Mateete A. Bekunda

Transformation of the Nitrogen Cycle: Recent Trends, Questions, and Potential Solutions

Humans continue to transform the global nitrogen cycle at a record pace, reflecting an increased combustion of fossil fuels, growing demand for nitrogen in agriculture and industry, and pervasive inefficiencies in its use. Much anthropogenic nitrogen is lost to air, water, and land to cause a cascade of environmental and human health problems. Simultaneously, food production in some parts of the world is nitrogen-deficient, highlighting inequities in the distribution of nitrogen-containing fertilizers. Optimizing the need for a key human resource while minimizing its negative consequences requires an integrated interdisciplinary approach and the development of strategies to decrease nitrogen-containing waste.

Research on nutrient flows and balances in East and Southern Africa: state-of-the-art

East and Southern Africa have soils that are still relatively fertile, notably those in the Highlands, associated with the Rift valley area. The lower areas are less well-endowed when it comes to soil fertility. At low agricultural intensity, this does not matter as nutrients cycle through the soil and the natural vegetation and losses are few. However, the past decades have shown high population increases, the adoption of continuous cultivation in areas that used to be under traditional shifting cultivation, and a decline of land productivity. The present review paper shows how much we know about the severity of this process and the technologies at hand that can stop it. The information provided shows that on the technical side much is known now, but research output is still poorly integrated into development. Although integrated nutrient management has been shown to be a panacea to combat nutrient depletion, there is a serious crisis of primary data on this subject.

Organic resource management in banana-based cropping systems of the Lake Victoria Basin, Uganda

The cultivation of plantain and cooking banana in humid areas of Uganda continues to grow in importance as rural population densities increase and as demand from urban areas intensifies. Difficulties accompany this importance, particularly soil depletion and intensification of pests and diseases of banana. We interviewed 510 farm families practising banana-based cultivation in six districts along the Lake Victoria Basin of southern-central Uganda to determine which resource management strategies are undertaken to mitigate limitations to banana cultivation and the importance of livestock and intercropping within those systems. Of the farmers interviewed, 97% reapply banana stalks and leaves to the banana mats on pruning and upon harvest, a practice that may contribute to banana weevil, stem nematode and sigatoka fungal attacks. Banana stalks were also applied as mulches to cash (4%) and field crops (2%) and used as livestock feed (10%). Farmers applied a wide range of additional resources to bananas including field crop residues (81%), burned residues (3%), on-farm manures (31%), compost (16%), external organic (17%) and chemical (4%) inputs. Of the organic inputs applied to bananas, bean trash (72%), maize stover (68%), cattle manure (45%) and composts (18%) were most frequently applied. It was necessary to consider at least five different organic inputs to account for more than 90% of farmer practices. Overall, intercropping was practised by 69% of the farmers. The six most encountered intercrops were, in decreasing order, beans, maize, cassava, Ficus nataliensis and fruit trees. When organic matter management was separated into five general categories depending on the reliance upon bananas, other crops, manures and composts as organic additions to soils, significant differences in reported average bunch weights were obtained. The farmers applying banana stalks, field crop residues and cattle manures reported the largest bunch weights (20.3 kg per bunch). Farmers relying upon banana stalks alone, banana stalks with field crop residues and either small livestock manure or domestic compost reported the lowest yields (13.1, 14.3 and 12.9 kg per bunch, respectively). We conclude that farmers are developing strategies to resist fertility depletion, in part through better recycling of on-farm resources and intercropping but greater reliance upon external inputs may be required to ameliorate declining banana yields.

Drivers of land use change and household determinants of sustainability in smallholder farming systems of Eastern Uganda.

Smallholder farming systems in sub-Saharan Africa have undergone changes in land use, productivity and sustainability. Understanding of the drivers that have led to changes in land use in these systems and factors that influence the systems’ sustainability is useful to guide appropriate targeting of intervention strategies for improvement. We studied low input Teso farming systems in eastern Uganda from 1960 to 2001 in a place-based analysis combined with a comparative analysis of similar low input systems in southern Mali. This study showed that policy-institutional factors next to population growth have driven land use changes in the Teso systems, and that nutrient balances of farm households are useful indicators to identify their sustainability. During the period of analysis, the fraction of land under cultivation increased from 46 to 78%, and communal grazing lands nearly completely disappeared. Cropping diversified over time; cassava overtook cotton and millet in importance, and rice emerged as an alternative cash crop. Impacts of political instability, such as the collapse of cotton marketing and land management institutions, of communal labour arrangements and aggravation of cattle rustling were linked to the changes. Crop productivity in the farming systems is poor and nutrient balances differed between farm types. Balances of N, P and K were all positive for larger farms (LF) that had more cattle and derived a larger proportion of their income from off-farm activities, whereas on the medium farms (MF), small farms with cattle (SF1) and without cattle (SF2) balances were mostly negative. Sustainability of the farming system is driven by livestock, crop production, labour and access to off-farm income. Building private public partnerships around market-oriented crops can be an entry point for encouraging investment in use of external nutrient inputs to boost productivity in such African farming systems. However, intervention strategies should recognise the diversity and heterogeneity between farms to ensure efficient use of these external inputs.

Biological management of water hyacinth waste in Uganda

ABSTRACT The recent biological invasion of water hyacinth (Eichhornia crassipes (Mart.) Solms) into lakes and rivers of East Africa has forced the implementation of mechanical harvesting around key harbours and dams, resulting in subsequent difficulties of waste disposal. Utilization of these wastes would assist in deferring costs of control, currently covered by international agencies. This paper reports the nutrient contents, mineralization patterns and potential for ensiling water hyacinth wastes. Whole chopped plants and tissues separated into leaves, petioles and roots were placed into litter bags, deployed as surface mulch or submerged in water and recovered over 16 weeks. The wastes consisted of 45% leaves, 26% petiole and 29% roots and contained 92% moisture. Decomposition was greater under surface mulched conditions and significant differences were observed between plant tissues. The time to 50% decomposition of whole plants was 21 and 74 days for mulched and submerged conditions, respectively. Mineralization of N and P was significantly delayed under anaerobic conditions. Shoots of fresh water hyacinth were chopped into 2 to 4 cm pieces, maize bran or molasses added at rates of 0, 10, 15, 20 and 25% on a fresh weight basis and fermented for 21 days. Without additives, the pH of water hyacinth alone was 7.33, suggesting poor silage quality. Addition of 15% maize bran or molasses resulted in silage of pH 4.1 and 4.2, respectively. Silage prepared with 15% maize bran contained 20% dry weight with 13% crude protein and 20% acid detergent fibre. Water hyacinth silage prepared with maize bran and molasses was readily accepted by goats and young steers. Waste disposal problems may be related to poor aeration within mounds and an alternative exists for use of the wastes as organic inputs to soils or as livestock feed.

Managing soils in Sub-Saharan Africa: Challenges and opportunities for soil and water conservation

In this 21st century, agriculture continues to be an important sector for sustainable development and poverty reduction in Sub-Saharan Africa. Research indicates that 1% growth in this sector translates into 2.5% growth in income for the poor people in the region. However, such growth is still low and per capita food production has been insufficient and decreasing over time because it is based on smallholder agriculture that often provides insufficient incentives to use land resources sustainably. Compounding problems include volatility in input prices, markets, and climate, declining farm sizes as a result of rising population pressures, weak extension services, low adoption of improved technologies, and limited government investments. In addition, Sub-Saharan Africa continues to experience destructive extraction, over-exploitation, and inadequate conservation of soil and water. More work needs to be done to demonstrate to policy makers, development partners, and society at large the full contribution that will be made to poverty alleviation by increasing and sustaining agricultural productivity through investments in soil rehabilitation, water harvesting and utilization, and reduction of land degradation. Several success stories of local soil and water conservation activities practiced by farmers in Sub-Saharan Africa exist, but the challenge is to scale these successes to wider implementation.

Nitrogen-neutrality: a step towards sustainability

We propose a novel indicator measuring one dimension of the sustainability of an entity in modern societies: Nitrogen-neutrality. N-neutrality strives to offset Nr releases an entity exerts on the environment from the release of reactive nitrogen (Nr) to the environment by reducing it and by offsetting the Nr releases elsewhere. N-neutrality also aims to increase awareness about the consequences of unintentional releases of nitrogen to the environment. N-neutrality is composed of two quantified elements: Nr released by an entity (e.g. on the basis of the N footprint) and Nr reduction from management and offset projects (N offset). It includes management strategies to reduce nitrogen losses before they occur (e.g., through energy conservation). Each of those elements faces specific challenges with regard to data availability and conceptual development. Impacts of Nr releases to the environment are manifold, and the impact profile of one unit of Nr release depends strongly on the compound released and the local susceptibility to Nr. As such, Nneutrality is more difficult to conceptualize and calculate than C-neutrality. We developed a workable conceptual framework for N-neutrality which was adapted for the 6th International Nitrogen Conference (N2013, Kampala, November 2013). Total N footprint of the surveyed meals at N2013 was 66kgN. A total of US

Decomposition of Crop Residues in Banana-Based Cropping Systems of Uganda

3050 was collected from the participants and used to offset the conference’s N footprint by supporting the UN Millennium Village cluster Ruhiira in SouthWestern Uganda. The concept needs further development in particular to better incorporate the spatio-temporal variability of impacts and to standardize the methods to quantify the required N offset to neutralize the Nr releases impact. Criteria for compensation projects need to be sharply defined to allow the development of a market for N offset certificates. S Online supplementary data available from stacks.iop.org/ERL/9/115001/mmedia

Approaches to reinforce crop productivity under rain-fed conditions in sub-humid environments in Sub-Saharan Africa

ABSTRACT In banana-based cropping systems of Uganda, complex strategies of organic resource management have developed. The traditional method of cultivation includes surface mulching the banana mats with the pseudostems, leaves and peels following harvests. Bananas are frequently intercropped and a wide range of other plant residues are retained as surface mulches. The most common of these intercrops are beans (Phaseolus vulgaris) and maize (Zea mays). The decomposition and nutrient release of banana pseudostems, leaves and peels, maize stover and bean trash was studied. Black plastic litter bags were placed in the field and recovered after 0, 2, 4, 8, 16 and 32 weeks. The effect of soil fauna was estimated by altering the screen openings of the litter bags (2 vs 5 mm). For fresh banana pseudostems, litter bags were place on the surface or buried to study the effect of soil incorporation. Litter materials were analysed for C, N, P, K and lignin. The results were fit to first order exponential decline and ...

Does crop diversity contribute to dietary diversity? Evidence from integration of vegetables into maize-based farming systems

Smallholder farming in much of Sub-Saharan Africa is rain-fed and thus exposed to rainfall variability. Among the climate variables, rainfall is projected to decline and have an overriding effect on crop productivity. With little opportunity for supplementary irrigation for the majority of farmers, a plausible strategy to maintain crop production under water-limited conditions includes balanced nutrient management for enhancing efficiency of use of limited soil water. Co-application of judicious rates of organic and mineral nutrient resources, particularly including the use of phosphorus (P) on P-limited soils, will facilitate development of an extensive crop rooting system for efficient exploration and capture of soil water, especially at a depth >0.8 m. This chapter explores case studies across Eastern and Southern Africa where various soil water conservation and nutrient management approaches have been used to gain ‘extra miles’ with limited available soil water. Firstly, an approach is described that varies nitrogen (N) fertilizer application across growing seasons, by adjusting N application rates to match current season rainfall trends. The approach offers opportunities for farmers to increase crop productivity to >6 t ha−1 in high agro-potential areas, compared to a ceiling of 4.5 t ha−1 for the fixed fertilization model, while minimizing economic losses due to investments in N fertilizer during drought years. Secondly, we deal with the subject of fertilization across nutrient gradients, where a poor agronomic N use efficiency of 35 kg grain kg−1 of N applied when soil organic carbon >0.5 %. Thirdly, the conservation agriculture (CA)-nutrient management nexus is examined, where maize yields in farmers’ fields with CA alone were barely 0.5 t ha−1 compared to an average of 2.5 t ha−1 for CA combined with fertilizers. Fourthly, a novel system that involves intercropping two legumes with contrasting phenology for enhanced cropping system functioning is described. Finally, an approach that can be used for co-learning with farmers on soil fertility management principles for risk management is presented. The data lead to the conclusion that the ‘doubled-up’ legumes system results in reduced fertilizer requirements for cereal crops grown in sequence, which benefits yield stability over time. Variable use of N fertilizer according to season quality and more tailored targeting of nutrients are vital for profitable investments in fertilizers in Africa. The Africa RISING project in Eastern and Southern Africa is currently harnessing some of these principles as vehicles for intensification of smallholder farming systems.