Nutrient balances in African land use systems across different spatial scales: A review of approaches, challenges and progress

Cobo, Juan Guillermo; Dercon, Gerd; Cadisch, Georg

doi:10.1016/j.agee.2009.11.006

Cited by 180 publications

(121 citation statements)

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“…Large disparities between agronomic P inputs and outputs pose major challenges for long-term management of water quality and agricultural productivity at all scales. However, regional agronomic P imbalances are difficult to address because they represent the aggregate effects of many complex factors, including nutrient management decisions by individual farmers, socioeconomic conditions, government policies, and environmental setting (4,12,33).…”

Section: Discussionmentioning

confidence: 99%

“…Bouwman et al (19) used a more conservative estimate of agricultural P loss via runoff and leaching based on 10% of total P inputs (roughly 2.4 Tg of P·y −1 using our estimates). Accounting for P losses from soils to water in areas with small P surpluses, such as sub-Saharan Africa, would possibly lead to results of small deficits in many locations, reflecting the small P deficits typically found in studies that considered P losses in that region (10,12,33). Occlusion of P in soils to less plant-available forms may also limit the effectiveness of surplus agronomic P to supplement crop growth, especially in highly weathered and P-limited tropical soils, such as those in parts of Brazil and East Africa (28), which may partially explain lower PUE in these areas.…”

Section: Discussionmentioning

confidence: 99%

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Agronomic phosphorus imbalances across the world's croplands

MacDonald

Bennett

Potter

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

718

462

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Increased phosphorus (P) fertilizer use and livestock production has fundamentally altered the global P cycle. We calculated spatially explicit P balances for cropland soils at 0.5°resolution based on the principal agronomic P inputs and outputs associated with production of 123 crops globally for the year 2000. Although agronomic inputs of P fertilizer (14.2 Tg of P·y −1 ) and manure (9.6 Tg of P·y −1 ) collectively exceeded P removal by harvested crops (12.3 Tg of P·y −1 ) at the global scale, P deficits covered almost 30% of the global cropland area. There was massive variation in the magnitudes of these P imbalances across most regions, particularly Europe and South America. High P fertilizer application relative to crop P use resulted in a greater proportion of the intense P surpluses (>13 kg of P·ha −1 ·y −1 ) globally than manure P application. High P fertilizer application was also typically associated with areas of relatively low P-use efficiency. Although manure was an important driver of P surpluses in some locations with high livestock densities, P deficits were common in areas producing forage crops used as livestock feed. Resolving agronomic P imbalances may be possible with more efficient use of P fertilizers and more effective recycling of manure P. Such reforms are needed to increase global agricultural productivity while maintaining or improving freshwater quality.agriculture | eutrophication | nutrient balances | phosphorus depletion D isparities between the nutrients applied to agricultural soils via fertilizer or manure and the nutrients removed by harvested crops result in nutrient imbalances that can influence environmental quality and productivity of agricultural systems (1). Growing consumption of inorganic phosphorus (P) fertilizers derived from mining of nonrenewable phosphate rock (2) has contributed to major increases in crop yields since the 1950s (3). Concurrent growth in fertilizer use and livestock production has more than tripled global P flows to the biosphere over preindustrial levels (4), resulting in P accumulation in some agricultural soils that acts as a driver of eutrophication in freshwater and coastal systems (5-7). At the same time, limited availability of P fertilizers in other regions has contributed to prolonged P deficits that can deplete soil P and limit crop yields (8-10). Although agricultural P surpluses and deficits have been documented for several regions (e.g., refs. 11 and 12), there is still limited understanding of the spatial patterns of P imbalances at the global scale.Patterns of nutrient imbalances across agricultural systems may reflect contrasting agricultural practices, economic development, and broader agricultural policies (1, 13). Understanding agricultural P use is key to managing global phosphate rock reserves (14) and mitigating the risk for potentially irreversible eutrophication of lakes (15). Despite considerable advances in the development of spatially explicit global nitrogen balances (e.g., ref. 16), most previous global P balance studi...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Agronomic phosphorus imbalances across the world's croplands

MacDonald

Bennett

Potter

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

718

462

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“…Partial nutrient balances (or budgets) are typically used to describe the stocks and fluxes (ins and outs) of a soil [65]. They have been calculated for many different regions and countries [66], and are often used in Africa to evaluate management practices that promote nutrient surpluses or deficits [42,[67][68][69]. In many SSA farming systems, certain soils suffer from nutrient depletion even if the whole farm or farming community does not.…”

Section: Types Of Degradation In Sub-saharan Africamentioning

confidence: 99%

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

et al. 2015

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Abstract:The primary cause of soil degradation in sub-Saharan Africa (SSA) is expansion and intensification of agriculture in efforts to feed its growing population. Effective solutions will support resilient systems, and must cut across agricultural, environmental, and socioeconomic objectives. While many studies compare and contrast the effects of different management practices on soil properties, soil degradation can only be evaluated within a specific temporal and spatial context using multiple indicators. The extent and rate of soil degradation in SSA is still under debate as there are no reliable data, just gross estimates. Nevertheless, certain soils are losing their ability to provide food and essential ecosystem services, and we know that soil fertility depletion is the primary cause. We synthesize data from studies that examined degradation in SSA at broad spatial and temporal scales and quantified multiple soil degradation indicators, and we found clear indications of degradation across multiple indicators. However, different indicators have different trajectories-pH and cation exchange capacity tend to decline linearly, and soil organic carbon and yields non-linearly. Future research should focus on how soil degradation in SSA leads to changes in ecosystem services, and how to manage these soils now and in the future. OPEN ACCESS

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“…Input intensifi cation strategies, on the other hand, place higher emphasis on the use of certifi ed seeds, mineral fertiliser, irrigation and other productivity-enhancing inputs. They argue that owing to negative soil nutrient balances caused by continuous cultivation with little or no addition of nutrients, enhanced food crop production in SSA is critically dependent on external nutrient inputs (Cobo et al, 2010;Sanchez, 2002).…”

Section: Introductionmentioning

confidence: 99%

Adoption of multiple agricultural technologies in maize production of the Central Rift Valley of Ethiopia

Ahmed¹

2015

Stud. Agr. Econ.

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Nutrient balances in African land use systems across different spatial scales: A review of approaches, challenges and progress

Cited by 180 publications

References 103 publications

Agronomic phosphorus imbalances across the world's croplands

Agronomic phosphorus imbalances across the world's croplands

The State of Soil Degradation in Sub-Saharan Africa: Baselines, Trajectories, and Solutions

Adoption of multiple agricultural technologies in maize production of the Central Rift Valley of Ethiopia

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