Assessing the influence of rice roots and root exudates on nitrogen mineralization in soil using a novel protocol

Shamim Ara Begum1, Md. Abdul Kader*1,3, Steven Sleutel2, Stefaan De Neve2

1Department of Soil Science, Bangladesh Agricultural University, Bangladesh

2Department of Soil Management, Ghent University, Belgium

3School of Veterinary and Life Sciences, Murdoch University, Murdoch, 6150 Australia


Classical nitrogen (N) mineralization experiments are done using uncropped soil, thus completely neglecting the influence of roots and root exudates. Therefore, experiments were conducted at two field sites in Bangladesh during ‘boro’ season (winter rice), using two rice cultivars (BRRI Dhan 29 and BINA Dhan6) to investigate the influence of rice roots and root exudates on N mineralization. Rice cultivars were transplanted in three replicated plots maintaining 25 x 15cm spacing along with three replicated uncropped plots as control. A novel method was used to identify the most suitable location to assess N mineralization in soil having actively growing rice plants. For this purpose, soil samples were collected from three locations in soil namely; 1) rhizosphere (0cm, at the rhizosphere), 2) middle of the two plants (7.5cm apart from rhizosphere) and 3) middle of two rows (12.5cm apart from rhizosphere). There was significant stimulatory effect of rice roots and root exudates on N mineralization at both filed sites. Significant influences of rice varieties were also observed, with BINA Dhan 6 having greater influence on N mineralization than BRRI Dhan 29. Sampling location also had a significant effect on measured N mineralization. The highest stimulatory effects of rice roots and root exudates were recorded when soil was sampled from rhizosphere. Sampling between the plants and between the rows had similar effects. In conclusion, rice roots and root exudates had a large influence on N mineralization and the best sampling location to determine the effects of actively growing rice roots and root exudates on N mineralization, was the rice rhizosphere.