G. P. Maro^1,, S. G. Mbwambo¹, H. E. Monyo¹, E. J. Mosi¹

The nutrient release potential of selected types of organic materials available in a coffee farming system was studied with three contrasting soils of Kilimanjaro Region, to broaden the ISFM options. An incubation experiment was conducted at TaCRI Lyamungu screenhouse between June and November 2019. The design was split plot RCD, three soil types Humi-Umbric Nitisols from Lyamungo, Eutric Cambisols from Kilacha and Humi-Rhodic Luvisols from Kikafu Chini as main factors, and different organic additives (cattle manure and leaves of Tithonia diversifolia, Tephrosia vogelii, Vernonia subligera and Adhatoda engleriana) as sub-factors. The organics were dried, crushed, sieved in a 6 mm sieve, mixed with the soils at 2% organic to soil ratio, moistened to field capacity and incubated in 10 litre plastic containers at room temperature. Duplicate soil samples were taken at day 0, 3, 8, 15, 26, 45, 74, 112 and 180 and analyzed for NH₄-N, NO₃-N, and available P. The total amounts of nutrients released during the incubation period were subjected to Analysis of Variance using COSTAT Statistical Software, with means separated by Tukey’s HSD at p ≤ 0.05. The nutrient release trends were more or less the same in all the three soil types. In terms of NH₄-N, NO₃-N and P, soil types, additives and their interactions were very highly significant (p < 0.001). In all the soil types, the four organics are fairly comparable to manure and can be used as its substitute. It was noted that soils differ in their responsiveness to organic treatments. Also unveiled was the potential of the wild plants such as Adhatoda, available in the wilderness around Mt. Kilimanjaro and Usambaras, which could be domesticated and planted at hedgerows for ISFM purposes. It also encourages the use of the semi-domesticated hedgerow plants like Tithonia and Vernonia; and Tephrosia as temporary shade plants.

organic materials, nutrient release, soil incubation, Kilimanjaro