The importance of copper in rice

Foliar analyses of rice plant samples from the two major rice granaries in Malaysia, MUDA and Kemubu Irrigartion Schemes indicated Cu to be low, being less than 2 ppm in straw at harvest in many sites.Soil analyses from 150 locations in Muda showed that only 10% of the sites had a Cu content that rangees from 4 to 7 ppm, 25% with 1 to 4 ppm and 65% less than 1 ppm.The soils with higher Cu content were generally the more inland riverine and mixed riverine-marine alluvial soils, while the coastal marine alluvial soils tended to have a lower Cu content.Based on foliar and soil analyses, it was possible to demarcate the Muda soils according to its Cu status.In the fluvial deposits of Kemubu, the highest mean Cu content of 9.8 ppm were in soils with a textural index of 70 to 80, 2.1 ppm to 4.0 ppm in soils with textural index of 50 to 70 and the lowest concentration of 0.53 ppm in soils with a textural index of 20 to 30.There was wide variation in Cu content in plants at the different growth stages and between the content in whole plant and Y-leaf at each growth stage.There was a general decline in Cu content in the plant particularly after the panicle initiation stage.The Cu concentration of Y-leaf was generally higher than that of the whole plant.Copper content of rice plants at the vegetative and panicle initiation stage had a highly significant positive correlation with yield.Tissue analysis at harvest did not have a relation to yield and thus is not a useful diagnostic stage for copper.Amongst the yield determining characters, 1000 grain weight was most influenced by Cu status of rice plant.The copper content in grain had a highly significant positive correlation with 1000 grain weight (r=0.21**) and a significant positive correlation with yield (r=0.13**). Between plant parts and stage of sampling the Y-leaf sampled at maximum tillering stage had a more consistent correllation between Cu content and yield characters.Similarly in the canonical correllation analysis, a highly significant positive correllation (r=0.43**)occurred between Cu content of Y-leaf at maximum tillering stage and first canonical variable of the yield characters.For accessing Cu nutritional status of the rice plant, it is recommended that sampling be done at maximum tillering stage and the plant part sampled be Y-leaf in preference to whole plant.The first field trial using Cu on the west coast in the marine alluvial soil in Tanjung Karang showed a significant increase in crop yield of 774 kg/ha or 16% with the application of copper at 5 kg/ha.Yield component analysis indicated that Cu caused a significant increased in 1000 grain weight.There was also a significant increase in plant height at harvest.Plant analyses showed that the Cu treatment resulted in high Cu concentration of 8.75 ppm in plant at 25 days after transplanting, compared with 2.75 ppm in the non-Cu plot.There was a decrease in Cu concentration in plant crop growth and at harvest the Cu content was 0.73 ppm in straw and 2.0 ppm in grain, while in the control plot was 0.23 ppm in straw and 0.85 in grain.A field trial in Mada showed a significant positive response to levels of copper and the optimum rate was at 12 kg/ha with 11% increase in yield.Field trials on Cu in the east coast was conducted at various locations in four different soil types of the Kemubu region and yield enhancement was 600 to 900 kg/ha with the application of 5 to 10 kg Cu/ha.The low Cu in some of the soils in the major rice areas of the country could be one of the reasons for the current tr.end of stagnating crop yields.