John Stephen Tenywa

Comparison of four low-technology composting methods for market crop wastes.

Four methods for composting, pit-cover (PC), pit-open (PO), above ground-open (AO) and above ground-covered (AC), were compared for their effect in accelerating compost maturity using market crop waste (MCW). The composting process was monitored through determining changes in temperature and pH, with compost maturity indices measured in terms of variations in water-soluble carbon (WSC), ammonium-N (NH(4)(+)-N) and nitrate-N (NO(3)(-)-N), and C/N, NH(4)(+)-N/NO(3)(-)-N, WSC/organic N and WSC/total N (TN). Total organic carbon (TOC), nitrogen (TN), potassium (TK) and phosphorus (TP) were also determined. Temperature rapidly increased from mesophilic to thermophilic and gradually reduced through maturation phases. A similar pattern was recorded for pH, which reached a slightly alkaline level at maturity. Composting significantly (p<0.05) decreased the concentrations of TOC, TN, TP, TK, NH(4)(+)-N and WSC and increased that of NO(3)(-)-N. All four low-technology composting methods used in this study produced mature composts within 63 days. Suitable maturity indicators for MCW compost were C/N ratio<12, WSC<1%, NH(4)(+)-N<400 mg kg(-1), NH(4)(+)-N/NO(3)(-)-N<0.2, WSC/TN, WSC/organic-N<1. On the basis of these indicators, the AC method generally enhanced maturity faster than the AO, PC and PO methods. Pit methods require less investment and are recommended for the smallhold farmers.

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

CRITICAL SOIL ORGANIC CARBON RANGE FOR OPTIMAL CROP RESPONSE TO MINERAL FERTILISER NITROGEN ON A FERRALSOL

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

Strategic nutrient management of field pea in southwestern Uganda

Soil Organic Carbon (SOC) is a major indicator of soil fertility in the tropics and underlies variability in crop response to mineral fertilizers. Critical SOC concentrations that interact positively with N fertilizer for optimal crop yield are less understood. A study was conducted on a Ferralsol in sub-humid Uganda to explore the critical range of SOC concentrations and associated fractions for optimal maize ( Zea mays L.) yield response to applied mineral N fertiliser. Maize grain yield response to N rates applied at 0, 25, 50 and 100 kg N ha −1 in 30 fields of low fertility (SOC 1.2%), medium fertility (SOC = 1.2–1.7%) and high fertility (SOC > 1.7%) was assessed. Soil was physically fractionated into sand-sized (63–2000 µm), silt-sized (2–63 µm) and clay-sized ( 1.2% SOC registered the highest agronomic efficiency (AE) and grain yield. Non-linear regression models predicted critical SOC for optimal yields to be 2.204% at the 50 kg N ha −1 rate. Overall, models predicted 1.9–2.2% SOC as the critical concentration range for high yields. The critical range of SOC concentrations corresponded to 3.5–5.0 g kg −1 sand-sized C and 9–11 g kg −1 for clay-sized C.

Precision of farmer-based fertility ratings and soil organic carbon for crop production on a Ferralsol

The highlands of south-western Uganda account for the bulk of field pea (Pisum sativum L.) produced and consumed in the country. The crop fetches a stable price, which is as high as that of beef, but it has remained outside the mainstream of the research process. Low soil fertility, unfortunately, is poised to eliminate the crop. Nitrogen, phosphorus and potassium have variously been reported as deficient on the bench terraces where crop production is primarily done. Strategic nutrient management requires that the most limiting nutrient is known in order to provide a foundation for designing effective and sustainable soil fertility management interventions. A study was conducted on upper and lower parts of the bench terraces on the highlands in south-western Uganda to identify the most required macro-nutrient(s) in field pea production. Treatments included: 0 and 25 kg N ha–1, 0 and 60 kg P ha–1, and 0 and 60 kg K ha–1, all applied factorially in a randomized complete block design. Parameters assessed included nodulation, nodule effectiveness for BNF and dry weight, shoot dry weight (SDW), and grain yield. Nutrient applications that resulted in the highest crop responses were considered as most required, and hence, most limiting to plant growth and yield. Phosphorus based nutrient combinations gave the highest increments in total and effective nodule numbers, as well as dry weight, irrespective of terrace position. On the other hand, N based combinations led to the highest shoot dry matter at flowering (39% higher over the control). The superiority of N was carried over up to final harvesting, with stover and grain yields edging out the other treatment regimes on either terrace positions.