International Journal of Farm Sciences 2(2) : 54-58, 2012 Aerobic rice- the next generation innovation in rice cultivation technology J RACHEL PREDEEPA Department of Biotechnology Alpha Arts and Science College, Porur, Chennai, Tamil Nadu Email for correspondence: ecoagripolicy@gmail.com ABSTRACT Rice crop scientists are aware of three facts: a) rice is the second most staple food crop, b) there is an increase in food demand and freshwater crises, and c) rice is a semi-aquatic crop requiring flooding of fields. The overall water use efficiency of the rice crop has been estimated to be very poor in contrast to the actual use of the water required for the current level of bounteous productivity. The lowland rice crops will require only 500 to 1000 litres of water for producing 1 kg of rice which is almost on par with the dryland cereal crops. Therefore rice scientists are working on a new genre of rice cultivars aerobic rice which is expected to be irrigated or rainfed without puddling water in the field. This technology limits the use of water within the field capacity, which will serve as a better option than the current water cultivation technologies. This will also require breeding new rice cultivars. The leading pioneers in breeding these kinds of rice cultivars are China (backed by IRRI), Brazil and India. Keywords: Rice; aerobic rice; transpiration; water use efficiency INTRODUCTION China being the topmost consumer and producer of rice is well aware of the upcoming shortage of rice and water. Chinese are also well aware that at the current productivity rate of rice crop and using these present cultivation techniques only lowland rice cultivars could meet the increasing demand for this crop. However taking into consideration the present and the future of freshwater crises people are turning towards novel rice cultivation techniques and in developing cultivars of rice that are efficient users of water and back these techniques. Chinese Agricultural University in collaboration with the International Rice Research Institute (IRRI) is currently working on a new genre of rice cultivars called aerobic rice. These cultivars are so named for the way they are being cultivated on any kind of land surface like the upland varieties with limited use of water and without stagnating or flooding the field with water despite the fact that rice is a semi-aquatic plant. What is not
Predeepa good about aerobic rice is that the water requirement of this is 50 to 70 per cent lesser than what is actually needed for the rice to grow and disappointingly the rice productivity is also 30 per cent lesser than the hybrid lowland rice varieties that came to the rescue last time which led to the Green Revolution in the 1960s. However scientists have not given up their hopes on aerobic rice cultivation. Nevertheless this is a dream come true project that was conceptualised using mathematical models by some Chinese scientists like Luo and his colleagues for an ACIAR funded project (http://www.mssanz.org.au/modsim05/ papers/luo.pdf). Bas Bouman a senior rice research scientist at the International Rice Research Institute said that the objective of the farmers is to cope with decreasing water availability while the rice scientists will be aiming to manage the freshwater crises by developing high productivity rice cultivars that can be grown by using water sparingly without crossing the requirements beyond the levels of field capacity like many of the other dryland crops. As the lowland rice cultivation is turning out to be impossible in countries like China and Brazil the need for breeding high yielding aerobic rice varieties has become a necessity and people are looking forward to make aerobic rice cultivation a dream come true. Water required for growing rice Field capacity is the moisture holding capacity of the soil which is a physical characteristic of the soil and is dependent on the osmotic and hydrostatic pressure of the soil. For example the particle diameter of clay is less than 2 µm while the surface area per gram ranges from 100 to 1000. Saturation point is the maximum amount of water that the field can hold and will do good for a crop that is usually grown under aerobic conditions. When this saturation point is crossed and more water in puddled in the field it is said to be waterlogged or flooded and this is the best point at which this semi-aquatic crop rice grows. Water is used by the plant in three scales- the plant, the crop and the field (Bouman 2009). Transport is the molecular and the ionic movement of water molecule from one location to another (Taiz and Zeiger 2006). The rice plant uses water which is the real water use of the plant scientifically by a process called transpiration which along with the water is believed to help in the upward flow of the essential nutrients from the soil to the plant above the soil surface. This transpired water not only cools off the plant but also helps in absorbing essential nutrients from the soil. The rice crop will involve the plant and the underlying soil wherein the water is lost besides transpiration (T) by a process called 55
Innovation in rice cultivation Fig 1. Water Use Efficiency in Various Rice Cultivation Technologies evaporation (E) which in conjunction with the process of transpiration is called evapotranspiration (ET). The water required for the plant deduced using pot culture and green house experiments revealed that the actual water requirement is only 500 to 1000 litres to produce 1 kg of rice. Thus the water used by the plant could later be used for the growth of less water requiring crops like wheat and legumes encouraging the habit of crop rotation and has been the practice as-of-to date in water scarce environments. Water efficient management strategies in rice production Rice being the staple food for Asia contributing nearly 35 to 80 per cent calorie intake has a drawback as a cultivable crop for the reason being this crop has very poor overall water use efficiency. Rice being a semi-aquatic crop puddling and soaking are unavoidable for these two steps. Preparing the field for growing rice helps to control weed, increase water retention, reduces soil permeability, eases field levelling and transplanting and saturation of top soil. This results in loss of water via percolation and seepage from the field together known as SP and by the crop which was discussed earlier. Of all these four only transpiration (T) is the actual use of water which results in better crop production and bounteous harvest. In aerobic rice cultivation technology the main aim is to reduce the loss of water via SP and E and allow the crop to be cultivated with enough water that 56
Predeepa will not cross beyond the field capacity; which means the crop can be grown like other dryland cereals for example wheat. In order to achieve this sprinkler irrigation method and other alike methods had been used for growing rice but the results of such studies have shown that growing rice under such conditions has reduced productivity drastically. The problem is that upland rice varieties have lower productivity while lowland varieties have been found to have bounteous harvest only under flooded field conditions. For this purpose new varieties have to be bred and IRRI has decided to term these new varieties bred as aerobic rice. The series of these cultivars of rice will be having the ability to grow like dryland cereals like maize and wheat and have productivity like lowland cultivars. These rice cultivars will be watered by using either rainfed or irrigation technologies without the need to puddle the field. There has been a small success in growing rice cultivars in this direction in countries like China, Brazil and India. The success of this program in Brazil will include the development of new varieties following a 20 year breeding program of japonica indica varieties which had the advantages of improved plant type and duration, desirable grain appearance and cooking behaviour besides the ability to grow under limited water supply conditions or what is presumed to be aerobic conditions in contrast to the traditional anaerobic conditions (Pinheiro et al 2006). Similarly a parallel study in China seems promising following a considerable significant success with the newly developed aerobic rice variety, Han Dao 502 which had the attributes of providing high yield under aerobic and flooded (anaerobic) conditions and did perform well in sales in the market also. The biggest advantage of using this rice cultivar in water scarce conditions in China was that this variety used 50 per cent lower amount of water for its growth, 55 per cent of lower labour and a total gross return ranging between 28 to 44 per cent (Bouman 2002). All series of aerobic rice in China were named as Han Dao of which the series number 502 was successful as this yielded much better under aerobic conditions lowland varieties. However under flooded conditions the lowland varieties performed better than the aerobic rice, Han Dao. The productivity of lowland cultivars was still better than Han Dao under its preferred aerobic conditions which means that there is still room for improvement and lot of work to be done to reach the dream of aerobic rice. But for now they have touched the tip of the iceberg in revolutionising rice cultivation. India did not lag in the development of aerobic rice cultivars and the country has currently two varieties to her credit which are also drought resistant, MAS 946-1 developed in March 2007 and MAS 26 in 2008 both being developed by University of Agricultural Sciences, Bangalore. The 57
Innovation in rice cultivation yield from these varieties was and seemed to be on par with the flooded lowland varieties with an average of 5.5 to 6 tonnes/ ha and required an awesome 60 per cent less water. Overall aerobic rice technology is a promising technology that can stir up another green revolution by increasing productivity of rice using less water and direct sowing and therefore requiring less seeds, less labour, less greenhouse gases (methane) and efficient fertilizer utilization. REFERENCES Bouman B 2002. Aerobic rice (Han Dao): a new way of growing rice in water short areas. In: Proceedings of the 12 th International Soil Conservation Organization Conference, 26-31 May 2002, Beijing, China, Tsinghua University Press, 175p. Bouman B 2009. How much water does rice use? Rice Today. January to March 2009. IRRI Newsletter. http://www.mssanz.org.au/modsim05/papers/luo.pdf. Pinheiro BdaS, Castro EdaMde and Guimaraes CM 2006. Sustainability and profitability of aerobic rice production in Brazil. Field Crops Research 97(1): 34-42. Taiz L and Zeiger E 2006. Plant physiology (4 th Ed). Blackwell publishers, Oxford, UK. Received : 2.10.2011 Accepted: 7.1.2012 58