Impact of bovine urine deposition on soil microbial activity,biomass, and community structure

Nitrogen (N) from urine excreted by grazing animals can be transformed into N compounds that have detrimental effects on the environment. These include nitrate, which can cause eutrophication of waterways, and nitrous oxide, which is a greenhouse gas. Soil microbes mediate all of these N transformations, but the impact of urine on microbes and how initial soil conditions and urine chemical composition alter their responses to urine are not well understood. This study aimed to determine how soil inorganic N pools, nitrous oxide fluxes, soil microbial activity, biomass, and the community structure of bacteria containing amoA (nitrifiers), nirK, and nirS (denitrifiers) genes responded to the addition of urine over time. Bovine urine containing either a high (15.0 g K⁺ l^?1) or low salt content (10.4 g K⁺ l^?1) was added to soil cores at either low or high moisture content (hereafter termed dry and wet soil respectively; 35% or 70% water-filled pore space after the addition of urine). Changes in soil conditions, inorganic N pools, nitrous oxide fluxes, and the soil microbial community were then measured 1, 3, 8, 15, 29 and 44 days after urine addition. Urine addition increased soil ammonium concentrations by up to 2 mg g d.w.^?1, soil pH by up to 2.7 units, and electrical conductivity (EC) by 1.0 and 1.6 dS m^?1 in the low and high salt urine treatments respectively. In response, nitrate accumulation and nitrous oxide fluxes were lower in dry compared to wet urine-amended soils and slightly lower in high compared to low salt urine-amended soils. Nitrite concentrations were elevated (>3 μg g d.w.^?1) for at least 15 days after urine addition in wet urine-amended soils, but were only this high in the dry urine-amended soils for 1 day after the addition of urine. Microbial biomass was reduced by up to half in the wet urine-amended soils, but was largely unaffected in the dry urine-amended soils. Urine addition affected the community structure of ammonia-oxidising and nitrite-reducing bacteria; this response was also stronger and more persistent in wet than in dry urine-amended soils. Overall, the changes in soil conditions caused by the addition of urine interacted to influence microbial responses, indicating that the effect of urine on soil microbes is likely to be context-dependent.     

A six year study of earthworm (Lumbricidae) populations in pasture woodland in southern England shows their responses to soil temperature and soil moisture

There are very few studies on the effects of temporal changes in soil properties on ecosystem engineers in UK soils. This study addresses this lack by presenting earthworm diversity data from a six-year seasonality study comprising 72 monthly samples from the litter and soil of pasture woodland in the New Forest, southern England. These data were analysed in the context of soil moisture and soil temperature, key factors affecting earthworm abundance, and factors likely to be strongly affected by future climate change. The data for the whole period were analysed using non-parametric regression and an additive model used to separate within-year and between-year effects. Seasonal patterns are present for all the common species, generally with a maximum in March and a minimum in September. A majority of the five commonest species show a strong decline in abundance during the two extremely dry periods (2002–2003 and 2006). In sharp contrast, the same species showed a relative increase during the very wet summer and autumn of 2007. There was, however, no significant overall trend in either the climate data or the earthworm species data. The epigeic species, Dendrobaena octaedra, showed the largest decline in the driest months which caused a crash to the point where there were no adults sampled during the four dry summer months of 2003. A second congeneric species, Dendrobaena attemsi, also epigeic, appears to have invaded the woodland during the six year period and is increasing rapidly in abundance. This may indicate the start of a shift in the distribution of the two species, as D. octaedra generally has a northern European distribution and is frost-tolerant, while D. attemsi has a southern European distribution and is more drought-tolerant. In contrast, the very wet summer of 2007 seems to have damped the usual periodic seasonal oscillations in earthworm numbers. Endogeic worm species do not show the D. octaedra seasonal pattern as obviously, probably because these species are able to move more freely through the soil and because they are able to aestivate. These changes are likely to be due to a combination of human movement of earthworms (e.g. D. attemsi) and variations in local climate.     

The relationship between physical activity and leg health in the broiler chicken

1.?The relationship between the physical activity and leg health of broiler chickens was assessed on a semi-commercial scale.

2.?Three batches of birds (2128 per batch) were raised under two lighting regimes during the photoperiod; either a step-wise change of light intensity alternating between an illuminance of 200 and 10 lx or a constant illuminance of 10 lx. The activity of focal individuals (24 per batch) was observed at 2, 4 and 6 weeks of age, and leg health assessed weekly, based on gait score, the prevalence of burns on the hock and foot pad, and angulation and rotation of the leg at the intertarsal joint. Cortical bone density and thickness and area moments of inertia of the mid-physis tibiotarsus were measured post mortem at 6 weeks of age.

3.?The step-wise change in light intensity did not affect overall performance, activity or leg health.

4.?An individual bird's activity did not affect its gait score, the prevalence of hock burn or foot pad burn, cortical density or thickness or shape of the tibiotarsus. Sex of the bird was the only factor to affect significantly the area moment of inertia in the horizontal and vertical planes of the tibiotarsus, with females showing a lower moment of inertia for both. No variable had a significant effect on cortical density or thickness. Mean cortical density was low across all birds and may indicate that, when allowed to move freely as much or as little as they choose, broiler chickens do not exercise enough or do not perform the higher impact activities required to affect bone quality.

5.?These findings imply that the activity of broiler chickens raised on a semi-commercial scale is unaffected by step-wise changes in light intensity and that other husbandry measures are needed to raise activity and hence improve leg health.     

Clinical and low field magnetic resonance imaging features of osseous cyst‐like lesions of the proximal sesamoid bones in seven horses

Osseous cyst‐like lesions of the proximal sesamoid bones (PSBs) were diagnosed in 7 horses. The diagnosis was achieved radiographically prior to magnetic resonance imaging (MRI) in only one horse, and in the other 6 horses the diagnosis was made using low field MRI (retrospective evaluation of the radiographs after the MRI revealed ill‐defined radiolucencies of the PSBs in 4 of these horses). The horses ranged in age from 3 to 12 years, and the affected limbs included 3 forelimbs and 4 hindlimbs. The onset of lameness was reported to be sudden in 6 horses and insidious in one, and the duration of lameness at the time of MRI ranged from 0.3 to 11 months. The degree of lameness in the 6 horses with sudden‐onset lameness was moderate to severe. Pain on flexion of the affected metacarpo(tarso)phalangeal (fetlock) joint or exacerbation of the degree of lameness following fetlock flexion was recorded in 4 of the 7 horses. The MRI findings in all cases included a focal high signal intensity lesion (all magnetic resonance sequences) at various locations in one PSB. Both septic and nonseptic aetiologies were identified. Four of the 7 horses were subjected to euthanasia due to persistent lameness, one remained chronically lame and only 2 were able to return to their previous level of exercise.     

Effects of plant species on microbial biomass phosphorus and phosphatase activity in a range of grassland soils

Soil P transformations are primarily mediated by plant root and soil microbial activity. A short-term (40 weeks) glasshouse experiment with 15 grassland soils collected from around New Zealand was conducted to examine the impacts of ryegrass (Lolium perenne) and radiata pine (Pinus radiata) on soil microbial properties and microbiological processes involved in P dynamics. Results showed that the effect of plant species on soil microbial parameters varied greatly with soil type. Concentrations of microbial biomass C and soil respiration were significantly greater in six out of 15 soils under radiata pine compared with ryegrass, while there were no significant effects of plant species on these parameters in the remaining soils. However, microbial biomass P (MBP) was significantly lower in six soils under radiata pine, while there were no significant effects of plant species on MBP in the remaining soils. The latter indicated that P was released from the microbial biomass in response to greater P demand by radiata pine. Levels of water soluble organic C were significantly greater in most soils under radiata pine, compared with ryegrass, which suggested that greater root exudation might have occurred under radiata pine. Activities of acid and alkaline phosphatase and phosphodiesterase were generally lower in most soils under radiata pine, compared with ryegrass. The findings of this study indicate that root exudation plays an important role in increased soil microbial activities, solubility of organic P and mineralization of organic P in soils under radiata pine.     

Mechanistic model for nitrous oxide emission via nitrification and denitrification

Seasonal and annual N₂O fluxes from urine-affected pasture were approximated with a mechanistic model based on Michaelis-Menten kinetics. The model combined the effects of soil nitrate-N, soil ammonium-N, soil temperature and soil moisture (all from the top 5cm) to calculate N₂O emissions from nitrification (F _nit ) and denitrification (F _den ), with total N₂O emission being the sum of the two (F _tot =F _nit +F _den ). Best results were obtained when different kinetic parameters were used for periods of constant soil moisture conditions and after heavy rainfalls when a rapid change of the soil moisture status occurred. Modelled N₂O emissions over a year were within the range of uncertainties of measured N₂O emissions. Results indicate that the spatial variability of N₂O emissions at times when all the model inupt variables were constant may be related to microorganism growth dynamics or enzyme production rates. Received: 2 October 1995