Short duration overnight cattle kraaling in natural rangelands leads to increased tree damage by elephants

Elephants are attracted to nutrient hotspots created through short duration overnight cattle corralling (hereafter kraaling) in natural rangelands at Debshan, a mixed cattle-wildlife private ranch in central Zimbabwe, causing severe tree damage. We determined the effect of age of nutrient hotspot (i.e., time after kraal use) on elephant use and the extent of tree damage. Elephant use and tree damage were assessed in nutrient hotspots of varying ages (6, 12, 24, 36 and 48 months after kraal use) and in surrounding landscape. We also compared Acacia karroo bark nutrient and soil nutrient concentration between nutrient hotspots (24 months after kraal use) and the surrounding landscape. Elephant use of nutrient hotspots was highest at 12 and 24 months after kraaling. The most severely damaged trees were in the 12-, 24- and 36-month-old nutrient hotspots. Acacia karroo bark nutrient concentrations (nitrogen, potassium, calcium, magnesium and iron) were higher in nutrient hotspots than surrounding vegetation, while soil nutrients (nitrogen, phosphorus, calcium and potassium) were higher in nutrient hotspots than surrounding landscape. We concluded that elephants mostly used nutrient hotspots 12 and 24 months after kraaling, while severe tree damage occurred 12, 24 and 36 months after kraal use.

Fungal Mineral Weathering Mechanisms Revealed Through Direct Molecular Visualization

Soil fungi facilitate the translocation of inorganic nutrients from soil minerals to other microorganisms and plants. This ability is particularly advantageous in impoverished soils, because fungal mycelial networks can bridge otherwise spatially disconnected and inaccessible nutrient hotspots. However, the molecular mechanisms underlying fungal mineral weathering and transport through soil remains poorly understood. Here, we addressed this knowledge gap by directly visualizing nutrient acquisition and transport through fungal hyphae in a mineral doped soil micromodel using a multimodal imaging approach. We observed that Fusarium sp. DS 682, a representative of common saprotrophic soil fungi, exhibited a mechanosensory response (thigmotropism) around obstacles and through pore spaces (~12 μm) in the presence of minerals. The fungus incorporated and translocated potassium (K) from K-rich mineral interfaces, as evidenced by visualization of mineral derived nutrient transport and unique K chemical moieties following fungal induced mineral weathering. Specific membrane transport proteins were expressed in the presence of minerals, including those involved in oxidative phosphorylation pathways and transmembrane transport of small molecular weight organic acids. This study establishes the significance of fungal biology and nutrient translocation mechanisms in maintaining fungal growth under water and nutrient limitations in a soil-like microenvironment.

Short duration overnight cattle kraaling in natural rangelands: does time after kraal use affect their utilization by wildlife and above ground grass parameters?

Short duration overnight cattle kraaling in natural rangelands creates nutrients hotspots attractive to a diverse suite of large mammalian herbivores. However, few studies have determined the use of these sites by large mammalian herbivores. We determined the number of animal sightings per day from camera traps and used them as proxies for use of these newly created nutrient hotspots of varying ages (1, 2, 3 and 4 years) and surrounding vegetation. Six mammalian herbivores of different sizes belonging to three feeding guilds viz. grazers (Burchell’s zebra Equus quagga burchelli and warthog Phacochoerus africanus), mixed feeders (impala Aepyceros melampus and African savanna elephant Loxodonta africana africana) and browsers (northern giraffe Giraffa camelopardalis giraffa and greater kudu Tragelaphus strepsiceros) frequently used these nutrient hotspots. The number of sightings per day of mammalian herbivores was determined during three periods of the year (January – wet season; June – early dry season; October – late dry season) to ascertain their use of these nutrient hotspots. In addition, above ground grass biomass and height was measured and related to grazer sightings. Furthermore, we tested if repeated grazing in the newly created nutrient hotspots stimulated grass compensatory growth. All the mammalian herbivores used the newly created nutrient hotspots similarly throughout the year, with impala the most active users. Grazer and browser use of nutrient hotspots was not influenced by their age, while mixed feeders mostly used the one year old sites. Grazer use of nutrient hotspots was not influenced by aboveground grass biomass and height. Repeated clipping (proxy for grazing) resulted in compensatory aboveground grass biomass growth in nutrient hotspots. Impala benefited the most and zebra the least from the creation of nutrient hotspots in natural rangelands. We conclude that creation of nutrients hotspots through short duration overnight kraaling results in rangeland heterogeneity that improves availability of herbivore foraging sites.

Combining sub-field scale soil sampling and GIS interpolation techniques for mapping nutrient hotspots

<p>The EU Water Framework Directive (WFD) aims to target prevalent poor water quality status. Of the various contributing sources agriculture is particularly important due to the high loading rates of sediment and nutrient losses associated with fertilisation, sowing, and cropping regimes. Understanding soil nutrient status and the potential pathways for nutrient loss either through point or diffuse sources is an important step to improve water quality from an agricultural perspective. Research has demonstrated extensive in-field variability in soil nutrient status. A sampling regime that explores this variability at a sub-field scale is necessary. Traditional soil sampling consists of taking 20-30 cores per field in a W-shaped formation to produce a single bulked core, however, it generally fails to locate nutrient hotspots at finer resolutions. Inappropriate generalised fertilisation and management recommendations can be made in which nutrient hotspots or deficient zones are overlooked. Gridded soil sampling can reveal the full degree of in-field variability in nutrient status to inform more precise and site-specific nutrient applications. High soil phosphorus levels and the concept of legacy nutrient accumulation due to long-term over-application of phosphorus fertiliser in addition to animal slurry is a problem across the island of Ireland.</p><p>This research aims to locate and quantify the presence of soil nutrient hotspots at several field-scale locations in the cross-border Blackwater catchment in Northern Ireland / Republic of Ireland. Based on 35 m sampling grids, the nutrient content at unsampled locations in each field was determined using GIS interpolation techniques. Particular attention was paid to phosphorus, given its role in eutrophication. Gridded soil sampling enables the identification of nutrient hotspots within fields and when combined with an analysis of their location in relation to in-field landscape characteristics and knowledge of current management regimes, the risk of nutrient or sediment loss potential may be defined. This research concluded that traditional W soil sampling of producing one average value per field is not appropriate to uncover the degree of spatial variability in nutrient status and is inappropriate for catchment management of agricultural systems for controlling nutrient losses. Soil sampling at multiple locations per field is deemed to be cost-prohibitive for many farmers. However, sub-field scale soil sampling and appropriate geostatistical interpolation techniques can reveal the degree of variability and suggest an appropriate resolution for field-scale nutrient management that may be necessary to achieve measurable improvements in water quality.</p>