• This email address is being protected from spambots. You need JavaScript enabled to view it.
  •  +98 13 33690925

Lowland rice culture since Green Revolution in Sri Lanka


By Dr. N. Senanayake

Retired Rice Scientist

Rice cultivation in lowlands of Sri Lanka also resulted in a kind of revolution locally along with the global Green Revolution. Following the invention of new varieties IR 8, IR 62, with fertiliser response and high yields at International Rice Research Institute (IRRI), the Philippines and their spread globally, the Department of Agriculture (DOA) also produced rice hybrids such as H4, H8 series in early 1970s by using our traditional varieties as parents. However, in a bid to defend the sudden imposition of organic agriculture in Sri Lanka, inorganic fertilizer use has been imposed suddenly on our farmers.

(See Figure 1)

It is only those who were in the DOA who know how difficult it was for our farmers to use locally bred hybrid rice varieties and the corresponding use of inorganic fertiliser. In fact, in spite of tireless efforts by the extension officers of DOA, it took nearly two to three decades for us to cultivate 70 percent (in 1980, IRRI report) of the arable area with high yielding varieties.

These achievements in lowland agriculture were not sudden but a result of long-term hard work by DOA officers. Our farmers have an attitude problem, possibly due to lack of education, and are not an innovative group of people who accept innovations as they appear.

However, today, farmers are much more educated and their attitudes may be different, but some of them are still backward in thinking. 

Use of Nitrogen fixing flora

In 1980s or 1990s, the DOA scientists and their international counterparts worked on nitrogen fixing plants like Azolla pinnata and Sesbania rostrata in rice fields as a Nitrogen supplement for rice growth. A considerable amount of money was spent on research and development of this technology but popularising its use faced several constraints and farmers did not adopt it unless they were forced to do so or provided with some sort of compensation. One of the main constraints was that the contribution from these plants could not sustain rice yields without addition of inorganic fertiliser. Today, these practices are haphazardly adopted by global rice farmers and none of the countries depend solely on them.

The constraints with regard to using the Azolla fern are several. It can be grown in wet soil and then ploughed under, generating a good amount of nitrogen-rich fertiliser (N 2-5%, P 0.1-1.6%, K 0.3-6% and many micro elements). Therefore, inoculation is necessary every season. In order to maintain the fern throughout the year, special multiplication nurseries are necessary to produce sufficient quantities of planting material as inoculant for further propagation. These nurseries require shade, an ample supply of water, plant nutrients, disease and pest control and some measures to protect the fern from extreme weather conditions. Super phosphate should be applied to the field for the fern nursery thrice—four days apart.

Azolla pinnata in Rice Field

Research work done globally also showed that in an open field under tropical conditions, a full cover of Azolla as monoculture could yield about 20 t/ha fresh weight. When intercropped with rice the growth rate decreases with the development of the rice canopy, but repeated inoculation and harvest of the fern can give an annual yield of up to 40-50 t/ha fresh weight. However, rice yields may increase only by 0.4-1.5 t/ ha when thus fertilised. Therefore, Azolla can only supplement N requirement of rice in the next cultivation season.

EM (Effective Microorganisms)


In another attempt, some tried to use the global EM technology in our country and requested the support of DOA. But the scientists of the calibre of Vidyajothi C. R. Panabokke, who was the Director of Agriculture of DOA, refused to use it on our soils, but some other institutes supported the move. Finally, EM technology was introduced here and private sector organisation, with its extension staff took up the challenge. It was used in some parts of the country. The problem with EM technology, anticipated by the scientists at that time, was that it would upset the microbial balance in our soils, which were in equilibrium through natural selection over many years, and if some alien microbe got into the local soil system, which could suppress our favourable microbes, there was no way to stop it from spreading or to control it and land could turn barren.

This writer once attended an international biofertiliser conference, where scientists discussed such adverse effects of microbial fertiliser use in some other countries.

The writer personally believes that CKDu in our country could have been caused by such an unfavourable microbe inadvertently entering our soils with EM solutions. The basis for this hypothesis is that CKDu was first reported from areas where EM technology became popular in rice cultivation. Moreover, heavy metal problems in many countries are due to solubilisation of these minerals, present in the soil, by microbial degradation. For example, high arsenic level in the paddy soils of Bangladesh due to variations indigenous soil properties as well as the microbially mediated biogeochemical interactions that control the biogeochemical cycling of arsenic in soil, has been reported by many scientists.

Therefore, as scientists we foresee problems that crop up when alien microbes are introduced into our soils because of the size of microbes and huge populations per unit weight of soil, and in such instances human error cannot be ruled out. Moreover, this technology was not practised by southern farmers and there are few or no CKDU patients in the area and if at all it may be due to migration of people.

System of Rice Intensification (SRI)

SRI was introduced to the country as an organic cultivation practice for rice. Its origin is in Madagascar, where a degraded rice soil producing 1.5 mt/ha was applied with 2 mt/ha organic matter and got a yield of around 4.5 mt/ha using SRI method. This was taken up by the then Deputy Minister of Agriculture, Salinda Dissanayke, who was very confident that we could reach 400 bu/acre yield with this method. Unique features of this method include transplanting seedling at low age smoothly, planting at higher spacing about 25 to 50 cm apart and providing just 2 mt/ha of organic matter at a time majority of our rice fields in the dry zone was getting about 100 to 120 bu/ac. This was a type of organic culture based on few assumptions, such as;

  1. High spacing produces high number of tillers
  2. High number of tillers produces same number of panicles
  3. Weeding carried out once or twice within hills to remove weed competition

This again was questioned by scientists in the DOA, who were marginally supportive of the method, because it a programme introduced the Ministry of Agriculture. They took up some research work, but finally rejected it because it failed to produce anticipated benefits. Non-agricultural promoters of SRI believe that a high number of tillers can bear a high number of panicles and all the tillers (primary, secondary and tertiary) can produce a similar sized panicle as that of the mother plant, which has been totally refuted and disproved by rice scientists.

It is true that high spacing can produce a high number of tillers with our high yielding varieties but rice plants do have some panicle-bearing and many panicle non-bearing tillers and the size of the panicle gradually decreases as the tiller number increases. SRI was promoted in the Mahaweli area and some farmers practised it for several seasons, but today no one practises it.

Shifting to organic agriculture

A complete shift to organic agriculture in the country was advocated by the authorities due to the increasing incidence of diseases such as cancer, toxicity due to inorganic fertiliser and agrochemicals and the CKDU issue. The reasons put forward by these scientists cannot be attributed solely to inorganic fertiliser and pesticide use in the country because we import a lot of agricultural and other produce from other countries which are heavy users of pesticides and inorganic fertiliser.

Being a rice scientist, I cannot comment much on organic agriculture as regards highland crops except for the fact that it can increase the cost of production, especially with regard to plantation crops because of the cumbersomeness of handling and distributing organic fertilizer. The vegetable plantation sector already uses organic fertiliser along with inorganic to get higher yields. But if farmers try to compensate for the inorganic fertiliser quota also with organic, problems concerning amounts of fertiliser to be used, soil texture and structure as well as possible toxicities will arise. However, we can forgo yields of up to 40 percent in the vegetables sector because consumers use only 40 percent of the total harvest due to waste in post-harvest handling, transport and retailing. Therefore, strict measures have to be taken to prevent this wastage along with shifting to organic agriculture and sustaining availability. If this action is not taken there will be a colossal reduction of vegetable production too in the country.

Rice cultivation is an entirely different type of agriculture, where the soil is in reduced conditions and lot of predictions, rules, anticipations are totally different from those of the highlands. To compensate for plant requirement, you have to add large quantities of OM. The anaerobic decomposition by microbial action on these OM of plant origin is slow due to lack of oxygen for the microbes to respire and to proliferate and some of the released nutrients are also used for their own growth and development, hence the nutrient availability for plant growth becomes low because of low rate of release of nutrients. Moreover, because of anaerobic conditions the OM decomposition ends up producing intermediate products such as organic acids, humic acid and methane instead of CO2 under oxidized conditions.

Humic acid and other organic acids increase the acidity of the soil and some nutrients are made unavailable for plant growth. If too high it will also kill the rice root system. On the other hand the release of methane has a detrimental effect on the ozone layer, with the global community blaming rice cultivators, for several decades, claiming that they contribute to reducing the ozone cover by producing methane in lowland rice cultivations. Therefore if we are to use OM and use OM in large quantities to meet the rice plant nutrient requirement of fertiliser responsive rice varieties, we will be producing enormous amount of methane gas while polluting the environment, leading to global warming.

The Ministry of Agriculture has recently recommended OM application of 500 kg/ha for other mineral elements and liquid fertilizer N for nitrogen requirement. However this amount of OM (assuming Farm Yard Manures) can only provide 2.0 kg/ha of P and 2.5 Kg/ha of K whereas the removal of these elements from field per crop according to literature is 6 kg /ha and 8 kg/ha assuming the national average of rice in Sri Lanka (4 mt/ha) and also all the rice straw is incorporated back in to the field. Comparing these figures it is noted that addition of FYM not OM is not enough and if OM is used these additions are still lower. However, poor yields may not be observed in first or second season because farmers have been dumping large amounts of P and K to their fields over the last few decades and there is a P and K soil bank as they get fixed in the soil.

But the final yield of any crop is decided by the amount of the most deficient nutrient element supplied. Unless these elements are supplied to the crop the final yield will be decide based on one of these deficient mineral elements as N is supplied adequately. Thus a yield decline in rice is inevitable if this recommendation is acted upon. Moreover, some scientists recommend the use of new technologies like Organic Liquid N and options such as Bio Char, without considering the cost of cultivation, the farmer attitudes and the foreign exchange deficit faced by the country.

Finally, rice is a labour-intensive crop and manual labour is a must for some operations even with mechanization. At the moment there is a severe shortage of labour and farmers forgo some important operations due to lack of labour. Organic agriculture requires more manual labour, under the present context. In such a situation if farmers believe that their crop yields are going to reduce due to non-availability of inorganic fertiliser they will not cultivate their fields, especially commercial farmers.

Therefore, the author believes that an immediate shift to OM in the country is detrimental to the country and rice farmers. It should be done in stages or more appropriately, after intensive research and after breeding new rice varieties which are low fertilizer responsive with some sort of drought tolerance. Moreover, attitudinal change among farmers is imperative, which will also take several years.

(The author is a retired rice breeder and agronomist with 36 years of experience in the DOA with post graduate training at the International Rice Research Institute (IRRI), Philippines. He served as a Research Fellow at IRRI and a Visiting Scientist at University of Sussex, UK. He also served as the Chairman, Rice Task Force of Ministry of Agriculture, between 1996 and 1997. After retirement he joined the Rajarata University, as a Senior Lecturer, where he worked for eight years. He received three presidential awards for his research in Sri Lanka, and a Sri Lanka patent.)

Source: island.lk