Rhizosphere Nitrification and Nitrogen Nutrition of Rice Plants as Affected by Water Management

Abstract

Redox status shapes the biogeochemistry and dominant biogeochemical processes in soil environment. Nitrification is a microbiologically mediated transformation affected by the oxygen availability in soil. Nitrification rate often determines the agronomic N use efficiency (NUE) since it affect the pool size of plant available N forms (NH4+) and NO3-) in soil. A mesocosm experiment was conducted using three rice varieties (PI312777, IR55423 and IR80508) to test the effect of soil water status on plant characters and nitrification in the rhizosphere. Two irrigation treatments as aerobic cultivation (AC) and continuously flooded condition (CF) were imposed. Plants were grown until 50 days after germination (DAG). At harvest, leaf nitrate reductase activity, physiological nitrogen use efficiency (PNUE), air-filled pore-space of roots, and biomass accumulation were determined. Also potential nitrification rate in the rhizosphere, soil moisture, pH, and NH4+ and NO3- contents at three soil depths were determined. Biomass production was nearly 50% lower under AC than under CF. Rooting depth and rhizosphere nitrification were significantly higher under AC than CF. Rice variety and water management affected the activity of nitrifies in the rice soils. Measured soil properties and plant traits correlated significantly (p < 0.05). Plant N status was significantly affected by water management regime resulting in higher PNUE but lower total N accumulation in rice shoots grown under AC than under CF. Better understanding of these interactions is needed to help farmers to manage N more effectively in relation to cultivars used and intended water management regime.Tropical Agricultural Research Vol. 24(1): 1-11 (2012)DOI: http://dx.doi.org/10.4038/tar.v24i1.7984

Keywords

• nitrification
• rhizosphere
• rice
• water