Water and weed management for aerobic rice

Abstract

Aerobic rice culture is a technology to improve the water productivity in rice culture. Water and weed management are two important aspects of this promising technology. It is well established that yield reduction in rice happen if the soil moisture level falls below the field capacity. Unlike in flooded conditions,weeds pose greater problem in aerobic rice production.A field study was undertaken at Agronomic Research Station (ARS), Chalakudy from September 2016 to January 2017 for developing appropriate water and weed management strategies for aerobic rice. The treatments comprised of three levels of irrigation in the main plot (irrigation at 10 mm cumulative pan evaporation (CPE), 20 mm CPE and 30 mm CPE) and five weed management treatments in the subplot (pre emergent herbicide oxadiargyl followed by hand weeding, oxadiargyl followed by 2,4- D sodium salt, oxadiargyl followed by bispyribac sodium at 20 days after sowing (DAS), hand weeding at 20 and 40 DAS and an unweeded control). Depth of irrigation was 3 cmand the total water applied including effective rainfall amounted to 933 mm, 574 mm, 403 mm in I1, I2 and I3 respectively. Irrigation at 10 mm CPE recorded higher values for growth parameters like plant height and number of tillers per meter as well as yield and yield attributes.Higher root volume also was recorded in these plots .Relative leaf water content and chlorophyll content were higher under frequently irrigated plots (10 mm CPE) than less irrigated plots. Moisture stress lead to inhibition of leaf production and decline in leaf area in aerobic rice. Higher availability of moisture, reduced stress, better growth and yield attributes contributed to higher yield under irrigation at 10 mm CPE. Moisture stress caused reduction of 44 percent grain yield under irrigation at 30 mm CPE over irrigation at 10 mm CPE. Hand weeding at 20 and 40 DAS resulted in better growth, yield and yield attributing factors of aerobic rice. Oxadiargyl followed by bispyribac sodium at 20 DAS and oxadiargyl followed by hand weeding at 20 DAS were the next bettertreatments which were on par.Weed competition resulted in 64 percent reduction in grain yield. Oxadiargyl when applied pre-emergent waseffective in controlling the first flush of weeds in the field. All the treatment combinations with oxadiargyl recorded the lower weed dry matter production and weed density. As the crop advanced to flowering, hand weeding at 20 and 40 DAS resulted in lower weed dry matter production and weed density. Better growth and yield in this treatment suggested a long critical period of weed competition in aerobic rice. Irrigation at 30 mm CPE registered the highest water productivity of 0.96 kg m-3, but with severe yield loss. Among weed management treatments hand weeding at 20 and 40 DAS recorded the highest water productivity (1.13 kg m-3) and the lowest was from unweeded control (0.37 kg m-3). Irrigation at 10 mm CPE in combination with hand weeding at 20 and 40 DAS registered the highest growth and grain yield (2791 kg ha-1) and recorded water productivity of 0.88 kg m-3. However irrigation at 10 mm CPE in combination with oxadiargyl followed by bispyribac sodium at 20 DAS resulted in the highest net return (Rs 51477 per hectare) and B:C ratio (2.3).