICAL CHANGES attributable to SRI
More tillers/plant -- 30-50, even 100+
Larger root systems – root pulling resistance of 28 kg /clump for 3 plants grown conventionally vs. 53 kg /plant for single SRI plants -- >5x per plant
Positive correlation tillers/plant and grains/panicle – no lodging
Comparison of high-yield rice in tropical and subtropical environments: I: Determinants of grain and dry matter yields J. Ying, S. Peng, Q. He, H. Yang, C. Yang, R. M. Visperas, K. G. Cassman, Field Crops Research , 57 (1998), p. 72.
“… a strong compensation mechanism exists between the two yield components [panicle number and panicle size]” with a “ strong negative relationship between the two components…” (emphasis added)
But in flooded (hypoxic) soil, rice roots remain close to the surface. At 29 DAT, about ¾ are in top 6 cm of soil (Kirk and Solivas 1997)
Rice plant roots grown in flooded soil form aerenchyma (air pockets) through disintegration of the cortex which is “often almost total…[after PI] the main body of the root system is largely degraded and seems unlikely to be very active in nutrient uptake” (Kirk and Bouldin 1991)
Yet in unflooded soil neither irrigated nor upland varieties form aerenchyma (Puard et al. 1989)
Root cross-sections for upland (left) and irrigated (right) varieties -- ORSTOM research by Puard et al. (1989)
Nature and growth pattern of rice root system under submerged and unsaturated conditions
S. Kar, S. B. Varade, T. K. Subramanyam, and B. P. Ghildyal,
Il Riso (Italy), 1974, 23:2, 173-179
Plants of the rice cultivar Taichung (Native) were grown in pots of sandy loam under 2 water regimes in an attempt to identify critical root-growth phases. Observations on root number, length, volume and dry weight were made at early tillering, active tillering, maximum tillering, and reproductive stages.
Rice root degeneration , normally unique to submerged conditions , increased with advance in plant growth. At flowering, 78% had degenerated . During the first phase under flooding, and throughout the growth period under unsaturated conditions, roots rarely degenerated.
Explanation of tiller and root growth in terms of phyllochrons
These are periodic intervals of plant growth common to all the gramineae species -- in rice, a phyllochron is usually from ~5-8 days
During each phyllochron , the plant produces from its apical meristem 1 or more phytomers (phytomer = a unit of a tiller, a leaf and a root)
Phyllochrons represent biological rather than calendar time – they are lengthened/shortened by a number of factors that can slow down or speed up the plant’s “biological clock”
SRI does require 25-50% more labor inputs , at least initially -- one study in Madagascar with 109 farmers found a 26% difference; Sri Lankan analysis found an 11% difference
But SRI time required is reduced as farmers gain skill and confidence; almost always the returns to labor are higher by 25-50%
Some farmers who have mastered SRI techniques report that they are labor-saving
If farmers are labor-constrained , it is most beneficial economically for them to use SRI on as much of their land as they have enough labor for , to capture higher returns to all their factors of production (land, labor, capital, water), and then to use remaining land for other purposes