Effect of Soil Ammonium Nitrogen on the Tillering-Habit of Rice Plant

Abstract

Field and growth cabinet experiments were carried out to clarify the relationship between the number of tillers at early growth stage (NT) and the amount of NH₄-N in soil and soil solution. In the growth cabinet experiments, zeolite was added to the soil at the rate of 0%, 1%, 2% and 10% of soil weight to modify CEC values of the soil. In field experiments, two fields with different CEC values were used. 1) In growth cabinet experiment, results revealed that with zeolite treatment, there is no difference in exchangeable NH₄-N in soil. However, big differences were noted in content of NH₄-N in soil solution (CAS) before transplanting, i.e., 17ppm, 7ppm, 3ppm and 0ppm in 0%, 1%, 2% and 10% zeolitetreated plots, respectively. The NT is not affected by CAS under high temperature condition (25°C, daytime ; 15°C night time). However, under low temperature condition (20°C/10°C), NT is in this order : 0%>1%=2%>10% zeolitetreated plots. 2) Results of the field experiments showed no difference in the amount of exchangeable NH₄-N between the two fields. However, higher CAS is observed in field with low CEC while relatively lower CAS in field with higher CEC. Higher NT was noted in low CEC than in higher CEC field in 1986 probably due to low temperature (13.8°C) during early tillering stage. In 1987, however, no difference in NT between the two fields was observed which can be attributed to high temperature (16°C) during early tillering stage. 3) In 1986, a negative correlation coefficient (r=-0.691*) between CEC and NT of different paddy fields in Shonai area was observed, while no relationship was observed in 1987 (r=0.264, ns). The CAS (or CEC) can affect NT only in the year where relatively low temperature at early growth stage of rice plant.