0317 Possible Soil Microbiological Explanations for High Yields with the System of Rice Intensification (SRI)
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0317 Possible Soil Microbiological Explanations for High Yields with the System of Rice Intensification (SRI)



Presenter: Norman Uphoff

Presenter: Norman Uphoff

The Cornell Agroforestry Working Group/ The Management of Organic Inputs in Soils of the Tropics Group (CAWG/MOIST) Seminar Series 2003, USA



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  • Prepared with information available as of February 1, 2003. These slides can be used or adapted, even translated, however SRI colleagues would be useful for explaining this methodology to others.
  • Picture provided by Gamini Batuwitage, Sri Lanka, of field that yielded 17 t/ha in 2000.
  • The "economist's $100 bill" refers to the joke about an economist and his friend who were walking together down the street one day when the friend saw a $100 bill on the sidewalk. Thinking that his friend, being concerned with money, would surely pick the bill up, he did not reach down himself. But the economist walked right by. The friend asked, didn't you see that $100 bill on the sidewalk? Why didn't you pick it up? The economist replied,It wasn't a real $100 bill. If it had been genuine, since people are rational, someone would have picked it up by now, so I am sure that it was a counterfeit, and I didn't want to waste any effort on it. Agronomists have regarded SRI with similar skepticism, dismissing it by saying if it were indeed as good as reported, it should have been discovered previously, given the many millions of farmers and thousands of scientists who have worked with rice. So, therefore, SRI must not be genuine. SRI contradicts a number of key concepts held by agronomists and economists, giving them reasons to reject it, without giving it an empirical evaluation. However, the evidence in support of SRI is mounting year by year, month by month.
  • Average yields where farmers have learned SRI methods, understand them and use them, are about 8 t/ha. In some countries, the average is not yet at that level, but given experience in Madagascar and Sri Lanka, we feel confident that 8 t/ha is a reasonable average to expect with SRI. Maximum yields reported are very controversial. We report data as accurately and truthfully as we can. Farmers have had harvests -- some whole-field, some sampled -- calculated to be 15-20 t/ha, so we report what we think is correct. Over time this will be substantiated by other or not. Water requirement reductions of 40-60% are often reported. That productivity for all four factors of production can increase at the same time goes against the conventional idea of necessary tradeoffs in factor productivity. We have often seen across-the-board productivity improvements, which are more important than yield. Farmers and countries get richer by raising productivity, not by attaining highest yield (because one has to consider the cost of attaining this). Costs of production have been reported to be reduced by 10-50%, depending on how the cost of labor is figured. Because no purchase of external inputs is necessary, cash costs of production invariably go down with SRI. Whether or not labor costs are reduced depends on various factors.
  • Dr. Janaiah visited Sri Lanka the last week of October, 2002, and talked with 30 farmers in four villages who had been practicing SRI and who could give him detailed data. He had previously done such an evaluation for IRRI of the costs and benefits of adopting hybrid rice, having been on the IRRI staff in Los Banos from 1999 to 2002. He found SRI to be a much more profitable innovation for rice production than adoption of hybrids. We have found that SRI methods give the highest yields with hybrid varieties so there is not necessary contradiction or competition between the two. The SRI results reported from the Philippines, by the Agricultural Training Institute of the Department of Agriculture, from trials with three varieties at its Cotobato center in Mindanao (slide 20), calculated that the cost of production per hectare was 25,000 pesos, while the value of the rice yield with SRI was 96,000 pesos, a return of almost four times. Thus there are other evaluations of net profit from SRI that are even more favorable than Janaiah's calculation.
  • As noted for Slide 7, we are hearing from farmers in a number of countries, that SRI is not more labor-intensive for them. However, we think it best to acknowledge that SRI can require more labor, at least in the first year or two. Studies in Madagascar have put this increase between 25 and 50%, with first-year farmers sometimes even higher. With a doubling of yield, the returns to labor are higher even so. We do not want to minimize -- indeed, we should emphasize -- that SRI requires more skill and knowedge. Farmers are expected not to adopt SRI methods but to gain an understanding of them, particularly why we recommend wide spacing, young seedlings, no continuous flooding, etc. They should adapt the specific practices to their local conditions. SRI was intended by Fr. de Laulanie and Association Tefy Saina to encourage farmers to become more independent thinkings and active innovators. The most objective limitation on SRI is the need for good water control to get best results. Continuous flooding as seen below, leads to root deterioration. Farmers who are part of a cascade (field-to-field) irrigation system will have a hard time managing water for SRI unless there is cooperation among neighbors. Once the economic profitability of SRI has been well established, farmers, governments and even donor agencies should be willing to make investments in improving irrigation infrastructure to make SRI management possible.
  • This slide gives the most essential understanding of SRI. These ideas come from the work of Fr. de Laulanie and from five years of student thesis research in Madagascar and experimentation by a growing number of scientists in countries outside Madagascar. These generalizations remain to be fully documented and calibrated by additional research, but we are confident that this "core" of SRI is solid.
  • We emphasize that these are "starting point" because farmers are expected and encouraged to do some experimentation and adaptation with these practices, based on their understanding of the core concepts. The reasons for transplanting young seedlings are given in Slides 34-39. Quick and careful transplanting is necessary so there is little or no trauma to the young roots, which would set back their subsequent growth. We recommend that the roots be laid gently into the soil, only 1-2 cm deep, with the root straight downward or at least horizontal (L-shaped) rather than being plunged vertically down into the soil which causes the tip of the root to invert back upwards (J-shaped). When there is such inversion, it takes days, even weeks, for the root to reposition itself for resumed downward growth. Single plants spaced widely have room for both the roots and canopy to grow vigorously, as they will with young seedlings and aerated soil. We recommend starting with 25x25 spacing, but with good soil (and the soil usually improves year-to-year with SRI culivation), higher yields will be achieved with 30x30 or 40x40 spacing. The highest yield we know was with 50x50 cm spacing once soil had been improved by plant, soil, water and nutrient management. So farmers should experiment with wider spacing each year to see whether it leads to better crop performance than 25x25. They can experiment with narrower spacing if they like. No continuous flooding at least up to panicle initiation is key. This can be done, however, either by adding small amounts of water each day to keep the soil moist but not saturated, and not watering the field for 3-6 days several times during the growing season to dry out the field, up to the point of surface cracking; or by flooding the field for 3-6 days, and then draining it and leaving it dry for 3-6 days, until there is enough cracking to make reflooding necessary. We are still learning how to manage water for best effect with SRI. The best practices for any particular farmer will surely depend on soil, climatic, topographic and other variables. We recommend that farmers keep 1-2 cm of water on the field after panicle initiation, up to 10 days before harvest when the field should be drained (as done with all irrigated rice cultivation systems). Possibly the soil should be kept more aerated than this after panicle initiation, but no systematic research has been done. Weeding is important, for soil aeration as well as removal of weeds. See Slide 44.
  • The data summarize our observations and measurements. Regarding panicle size, we have had single panicles with as many as 900 grains, but this is so fantastic, few will believe it. The maximum of number of fertile tillers observed so far is 140, with 50x50 spacing. The most important phenotypic difference is the last one, discussed in Slides 21-22.
  • This picture was contributed from Cambodia by Koma Yang Saing (CEDAC). Viewers should try to imagine the very small single young seedling from which this massive plant grew.
  • This helps to explain our problem of "the agronomists' $100 bill." SRI is quite "counterintuitive." Indeed, it even sounds crazy. But we have experience and evidence that this "less is more" dynamic operates, and subsequent slides provide a number of scientific explanations for why fewer or smaller inpouts produce more in the case of irrigated rice
  • This figure is from research from the China National Rice Research Institute reported at the Sanya conference in April 2002 and published in the Proceedings. Two different rice varieties were used with SRI and conventional (CK) methods. The second responded more positively to the methods in terms of leaf area and dry matter as measured at different elevations, but there was a very obvious difference in the phenotypes produced from the first variety's genome by changing cultivation methods from conventional to SRI.
  • Usually we find researchers getting higher yields with new methods and farmers having difficulty "replicating" those results on their own fields. With SRI, we have often the opposite situation: researchers get lower yield on-station than farmers get in their fields. This remains to be thoroughly documented and fully explained. Fortunately, there is growing interest from crop and soil scientists after a number of years of skepticism and even resistance. We want to acknowledge, and express our appreciation for, the work of Fr. Henri de Laulanie, who developed SRI as a labor of love and innovative "lay science" during 34 years of living in Madagascar. He came there from his native France in 1961 and synthesized SRI first in the 1983-84 season. He had been educated in agriculture at the best French agricultural university (ENA) before World War II (1937-39) and before entering a Jesuit seminar (1941-45). So he knew basic agricultural science. But he had not learned about rice in France, so learned about it from and with farmers. The following slide shows Fr. de Laulanie visiting a farmers' field shortly before he died in 1995. In 1990, with his friends Sebastien Rafaralahy and Justin Rabenandrasana, Fr. de Laulanie formed Association Tefy Saina, a Malagasy NGO dedicated to improving rural conditions in Madagascar, including through the dissemination of SRI. Sebastien and Justin, now President and Secretary-General of Tefy Saina, are seen in Slide 17.
  • The bolded numbers are arithmetic averages for a number of SRI trials/evaluations in each country. Some of the data sets are from on-farm trials (with the number of farmers involved shown in parentheses) or from on-station trials. The range of results reported is also shown in each cell. The Comparison Yield figures are not national average figures, often lower, but averages for the trials or farmer practice using standard cultivation methods. The Maximum SRI yields are the highest yields reported in each data set.
  • Bruce Ewart, ADRA representative in Indonesia, got 7 farmers in West Timor to try SRI methods in 2002, with the encouragement of Roland Bunch. These are better farmers than their peers, as seen from their yield that season with current methods (4.4 t/ha), more than double the usual yield in the area. Their SRI plots averaged 11.7. Farmers working with ADRA in Lampung, Sumatra, got 8.5 t/ha with SRI methods compared to their usual production of 3 t/ha. Pablo Best reported that when farmers in Pucallpa, a lowland jungle area, tried SRI, they got a yield of 8 t/ha, four times their previous average, and not needing to do 8-10 hours/day of bird scaring at the end of the season because with SRI, the heavy panicles hung downward (but not lodging) so that birds could not get to them. Instead of letting cattle graze on the regrowth after harvest, the rice was allowed to produce a second (ratoon) crop, which was 5.5 t/ha, 70% of the first. Controlled trials in Benin, having read the account of SRI in ECHO Development Notes, found about a 5-fold difference in yield between SRI and conventional practice. The Agricultural Training Institute in the Philippines tried SRI methods with three varieties in Cotabato, Mindanao, and got an average yield of 12 t/ha, three times the usual yield in that area. The economic return averaged 290% as the value of rice produced was almost four times the cost of production.
  • This begins a consideration of the "science" behind SRI. This statement from an article by a number of leading rice scientists, published in a leading agronomy journal, states the standard scientific understanding of how irrigated rice grows: if there are more panicles per plant, there will be fewer grains per panicle, a manifestation of "the law of diminishing returns." This means that it is unpromising to increase rice plant tillering substantially, so rice breeding strategies, and particularly the "super-rice" being developed at IRRI, have aimed to reduce tillering. We find that with SRI methods, as seen in the next slide, there is a POSITIVE correlation, as plants with more panicles also have larger panicles. This is because SRI plants maintain a large and intact root system, as discussed below, making them "open systems" in which there is no necessary tradeoff (partitioning of photosynthate) between tillers and grains. With root degradation under continuously flooded conditions, rice plants are "closed systems" and there is a zero-sum relationship between tillering and grain-filling.
  • This was one of the first data sets that began laying a scientific foundation for SRI. Data were gathered from 76 farmers around Ambatovaky, a town on the western side of the peripheral zone around Ranomafana National Park in Madagascar, during the 1996-97 season. We had confidence in the field worker who collected the data, Simon Pierre, who had worked with Fr. de Laulanie before his death. The correlation between number of tillers per plant and number of grains per panicle was +.65, rather than the negative one expected from the literature. We have seen this positive relationship many times since this first analysis was done.
  • Here we look just at the effect of young seedlings, on better and poorer soil, at Anjomakely. The synergistic effect of compost with aerated soil is seen in the bottom three lines. Compost with saturated soil does less well (7.7 t/ha) than NPK with aerated soil (8.77 t/ha), but compost with aerated soil does by far the best (10.35 t/ha) on better soil. The same relationship is seen on poorer soil (right-hand column).
  • This slide speaks for itself. The Kirk and Solivas statement was for flooded rice 29 DAT. This exact number can vary according to variety, soil type and irrigation practices, but it is agreed that the roots of continuously flooded rice remain in a "mat" near the surface, because the roots are trying to capture dissolved oxygen in the irrigation water. In such a situation, the roots begin degenerating after about 2 weeks of continuous flooding, as documented by Kar et al. There is practically no research on this process, since it has been characterized as "senescence" and thus as a natural (and an unavoidable) biological process. In fact, as the research by Puard et al. shows, the formation of aerenchyma (air pockets) in rice roots under flooding is a man-made process, leading to root degeneration.
  • These pictures of cross-sections of rice root, from French research. The upper-left cross-section is of an 'upland' variety grown under upland, i.e., unflooded, and the lower-left, the same variety grown under flooded conditions. The upper-right cross-section is of an 'irrigated' variety grown under flooded conditions -- note the larger, more regular air pockets formed by degeneration of the root's cortex -- and the lower-right, of the same variety grown under unflooded conditions. There is every reason to believe that the upper-left and lower-right cross-sections are the more 'natural' or 'normal' condition, and that the lower-left and upper-right represent adaptations, for the plant root tissues to survive longer as oxygen can diffuse through these air pockets. But this will not keep the tissues alive throughout the growth cycle, as seen from Slide 29.
  • This is the abstract for an article that documented this process of root degeneration. Unfortunately, it was published in a little-read journal. The exact number (78%) can vary according to variety, soil type, etc., but this phenomenon is well known. Only it is not regarded as a serious impediment for rice production.
  • This is a figure also from research reported by the China National Rice Research Institute to the Sanya conference and published in its proceedings. It shows how the roots of the same variety (two varieties shown) grow deeper into the soil with SRI methods compared to conventional ones (CK).
  • This figure from report by Nanjing Agricultural University researchers to the Sanya conference, and reproduced from those proceedings, shows that the oxygenation ability of rice roots growing under SRI conditions are about double the ability, throughout the growth cycle, compared to the same variety grown under conventional conditions.
  • This picture from Sri Lanka shows two fields having the same soil, climate and irrigation access, during a drought period. On the left, the rice grown with conventional practices, with continuous flooding from the time of transplanting, has a shallower root system that cannot withstand water stress. On the right, SRI rice receiving less water during its growth has deeper rooting, and thus it can continue to thrive during the drought. Farmers in Sri Lanka are coming to accept SRI in part because it reduces their risk of crop failure during drought.
  • This gets into the most complicated part of the explanation for SRI success, drawing on knowledge that is available in the literature but seldom known by scientists who do not read Japanese or who did not have teachers educated in Japan. T. Katayama studied tillering in rice, wheat and barley during the 1920s and 1930s, but never published his results until after the war (1951), and his book has not been translated into English. Fortunately, Fr. de Laulanie happened to read a book in French which reports on Katayama's concept of "phyllochrons," regular intervals of plant growth (emergence of phytomers -- units of a tiller, a leaf and a root -- from the apical meristem of grass family (gramineae) species. In rice, phyllochrons can be as short as 5 days with good growing conditions, but as long as 8-10 days with adverse conditions. The number of phyllochrons emerging in consecutive periods increases according to a regular pattern known in biological science and mathematics as "a Fibonacci series," where the number emerging in each period is equal to the total the numbers that emerged in the preceding two periods. [Look at numbers in bottom line of the slide, and then at the numbers for rice tillering in the next two slides]
  • This shows graphically what happens according to the numbers shown in the preceding table (Slide 35). Note that with SRI practices, which create a large and actively functioning root system for the plant, there is no fall-off in tillering before PI. With conventional rice growing practices, a period known as "maximum tillering" PRECEDES panicle initiation, as the earlier growth in tillering rate 'peaks' and subsides. We need more systematic monitoring of tillering rates in SRI and conventionally grown rice to put some parameters on this difference. But we know that this kind of "explosion" in tillering does occur with proper use of SRI practices, which support a large root system, and we know that "maximum tillering" occurs before PI with conventional plants.
  • This summarizes what we know about phyllochrons and their effect on rice plant performance. It reiterates the need to consider what is happening below ground, with the roots, even though they are not seen. They are the basis for increased productivity, in conjunction with a more microbiologically active rhizosphere.
  • This picture was provided by Koma Yang Saing (CEDAC) of a pleased Cambodian farmer, showing the size of a massive root ball with a SRI rice plant.
  • This is known by plant scientists, but it has not been integrated into agronomic research strategies. There is a saying, "you can lead a horse to water, but you cannot make it drink." We want to emphasize that "you can provide large amounts of N to rice plants' roots, but you cannot make the roots take N up unless the plant needs it." This probably applies for other nutrients, but we have not seen research on this. The statements cited here are from IRRI and Cornell agronomists. The usual reaction we get hen pointing this relationship out is that this is already known, nothing new. It helps to explain why average uptake (efficiency) of N application is in the range of 20-30%.
  • This figure shows the yields associated with different numbers of mechanical hand weedings (with rotating hoe) for 76 farmers around Ambatovaky in 1996-97 (same as Slide 22). Two farmers did only manual weeding. They got about 6 t/ha yield, more than double the typical yield in the area. The 35 farmers who did 1-2 weedings, the minimum recommended, got 7.5 t/ha, triple the typical yield. The 24 who did 3 weedings got 9.2 t/ha, four times more, while the 15 who did 4 weedings, got 11.7 t/ha, about 5 times. Beyond 2 weedings, we think that the benefit is not really from the weeding but from the active soil aeration during the latter part of the vegetative growth phase. This is an area where controlled studies should be done. So far, all we have is data from farmers' fields. In other soils and other conditions, the absolute numbers will surely be different, but we think the pattern will hold up. On the very poor soils around Morondava, Frederic Bonlieu, doing research with 72 farmers practicing SRI for his thesis from Angers University in France, found that additional weedings added about 0.5 t/ha to yield, other things being equal. The same pattern we seen, but it was more linear and with less increment per weeding.
  • These last slides get into an area of SRI explanation that is more tentative, but probably more important for highest SRI yields. There is a lot of country-to-country variation in SRI results, and also within countries, much larger variations than can be explained by differences in practices or by differences in soil chemical and physical properties. We cite an observation by S. K. DeDatta in his well-known text on rice. We add our own emphasis to underscore our conclusion that there needs to be much more consideration of soil microbes and their contributions to rice yield. There is, however, little research on this subject, so DeDatta devoted very few pages to this compared to genetic, soil and other factors.
  • These are just the most obvious contributions. Our understanding of this netherworld is limited, though fortunately there are a growing number of microbiologists using very advanced modern techniques, such as DNA analysis, to map and track what is going on in the soil. The discussion that follows is can be viewed as introductory or superficial, or both.
  • Most people know that leguminous plants "fix" N in their roots through nodules on the roots inhabited by certain bacteria, rhizobia. And by implication, most thinks that non-leguminous plants "do not fix nitrogen." This is correct in terms of locus, but it misleads. All of the gramineae species (rice, wheat, sugar cane, etc.) have free-living bacteria in their root zones (referred to as 'associated' microbes) that fix N. Even in fertilized crops, a majority of the N taken up by the roots is from organic sources. And there is evidence that adding inorganic N to the root zone inhibits or suppresses the roots' and microbes' production of nitrogenase, the enzyme needed to fix N. So there is a tradeoff, in that adding inorganic N fertilizer reduces the N that is produced by natural biological processes. Or most relevance to SRI is research published more than 30 years ago reporting that when aerobic and anaerobic horizons of soil are mixed, BNF increases greatly compared to that originating from either aerobic or anaerobic soil. This suggests that the water management and weeding practices of SRI could be actively promoting N production in the soil. We have no research results to support this inference (though see data in Slide 49), but the yield increases with SRI practices require large amounts of N. BNF is the most plausible explanation.
  • Johanna Dobereiner has spend almost 40 years working on BNF particularly in sugar cane in Brazil, but also looking at BNF in other non-leguminous crops. Her 1987 book is the most extensive consideration of this subject, though there are a number of symposia also providing scientific information. In Brazil, it is well documented that BNF provides 150-200 kg/ha of N to the crop -- provided that soil has not been previously fertilized with inorganic N for some years, and provided (this is a little hard to understand) the sugar cane cultivars have not been fertilized for several generations. Applying N to the soil or to cultivars inhibits production of nitrogenase needed for BNF. Dobereiner's work is regarded as "controversial" within the agronomy profession because many efforts to replicate her results have failed. But this could be due to a mechanistic (non-biological) concept of the process, not appreciating how prior use of inorganic N can affect BNF potential, an effect documented in the literature (see van Berkum and Sloger).
  • These data from a study done by Fide Raobelison under the supervision of Prof. Robert Randriamiharisoa at Beforona station in Madagascar, and reported in Prof. Robert's paper in the Sanya conference proceedings, give the first direct evidence to support our thinking about the contribution of soil microbes to the super-yields achieved with SRI methods. The bacterium Azospirillum was studied as an "indicator species" presumably reflecting overall levels of microbial populations and activity in and around the plant roots. Somewhat surprisingly, there was no significant difference in Azospirillum populations in the rhizosphere. But there were huge differences in the counts of Azospirillum in the roots themselves according to soil types (clay vs. loam) and cultivation practices (traditional vs. SRI) and nutrient amendments (none vs. NPK vs. compost). NPK amendments with SRI produce very good results, a yield on clay soil five times higher than traditional methods with no amendments. But compost used with SRI gives a six times higher yield. The NPK increases Azospirillum (and other) populations, but most/much of the N that produced a 9 t/ha yield is coming from inorganic sources compared to the higher 10.5 t/ha yield with compost that depends entirely on organic N. On poorer soil, SRI methods do not have much effect, but when enriched with compost, even this poor soil can give a huge increase in production, attributable to the largest of the increases in microbial activity in the roots. At least, this is how we interpret these findings. Similar research should be repeated many times, with different soils, varieties and climates. We consider these findings significant because they mirror results we have seen in other carefully measured SRI results such as the Anjomakely factorial trials (Slide 24) and the previous season's trials with SRI at Beforona (10.2 t/ha).
  • These data are taken from the article by Ladha et al. (1998) but they did not draw any implication from their finding that optimum N fertilizer application was LOWER for late-maturing varieties than for early-maturing varieties -- and that the late-maturing varieties had higher yield with less fertilizer application than did early-maturing varieties. If volatilization and leaching of nutrients, particularl N, is as big a problem as stated in the article, these numbers should have been reversed. If, on the other hand, the N applied can "prime" soil microbiological processes that contribute to plant nutrition, a smaller amount over time could give higher yield. This is speculation, but it is consistent with relationships observed with SRI. It seems worth exploring.
  • The increase in yields around Ranomafana National Park during 1994/95-1998/99 from 2 t/ha to 8 t/ha ith SRI were quite inexplicable given that soil analyses by North Carolina State found on average that available P was only 3-4 ppm, which is less than half the minimum usually considered necessary for an acceptable yield. SRI farmers got twice as much as an acceptable yield without adding any P to the soil. Where did the P come from? The research reported by Turner and Haygarth in NATURE (May 17, 2001) could explain this since SRI methods involved alternate wetting and drying of the soil which the authors showed greatly increased levels of P in the soil solution, almost all from organic sources. They suggested that this effect probably applies for other nutrients too, but they were measuring only P.
  • Mycorrhizal associations have been largely ignored in rice because most is grown under continuously flooded conditions, which are inhospitable to growth of funguses. Yet we now know that 80-90% of plants depend in small to large part on the nutrient acquisition of funguses that "infect" their roots and provide access to a much larger volume of soil through the network of hyphae (filaments) that spread out in all directions. These hyphae acquire water and nutrients that ar shared with the plant, particularly P but also many others. Mycorrhizal hyphae are thinner even than hair roots so can access places in the soil that the root system cannot. One study found that "infected" plants could grow as well with 1/60th as much P in the soil as could "uninfected" plants, reported in the review on mycorrhizae by M. Habte and N.W. Osorio, Mycorrhizas: Producing and applying arbuscular mycorrhizal inoculum (2002). This is available on the web in The Overstory, #102
  • Research conducted in Egypt where farmers have for centuries alternated growing rice and berseem (clover) has shown that free-associated rhizobia in the root zone of rice (not living in nodules as they do on a legume) are abundant in this soil and have many measurable beneficial effects on rice growth. Surprisingly, the rhizobia do not contribute BNF for rice. Instead they stimulate nutrient uptake and plant growth in other ways. More research should be done on this particular microbe to understand what it could contribute to plant growth more generally. See Y. G. Yanni, et al., The beneficial plant growth-promoting association of Rhizobium leguminosarum bv. trifolii with rice roots, AUSTRALIAN JOURNAL OF PLANT PHYSIOLOGY, 28 (2001), pp. 845-870.
  • Research on rhizosphere function and dynamics is increasing. See the literature review by Robert Pinton et al., THE RHIZOSPHERE: BIOCHEMICAL AND ORGANIC SUBSTANCES AT THE SOIL-PLANT INTERFACE (Marcel Dekker, 2000) which gives an up-to-date review of what is currently known about this domain, with chapters on root exudation,rhizo- deposition, the contributions of mycorrhizae, etc.
  • This review of what is known, and what we think we know, about SRI is not a conclusive or final discussion of the subject. We expect that in 3-5 years' time, much more will be known as scientists become engaged on these topics and as farmers and NGOs continue producing new data that begs for explanations. The two main areas for research that have emerged from our SRI experence is (a) the growth and performance of roots, and (b) the dynamics and contributions of soil microbes. Both of these areas of research should be useful for improving the production of other crops. The explanations for greater root growth with SRI are quite straightforward: young seedlings, wide spacing, aerated soil. What results from this remains to be better documented and explained.
  • More complicated and difficult to examine and understand than roots will be soil microbial dynamics, though these two subjects should be looked at jointly, not totally separately. The contributions of exudates to microbial growth are well documented in Pinton et al. (2001), but we do not know much about this process for irrigated (SRI) rice.
  • This is a SRI rice nursery in Sri Lanka, showing one way (but only one of many ways) to grow young seedlings. The soil in this raised bed was a mixture of one-third soil, one-third compost, and one-third chicken manure. (The flooding around it is because the surrounding field is being readied for transplanting; normally there would not be so much water standing around the nursery.)
  • Here the seedlings are being removed. We would recommend that they be lifted with a trowel, to have minimum disturbance of the roots, but these seedlings are so vigorous that this manual method is successful. This farmer has found that his seedlings, when transplanted with two leaves at time of transplanting, already put out a third leave the next day after transplanting, indicating that there was no transplant 'shock.'
  • Here the field is being 'marked' for transplanting with a simple wooden 'rake.' If the soil is too wet, these lines will not remain long enough for transplanting. There are drains within the field to carry excess water away from the root zone.
  • Here are seedlings being removed from a clump for transplanting. Note that the yellow color comes from the sunlight reflecting off the plant. The plant's color is a rich green, indicating no N deficiency.
  • Here the seedlings are being set into the soil, very shallow (only 1-2 cm deep). The transplanted seedlings are barely visible at the intersections of the lines. This operation proceeds very quickly once the transplanters have gained some skill and confidence in the method. As noted already, these seedling set out with two leaves can already have a third leaf by the next day.
  • The SRI field looks rather sparse and unproductive at first. Up to the 5th or 6th week, SRI fields look rather miserable, and farmers can wonder why they ever tried this method and 'wasted' their precious land with such a crazy scheme. But the SRI plot here will yield twice as much rice as the surrounding ones once the rapid tillering (and root growth) begins between 35 and 45 days.
  • This is one of many happy Sri Lankan farmers with his SRI field nearing harvest time. Some young farmers have taken up growing "eco-rice," i.e., traditional varieties grown organically to be sold for a much higher price than conventional HYV rice, because of better texture, taste, smell and aroma and more assurance of healthy food. SRI in this way is starting to contribute to the preservation of rice biodiversity. As noted above, SRI methods work well with hybrid varieties and HYVs. These give the highest yields with SRI methods. But as SRI methods can double or triple traditional-variety yields, these old varieties become economically more advantageous with SRI. Much more remains to be learned about and from SRI. But we have now enough accumulated evidence, based on experience in farmers' fields, not just on experiment stations, and consistent with what is known in the literature (though often not previously connected up to promote increased rice productivity), to have confidence that this methodology will contribute to greater food security and a better environment. SRI, developed by Fr. de Laulanie and promoted by his friends in Association Tefy Saina, and by a growing number of colleagues in many countries around the world, could help to improve other crop production. The world does not need a doubling of rice production, but it does need increased productivity in the rice sector, as this is the largest single agricultural sector in the world in terms of the resources devoted to it. By raising the productivity of land, labor, water and capital in the rice sector, we should be able to meet our staple food needs with less of these resources, which have significant opportunity costs. We hope that SRI methods will enable farmers to redeploy some of their land, labor, water and capital to producing other, higher-value and more nutritious crops, thereby enhancing the well-being of rural households and urban populations. The urban poor should benefit from lower prices for rice that will follow from higher productivity. SRI is not a labor-intensive method that will 'keep rice production backward,' as was alleged by its critics in Madagascar for many years, but a strategy for achieving diversification and modernization in the agricultural sector.

0317 Possible Soil Microbiological Explanations for High Yields with the System of Rice Intensification (SRI) 0317 Possible Soil Microbiological Explanations for High Yields with the System of Rice Intensification (SRI) Presentation Transcript

  • From: Bruce Ewart <brucea@indo.net.id> To: Norman Uphoff <ntu1@cornell.edu> Subject: Many Thanks Date: Tue, 25 Feb 2003 07:42:57 +0700
    • Dear Norman,
    • … Was in Lampung last week, and the crops planted for the video are great. At 65 days, one crop will average about 65 tillers, and some are over 100 tillers, so the farmer and we are expecting a good crop. There is a good uptake of the system. In one village, there were 3 trials last year, and now 200 farmers are trying SRI. Some were so convinced by the trials that they are planting all SRI. The consensus now is that there is no more work required with SRI, and one farmer with 2 ha (very big crop here) considers that there is less work. He should know as he pays for all his labour. Thanks for keeping me in the loop. Regards,
    • Bruce Ewart [Indonesia director for ADRA]
  • Possible Soil Microbiological Explanations for High Yields with the System of Rice Intensification (SRI) Norman Uphoff CIIFAD
  • More tillers and more than 400 grains per panicle
  • SRI ‘too good to be true’? (like the economist’s $100 bill)
    • It goes against many concepts and beliefs of agronomists and economists: yield ceiling, soil depletion, tradeoffs, diminishing returns, etc.
    • However, there is increasing evidence that SRI greatly raises rice productivity
    • SRI is being used successfully by
      • a growing number of farmers in
      • a growing number of countries (16+)
    • But SRI is a work in progress (Q’s > A’s)
    • Average yields about 8 t/ha
    • Maximum yields can be twice this
    • Water required reduced by 50%
    • Lower costs of production
    • No need to change varieties (seeds)
    • Little or no need for fertilizers and agrochemicals (greater resistance)
    • Increased factor productivity -- the most important consideration
  • SRI Data from Sri Lanka
    • SRI Standard
    • Yields (tons/ha) 8 4 +88%
    • Market price (Rs/ton) 1,500 1,300 +15%
    • Total cash cost (Rs/ha) 18,000 22,000 -18%
    • Gross returns (Rs/ha) 120,000 58,500 +74%
    • Net profit (Rs/ha) 102,000 36,500 +180%
    • Family labor earnings Increased with SRI
    • Water savings 40-50%
    • Data from Dr. Janaiah Aldas, formerly economist at IRRI, now at Indira Gandhi Development Studies Institute, Mumbai, based on visit to Sri Lanka and interviews with SRI farmers, October, 2002
    • SRI is more labor-intensive , at least initially -- but may become labor-saving
    • SRI requires greater knowledge/skill from farmers to become better decision-makers and managers -- but this contri-butes to human resource development
    • SRI requires good water control to get best results, make regular applications of smaller amounts of water -- investment?
  • The basic idea of SRI is that RICE PLANTS DO BEST when
    • Plant ROOTS can grow large and deep having been transplanted carefully with seedlings experiencing little trauma, and with wider spacing between plants ; and
    • Rice plants are growing in SOIL that is kept
    • well aerated , never continuously saturated,
    • with abundant and diverse populations of
    • soil microbes that aid in plant nutrition
  • ‘ Starting Points’ for SRI:
    • Transplant young seedlings , 8-15 days (2 leaves) -- 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)
    • Weeding with rotating hoe early (10 DAT) and often -- 2 to 4 times
    • Application of compost is recommended
    • These are adapted to local situations
  • SRI practices produce a different RICE PHENOTYPE:
    • Profuse TILLERING -- 30 to 50/plant, 80-100 possible, sometimes 100+
    • Greater ROOT GROWTH -- 5-6x more resistance (kg/plant) for uprooting
    • Larger PANICLES -- 150-250+ grains
    • Often higher GRAIN WEIGHT -- 5-10%
    • A POSITIVE CORRELATION between tillers/plant and grains/panicle
  • SRI goes against LOGIC
    • LESS PRODUCES 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 as much water gives higher yield
    • Fewer or no external inputs are associated with greater output
    • Different phenotypes from rice genomes
  • Plant Physical Structure and Light Intensity Distribution at Heading Stage (CNRRI Research: Tao et al. 2002)
  • These results more often come from farms than experiment stations
    • But increasing number of scientists are working on SRI -- in China, Indonesia, India, Bangladesh, Cuba, etc.
    • SRI is the due entirely to the work of Fr. Henri de Laulanié, S.J . (1920-1995), trained in agriculture at INA (1937-1939)
    • He lived and worked with farmers in Madagascar, 1961-1995; SRI from 1983
    • SRI being promoted by Malagasy NGO, Association Tefy Saina , assisted by CIIFAD
  • Data from Sanya Conference
  • Average Yields Impressive: Certain Cases Hard to Explain
    • Indonesia -- West Timor (ADRA)
    • Yield with current methods -- 4.4 t/ha
    • Yield with SRI methods -- 11.7 t/ha
    • Peru -- Pucallpa, jungle area
    • Previous yields -- 2 t/ha, with more labor
    • SRI yield -- 8 t/ha, with less labor
    • + Ratoon crop = 70% of first crop -- 5.5 t/ha
    • Benin -- controlled trial: 1.6 vs. 7.5 t/ha
  • Effect of Young Seedlings
    • Better Poorer
    • SS/20/3/NPK 3.00 2.04
    • SS/ 8 /3/NPK 7.16 3.89
    • SS/ 8 / 1 /NPK 8.13 4.36
    • AS / 8 /3/NPK 8.15 4.44
    • AS / 8 /3/ Comp 6.86 3.61
    • SS/ 8 / 1 / Comp 7.70 4.07
    • AS / 8 / 1 /NPK 8.77 5.00
    • AS / 8 / 1 / Comp 10.35 6.39
  • Critical Factor is Root Growth
    • 3/4 of rice roots in continuously flooded soil remain in top 6 cm (Kirk and Solivas 1997)
    • 3/4 of rice roots in continuously flooded soil degenerate by time of flowering (Kar 1974)
    • Air pockets (aerenchyma) form in roots of rice plants when continuously flooded
    • These air pockets enable rice plants to survive under submerged conditions
    • But submerged plants do not thrive --
    • lacking oxygen, their roots degenerate
  • Dry Matter Distribution of Roots in SRI and Conventionally-Grown Plants at Heading Stage (CNRRI research: Tao et al. 2002) Root dry weight (g)
  • Root Activity in SRI and Conventionally-Grown Rice (Nanjing Agr. Univ. research: Wang et al. 2002) (Wuxianggeng 9 variety)
  • With young transplants and vigorous root growth ,
    • TILLERING is much greater
    • This can be explained in terms of phyllochrons -- interval of plant growth found in all “grass” species
    • Discovered by Japanese scientist Katayama in 1920s-30s
    • Tillering pattern follows sequence of ‘ Fibonacci series ’ -- 1, 1, 2, 3, 5, 8, 13...
  • With best growing conditions, the phyllochrons are shorter
    • So more periods of growth can be completed before the rice plant switches from
    • vegetative growth phase
    • to reproductive phase
    • With more tillering , there is also more root development
  • SRI capitalizes on the fact that the uptake of N is a demand-led process
  • Benefits are observed from soil aeration during the vegetative growth period
  • Soil microbial activity is critical for plant nutrition and SRI performance
    • “ 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)
  • Bacteria, funguses, protozoa, amoeba, actinomycetes, etc.
    • Decompose organic matter , making nutrients available
    • Acquire nutrients that are unavailable to plant roots
    • Improve soil structure and health (water retention, pathogen control)
  • Biological Nitrogen Fixation
    • Microorganisms -- particularly bacteria, both aerobic and anaerobic -- can fix nitrogen (N) from air into forms available to plant roots
    • Research has shown that when aerobic soil and anaerobic soils are mixed , rather than having only aerobic soil or only anaerobic soil, BNF is greatly increased (Magdoff and Bouldin, 1970)
    • BNF can occur with all gramineae -- not limited to leguminous species
    • In flooded paddies, BNF is limited to anaerobic processes -- SRI provides aerobic conditions as well
    • BNF must be occurring for the higher yields observed; not enough N measured in the soil
    • Use of chemical fertilizers inhibits the production by the roots and microbes of nitrogenase , the enzyme needed for BNF (van Berkum and Sloger 1983)
  • This helps to solve puzzle
    • Why were many Madagascar farmers putting their compost for SRI on their contra-saison crop -- not on rice crop?
    • Both crops reportedly gave better yield
    • This makes no sense if LEACHING and VOLATILIZATION are big problems, or if nutrients are ‘used up’ by plants
    • It makes sense, however, for BNF
  • Phosphorus Solubilization
    • Aerobic bacteria can acquire phosphorus from unflooded soil for their own use
    • When the soil is flooded, these bacteria die (lyse) and release their contents into the water that permeates the soil
    • When the soil dries again, surviving bacteria begin their growth again
    • Soluble P can increase by 185-1,900% by such ‘mining’ of the soil that increases nutrient supply (Turner & Haygarth, 2001)
  • Microbiological ‘Weathering’ of Soil?
    • Soluble P can increase by 185-1,900% by microbiological ‘mining’ of the soil (Turner & Haygarth, 2001)
    • Speculation that this process operates increase supply of other nutrients too
    • Under ‘natural’ conditions, ‘depletion’ of soil is very rare occurrence -- due to microbiological processes
  • Mycorrhizal Associations
    • Mycorrhizal funguses ‘infect’ plant roots
    • They send out hyphae (filaments/threads) in all directions and expand the volume of soil that the plant can extract nutrients from by 10-100 times
    • Mycorrhizae are very good at harvesting phosphorus -- increased efficiency by 60x
    • Mycorrhizae cannot grow in anaerobic soil conditions, so cannot benefit irrigated rice
  • 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
  • Root Exudation
    • Plant stems & roots are ‘two-way’ streets
    • 30-60% of the energy (sugars, proteins) made in the canopy is sent to the roots (Pinton et al., 2000)
    • 20-40% of this energy supply is exuded by the roots into the soil -- feeding the bacteria, funguses, etc. in the root zone
    • Root cells also die and provide energy to microbes through rhizodeposition
    • Plants gain more than they lose from this
  • SRI Supports the Motto of Organic Farmers
    • Don’t try to feed the plant --
    • Feed the soil -- and the soil will feed the plant
    • Emphasis on symbiosis between plants and soil microorganisms
  • SRI can be seen as an agronomic system for:
    • Plant management -- young seedlings, careful transplanting, wide spacing
    • Soil and water management -- leveling, ‘minimum of water’ for soil aeration
    • Nutrient management -- increase SOM
    • Microorganism management -- result of the above, promoted by root exudation
  • SRI Raises More Questions than we have answers for
    • Many of the answers will be found in the growth and functioning of ROOTS, which grow better from:
    • WIDE SPACING, and in
    • Answers will also be found in SOIL MICROBIAL DYNAMICS -- in the abundance & diversity of soil microbes (bacteria, fungi)
    • Microbes grow better in:
    • SOIL not continuously flooded ,
    • with more soil organic matter
    • Microbes benefit from exudation resulting from more root growth
  • .
    • More information is available
    • on the SRI WEB PAGE :
    • http://ciifad.cornell.edu/sri/
    • including Sanya conference proceedings,
    • available on CD ROM discs
    • [email_address]
    • [email_address]
    • [email_address]