Banana is an important crop in high altitude areas of Tanzania, grown widely both as a food staple and as the main source of income. However, its production is constrained by low soil fertility, a result of gradual nutrient mining by the crop. Currently, soil fertility management in banana-based farming systems in the country relies mainly on applications of animal manure. However, the amount of manure produced in most farms is not enough to replenish soil fertility due to the small number of animals kept by smallholder resource-poor farmers who are the major producers in the country. Field experiments were conducted at three sites with varying soil types and contrasting weather conditions along the altitudinal gradients on the slopes of the volcanic mountains of Kilimanjaro and Meru, northern Tanzania to (1) investigate the effect of mineral nitrogen (mineral N) fertilizer applications on the growth and yield of Mchare banana (Musa spp., AA, a traditional East African highland cooking banana sub-group), at the four levels of 0, 77, 153, and 230 kg N ha −1 year −1 as a starter strategy to improve the current soil fertility management strategies, and (2) evaluate the effect of the combined use of inorganic and organic N sources on growth and banana fruit production as an alternative strategy to manage soil fertility and minimize animal manure requirements. The treatment factors were trial sites (Tarakea, Lyamungo, and Tengeru) as the main factor and N fertilization strategies (as urea alone, sole cattle manure, and in combination with urea, sole common bean (Phaseolus vulgaris L.) haulms as well as in combination with urea) as a sub factor. Bean haulms and cattle manure were applied each year for two years. Fertilization at 153 kg N ha −1 year −1 derived solely from urea significantly (p < 0.001) resulted in high yield increment of up to 42% relative to the control. However, the increase was highest (52%) with the same N dose derived from cattle manure in combination with urea at 50% substitution. Sole bean haulms resulted in a smaller yield increment, the same as the lowest N dose from the sole urea fertilization treatment. The study concludes that soil fertility management in smallholder banana-based farming systems should not solely rely on animal manure and mineral fertilizers.
<p>The East African Serengeti ecosystem hosts a great range of mammals and one of the world&#8217;s largest seasonal ungulate movements, with over 1.3 wildebeest and several hundreds of thousands of zebras and antelopes migrating through the region in a regular pattern. While climatic and biological drivers for this migration have been studied in great detail, the role of rock chemistry, weathering and resulting soil diversity as a source for nutrient provision has so far been largely neglected and needs detailed and systematic study.</p> <p>Geological processes provide important controls on long-term ecosystem dynamics. Volcanic eruptions, earthquakes, and rock weathering influence soil edaphic properties, which represent the ability of soils to provide vital plant-available nutrients, which therefore control grazing patterns of herbivores, particularly during birthing and lactating seasons. Studying the geological role in providing and distributing essential nutrients is critical to understand long-term drivers and stability of animal migrations in dynamic ecosystems. We have carried out a field reconnaissance study in the Serengeti National Park, with the aim to study variations in nutrient variability in soils and vegetation in relation to the chemical composition of soil parent material, i.e. volcanic or metamorphic rocks and sediments derived from those rock units, and under consideration of climatic variations.&#160;First results show that the Serengeti ecosystem can be subdivided into three geo-edaphic subregions that correlate with seasonal wildebeest grazing habitats.</p> <p>(1) The southeastern Serengeti (wet-season grazing), is characterized by soils developed on volcanic ash derived from recent eruptions of the Ol Doinjo Lengai carbonatite volcano. Here, we have identified deeper organic-rich soils with andic and vitric properties and varying amounts of carbonate concretions or near-surface calcrete horizons. High Na, K, and Ca levels of volcanic ashes suggest high levels of those elements in soils and vegetation in this region, also because the precipitation is lowest in this area.</p> <p>(2) In the central Serengeti (short-term transitional grazing), soils develop on Archean basement rocks including granitic gneisses, phyllites and banded iron formations. Geochemical signatures of these rock types suggest that soils in this region have lower levels in Ca, Mg, and plant available P, compared to the SE Serengeti, which is supported by the transitional nature of this grazing habitat.</p> <p>(3) Soils in the Northern Serengeti (dry-season grazing) develop on a diverse patchwork of Archean basement rocks as well as basaltic lavas and thick fluvial deposits. North of Mara river, the Insuria fault &#8211; a large normal fault of the East African Rift&#160; - creates a wide sedimentary basin dominated by soils developed on basaltic sediments. Here, higher precipitation leads to stronger weathering and leaching of nutrient elements.</p> <p>Our preliminary results suggests that geochemical variations together with continuous (syngenetic) pedogenesis through active volcanism or tectonic faulting and related fault scarp erosion created regions of high edaphic quality in the north and southeast of the Serengeti ecosystem, and that the patchy nature of soil edaphics is important to understand the underlying drivers of large scale migration of grazing animals in this region.&#160;</p>
The rise in global human population, coupled with the effects of climate change, has increased the demand for arable land. Soil fertility has been the most affected, among other things. Many approaches to soil fertility management have been proposed by studies in Sub-Saharan Africa (SSA); however, the question of sustainability remains. Nutrient monitoring (NUTMON), which combines biophysical and socio-economic features for soil fertility management, gives an in-situ soil fertility status of a given land use system, which ultimately provides guidance in proposing appropriate soil management techniques in a given land use system. In this review, the Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) approach was deployed for a systematic search of the literature materials. The review evaluated various studies on nutrient monitoring in SSA soils in order to understand the socioeconomic attributes and their influence on farming systems, as well as nutrient flow and balances. The review identified two dominant smallholder farming systems in SSA: mixed crop-livestock and mixed crop farming systems. Also, this review revealed that most nutrient balance studies in SSA have been done in mixed crop and livestock farming systems. However, regardless of the farming systems, the overall mean nutrient balances in all studies, particularly those of nitrogen (N) and potassium (K), were negative, indicating significant nutrient mining. The review further revealed a vast range of biophysical soil fertility management technologies; however, their adoption has been limited by socio-economic aspects including land ownership, gender, financial position, literacy level, and access to inputs. Therefore, in view of this situation, integrating biophysical and socioeconomic disciplines could address the problem of soil nutrient depletion holistically, thus decreasing the existing negative nutrient balances in the SSA region.
Maize (Zea mays) stover produced in the drier lowland areas on the volcanic foot slopes of Mount Kilimanjaro serves as an important additional fodder for smallholder zero-grazed dairy cattle farming in the humid highland areas of the region. The obtained cattle manure is used to replenish nutrients and manage soil fertility in banana-based agroforestry homegardens of the highlands, which contributes significantly to sustaining crop production, thus food security and the livelihoods of the community. The study aims to provide a preliminary evaluation of the amounts of stover removed from smallholder maize-based fields in the lowlands and the subsequent nutrient flows to the banana-based agroforestry homegardens of the highlands. In 54 smallholder maize fields selected at random from 11 villages in the Hai and Siha districts of the Kilimanjaro region, we conducted an agronomic survey to record the types and amounts of fertilizer used, plant spacing at harvest, and maize stover biomass yield. Most of the surveyed maize-based fields received inadequate nutrient inputs, which were limited to mineral nitrogen alone if any. Of the surveyed fields, 16.7% received recommended amounts of 74 kg N ha–1 by the Ministry of Agriculture, 46.3% sub-optimal amounts and 37.0% did not receive fertilizer at all. Plant density was only 50% of the recommended population density. While this was only a preliminary study on nutrient flows between maize and banana-based agroecosystems, our findings demonstrated that potassium exports via harvested banana bunches exceeded the inputs in the homegardens. We conclude that (i) soil fertility management techniques, preferably integrated soil fertility management, suitable for small-scale maize production in the lowlands should be formulated while optimizing plant density to increase production, (ii) maize-based agroforestry farming system adapted to drier conditions to deal with windstorm and soil erosion problems in the lowlands is urgently needed, and (iii) wider and more detailed research on nutrient flows between maize and banana-based agroecosystems should be conducted to document their respective soil nutrient balances and the sustainability of such practice.
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