Effect of N fertilizer on the emergence and seedling growth of Eleusine indica in aerobic rice systems

Weed has become one of the most serious problems in aerobic rice systems. Weed management in aerobic rice system needs a manipulation of optimum N fertilizer application to control the weed and simultaneously enhance aerobic rice growth performance. In this study, three types of N sources (urea, ammonium sulphate and ammonium nitrate) with concentration starting from (0, 60, 120, 180 and 240 kg ha) were evaluated for effective control of the bioassay species, Eleusine indica, while observing the rice injury level. The data on weed (emergence and shoot fresh weight), while rice growth (root length, shoot fresh weight, shoot height and leaf greenness) was collected in this study. It was found that urea at a higher application rate of 240 kg ha strongly inhibit the emergence and shoot growth of E. indica by >78%. Conversely, ammonium sulphate and ammonium nitrate gave moderate inhibition (58-65% inhibition) on weed emergence and shoot growth at higher application rates of 240 kg ha, respectively. Significant stimulation effect on rice root growth, shoot height, shoot fresh weight and leaf greenness was noticed at a low application rate of 60 kg ha urea, while ammonium sulphate and ammonium nitrate only exerts its stimulation effect starting at 120 kg ha. Stimulation effect on the rice growth was likely negligible at 0 and 4 DAS across urea, ammonium sulphate and ammonium nitrate application rates. However, the rice plants growth increases with increasing growth stage. The finding suggest that application of urea at 240 kg ha starting from 8 DAS of rice growth stage was the most efficient application rate in inhibiting E. indica with the stimulation effect on the growth of rice seedlings.