Chapter 11: DEMONSTRABLE DIFFERENCES IN RICE PHENOTYPES
Most of the comparisons made between SRI-grown rice plants and their kin grown by conventional methods have been in terms of crop yield, and probably always will be. Yield numbers are easy to grasp, and food production is an immense challenge facing farmers, their families, their countries, and indeed humankind. But a more complete understanding of what happens as a result of SRI crop management comes from considering various ways in which SRI practices affect the growth and performance of rice plants of a given variety (genotype).
In this chapter, we consider five ways in which SRI practices have been seen to change the growth patterns and results of rice cultivation. Each section gives insights into the systemic nature of SRI effects even though different outcomes are being measured and reported. These show SRI is more broad-gauge than most technologies.
We first consider research that shows how SRI methods alter the structure and functioning of rice plants, differences referred to technically as differences in plant morphology and plant physiology. Then we look at an unanticipated ‘bonus’ with SRI; when the grain harvested from SRI fields is milled, to remove the husks around the grain and to polish the grains, there is a higher milling outturn. This technical term means that a higher proportion of the harvested rice is edible and not broken during the milling process. As a consequence, SRI methods add about 10% or more to the world’s rice supply than just the increase in paddy rice production that is achieved. The latter is what is referred to most of the time in this book.
We also discuss how SRI management shortens the crop cycle, the time from planting to harvesting. This means that SRI’s higher yields are produced in less time, which is a boon to farmers. Also, reports from various countries have documented how the practice of mechanical soil-aerating weeding can in combination with the other SRI practices raise crop yield and enhance rice phenotypes. Further, researchers have found that rice grains grown with SRI methods have higher concentrations of important micronutrients that are needed for human nutrition. This means SRI has effects on food quality as well as quantitative impacts.
MEASURABLE DIFFERENCES IN RESULTING RICE PLANTS
The first thorough study of the impacts of SRI management on rice plants’ morphology and physiology was done by Amod Thakur, a senior plant physiologist at ICAR’s Indian Institute for Water Management in Bhubaneswar, India, with colleagues there. As noted in Chapter 9, Amod’s interest in evaluating SRI was sparked by a published dismissal of SRI by IRRI scientists who showed no interest in how SRI methods can improve the performance of individual plants. They were ignoring their own data that showed individual SRI plants yielding as much as six plants of the same variety that had been grown with standard methods. Amod wondered whether this was in fact true, and if true, how could this be possible?
Without contacting Cornell or anyone else, only getting permission from his institute superiors, Amod conducted three years of trials, planting always the same rice variety and varying only the management practices. He used the SRI practices listed on the Cornell SRI-Rice website versus the best management practices recommended at that time by India’s Central Rice Research Institute in nearby Cuttack. Only after his first article on the results was summarily rejected by a leading agronomy journal did Amod make contact with Cornell to see if we could help to strengthen the presentation of his research findings for publication.
A series of research articles reporting on these findings was subsequently published in a number of respected agronomy journals after going through peer-review. Below are summary tables of the results from Amod’s and his colleagues’ research that documented the phenotypic changes induced by SRI practices, first in terms of the size and weight of different plant organs, and then, evaluating their processes of growth and performance.
Comparisons per plant, per hill, and per unit area (m²) are all relevant, contrasting SRI plants with others grown according to rice scientists’ recommended management practices (RMP). While it is important to look at the characteristics of individual plants, one needs of course to consider changes on an area basis since farmers with limited land resources need to be maximizing their yield per unit area, not being satisfied just with growing spectacular plants.
Effects of rice management practices on morphological characteristics of
Plant roots, tillers, leaves, and canopy structure in rice
ᵃ Canopy angle was measured with a protractor using the following equation: CA (in degrees) = 180 - (θ₁ + θ₂), where θ₁ and θ₂ are the angles of inclination of the outermost tillers from a horizontal orientation on both sides, measured at flowering stage. NS = difference not statistically significant.
Effects of rice management practices on roots functions,
physiological parameters, and N-uptake in rice
* Measurements were taken after harvest FW = fresh weight
Effects of rice management practices on yield-contributing characteristics,
grain yield, straw weight, and harvest index
The average percentage increase of individual plant traits for these multiple measurements was 47%, while the average increase where measurements were made on a ‘per hill’ basis (one plant for SRI hills vs. three plants in RMP hills) was 145%, reflecting the wider spacing and greater room for roots and canopy to grow. On an area basis (per m²), SRI increases averaged 28%, all together contributing to average yield increases of 40% to 50%, depending on the trials.
Amod’s research underscored that wider spacing is something to be optimized under a given set of conditions, not assuming or proposing a single plant density that is optimal for all SRI. Amod’s first-year trials showed that under the soil and climatic conditions of his research station in Bhubaneswar, 20 × 20 cm spacing together with the other SRI practices gave a better yield than the 25 × 25 cm spacing usually recommended for SRI.
In locations where soil and climatic conditions are more favorable, it has been found that 30 × 30 cm spacing can give the highest yields. But in most evaluations of spacing, planting single plants at 25 × 25 cm (16 plants per m²) has given best results. In Amod’s trials however, having 25 plants per m² rather than 16 plants proved to be most productive when used in conjunction with the other SRI methods. Farmers’ usual spacing in the Bhubaneswar area was 10 to 15 cm, about 60 hills per m² with the total number of plants per square meter depending on how seedings were transplanted in each hill, 3, 4 or more, 180 to 240 plants per m².
An interesting finding from Amod’s research was that the variety of angle (86°). With wider spacing, its tillers grew more horizontally and when given more space to grow, the variety’s greater number of leaves grew more upright. This meant that there was more leaf area exposed to the sun, and this plant more effect posture reduced the amount of shading of leaves by other leaves.
Consequently, Amod found that SRI plants’ light interception was 89% compared to 78% with the same variety grown conventionally. Under SRI management, the rice plants were harvesting 15% more of the solar energy that reached the field. This was a demonstrable and quantifiable phenotypical advantage of SRI-grown rice plants that contributed to their greater yield.
Measurements of plant parameters done in other countries have given similar results, but the findings of Amod and his colleagues are reported here because they are the most complete set of morphological and physiological comparisons between SRI and conventionally-grown rice plants published so far. These findings present strong evidence of SRI’s multiple management effects on phenotype.
HIGHER MILLING OUTTURN AND BETTER GRAIN QUALITY
An early indication of SRI’s having advantages beyond just raising the yield of unmilled rice harvested from farmers’ fields came during a visit to Sri Lanka in 2002. One of the few Agricultural Ministry officials who had taken a personal interest in SRI up to that point, Abeygunawardane, told me that after the first season of SRI use in the Mahaweli System H irrigation scheme, rice millers there were coming to talk with SRI farmers during the next season, while their SRI crop was still ripening and not yet harvested. They offered to pay the farmers 10% more per bushel for their SRI paddy rice than the prevailing price being paid to other farmers. This sounded amazing.
Why would millers pay more for SRI paddy rice? I asked. “Because millers have seen that the panicles of SRI rice have fewer unfilled grains,” the official responded, something confirmed in most scientific studies of SRI. “When SRI paddy rice is milled, there is less chaff to discard.”
Also, he said, when SRI paddy rice is milled, there are more whole grains of rice to sell because fewer grains get broken in the process. Unbroken grains, called head rice, command a higher price in the market than do broken grains, so millers can get more profit from a given amount of unmilled rice. Paying farmers a higher price for their SRI paddy rice with them some of the windfall gain from SRI. Later we learned that rice grains that are more resistant to breakage during milling have generally higher content of nitrogen, indicative of more amino acids.
This was just an anecdotal report, not the result from any scientific study. But it seemed reliable because rice millers are regarded as some of the most unsentimental human beings on earth, never voluntarily losing money on any transaction. If they were willing to pay 10% more for SRI paddy rice, this must be yielding them more than a 10% increase in profit.
Reports subsequently came in from other countries about a difference in milling outturn, the amount of polished rice that remains after the harvested paddy rice has been milled to remove the husks and bran from around the grain.
When I visited Cuba in 2004, I talked with the farm manager at a sugar plantation there (the first to take up SRI for growing its rice crop, Chapter 46). The plantation milled its own paddy rice, so I asked him about his experience with milling SRI rice. He said that from their two seasons of growing and milling SRI rice, they had calculated that the outturn rate was 13% to 17% higher than before, a significant addition to the amount of edible rice that they could sell or consume, over and above what they were harvesting from the field.
Later that year, some properly scientific evidence on this subject came to hand. At a large Chinese national rice conference held in Harbin, to which I had been invited to give a keynote on SRI, Prof. Ma Jun of Sichuan Agricultural University presented a paper on his evaluations of SRI, adding evidence to my presentation.
Among other things, Ma had evaluated the impact that SRI practices had on grain quality. As seen in his tables reproduced below, his research had documented 16% to 17% less breakage of rice grains during milling. Thus, there was more food coming from each bag of rice harvested from rice paddies. Ma had also measured and could report that SRI grains had less chalkiness, an undesirable quality that affects grains’ cooking, eating and nutritional characteristics and hence the grains’ market value.
* Averages calculated for three spacings with replicated trials.
** ‘Head rice’ refers to unbroken grains of rice.
When my wife Marguerite and I visited villages in Tripura state of India in 2007, we asked farmers in a dozen villages what was their rate of milling outturn? Farmers in these communities took their harvested paddy rice to a local miller to be de-husked and polished, paying for his services and possibly selling him some of their rice if they had produced more than was needed for their subsistence. They reported about 18% more milled rice remaining after the SRI paddy rice they had harvested was milled.
In Kenya, analyses of SRI-produced grains after milling found 10% more unbroken grains (head rice) and one-third less broken grain (rice fragments). When the milled rice was run through a color sorter, there were 21% fewer discolored grains which lower the market value of the rice. Bags of unmilled SRI paddy rice weighed 100 to 110 kg compared to the usual weight of conventionally-grown paddy, 80 to 90 kg.
These quantitative and qualitative considerations add to the value of the rice produced with SRI methods. Note that almost all of the data on yield presented in this book are for unmilled paddy rice, not milled, polished, edible rice, which is the purpose of rice production.
With SRI production methods, there is ‘bonus’ for both farmers and consumers, and especially for farmers if they get paid for quality as well as for quantity. Per tonne of paddy rice harvested from fields and reported as yield, with SRI management there will be 10% to 15% more food actually produced because of higher milling outturn. SRI can thus contribute more to families’ food security and to national food stocks than the amount of increase that is reported in terms of harvested paddy rice.
This is not a trivial difference. An increase of 10-20% in the production of food equals or surpasses the yield enhancement that is credited to the heterosis effect with hybrid rice varieties, compared to the yield of their inbred HYV counterparts.
Beyond the objectively measurable quality of chalkiness, it is often reported by farmers and consumers that the taste, aroma and texture of SRI rice grains are superior to those for the same variety when it is grown with conventional methods. These other qualities of grain have been the subject of some research over the years, but most evaluations have been rather subjective, like the evaluation of tea by trained tea tasters who grade and rank teas according to qualities discerned with the tongue’s taste buds and the nose.
Miyatty Jannah in Indonesia whose contributions to SRI work are reported at various times in this story told me that the local rice merchant in her village offered her a premium of price of 30% more per kg for her SRI paddy rice, without her asking for this, because he could see that the higher quality of her rice would earn him a better price in the market. In some places, SRI grains are purchased to be used as seed grain because of their size and regularity, so this means that the farmer-producers can receive a premium price.
Higher grain quality is reported by farmers and consumers often enough so that it is mentioned here even if there is there is not yet much objective evidence to be presented. That was a study done in Malaysia to assess quality differences. In taste-testings with established criteria, SRI grains were scored higher on all of the attributes compared. Many anecdotal reports could be noted, but they are not conclusive. Quality assessment is an area where research remains to be done. There is another aspect of grain quality that is quite measurable, nutrient content and value, discussed separately below with published research results.
YIELD ENHANCEMENT FROM SOIL-AERATING WEEDING
One of the first data sets from Ranomafana that triggered rethinking about methods of rice production is shown below, much neater than when it was first sketched out on notebook paper. It shows a direct correlation between the SRI practice of doing mechanical weeding and the resulting rice plants. This is one area where a direct connection can be made between a certain SRI practice and a measurable phenotypic effect.
After the 1997-98 season, one of Tefy Saina’s trainers, Simon-Pierre Rafanomezantsoa, provided me with detailed yield figures as well as with the number of times that each of the 76 farmers in his zone of responsibility around Ambatovaky had weeded his or her SRI plot with a mechanical weeder as recommended. Simon-Pierre was the best-trained of the Tefy Saina trainers and very dedicated to his work, having understudied Fr. Laulanié before the priest’s death. So, his data were considered quite reliable. (Simon-Pierre’s data on panicle size relative to tiller production per plant were reported in a graph in Chapter 4.)
Simon-Pierre’s figures showed that farmers who had done more mechanical weedings (in conjunction with transplanting young seedlings, wider spacing, more organic matter, and no continuous flooding) achieved demonstrably higher yields. The two farmers who had done only hand weeding with no mechanical weeding got a yield that was more than double the usual average in that community. Not a bad result. But those farmers who had done one or two weedings (N=35) got about 25% more yield, while those who did three weedings (N=24) had yields about 50% higher. And those who did four weedings (N=15) were able to produce almost twice as much rice as those who had done only hand weeding with no disturbance of the soil’s surface. This was the first time that the relationship between mechanical weeding and crop yield had been systematically evaluated.
These were not controlled experiments, simply data from farmers’ fields. So we could not know, for example, how much compost had been applied, or how much chemical fertilizer might have been used. (Most of these farmers were too poor to afford this.) Possibly those farmers who weeded mechanically more often also used all the other SRI practices more diligently. These were rough-and-ready statistics, but the differences were too great to be dismissed as ‘not significant.’ The data gave rise to thinking about ‘active soil aeration’ to complement and amplify the effects of ‘passive soil aeration’ that resulted from intermittent irrigation.
This same effect was reported a few years later by Rajendra Uprety from Morang district in Nepal. During the 2005 summer monsoon season, the 412 farmers who used SRI methods got average yields of 6.3 tonnes per hectare, while the average for other farmers in the district was only 3.1 tonnes. SRI trainers had recommended that farmers do at least two mechanical weedings of their SRI fields, so that is what most of the farmers (89%) did. But some did only one weeding, and a few did three weedings. Their respective yields (and ranges of yield) are shown below in tonnes per hectare.
Since the data are from a large number of farmers and there was no evident difference among them in terms of the application of compost or fertilizer, the differentials in yield can be attributed mostly if not entirely to differences in weeding. Doing two weedings instead of one raised yield by 14%, other things being apparently equal. Doing a third weeding raised the yield by another 34%. It is unfortunate that none of the farmers did four weedings.
The extra work was a very cost-effective investment because an additional yield of two tonnes would be worth about US$ 400, many times the cost of doing the extra weeding. A weeding would require between 6 and 8 days of labor with a cost of about US$ 20-25, or US$ 40 at most. Weeding one hectare by hand, on the other hand, required more than twice as much labor, about 15-20 man-days.
That SRI methods doubled average yields was something of developmental significance, but the increments attributable to mechanical weeding were also of scientific interest. They suggested that ‘weeding’ involved more than just controlling weeds. Such results reinforced our concern with active soil aeration and heightened interest in what the life in the soil might be doing. Meanwhile, a matter of psychological or behavioral interest was why more farmers did not avail themselves of this profitable opportunity, something that was puzzling also in Madagascar.
Three years later, we got further data on the effects of active soil aeration, from Afghanistan where the Aga Khan Foundation program had introduced SRI in Baghlan province in the northeast. Its technicians reported the relationship seen below between the number of mechanical weedings and resulting yield. These data were from 42 farmers using SRI methods in the 2009 summer season. The numbers in each group were not large, but the relationships were very similar to what had been seen around Ambatovaky in Madagascar. It was the pattern rather than the specific numbers that prompted interest in understanding better what was going on in the soils and in the plants when SRI methods were used.
An interesting comment on for this data set from Afghanistan is the fact that the four farmers who did four mechanical weedings, the rightmost bar, were all second-year SRI farmers. Part of their success could be attributed to the knowledge, skill and confidence with which they used the new methods. But their first-year results had presumably satisfied them that the recommended SRI practices were productive, making them more willing to invest time and effort in churning up the soil between their rice plants, not just to bury weeds but to enhance the plants’ vigor and performance. Afghan farmers reported other phenotypic effects like SRI plants’ greater resistance to pests and disease. But no systematic data on this were reported.
SHORTER CROP CYCLE: LESS TIME TO REACH MATURITY
A phenological effect that has been often reported is that SRI-grown rice crops mature more quickly. The first systematic assessment of this was reported from Nepal by Rajendra Uprety in 2005 from Morang district, where over 400 farmers had used SRI methods with 8 different varieties. On average, their rice crop yields doubled with SRI management, 6.3 vs. 3.1 tonnes per hectare, as noted in the preceding section.
The data gathered also showed, as seen below, that these farmers were able on average to harvest their higher rice yields 16 days sooner than the usual period of time (duration) that plant breeders in Nepal had advertised for their respective varieties. The thesis research of Krishna Dhital reported in Chapter 9 showed that the reduction in time to maturity was not focused at any one particular stage of development, but instead was fairly similar across the various stages of growth.
ᵃ As advertised by the breeders of these respective varieties.
This effect was not unique to Nepal. In the SRI experience reported in the preceding chapter from Darveshpura village in Bihar state of India, the record yields achieved there were harvested 10 days sooner than was expected for the hybrid varieties planted.
A study done in Bangladesh evaluating 16 rice varieties under SRI management found that all of the varieties showed earlier maturity, by 3 to 23 days, than was expected by rice breeders. The average reduction in the crop cycle was by 12 days.
In Laos, the monitoring unit of an EU-funded project there (Chapter 8) found similar acceleration of rice crop maturation. When farmers can harvest their crop sooner, this means that the crop is less exposed to climatic stresses and to the hazards of pests and disease.
How much shortening of the crop cycle results from SRI management is of course variable, influenced by climate, soil and other conditions as well as by varietal differences. In general, the effect has been more prominent at higher latitudes than nearer to the equator, suggesting that day length during the growing season plays a role.
Mobilization of the soil biota is probably also an important factor, but there has not been enough study of this phenomenon to have an explanation of how and why rice genomes express their productive potential not only more generously but with significant acceleration.
NUTRITIONAL VALUE OF RICE GRAINS: MORE MICRONUTRIENT CONTENT
Another effect of SRI management methods, this one quite unexpected, is that the micronutrient content of SRI rice grains is higher, often much higher, when the new methods are employed. Thus, nutritionally the quality as well as the quantity of food produced is increased , another phenotypical effect induced by SRI practices.
Considerable effort is now focusing on the breeding of crop varieties that are richer in micronutrients. But SRI offers an agronomic means to biofortify grain, making SRI’s quantitative increases in rice production accompanied by important qualitative improvement.
Micronutrient malnutrition, often referred to as ‘hidden hunger,’ is a worldwide problem, most acutely observed in terms of iron (Fe) and zinc (Zn) deficiencies, but other micronutrient deficits in diet are also notable, such as for copper (Cu) and manganese (Mn).
Three studies from leading agricultural research institutions in India have shown that both the straw and grains of SRI-grown plants have higher micronutrient content, the first of these studies also examining linkage with the abundance and activity of microorganisms in the soil. More research remains to be done on these relationships, but there is enough evidence, summarized here, to warrant considering how crop management practices can elicit phenotypical responses that improve the value of the food grown and consumed, a kind of agronomic rather than genetic biofortification.
The first work on this subject was done by researchers at the Indian Agricultural Research Institute (IARI) in New Delhi. It was published in the Journal of Plant Nutrition after considerable delay despite the evident merit and significance of the research. As microbiologists, the researchers were interested in the interaction of soil organisms with different crop management methods. They anticipated that SRI practices would create a more favorable environment for microbial growth and activity.
The research studied the effects of inoculating seedlings (either 12 days or 30 days old) with several biofertilizer suspensions of cyanobacteria, commonly referred to as blue-green algae (BGA), or with Rhizobial bacteria or with Trichoderma fungi. The rice plants were then grown with either SRI or conventional practices.
Irrespective of the fertilization regime, most of the time (86%) the younger seedlings and SRI practices outperformed conventional practice in terms of micronutrient content of the grains (Fe, Zn, Cu and Mg). In trials with no fertilization, SRI grains had more than double the micronutrient content of conventionally-grown grains. With recommended applications of NPK fertilizer, the concentrations of micronutrients were also doubled in the SRI grains.
Cutting the concentration of inorganic N fertilization in half, but keeping P and K at recommended levels, reduced the SRI advantage in micronutrient concentrations, except for zinc. But using this lower level of inorganic fertilization with different biofertilizers (blue-green algae, Rhizobia and/or Trichoderma) usually boosted the micronutrient content substantially. SRI methods had less of a boosting effect for magnesium, but a very great effect for zinc. Summary details are given in the table below.
With all of the biofertilizer treatments, the microorganisms would have been playing a major role in the decomposition and mineralization of organic matter as well as in transforming inorganic nutrients into plant-available forms. The researchers noted that while these effects on nutrient concentrations in the grain were seen already within one season, the effects of inoculation for biofertilization would probably have been stronger if the trials had been carried out for several seasons because soil biological dynamics can increase over time.
Further trials analyzing micronutrient uptake and concentration in rice grains under SRI crop management have been undertaken by other Indian scientists. Anchal Dass and colleagues at IARI, who were working more from an agronomic than a microbiological perspective, focused more on the effects of water management than on those of soil biota, but they documented similar effects as those shown by Prasanna and her colleagues.
As seen in the table below, SRI management significantly enhanced the uptake of a secondary nutrient, sulfur (S), and of the micronutrients Zn, Fe, Mn and Cu in both the grain and the straw compared to the levels of these nutrients in rice plants that were grown with conventional rice crop management.
Intermittent irrigation was found to be better for nutrient uptake than was continuous flooding, but the uptake of S, Zn and Cu in grains was greatest when irrigation water was given 1 day after the disappearance of ponded water on the soil surface, whereas Fe and Mn were taken up the most when irrigation water was resupplied 3 days after ponded water disappeared.
Further research on this subject by Amod Thakur and colleagues at ICAR’s Indian Institute of Water Management in Bhubaneswar produced similar findings. They focused on different nutrient management practices – fully organic vs. ‘integrated’ nutrient management (INM), which combines both organic and inorganic sources of nutrients – as these interact with either SRI or conventional crop management methods.
The first table below shows micronutrient uptake into the grains on an area basis (kg per ha) in response to either SRI or conventional rice crop management when the provision of nutrients to the soil was either ‘integrated’ or fully organic. The second table evaluates nutrient concentrations in the grain (mg of micronutrient per kg of grain). It is seen that micronutrient concentrations are consistently and significantly greater under SRI management, and that organic nutrient provision was generally superior in this regard compared with INM.
Effects of cultivation practices and nutrient management on
micronutrient uptake into rice grains (kg per ha)
Effects of cultivation practices and nutrient management on
the concentration of Fe, Zn, Cu, Mn in rice grains (mg per kg)
Much more research remains to be done on this subject, but each study’s findings appear more robust because each of the three, focusing respectively on microbiology, water management, and nutrient management, found similar dynamics and results when SRI methods were used for growing rice.
The model for explanation that has been emerging from the various research undertakings is that SRI practices as independent variables affect both root growth (Chapter 4) and soil biology (Chapter 5) as dependent variables. In particular, SRI practices stimulate the abundance, diversity and activity of the soil biota, including microorganisms. The enhancement of microbial services among other things supports the uptake of more micronutrients, not just macronutrients, and of more complete suites of these micronutrients.
This capacity in turn supports the functioning of the plants’ metabolism, including the synthesis of enzymes which require a great variety of micronutrients for their formation. Having a more complex and complete ensemble of enzymatic activity could account for effects such as the acceleration of rice crops’ growth cycle and the enhancement of nutrient quality in terms of micronutrients, as well as increasing the mostly-carbohydrate quantity of grain produced. However, these are explanations that will require more research to become elaborated and established. They will not become accepted on the basis of one or a few research projects.
In the meanwhile, because the known effects of SRI crop management are all benign, there is no evident reason why harm would result from utilizing these ideas. It makes sense for farmers to be applying them and further diversifying and refining the methods on the basis of experience.
Vernon Ruttan, IRRI’s first agricultural economist and founder-president of the Agricultural Development Council, in a private communication once suggested that SRI was something like the Wright brothers’ invention of the airplane, where technology proceeded rather than followed from science.
In the Wright brothers’ case, the technology of flight preceded the science of flight. Theories of aerodynamics had to catch up with the speed and height of airplanes’ trajectories. Eventually aeronautical science could further accelerate and guide the technological advances. More interaction between practice and theory should help to build a better understanding of the dialectic between genes and their expression and should enhance the benefits therefrom.
* * * * * * * *
This far, the story of SRI has been mostly agronomic, with some linkages to microbiology and genetics and also to economics. In the next chapter, we consider how SRI relates to larger concerns with climate and the environment. In Chapter 13, we then look at how the ideas and practices of SRI, developed for irrigated rice production, were extended to the cultivation of unirrigated upland rice which relies primarily on rainfall. And then in Chapter 14 we consider how they were extrapolated further to the growing of many different crops beyond rice.
In the other chapters that then follow in Part I we consider further amplifications of SRI that built upon the agronomic insights of this unprecedented innovation as they were taken into many other areas. An annex at the end of this first Part summarizes syntheses of the various elements and effects that together present and explain the System of Rice Intensification.
Understanding of how to get greater productivity from the inputs that are used to cultivate rice and other crops – seeds, land, labor, water, compost or other nutritional supplements, and capital – has been accretionary, building up over time. The various practices of SRI that respectively and collectively facilitate plant genomes’ fuller expression of their inherent potential to produce larger, stronger, more robust and more beneficent phenotypes have been seen to be effective in the field, but they are confirmed by scientific studies.
NOTES AND REFERENCES
 When paddy rice is milled to remove its outer husks and the bran around its grains, the husks are discarded, although they can have various non-food uses. Grains that are broken during milling can be used in prepared foods or as animal food, but they cannot be sold for a good price because consumers prefer and buy whole polished grains, or at least grains not badly broken. Rice that has only been de-husked, with most of the bran which contains vitamins and minerals still around the grain, is called ‘brown rice’ and is more nutritious.
Bran is a by-product of milling, not a waste product, because it can be used to enrich human diets and for oil extraction, while among other things, husks can be burned as a fuel to produce of heat. Some farmers use rice husks for crop protection, sprinkling them on the ground between plants, because the sharp edges of husks cut the soft underside of snails and deter them from eating rice plants in the field.
The husk is about 20% of a paddy rice grain, and the bran another 10%. Depending on growing practices, temperature, and the fertility of the soil, 5% to 25% of the husks in harvested paddy rice will be empty as grains did not form within them. The number of ‘blanks’ will lower the percentage of milling outturn, as will the breakability of the grains. Paddy rice yields are thus gross production, while the net food production is the milled white rice, 60% to 70% of the harvested yield.
 A.K. Thakur, N. Uphoff and E. Antony, ‘An assessment of physiological effects of system of rice intensification (SRI) practices compared with recommended rice cultivation practices in India,’ Experimental Agriculture, 46: 77–98 (2010); A.K. Thakur, S. Rath, S. Roychowdhury and N. Uphoff, ‘Comparative performance of rice with system of rice intensification (SRI) and conventional management using different plant spacings,’ Journal of Agronomy and Crop Science, 196:146–159 (2010); A.K. Thakur, S. Rath, and A. Kumar, ‘Performance evaluation of rice varieties under the System of Rice Intensification compared with the conventional transplanting system,’ Archives of Agronomy and Soil Science, 57:223–238 (2011); A.K. Thakur, S. Rath and K.G. Mandal, ‘Differential responses of system of rice intensification (SRI) and conventional flooded rice management methods to applications of nitrogen fertilizer,’ Plant and Soil, 370:59–71 (2013); A.K. Thakur, R.K. Mohanty, D.U. Patil and A. Kumar, ‘Impact of water management on yield and water productivity with system of rice intensification (SRI) and conventional transplanting system in rice,’ Paddy and Water Environment, 12:413–424 (2014).
 The data in the tables below are compiled from the articles cited in preceding endnote.
 Evaluations done at the Sampoerna station in Lombok province of Indonesia, for example, found 30×30 cm spacing to give higher yield. Tehnik dan Budidaya Penanaman Padi System of Rice Intensification (SRI), Pusat Pelatihan Kewirausahaan Sampoerna, Lombok. As discussed in Chapter 34, this research station was one example of corporate support of SRI. Note also that in the experience of Ralalarison, 50×50 cm spacing gave the highest yield, but only after six years of using SRI methods on the same soil.
 M.S. Leesawatwong, S. Jamjod, J. Kuo, B. Dell and B. Rerkasem, ‘Nitrogen fertilizer alters milling quality and protein distribution in head rice.’ Poster for 4ᵗʰ Intl. Crop Science Conference, Brisbane (2004). Higher nitrogen content would be correlated with more protein content.
 See trip report, p. 12.
 Ma’s paper was published the following year: F.Y. Xu, Jun Ma, H.Z. Wang, H.Y. Liu, Q.L. Huang, W.B. Ma and B.F. Ming, ‘Rice quality with the cultivation of SRI,’ Acta Agronomica Sinica, 32: 577-582 (2005), in Chinese. The article’s abstract in English read: “The rice quality under the cultivation of the System of Rice Intensification (SRI) was studied, using the high-yielding hybrid rice Xieyou 527 as the material. … SRI could improve rice quality, especially with increase in the rate of milled rice and head milled rice, and decrease in the percentage of chalky kernels and chalkiness, but with no marked effect on kernel shape and amylose content. … SRI had not only high chlorophyll content of leaves, slow senescence of leaves, but also high … transformation of the dry matter from stems and sheaths to panicles during the grain-filling period compared with TC [traditional cultivation].”
 See trip report, p. 1.
 B.M. Mati, W.W. Nyangau, J.A. Ndiiri and R. Wanjogu, ‘Enhancing production with saving water through the System of Rice Intensification (SRI) in Kenya’s irrigation systems,’ Journal of Agriculture, Science and Technology, 20: 24-39 (2019).
 The yield improvement attributable to heterosis (hybridization) is 15-20%, according to FAO, Hybrid Rice for Food Security (2004).
 I.N. Haqim, A. Abdullah and A. Isahak, ‘Physicochemical, vitamin A and sensory properties of rice obtained by System of Rice Intensification (SRI),’ Sains Malaysiana 42: 1641-1646 (2013).
 Two discussions with farmers stand out in memory. In Sri Lanka when meeting with farmers there in 2003, one farmer stood and said that he sells his ‘regular’ rice but keeps his SRI rice for home consumption. Why? Because when SRI rice is cooked for the evening meal, what is left over for morning breakfast, before he goes to the field, is still intact and tasty, whereas ‘regular’ rice grains are mushy and not as palatable. In Tripura state of India, when my wife and I asked village women whether they found any difference in grain quality, all agreed that SRI rice is ‘better.’ Why? Because the grains are more uniform in size and thus they are easier to cook to the same consistency. Their husbands preferred this, to have few grains that are undercooked or overcooked. These are subjective judgments, but they are repeated.
 Another consideration was the ‘green manure effect,’ where using the mechanical weeder, rather than pulling up and removing weeds, would bury weed growth in the soil. Prof. T.M. Thiyagarajah at Tamil Nadu Agricultural University who investigated this in the early 00s documented yield enhancement from mechanical weeding which he attributed to soil fertility enhancement with green manure (weeds). Whether the effect was due to soil aeration or to increased organic matter in the soil could not be readily determined. Having more soil organic matter would support larger microbial populations in the soil and more microbial activity, as would having higher levels of oxygen in the soil.
 V. Thomas and A.M. Ramzi, ‘SRI contributions to rice production with water management constraints in northeastern Afghanistan,’ Paddy and Water Environment, 9: 101-109 (2011).
 Phenology is the branch of plant science that studies plants’ stages of growth, their timing, and the effects of seasonal and environmental factors on these.
 When visiting Morang district in 2006, one farmer whose fields I visited pointed out to me how his SRI field would be ready for harvest 25 days sooner than his adjacent field planted with the same variety. See trip report, p. 10.
 M.C. Diwakar, A. Kumar, A. Verma and N. Uphoff, ‘Report on the world record SRI yields in kharif season 2011 in Nalanda district, Bihar state, India,’ Agriculture Today (New Delhi), June, 53-56 (2012).
 T. Uzzaman, R.K. Sikder, M.I. Asif, H. Mehraj, and A.F.M. Jamal Uddin, ‘Growth and yield trial of sixteen rice varieties under System of Rice Intensification,’ Scientia Agriculturae, 11: 81-89 (2015).
 The rice crops of three groups of farmers were monitored: those who had participated in the project’s SRI training (N=51), their neighbors who got no training but who could have been exposed to SRI indirectly (N=59), and farmers living in other villages where there was no training (N=57). The rice of 96% of the first group matured in less than 135 days, while 49% and 38% of the rice plots of the other two groups were harvested beyond 135 days. From Table 47 of Hemantha Kumar Pamarthy, Monitoring, Evaluation and Learning (MEL) Study for understanding the pattern of change resulting from the capacity building interventions under the ‘Sustaining and Enhancing the Momentum for Innovation and Learning around the System of Rice Intensification (SRI) in the Lower Mekong River Basin Project’ in Laos PDR, ACISAI, Asian Institute of Technology, Bangkok (2018).
 W.H. Pfeiffer and B. McClafferty, ‘HarvestPlus: Breeding crops for better nutrition,’ Crop Science, 47: 88–105 (2007).
 R.D. Graham, ‘Micronutrient deficiencies in crops and their global significance,’ 41-61, in J. Alloway, ed., Micronutrient Deficiencies in Global Crop Production, Springer, Netherlands (2008).
 A. Adak, R. Prasanna, S. Babu, N. Bidyarani, S. Verma, M. Pal, Y.S. Shivay and L. Nain, ‘Micronutrient enrichment mediated by plant-microbe interactions and rice cultivation practices,’ Journal of Plant Nutrition, 39: 1216-1232 (2016).
 A. Dass, S. Chandra, N. Uphoff, A.K. Choudhary, R. Bhattacharyya and K.S. Rana, ‘Agronomic fortification of rice grains with secondary and micro-nutrients under different crop management and soil moisture regimes in the north Indian plains,’ Paddy and Water Environment, 15: 745-760 (2017).
 A.K. Thakur, K.G. Mandal and S. Raychaudhuri, ‘Impact of crop and nutrient management on crop growth and yield, nutrient uptake and content in rice,’ Paddy and Water Engineering (2019) http://doi.org/10.1007/s10333-019-00770-x.
 Integrated nutrient management relied primarily on inorganic NPK fertilizers but included also decomposed cow manure to enhance soil organic matter. In the organic fertilization treatments, decomposed cow manure was applied along with a preceding green-manure crop (Sesbania) and the application of vermicompost. The same total amounts of nitrogen (N) were applied to all of the trials, but the form in which N was provided differed between organic and INM trials.
 Mean values followed by different letters in a column denote a significant difference (P≤0.05) between the treatments according to Duncan’s multiple range test.
 For a fascinating account of this innovation see David McCullough’s history of this achievement, The Wright Brothers, Simon & Schuster, New York (2015).