Soil-Inorganic Nitrogen Changes In Rice Fields Under Selected Crop Management Interventions And Hydrological Conditions In Kilombero Floodplain, Tanzania

ABSTRACT

A study was conducted at Ifakara Morogoro Region with a purpose of investigating the effect of selected crop management interventions and hydrological conditions on soil NH4 + and NO3 - content. Study sites were located at Valley Middle and Fringe sites as distinct hydrological zones. An experiment, in a complete Randomized block design, with six treatments: 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) was laid down in three replicates. SARO 5 rice variety was used as a test-crop. The trials were set during the 2014/15 pre-season and 2015/16 main season. Data was collected from 0-10cm soil depth. A Two-way ANOVA and post hoc – Tukey HD test statistical analyses were performed using GenStat Programme. Pre-season NH4 + showed 3 patterns: initial increase to peak values within 3 and 6 weeks for the Fringe and Middle sites, a period of decline (7 th to 9 th week, Middle, and 4th to 6th Fringe) and a period of increase (from 7th, Fringe and 10th week, Middle). Highest peak NH4 + values were at the Middle site (TR6 - 0.007401, TR5 - 0.004776, and TR4 - 0.04525, g/kg soil and TR4 - 0.004524, TR5 - 0.004595 g/kg soil). Peak NH4 + values differed significantly among treatments, following the trend: TR6>TR5>TR3>TR4>TR1>TR2 and TR4>R6=TR5=TR3+TR2>TR1 at the Middle and Fringe sites, respectively. Nitrate content decreased within 1-2 weeks both sites to attain the least values between 4 and 7 weeks and rose steadily to 10. Rice cropping season NH4 + and NO3 - variation showed a similar trend for both sites, apart for a sudden increase in the treatments with N input at week 8 and 10. Hydrological conditions did not significantly influence the NH4 + and NO3 - (P = 0.05) content. The study recommends repeating the work under controlled conditions.