Toward a nitrogen footprint calculator for Tanzania

Abstract

We present the first nitrogen footprint model for a developing country: Tanzania. Nitrogen (N) is a crucial element for agriculture and human nutrition, but in excess it can cause serious environmental damage. The Sub-Saharan African nation of Tanzania faces a two-sided nitrogen problem: while there is not enough soil nitrogen to produce adequate food, excess nitrogen that escapes into the environment causes a cascade of ecological and human health problems. To identify, quantify, and contribute to solving these problems, this paper presents a nitrogen footprint tool for Tanzania. This nitrogen footprint tool is a concept originally designed for the United States of America (USA) and other developed countries. It uses personal resource consumption data to calculate a per-capita nitrogen footprint. The Tanzania N footprint tool is a version adapted to reflect the low-input, integrated agricultural system of Tanzania. This is reflected by calculating two sets of virtual N factors to describe N losses during food production: one for fertilized farms and one for unfertilized farms. Soil mining factors are also calculated for the first time to address the amount of N removed from the soil to produce food. The average per-capita nitrogen footprint of Tanzania is 10 kg N yr À1 . 88% of this footprint is due to food consumption and production, while only 12% of the footprint is due to energy use. Although 91% of farms in Tanzania are unfertilized, the large contribution of fertilized farms to N losses causes unfertilized farms to make up just 83% of the food production N footprint. In a developing country like Tanzania, the main audiences for the N footprint tool are community leaders, planners, and developers who can impact decision-making and use the calculator to plan positive changes for nitrogen sustainability in the developing world.

Beef and coal are key drivers of Australia’s high nitrogen footprint

“…In most countries, production of legumes and seafood is the most efficient while the production of beef is the least efficient in terms of Nr use678923 (Table 1, Supplementary Table 4). Although vegetables and fruits have large VNFs because of low N use efficiency in these production systems2425, the Nr loss per serving of vegetables or fruits is low due to the very low N content compared to other food types9.…”

“…Although vegetables and fruits have large VNFs because of low N use efficiency in these production systems2425, the Nr loss per serving of vegetables or fruits is low due to the very low N content compared to other food types9. Beef production is the least efficient way of using N and supplying dietary protein in most countries that have completed their calculation of VNFs678923, mainly due to the large feed requirements and their high basal metabolic rate26. An analysis of the environmental impacts of the various livestock categories in the United States had a consistent finding6827.…”

Dilemma of nitrogen management for future food security in sub-Saharan Africa – a review

“…In addition to AE N , indices related to environmental sustainability like N budgets (Leip et al 2011;Eurostat 2013;Özbek and Leip 2015) and N footprint Hutton et al 2017) are important for informing practices and policies intended to minimise N loss to the environment, while optimising crop and energy production. Good N management must therefore reduce both N accumulation (Vitousek et al 2009;Leip et al 2011) and N mining (Edmonds et al 2009;Bekunda et al 2010;Kihara et al 2015), which can be detected through N budgets, as both have negative environmental impacts.…”

“…The N footprint tool is useful for identifying hotspots of N losses to the environment, simulating mitigation options, and informing policy decisions for good N management through raising awareness of social responsibilities Davidson et al 2016). The application of the tool showed that in many countries the largest portion of the N footprint was associated with food production, with N accumulation in selected countries like the United States of America, whereas N mining occurred in countries like Tanzania in SSA (Hutton et al 2017). Nitrogen footprint assessments would therefore represent a great opportunity to reduce N mining in SSA through identification of potential N available for recycling in crop production.…”

Technical opportunities to reduce global anthropogenic emissions of nitrous oxide

“…Likewise, introducing more fertilizer in low-N areas (Sub-Saharan Africa: see also Hickman et al 2015) will have less effects on emissions than otherwise expected-at least as long as uniform conditions apply. Hutton et al (2017) point out that for Tanzania only 10% of farms receive all the mineral fertilizer available-if we assume that additional fertilizer is not just distributed on all farms evenly, but just extends the share of farms receiving fertilizer, the non-linearity effect disappears. Appropriate allocation of fertilizer application in future scenarios thus will remain a challenge.…”