Fate of 15N tagged urea leached with infiltrating water under pigeonpea and rice plus pigeonpea intercropping systems

Pigeonpea and rice plus pigeonpea were grown in field plots, with tensiometers at depths of 90 and 105 cm and a neutron access tube reaching 120 cm. Tagged urea (with 4 per cent 15N atom excess) solution to provide 60 k g N ha-1 was applied and displaced, allowing 5 cm irrigation water to infiltrate the plots when the crops were 60 days old. Above ground plant samples together with soil samples collected from 0-15, 15-30, 30-45, 45-60, 60-75 and 75-90 cm of soil depths at 20 and 44 h after initiation of leaching were used for 15N determinations. Results show that the migration of the added fertilizer N due to leaching below 105 cm soil depth after 44 h was 1.14 per cen t and 0.70 per cent of the added urea-N for pigeonpea and rice plus pigeonpea, respectively. The amounts of added N denitrified and immobilized were estimated to be 14.80 and 2.63 per cent for pigeonpea and 10.16 and 3.00 per cent for rice plus pigeonpea, respectively. The empirical transformation rate coefficient s of ureolysis (urea hydrolysis), NH4-oxidation and NO3-reduction at the rootzones of the 60-day old crop worked out to be 0.040h-1, 0.020h-1 and 0.045h-1 for pigeonpea and 0.038h-1, 0.018h-1 and 0.030h-1 for rice plus pigeonpea during the 44 h period. (author). 11 refs., 6 tables