Soil-inorganic nitrogen changes in rice fields under selected crop management interventions and hydrological conditions in Kilombero Floodplain, Tanzania

A DISSERTATION SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN MANAGEMENT OF NATURAL RESOURCES FOR SUSTAINABLE AGRICULTURE OF SOKOINE UNIVERSITY OF AGRICULTURE. MOROGORO, TANZANIA.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 (7th to 9th 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