Movement of Nitrogen in Flooded Soil Planted to Rice1

NUMEROUS studies have been made to determine and evaluate the nitrogen changes that take place in flooded soil planted to rice. Additions of nitrogen to nitrogen-deficient soils used for growing rice frequently do not increase yields of rice in proportion to the increases obtained with other crops. The results of earlier experiments at this station have shown that there are appreciable losses of nitrogen as ammonia by volatilization from flooded soil when the rice crop is not present. The high temperature and alkaline reaction that prevail in the flood water on rice are partly responsible for this loss. Increases in nitrogen that have been observed in the presence of a crop are at least partially responsible for preventing a more rapid decline in the nitrogen fertility of flooded soil. Anaerobic bacteria are probably not entirely responsible for the increase because of their inability to fix as much nitrogen as has been found in some cases. Many workers credit the blue-green algae with the fixation of nitrogen that occurs in flooded soils. Rice fields in China have been producing subsistence yields of grain for four thousand years with little or no fertilization. A plot at the Rice Experiment Station at Crowley, Louisiana has been planted to rice for the past 54 years and has not received any fertilizer. The average yield since 1920 has been 23.6 bushels per acre. There appear to be some recuperative processes which prevent soils planted to rice from deteriorating to the low degree which crop and surface removals indicate they might. It is logical to assume that these recuperative processes are identified with nitrogen fixation. The purpose of this study was to determine and evaluate the nitrogen changes that take place in flooded soil during the growing season, as affected by soil reaction, the presence of the rice crop, fertilizer treatments, and algae. The work was conducted in the greenhouse. A moderately acid soil and an almost neutral soil were used to compare nitrogen changes at the different reactions. The soil was placed in water-tight earthenware jars to prevent the loss of nitrogen in drainage water. The soil in half the jars was left unplanted in order that the effect of a crop on changes in nitrogen might be evaluated. The algae were killed in half the jars to study the effects of algae. Every effort; was made to simulate field conditions of temperature and light in the greenhouse. The crop was grown during the normal growing season. ' HISTORICAL