Lowland rice culture since Green Revolution in Sri Lanka

By Dr. N. Senanayake
Retired Rice Scientist

( Continued from yesterday)

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.)