4 Conservation Agriculture in Rice-Based Cropping Systems: Its Effect on Crop P erformance M. A. Islam 1 , R. W. Bell 1 , M. E. Haque 2 , C. Johansen 3 , M. Jahiruddin 4 and W. Vance 1 1 School of Veterinary and Life Sciences, Murdoch University, 90 South Street, Murdoch WA 6150 Australia, Email: M.Islam@murdoch.edu.au ; R.Bell@murdoch.edu.au; W.Vance@murdoch.edu.au 2 International Development Enterprises- Bangladesh (iDE), Email: enamul.haque@ide-bangladesh.org ; 3 Consultant, Leeming, Australia, Email: cjo41802@bigpond.net.au ; 4 Department of Soil Science, Bangladesh Agricultural University, Mymensingh, Bangladesh, Email: m_jahiruddin@yahoo.com Introduction: Conservation agriculture (CA) systems are yet to be developed for the intensive rice-based cropping systems (3 crops in a year, comprising rice (Oryza sativa L.) plus additional cereal, legume and/or oilseed crops) that are common across the Eastern Indo-Gangetic Plain (EIGP). Farming systems in EIGP are characterized by two key edaphic influences, viz: puddling soil for transplanting rice, which destroys the soil structure through intensive tillage and; removal or burning of crop residues before sowing that limits the recycling of organic matter to soils. Neither of these practices is consistent with the full implementation of CA in the intensive rice-based cropping systems. Implementing CA in the rice-based crop system is feasible using a novel unpuddled transplanting approach to establish rice. In this method of crop establishment (see Haque et al. these proceedings), a strip of soil is tilled (5-7 cm width and 7-10 cm depth) by rotating tines. The soil is flooded to allow the tilled strip to soften before seedlings are transplanted into the strip. Conservation agriculture practices for crops apart from rice are already developed in this region. The objective of the present study was to assess CA based on strip tillage (including unpuddled transplanting for rice) compared to conventional tillage in intensive cereal-dominant and legume-dominant crop rotations. Key questions were: how critical is it for increased residue retention to enable the CA system to be productive and; how long is the transition phase before the main benefits of CA for crop yield become apparent? Material and methods: Long term field experiments were carried out for 3 years (2010–11 to 2012–13) at two different agro- ecological zones and soil types in Bangladesh (Alluvial area-24°28 N, 88°46 E and High Barind Tract- 24°31 N, 88°22 E) to evaluate the effects of tillage (strip tillage-ST, bed planting-BP and conventional tillage-CT) and residue management systems [high residue- (50 % previous cereal crop residue or 100 % of legume residue); low residue-(20 % previous cereal crop residue or 0 % (only root dry matter was retained in soil) legume residue)] on growth and yield of the three crops in the rotation: lentil (Lens culinaris Medik.) or wheat (Triticum aestivum L.) in the cool-dry season; mung bean (Vigna mungo L.) in the early wet season and transplanted rice in the main wet season. In the interests of brevity the bed planting results are not presented and neither are results for mung bean included in additive yields for the cereal-dominated rotation. Results and discussion: In both zones, with legume-dominated (lentil- mung bean- rice) and cereal-dominated rotations (wheat- mung bean- rice), minimum tillage (ST) initially decreased yield of the cool season crop in first year (P<0.05) but in the second year there was no difference with CT and in the third growing season in the sequence, cool season crop yields (lentil and wheat) were increased under ST (P<0.05) (data not shown). In the first growing season though there were no residue effect on yields but in the following year higher residue retention produced higher yield for both cool season crops (P<0.05). Over two years covering seven crops, the additive yield was comparable between ST and CT (Fig. 1). In the legume-dominant