Effect of Growing Rice on Nitrogen Mineralization in Flooded Soil

Abstract

Only a smally fraction of the total organic N in soils is mineralized to the plant‐available forms during a cropping season. The mineralization process and the availability of mineral N in soils are affected by various environmental factors and management practices, including the presence of growing plants. This study was conducted to determine the effect of rice ( Oryza sativa L.) on mineral N availability in a flooded Maahas soil (Typic Tropaquept). Available N, extractable NH 4 ‐ and NO 3 ‐N in soil plus N accumulated in plants, referred to as mineral N availability , was significantly higher in planted than in unplanted soils. Increased N availability may result from reduced loss or enhanced supply of mineral N in the presence of growing plants. Average increase in mineral N supply in freshly flooded soil was 31% due to growing of rice through the first month (0–30 d) and 62% through the second month (30–60 d) of its life cycle. In soils under prolonged flooding, average increases in the mineral N supply due to 2 mo rice growing during the vegetative stage (10–70 d) were 14 to 47% depending on the initial mineral N status of the soils. The gain in mineral N achieved by growing rice plants was higher in soils with a low than a high initial mineral N content. Rice genotypes differed in their ability to increase mineral N availability in flooded soils, and the stronger influences were associated with higher dry‐matter yields of the plants (shoot plus root). Soil N availability to wetland rice, especially in soils with low mineral N supply, thus may be considerably enhanced by selection of efficient genotypes.