Animal Treading Research Articles

Field-scale management and environmental drivers of N2O emissions from pasture-based dairy systems

Emissions of N2O from two dairy farms with different grazing intensity responded non-linearly to increasing soil nitrate availability and total rainfall. Higher N2O emissions were observed immediately after grazing, due to the possible increased incidence of N deposition from animal excreta, increased soil compaction and low plant N uptake. The spatial distribution of N2O fluxes and soil nitrate contents reflected the effect of animal treading and excreta N deposition with N2O fluxes in the proximity of field gateways 11 times higher than the field average. Three years average annual N2O emissions were 6 times higher (9.3 ± 2.6 kg N2O-N ha−1 y−1) in the high grazing intensity farm than in the low grazing intensity farm (1.6 ± 0.2 kg N2O-N ha−1 y−1). This corresponded to 2% and 0.9% of the fertiliser N inputs lost as N2O for the high and low intensity farm, respectively. The GHG intensity (N2O emitted per kg of fat and protein corrected milk FPCM) for the intensive system was only almost two times higher than the non-intensive system (0.12 vs 0.08 kg CO2-eq per kg FPCM y−1 for the high and low intensity system, respectively). The high occurrence of N load hotspots near animal gateways in this study underlines the necessity to account for the spatial N variation in dairy grazing systems. Integrating the spatial management of N loads into improved farming practice has therefore significant scope to reduce N2O emissions and N losses from dairy grazing systems.

Soil‐Gas Diffusivity and Soil‐Moisture effects on N2O Emissions from Intact Pasture Soils

Grazed pastures are recognized as a dominant source of nitrous oxide (N2O), a highly potent greenhouse gas. Studies have examined soil physical controls on N2O emissions, including soil moisture status. Limited attempts to link N2O emissions with soil‐diffusivity (Dp/Do), using repacked soil cores, have shown peak N2O emissions to align with a relatively narrow window ofDp/Do, despite a relatively wide range in water‐filled pore space (WFPS), across a range of soil bulk densities. Such detailed studies have not been performed withintactsoil cores. We investigated the effects of soil‐water characteristic (SWC) andDp/Doon N2O emissions from intact soil samples, retrieved at three depths (0–5, 5–10, 10–15 cm) from three perennial pasture sites that received a KNO3solution (1800 mg, N mL−1). We observed distinct fingerprints of SWC andDp/Do, which showed clear effects of soil structure on diffusion‐controlled gas emissions. Depth‐wise variation in soil moisture diminished as the soil was subjected to higher matric potential (> ∼ ‐100 kPa). Variation inDp/Do, was more pronounced in the dry soil (> ∼ ‐1000 kPa), being largely constrained by soil moisture in wet soil (∼ ‐100 kPa) with little depth‐wise variation. Measured N2O fluxes peaked within narrow ranges of WFPS andDp/Do, 0.90–0.95 and 0.005–0.01, respectively. The value ofDp/Docan be determined using parametric models and presents a pasture management (e.g., irrigation, soil physical disturbance such as pasture renovation and animal treading)) tool to minimize N2O emissions: soilDp/Doshould be maintained above a range of 0.005–0.01 to minimize N2O emissions.Core IdeasPeak N2O fluxes fromintactsoil cores occurred when diffusivity ranged from 0.005–0.01This peak N2O flux diffusivity range was 0.005–0.01 regardless of soil or depth (0–15 cm)The diffusivity range for peak N2O flux equalled that observed inrepackedsoil coresDiffusivity values are readily determined and add to the suite of soil management tools

Tillage, compaction and wetting effects on NO3, N2O and N2 losses

Denitrification is sensitive to changes in soil physical properties that affect solute transport, air content and gas diffusion. Using lysimeters, containing intact soil from intensively tilled (IT) and no-tilled (NT) soil used to grow forage crops, we examined how simulated animal treading at different moisture contents (above and below field capacity; >FC and <FC respectively) affected losses of nitrous oxide (N2O), dinitrogen (N2) and nitrate (NO3). We applied 15N-labelled NO3 (250kg N ha–1) to the soil surface after treading (applied at 220 kPa to 40% of the soil surface), or to untrodden soil. Drainage occurred following weekly application of water over the experiment (two pore volumes over 84 days). Treading at >FC greatly increased denitrification, especially from IT soil and produced the greatest amount of N2 (64kg N ha–1), N2O (8.2kg N ha–1), as well as the lowest N2O to N2O+N2 ratio (0.08) and NO3 leaching (136kg N ha–1 below 30cm). In both the uncompacted or compacted soils <FC, emissions of N2O were greater (1.5–2.7% of N applied) and the N2O to N2O+N2 ratios were closer to 0.2 compared to compaction at >FC. Treading at <FC had minimal or no effect on denitrification compared to untrodden soil. Fluxes of N2 and N2O were strongly influenced by the weekly irrigation–drainage cycle. The N2 production and reduction in NO3 leaching were best correlated with increases in microporosity and reduced saturated hydraulic conductivity following treading. Although recovery of 15N was high (84.3%), the remainder of the balance was likely lost as either N2 or, of greater concern, as N2O. Practically, animal trampling on wet soils, especially when recently cultivated, should be avoided.

Changes in composition and functional soil properties in long-term no-till integrated crop-livestock system

Integrated Crop-Livestock Systems (ICLS) are an important alternative to winter fallow and increase the sustainability of production systems, by combining agricultural with livestock production. The hypothesis of this study was that load applied by animals in moderate grazing does not promote further soil structural degradation. The objective of this study was to demonstrate changes in soil structure, mechanical behavior, and water and air permeability caused by different intensities of grazing in ICLS. The experiment consisted of a 15-years old ICLS, managed with soybean Glycine max in the summer and black oat Avena strigosa + ryegrass Lolium multiflorum in winter with continuous grazing by beef cattle. The treatments consisted of different grazing intensities determined by sward height, namely 0.10 m (heavy grazing) and 0.30 m (moderate grazing), and a control (without grazing), in an experimental design of randomized blocks with three replications. Undisturbed soil samples were collected in core samplers in the 0–0.05, 0.05–0.10, and 0.10–0.20 m soil layers, in two evaluation times: (i) post soybean (immediately after soybean harvest, and before pasture sowing or animal grazing), and (ii) after grazing (immediately after withdrawing the animals from the area and before soybean sowing), respectively in April and November 2015. Soil bulk density, macroporosity, microporosity, air permeability, saturated hydraulic conductivity, precompression stress, compressibility coefficient, decompression coefficient, and cyclic compressibility index were determined. The results indicate grazing increases the compaction state of the soil surface mainly in the post grazing period by the direct effect of animal treading. However, there is a mitigation effect during the soybean cycle, evidencing the soil's regeneration capacity in ICLS, provided by intense biological activity, wetting-drying cycles, and decomposition of pasture roots that regenerate soil structure. Moderate grazing is a better option than intense grazing, but without soil improvements when compared to the non-grazed system.

Compaction influences N2O and N2 emissions from 15N-labeled synthetic urine in wet soils during successive saturation/drainage cycles

Nitrous oxide emitted from urine patches is a key source of agricultural greenhouse gas emissions. A better understanding of the complex soil environmental and biochemical regulation of urine-N transformations in wet soils is needed to predict N2O emissions from grazing and also to develop targeted mitigation technologies. Soil aeration, gas diffusion and drainage are key factors regulating N transformations and are affected by compaction during grazing. To understand how soil compaction from animal treading influences N transformations of urine in wet soils, we applied pressures of 0, 220 and 400 kPa to repacked soil cores, followed by 15N-labeled synthetic urine, and then subjected the cores to three successive saturation–drainage cycles on tension tables from 0 to 10 kPa.Compaction had a relatively small effect on soil bulk density (increasing from 0.81 to 0.88 Mg m−3), but strongly affected the pore size distribution. Compaction reduced both total soil porosity and macroporosity. It also affected the pore size distribution, principally by decreasing the proportion of 30–60 μm and 60–100 μm pores and increasing the proportion of micropores (<30 μm).Rates of urine-N transformations, emissions of N2 and N2O, and the N2O to N2 ratio were affected by the saturation/drainage cycles and degree of compaction. During the first saturation–drainage cycle, production of both N2O and N2 was low (<0.4 mg N m−2 h−1), probably because of anaerobic conditions inhibiting nitrification. In the second saturation/drainage cycle, the predominant product was N2 at all compaction rates. By the third cycle, with increasing availability of mineral-N substrates, N2O was the dominant product in the uncompacted (max = 4.70 mg N m−2 h−1) and 220 kPa compacted soils (max = 7.65 mg N m−2 h−1) with lower amounts of N2 produced, while N2 was produced in similar quantities to N2O (max = 3.11 mg N m−2 h−1) in the 400 kPa compacted soil. Reduced macroporosity in the most compacted soil contributed to more sustained N2 and N2O production as the soils drained. In addition, compaction affected the rate of change of soil pH and DOC, both of which affected the N2O to N2 ratio.Denitrification during drainage and re-saturation may make a large contribution to soil N2O emissions. Improving soil drainage and adopting grazing management practices that avoid soil compaction while increasing macroporosity will reduce total N2O and N2 emissions.

Sources of N2O–N following simulated animal treading of ungrazed pastures

It has been previously hypothesised that the treading of pastures by grazing animals can increase nitrous oxide (N2O) emissions as the result of reduced plant N uptake. In addition, grazing animals urinate and defecate on to soils which can also increase the N2O emissions. To avoid these additional N inputs, a treading machine was used in two field experiments where the pre-grazing dry matter (DM) was present or removed to test the above hypothesis. The N2O emissions were measured for 47 and 30 days afterwards, respectively. The soil nitrate (NO3−–N) pool was 15N labelled prior to treading in Experiment 2. Treading induced greater N2O emissions and reduced herbage DM yields (by 31%–41%) and soil NO3−–N concentrations when soil gravimetric water contents ranged from 0.45 to 0.63 g water/g soil. A comparison of treading in the presence and absence of pre-grazing DM showed that reduced plant N uptake did not induce greater N2O emissions. Rather, the 15N labelling of the NO3−–N pool indicated this pool contributed to the N2O emissions under treading. In addition, 15N labelling showed other soil–N pools became available as a consequence of either, (1) treading inducing soil perturbation and releasing N from the soil organic matter–N and/or plant root–N pools, or (2) as a result of simulated grazing causing the release of plant root–N. Soil water soluble carbon (C) also increased under treading in the absence of pasture, supporting the theory that organic–N was released from either the soil organic matter (OM) or plant root pools. Further research should investigate the effect of treading on the turnover and contribution of organic–N pools (roots, OM) in pasture soils in order to more fully understand the contributions these make to background N2O emissions and effects on N and C cycling in pasture soils.

Spring and autumn animal treading effects on pre-grazing herbage mass and tiller density on two contrasting pasture types in Ireland

A perennial ryegrass (Lolium perenne L.)-dominated sward on a well-drained soil (Experiment 1) and a creeping bent (Agrostis stolonifera L.)-dominated sward on a poorly drained soil (Experiment 2) were subjected to four treading treatments: control (C, no damage), light damage (L), moderate damage (M) or severe damage (S) to quantify the effects on herbage dry-matter (DM) production and tiller density. In Experiment 1, treading damage was imposed in spring. In Experiment 2, one-third of the site was damaged in autumn, one-third in spring and one-third in both spring and autumn. Both sites were rotationally grazed after treading treatments. Pre-grazing herbage mass was measured eight times in Experiment 1 and seven times in Experiment 2 on each plot, and tiller density was assessed four times in each experiment. In Experiment 1, pre-grazing herbage mass was reduced by 30% in S plots at the first harvest after damage, but cumulative pre-grazing herbage DM production was not different between treatments (12·7 t DM ha−1). In Experiment 2, annual cumulative pre-grazing herbage mass was reduced by between 14 and 49%, depending on intensity of treading damage event and season when damage occurred. Tiller density was not affected by treatment in either experiment. A perennial ryegrass-dominated sward on a well-drained soil was resilient to heavy treading damage. A creeping bent-dominated sward on poorly drained soil requires a more careful grazing management approach to avoid major losses in cumulative pre-grazing herbage mass production during wet weather grazing events.

Short-term effects of different pasture improvement treatments on the physical quality of an andisol

Abstract The improvement of degraded pastures is important for increasing pasture herbage mass and animal production in southern Chile. While research has normally focused on how animal treading affects soil compaction, no major work has yet been done to define the impact of pasture improvement managements on soil physical functions, particularly when the initial situation is a degraded pasture. Thus, the aim of this study is to define the short-term effects of different pasture improvement managements on the physical quality and related processes of a volcanic ash soil. Four treatments were defined: two tilled, fertilized and seeded plots (T1 and T2), one non-tilled and non-fertilized plot (T3) and one non-tilled and fertilized plot (T4), all of which were compared to the initial situation of a highly degraded pasture (IS). Undisturbed soil samples were collected (1-10 cm) and the volumetric water content and temperature was continuously monitored at the 10 cm depth. The short-term effects of pasture improvement managements on soil physical quality and related processes differed in relation to the treatment method. As compared to the non-tilled plots, the aggregate destruction after tillage induced an increase in the water holding capacity, but a decrease in the air capacity and pore-continuity values due to grazing. The physical quality assessed by the S-Index reflected a good soil structural quality (S > 0.035). The tilled plots presented a higher S-Index as compared to the non-tilled plots, which is related to a slightly lower mechanical strength and larger water holding capacity. The latter also increased due to tillage and was positively correlated to pasture yields during the first intensive soil drying. Soil temperature differences between treatments were assessed and can be related to the higher water contents in the tilled plots and the presence of broad-leaf species in the non-tilled pastures. Finally, in order to properly understand how the implementation of pasture improvement managements affects the soil physical quality and related processes, long-term studies are required.

Anaerobic oxidation of methane in grassland soils used for cattle husbandry

Abstract. While the importance of anaerobic methane oxidation has been reported for marine ecosystems, the role of this process in soils is still questionable. Grasslands used as pastures for cattle overwintering show an increase in anaerobic soil micro-sites caused by animal treading and excrement deposition. Therefore, anaerobic potential methane oxidation activity of severely impacted soil from a cattle winter pasture was investigated in an incubation experiment under anaerobic conditions using 13C-labelled methane. We were able to detect a high microbial activity utilizing CH4 as nutrient source shown by the respiration of 13CO2. Measurements of possible terminal electron acceptors for anaerobic oxidation of methane were carried out. Soil sulfate concentrations were too low to explain the oxidation of the amount of methane added, but enough nitrate and iron(III) were detected. However, only nitrate was consumed during the experiment. 13C-PLFA analyses clearly showed the utilization of CH4 as nutrient source mainly by organisms harbouring 16:1ω7 PLFAs. These lipids were also found as most 13C-enriched fatty acids by Raghoebarsing et al. (2006) after addition of 13CH4 to an enrichment culture coupling denitrification of nitrate to anaerobic oxidation of methane. This might be an indication for anaerobic oxidation of methane by relatives of "Candidatus Methylomirabilis oxyfera" in the investigated grassland soil under the conditions of the incubation experiment.

The effects of dairy cow weight on selected soil physical properties indicative of compaction

AbstractThe effect of treading by dairy cows of three different weights on soil physical properties was investigated under different soil moisture deficit (SMD) treatments in the south of Ireland. SMD was used as a readily predicable surrogate for volumetric water content. Animal treading in grassland ecosystems is known to affect soil and vegetation properties, which can influence agricultural system productivity. Treading action can result in reduced soil water infiltration and increased runoff. In Ireland short winter housing and early spring turnout are key elements of low cost grass based production. However, there is potential for soil damage as a consequence of animal treading during early spring and late autumn. This study shows that SMD is the main factor affecting changes in bulk density (BD), soil shear strength, penetration resistance (PR) and total porosity. At high SMD (dry), soil was less sensitive to trampling damage than at low SMD (wet). At SMD 0 mm, BD increased by 6.1% post trampling, whereas it only increased by 3.1, 4.0 and 0.5% at SMD 11, 14, and 29 mm, respectively. Average soil BD was 2.3% greater immediately post trampling, and 4.6% greater in the hoof marks. PR was significantly greater following trampling by the heavy weight cow compared with the light or medium weight cow. There was no significant effect of cow weight on soil water content or soil BD. The results indicate that forecasted SMD can be used as a management input for rotational grazing systems to protect soil quality.

Effects of tillage, simulated cattle grazing and soil moisture on N2O emissions from a winter forage crop

Nitrous oxide (N2O) emissions to the atmosphere from grazed pasture can be high, especially from urine-affected areas. When pastoral soils are damaged by animal treading, N2O emissions may increase. In New Zealand, autumn-sown winter forage crops are often grown as a break-crop prior to re-sowing pasture. When these crops are grazed in situ over winter (as is common in New Zealand) there is high risk of soil damage from animal treading as soil moisture contents are often high at this time of year. Moreover, the risk of soil damage during grazing increases when intensive tillage practices are used to establish these forage crops. Consequently, winter grazed forage crops may be an important source of N2O emissions from intensive pastoral farming systems, and these emissions may be affected by the type of tillage used to establish them. We conducted a replicated field experiment to measure the effects of simulated cattle grazing (mowing followed by simulated treading and the application of synthetic urine) at three soil moisture contents ( field capacity) on measured N2O emissions from soil under an autumn (March) sown winter forage crop (triticale) established with three levels of tillage intensity: (a) intensive, IT, (b) minimum, MT, or (c) no tillage, NT. In all treatments, bulk density in the top 7.5 cm of the soil was unaffected by treading when simulated grazing occurred at field capacity, and by 10% in the MT plots trodden at > field capacity. Treading did not significantly increase the bulk density in the NT plots. Emissions of N2O from the tillage treatments decreased in the order IT > MT > NT. N2O emissions were greatest from plots that were trodden at > field capacity and least from plots trodden at field capacity. The N2O emission from urine-amended NT plots that were trodden at < field capacity was 2.0 kg ha−1 over 90 days (0.25% of the total urine N applied). Decreasing the intensity of tillage used to establish crops and restricting grazing when soils are wet are two of the most effective ways to minimise the risk of high N2O emissions from grazed winter forage crops.

Pasture yield and soil physical property responses to soil compaction from treading and grazing—a review

This paper reviews animal treading and the associated effects on soil physical properties and pasture productivity from treading-induced soil compaction and pugging. Response curve relationships between soil physical properties (e.g. macroporosity, air-filled porosity, bulk density) and pasture and crop yield are reviewed. Optimum soil macroporosity for maximum pasture and crop yield ranges from 6 to 17% v/v, but there is a paucity of yield response curves for pastoral systems, particularly critical or optimum values of soil physical properties. There is little information available on the effects of cattle treading on soil physical properties and consequently pasture yield in seasons when soil pugging and poaching is minimised. Such information is needed to provide practical and rigorously tested decision support tools for land managers during grazing seasons. Knowledge of yield response curves, and critical or optimum values of soil physical properties for field pasture-based grazing systems, is required for improved farm-system production and economic decision support.

Atributos físicos do solo e rendimento de soja em sistema plantio direto em integração lavoura-pecuária com diferentes pressões de pastejo

A integração da atividade de lavoura com a de pecuária no sistema plantio direto (SPD) em áreas que permanecem apenas com culturas de cobertura no inverno pode se tornar uma opção de renda para os produtores de grãos no verão, no Sul do Brasil. No entanto, muitos deles relutam em adotar esse sistema de integração, em razão dos possíveis efeitos negativos do pisoteio sobre atributos do solo, principalmente aqueles relacionados à compactação. Este trabalho foi realizado visando determinar as alterações promovidas pelo pisoteio animal sobre atributos físicos do solo e verificar se as alterações resultantes desse pisoteio têm influência no estabelecimento e no rendimento da cultura da soja. O experimento foi realizado em Latossolo Vermelho distroférrico, com pastagem de aveia-preta + azevém, manejada em diferentes alturas da pastagem (10, 20, 30 e 40 cm), e uma área não-pastejada. Após o ciclo de pastejo, não houve alterações na densidade, na porosidade e na compressibilidade, independentemente da altura da pastagem. No entanto, a densidade e a compressibilidade foram maiores e a porosidade menor nas áreas pastejadas, em relação à não-pastejada. A população inicial de plantas e o rendimento de soja não foram afetados pelas alterações nos atributos físicos do solo.

Effects of cattle husbandry on abundance and activity of methanogenic archaea in upland soils

In the present study, we tested the hypothesis that animal treading associated with a high input of organic matter would favour methanogenesis in soils used as overwintering pasture. Hence, methane emissions and methanogen populations were examined at sections with different degree of cattle impact in a Farm in South Bohemia, Czech Republic. In spring, methane emission positively corresponded to the gradient of animal impact. Applying phospholipid etherlipid analysis, the highest archaeal biomass was found in section severe impact (SI), followed by moderate impact (MI) and no impact. The same trend was observed for the methanogens as showed by real-time quantitative PCR analyses of methyl coenzyme M reductase (mcrA) genes. The detection of monounsaturated isoprenoid side chain hydrocarbons (i20:1) indicated the presence of acetoclastic methanogens in the cattle-impacted sites. This result was corroborated by the phylogenetic analysis of mcrA gene sequences obtained from section SI, which showed that 33% of the analysed clones belonged to the genus Methanosarcina. The majority of the sequenced clones (41%) showed close affiliations with uncultured rumen archaeons. This leads to the assumption that a substantial part of the methanogenic community in plot SI derived from the grazing cattle itself. Compared to the spring sampling, in autumn, a significant reduction in archaeal biomass and number of copies of mcrA genes was observed mainly for section MI. It can be concluded that after 5 months without cattle impact, the severely impact section maintained its methane production potential, whereas the methane production potential under moderate impact returned to background values.

Modelling to analyse the impacts of animal treading effects on soil infiltration

AbstractAnimal treading can change soil physical properties, and thus is an important factor in hydrological modelling. We investigated the impacts of animal treading on infiltration by using a series of rainfall simulation experiments at Whatawhata Research Center, Waikato, New Zealand. The study identified significant variables for estimating soil steady‐state infiltration at a micro‐site (0·5 m2) and fitted the Green and Ampt equation by modifying or including variables for soil and water parameters and animal activities on grazing paddocks. A regression function for estimating steady‐state infiltration rate was created for each of four scenarios: between tracks (inter‐track), track, easy slope with ash soil, and easy slope with clay soil. Significant variables included the number of days after treading, antecedent soil moisture, field capacity, percentage of bare ground, bulk density, and the high degree of soil damage (damage not compacted). Regression models explained more than 71% of the variance in steady‐state infiltration for three scenarios, but only 53% for the easy slope with clay soil. The remodified Green and Ampt equation provided satisfactory estimation of infiltration for all scenarios (accuracy &gt; 80%), and thus enables us to use the modified model for Waikato hill country pastures of different topography, soil physical condition, season and grazing management. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Natural recovery of soil physical properties from treading damage of pastoral soils in New Zealand and Australia: A review

This paper reviews natural recovery of deteriorated soil physical condition under animal treading in grazed pastoral systems, particularly in New Zealand and Australia. While much research has focused on soil compaction and physical deterioration from animal treading, there has been much less focus on natural recovery of soil physical properties after treading damage has occurred. Natural recovery of deteriorated soil physical condition improves soil properties including hydraulic conductivity, macropore volume and bulk density. Soil physical condition naturally recovers when animals are partially or completely excluded from pasture, although improvements are likely to be limited to no deeper than 10-15 cm soil depth, under common grazing practice or animal exclusion. However, the physical deterioration and natural recovery processes are linked in a cycle. Natural recovery of soil physical condition in this cycle is therefore important when evaluating management practices affecting soil deterioration on-farm, field trial interpretation, and ungrazed riparian zone soil structure. This review also discusses directions of future research to enhance soil management, including quantifying and evaluating soil physical deterioration and natural recovery. Several knowledge gaps relating to pastoral agriculture in New Zealand and Australia, particularly under rotational grazing management on intensive dairy farms are discussed. Further research is required into the consequences of farm management practices that enhance natural rejuvenation of degraded soils. Consequently, integration of both deterioration and natural recovery of soil physical condition in the soil compaction and recovery cycle is needed to improve farm system evaluation and management. Natural recovery of soil condition when animals are partially or fully excluded from grazing is therefore important in management and modelling of pastoral and ungrazed riparian soil, and subsequent environmental impacts.

Animal treading during wet soil conditions reduces N2 fixation in mixed clover-grass pasture

A field experiment was carried out over 12 months to determine the effect of animal treading on N2 fixation in a mixed white clover-ryegrass pasture. The experimental site was defoliated by mowing for the duration of the study. A single treading event of moderate or severe pugging intensity was initiated in plots during wet spring conditions by using dairy cows at varying stocking rates (4.5 cows 100 m−2 for 1.5 or 2.5 h, respectively). Inputs of dung and urine onto the plots was avoided by overnight housing of the cows and interception of excreta during the pugging event. Soil air-filled porosity decreased from 21% in the non-pugged control to 15–16% in pugged treatments by day 3. Bulk density of soil was not significantly affected by pugging. Soil inorganic N concentration increased in pugged treatments, and was 4-fold greater on day 28 in severely pugged plots compared to non-pugged plots. White clover plant density and plant size was markedly lower in pugged treatments (up to 85% and 72% reduction, respectively under severe pugging). White clover growth was most affected during the first 156 days after pugging (up to 90% decrease under severe pugging), leading to an annual clover dry matter production loss of 9% and 52%, respectively. The proportion of clover N derived from atmospheric N2 (%Ndfa; estimated by 15N dilution) was initially reduced (to a lower limit of 43%) by severe pugging (days 28–71) before recovery to control levels (90%) by day 91. Annual N2 fixation in clover herbage decreased significantly from 76 kg N ha−1 yr−1 in the non-pugged control, to 66 and 36 kg N ha−1 yr−1 under moderate and severe pugging, respectively. Most of this difference was evident within the first 156 days after pugging. Our data indicates that the major loss in fixed N2 input under pugging was due to reduced clover growth and production resulting from pugging damage and loss of residual white clover biomass by hoof action.

Animal treading stimulates denitrification in soil under pasture

The effects of animal treading on denitrification in a mixed ryegrass-clover pasture were studied. A single treading event of moderate or severe intensity was applied in plots during spring by using dairy cows at varying stocking rates (4.5 cows 100 m −2 for 1.5 or 2.5 h, respectively). Treading caused a significant short-term 21 days) increase in denitrification. Denitrification rates reached a maximum of 52 g N 2O-N ha −1 day −1 at 8 days after severe treading compared to 2.3 g N 2O-N ha −1 day −1 under nil treading. Thereafter, denitrification rates declined, and were similar to non-trodden control plots after 28 days. Soil aeration, was significantly reduced by treading as expressed by water-filled porosity. In addition, soil NH 4 +-N and NO 3 −-N concentrations were also increased by treading. We propose that the underlying processes involved in increasing denitrification under treading were two-fold. Firstly, treading caused a temporary (e.g. 3 days after treading) reduction in soil aeration through soil physical damage, and secondly, reduced soil N utilisation prompted by reduced plant growth led to increased soil NH 4 +-N and NO 3 −-N availability. This study shows that treading, without the influence of other grazing animal factors (e.g. excretion), can cause a large short-term stimulation of denitrification in grass-clover pastures.

Nitrous oxide fluxes in soil as influenced by compaction

In grazed-pastures animal treading is an important cause of soil compaction. Soil compaction influences the denitrification rate as well as the amounts of nitrous oxide (N2O) and dinitrogen (N2) production in the soil mainly through its impact on soil moisture conditions and porosity. A field experiment was undertaken to determine the loss of nitrogen (N) through N2O emission from different N sources as affected by a compaction treatment. Experiment comprised of two main treatments (uncompacted and compacted) to which four N sources (cattle urine, potassium nitrate, ammonium sulphate and urea at the rate of 600kg N/ha) and a control (water only) were applied, each replicated four times. Compaction was obtained through driving close parallel tracks by the wheels of the vehicle. Var ious soil properties related to soil compaction (b ulk density, water filled pore space (WFPS), oxygen diffusion rate (ODR)) were measured. The N2O fluxes were measured for 3 months (between 10th September and 4th December, 2002) using closed chamber technique. Overall, the bulk density of compacted soil was 12.8 % higher than that of the uncompacted soil. Results suggest that maximum compaction occurred in the top 0-2 cm layer. Soil matric potential measured at the 0-5 cm soil depth suggests that uncompacted soil had lower water content, except at low matric suctions, than compacted soil. The ODR in uncompacted soil was 79.3% higher than that in the compacted soil. Compaction caused a seven fold increase in N2O emission. Nitrate source was the most effective of all the treatments in causing potential emission. Under compacted soil 9.87% of the total N applied in form of nitrate was emitted whereas under uncompacted soil this loss was only 0.54%. N2O loss was found to decrease progressively from the time of application of N treatments. Total N2O emission for the three month experimental period ranged from 2.62 to 61.74 kg N2O-N/ha for compacted soil and 1.12 to 4.37 kg N2O-N/ha for uncompacted soil. Keywords: compaction, grazed pastures, Nfertilisers, nitrous oxide emissions, urine-N

A mechanical hoof for simulating animal treading under controlled conditions

Treading by grazing animals can have a significant adverse effect on soil properties and plant growth, particularly under wet soil conditions. It may also affect water and nutrient movement over and through soil. It is difficult to assess treading with live animals under controlled conditions, when the field plots are small or where there are instruments installed. This paper describes a mechanical cow hoof device which can overcome these difficulties. The mechanical hoof consists of an artificial hoof made of mild steel mounted onto a compressed air ram, which, in turn, is driven by an air compressor system. Treading pressure, treading speed, duration of hoof‐soil contact, and intensity and location of treading can all be controlled. Tests of the mechanical hoof in a simple field plot experiment showed that, over a 5–8‐month period, treading increased bulk density (from 1.18 to 1.29 Mg m‐3), decreased macroporosity (diam. > 30 μm) (from 16.5% to 10% v/v) in the top 10 cm soil, and reduced pasture yield (from 100 to 91% of relative dry matter yield). The mechanical hoof device can serve as a useful tool for studying the effect of treading on soil quality indicators, water and solute movement, and plant production under controlled conditions.