Fredrick O. Ayuke

Bio: Fredrick O. Ayuke is an academic researcher from University of Nairobi. The author has contributed to research in topics: Soil biology & Tillage. The author has an hindex of 12, co-authored 43 publications receiving 704 citations. Previous affiliations of Fredrick O. Ayuke include International Center for Tropical Agriculture & Swedish University of Agricultural Sciences.

Global distribution of earthworm diversity

Abstract: Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, and biomass. We found that local species richness and abundance typically peaked at higher latitudes, displaying patterns opposite to those observed in aboveground organisms. However, high species dissimilarity across tropical locations may cause diversity across the entirety of the tropics to be higher than elsewhere. Climate variables were found to be more important in shaping earthworm communities than soil properties or habitat cover. These findings suggest that climate change may have serious implications for earthworm communities and for the functions they provide.

Short-term influence of biochar and fertilizer-biochar blends on soil nutrients, fauna and maize growth

Abstract: Use of inorganic fertilizers in smallholder cropping systems in Africa is often becoming inefficient due to increasing unresponsiveness to fertilizer application. A study was conducted for 2 years (four seasons) to assess the effects of biochar made from Prosopis juliflora (Sw.) DC. biomass on nutrients, fauna abundance and subsequent influence on maize planted in a nitisol. There were 12 amendments comprising: (i) biochar applied alone at a rate of 5 and 10 Mg ha−1; (ii) three fertilizer types applied separately (di-ammonium phosphate (18:46:0), urea (46:0:0) and composite NPK (23:23:0)); (iii) six fertilizer + biochar blends of the three fertilizer types and two biochar rates (0.05 and 0.1 Mg ha−1); and (iv) a control with no inputs. Treatments were replicated four times in a randomized complete block design. The amendments were applied in the first two seasons, while the last two were used to assess residual effects. At the end of the first two seasons, total C and N were higher in soils where biochar or fertilizer + biochar was applied, with more than 15.0 g C and 1.9 g N kg−1, compared to 10.4 g C and 1.0 g N kg−1 in control plots. Available P and exchangeable K were over 200% and 100% higher in biochar or fertilizer + biochar amended than control soils, respectively. Application of biochar had no effects on macrofauna such as beetles, centipedes, millipedes, termites and ants, but attracted earthworms. Soil that received 10 Mg biochar ha−1 recorded twice the number of earthworms (207 individuals m−2) compared to soil with 5 Mg biochar ha−1 (105 individuals m−2) and control (97 individuals m−2). Soils which received biochar, with or without fertilizer, had higher taxonomic richness (7.0 species) compared to soils which received DAP (2.8) or NPK (3.8). Nematodes, particularly bacterivorous groups, decreased by more than eight times with biochar application. In the first and second seasons, 5.6 Mg maize grain yield ha−1 was obtained from plots amended with biochar (without fertilizer), which was about six times higher than that harvested from unfertilised control at 0.9 Mg ha−1. Yield differences in plots where fertilizer was applied with or without biochar were not significant. Yield in the third and fourth seasons declined to 3.2 and 1.5 Mg ha−1, irrespective of fertilizer type or biochar amounts.

Soil macrofauna abundance under dominant tree species increases along a soil degradation gradient

Abstract: Soil macrofauna contribute to key soil functions underpinning soil-mediated ecosystem services. There is limited understanding about the role of trees as ‘resource islands’ for soil macrofauna in agricultural landscapes and how this interaction is affected by soil degradation status. The study assessed the spatial influence of three dominant trees namely, Croton megalocarpus , Eucalyptus grandis and Zanthoxylum gilletii , on soil macrofauna abundance, along a soil degradation gradient resulting from continuous cultivation for 10, 16 and 62 years. It was hypothesised that spatial variation in soil macrofauna abundance is affected by duration of cultivation, tree species and distance from the tree trunk. Soils cultivated for 10 years showed highest soil nutrient levels. Notably, soil C and N were higher below the canopy of C. megalocarpus (64.6 g kg −1 C; 6.7 g kg −1 N), than E. grandis (58.7 g kg −1 C; 5.9 g kg −1 N) and Z. gilletii (54.5 g kg −1 C; 5.6 g kg −1 N) after 10 years of cultivation. Similar trends were also found after 16 and 62 years of cultivation, although the mean values for the two elements were below 40.0 g kg −1 and 4.0 g kg −1 , respectively. Higher soil macrofauna abundance was found after 16 and 62 years of cultivation, though this was dependent on tree species and soil macrofauna group. Earthworm abundance was highest below the canopy of Z. gilletii averaging 389 individuals and 160 individuals m −2 , respectively, compared to 14 individuals m −2 after 10 years of cultivation. Conversely, beetles showed higher numbers under E. grandis and C. megalocarpus than under Z. gilletii . Highest numbers of termites and centipedes were found under E. grandis after 16 years of cultivation. These findings support the importance of a diverse tree cover in agricultural landscapes to conserve soil macrofauna communities and the contribution of their activity to soil ecological functions.

Restoring Soil Quality to Mitigate Soil Degradation

Abstract: Feeding the world population, 7.3 billion in 2015 and projected to increase to 9.5 billion by 2050, necessitates an increase in agricultural production of ~70% between 2005 and 2050. Soil degradation, characterized by decline in quality and decrease in ecosystem goods and services, is a major constraint to achieving the required increase in agricultural production. Soil is a non-renewable resource on human time scales with its vulnerability to degradation depending on complex interactions between processes, factors and causes occurring at a range of spatial and temporal scales. Among the major soil degradation processes are accelerated erosion, depletion of the soil organic carbon (SOC) pool and loss in biodiversity, loss of soil fertility and elemental imbalance, acidification and salinization. Soil degradation trends can be reversed by conversion to a restorative land use and adoption of recommended management practices. The strategy is to minimize soil erosion, create positive SOC and N budgets, enhance activity and species diversity of soil biota (micro, meso, and macro), and improve structural stability and pore geometry. Improving soil quality (i.e., increasing SOC pool, improving soil structure, enhancing soil fertility) can reduce risks of soil degradation (physical, chemical, biological and ecological) while improving the environment. Increasing the SOC pool to above the critical level (10 to 15 g/kg) is essential to set-in-motion the restorative trends. Site-specific techniques of restoring soil quality include conservation agriculture, integrated nutrient management, continuous vegetative cover such as residue mulch and cover cropping, and controlled grazing at appropriate stocking rates. The strategy is to produce “more from less” by reducing losses and increasing soil, water, and nutrient use efficiency.

Global Multi-resolution Terrain Elevation Data 2010 (GMTED2010)

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Global meta-analysis of the relationship between soil organic matter and crop yields

Abstract: . Resilient, productive soils are necessary to sustainably intensify agriculture to increase yields while minimizing environmental harm. To conserve and regenerate productive soils, the need to maintain and build soil organic matter (SOM) has received considerable attention. Although SOM is considered key to soil health, its relationship with yield is contested because of local-scale differences in soils, climate, and farming systems. There is a need to quantify this relationship to set a general framework for how soil management could potentially contribute to the goals of sustainable intensification. We developed a quantitative model exploring how SOM relates to crop yield potential of maize and wheat in light of co-varying factors of management, soil type, and climate. We found that yields of these two crops are on average greater with higher concentrations of SOC (soil organic carbon). However, yield increases level off at ∼2 % SOC. Nevertheless, approximately two-thirds of the world's cultivated maize and wheat lands currently have SOC contents of less than 2 %. Using this regression relationship developed from published empirical data, we then estimated how an increase in SOC concentrations up to regionally specific targets could potentially help reduce reliance on nitrogen (N) fertilizer and help close global yield gaps. Potential N fertilizer reductions associated with increasing SOC amount to 7 % and 5 % of global N fertilizer inputs across maize and wheat fields, respectively. Potential yield increases of 10±11 % (mean ± SD) for maize and 23±37 % for wheat amount to 32 % of the projected yield gap for maize and 60 % of that for wheat. Our analysis provides a global-level prediction for relating SOC to crop yields. Further work employing similar approaches to regional and local data, coupled with experimental work to disentangle causative effects of SOC on yield and vice versa, is needed to provide practical prescriptions to incentivize soil management for sustainable intensification.