Interaction of soil-inorganic nitrogen in rice fields of Kilombero Floodplain, Tanzania

Abstract

Abstract. Yobele AB, Kilasara M. 2021. Interaction of soil-inorganic nitrogen in rice fields of Kilombero Floodplain, Tanzania. Intl J Bonorowo Wetlands 11: 32-47. At Ifakara Morogoro Region, a study was done to determine the effect of selected crop management interventions and hydrological conditions on soil NH₄⁺ and NO₃^- concentration. The study chose Valley Middle and Fringe locations as distinct hydrological zones. Three repetitions of an experiment with six treatments were laid down: semi-natural vegetation (TR1), farmers practice (TR2), bunding alone (TR3), bunding + 60 kgN/ha (TR4), bunding + 120 kgN/ha (TR5), and bunding+Lablab green manure (TR6). As a test crop, the SARO 5 rice variety was employed. The trials took place during the pre-season of 2014/15 and the regular 2015/16. Data were gathered from a depth of 0-10 cm in the soil. Using the GenStat Program, two-way ANOVA and post hoc-Tukey HD test statistical analyses were done. Pre-season NH₄⁺ concentrations followed three distinct patterns: an initial increase to peak levels within 3 and 6 weeks for the Fringe and Middle sites, a fall (7^th to 9^th week for the Middle, and 4^th to 6^th week for the Fringe), and an increase (from 7^th, Fringe and 10^th week, Middle). The Middle site had the highest peak NH₄⁺ levels (TR6-0.007401, TR5-0.004776, and TR4-0.04525, g/kg soil, and TR4-0.004524, TR5-0.004595, g/kg soil, respectively). At the Middle and Fringe locations, peak NH₄⁺ values varied considerably between treatments, following the trend TR6>TR5>TR3>TR4>TR1>TR2 and TR4>R6=TR5=TR3+TR2>TR1. Nitrate levels declined within 1-2 weeks at both sites, reaching their lowest levels between 4 and 7 weeks, and then gradually increased to 10. Rice cropping season NH₄⁺ and NO₃^- variation followed a similar pattern for both locations, except a sharp increase in treatments with N input during weeks 8 and 10. Hydrological conditions had no significant effect on the NH₄⁺ and NO₃^- levels (P = 0.05). The study advises that the experiment be repeated under controlled conditions.