Return Of Excreta Research Articles

Nitrous oxide emissions from soils due to inputs of nitrogen from excreta return by livestock on grazed grassland in the U.K.

Nitrous oxide (N 2O) emissions from different soils under grass were measured after treatment with cow dung and urine in field trials conducted during two separate seasons and in laboratory incubation experiments. N 2O emission rates were much higher during autumn-winter than during spring-summer, and in the case of well-drained soil were substantial for both excreta types (207 mg N 2ON kg −1 of deposited dung and 197 mg N 2ON kg −1 of urine in autumn-winter). The corresponding data for poorly-drained soil were 0.2 mg (dung) and 148 mg (urine). Emissions continued over much longer periods (∼ 60 days) from sandy and stony loams than from a silty clay loam (∼ 30 days) under both field and laboratory conditions, and were not solely dependent on soil NO 3 − or NH 4 + status but also related to other factors including soil moisture, rate of plant growth and carbon availability. Results suggest that N 2O production occurred during both nitrification and denitrification processes. Emission rates of up to ∼ 1590 μg N 2ON h −1 m −2 occurred in the field, while small rates of deposition to the soil were occasionally observed. Under laboratory conditions, similar treatments produced large emissions from loam soils having pH of 4.5–6.5 and zero emissions from a peat soil with pH of 3.8. The ratio of nitrogen released as N 2O to the amount of N excreted by the livestock varied from ∼ 0% (summer) to 0.8–2.3% (winter), consistent with loss rates observed for mineral fertilizers.

Sulphur cycling and its implications on sulphur fertilizer requirements of grazed grassland ecosystems

The need for assessing sulphur (S) requirements in intensively-managed grassland ecosystems is becoming increasingly important because of the worldwide emphasis on sustaining non-renewable fertilizer resources and reducing atmospheric S emission. This paper reviews major factors affecting S cycling and efficient utilization of S fertilizers and soil S reserves in grazed grasslands. Models used for quantitatively describing S cycling in these ecosystems are also discussed. The review shows that most (95%) of the total soil S in intensively managed grazed grasslands is present as organic S and the remainder is in readily soluble and adsorbed S. Soil organic S that has been accumulated with time in grazed grasslands receiving regular S fertilizer applications can provide a significant amount of S for plant S nutrition. Carbon-bonded S is the major (50–85%) form of soil organic S, owing to the regular return of animal excreta and plant litter. Grazing animals have a major effect on the amount and rate of S cycling as most (87–90%) of S ingested by grazing animals is returned to soils as excreta. Excretal S is either recycled or subjected to leaching losses and transferred to stock camps. Leaching losses are expected to be higher in camp than in non-camp areas as camp soils contain higher soil organic and inorganic S fractions. Likewise more soil organic S is mineralized in camp than non-camp soils. This may provide S exceeding that taken up by plants and hence could lead to substantial S leaching losses in camp areas. This review identifies the lack of quantitative data on: (1) effects of soil microbial activity and plant S uptake on the fate of applied S fertilizers and excretal S in grazed grassland; (2) rates of soil S transformations as influenced by management and seasonal variables; (3) the contribution of soil organic S to plant S uptake and leaching losses in camp and non-camp areas of grazed grasslands. This scarcity of quantitative data is a major constraint in the development of dynamic S cycling models for predicting rates of S cycling and for estimating plant S requirements in grassland ecosystems where S cycling has not attained a steady state. When a steady state exists, mass-balance S models are more reliable than the traditional practice of using only soil or plant S tests for assessing long-term annual plant S rerequirements.

Micrometeorological studies of ammonia emission from sheep grazed swards

SUMMARYLosses of ammonia (NH3) through volatilization from the excretal returns from sheep grazing a range of swards in S.E. England were determined over two seasons. Four swards were examined: grass + 420 or 0 kg N/ha per year, grass/white clover and clover monoculture. These were grazed continuously to sustain a constant sward height of 6 cm. The patterns of NH3-N concentration above the sward changed with treatment and throughout the season: there were, on occasion, irregularities in the concentration profiles which may have been due to differential behaviour of paniculate and gaseous forms. Significant losses of NH3 occurred on all treatments, although on some occasions the low input systems appeared to be acting as sinks rather than sources of NH3. There were trends for the losses to be greater during the middle of the grazing season. In contrast to previous studies there was little relationship between seasonal N losses and changes/differences in dietary N content. The overall losses, whether on a per unit area or per animal basis, were generally in the order, clover > grass + 420 kg N > grass+ 0 N > grass/clover. Mean annual losses from grass + 420kg N and grass/clover were 94 and 1·2 kg N/ha, respectively. For a comparable fertilizer N treatment, losses were lower than previously found with swards which were rotationally grazed by cattle. The present losses, although dependent upon level of N input, whether from fertilizer or from biological fixation, were relatively small, ranging from 05 to 11·2 kg N/ha per year, and represented small proportions of either the N input to the system or the excretal returns from the animals.

Effects of grazing and nitrogen fertiliser on the soil microbial biomass under permanent pasture

AbstractCarbon and nitrogen in the soil microbial biomass were measured on eight occasions during a grassland production season, under swards of perennial ryegrass receiving 210 or 420 kg N ha−1 per year or of ryegrass/white clover receiving no fertiliser N. The swards were either cut or grazed at monthly intervals. Soil microbial biomass C increased under all treatments in late April before declining until late July and rising slowly towards the end of the season. Values for microbial C under cutting and grazing were not significantly different but were usually larger under grass/clover than under grass. In contrast, the smallest values for soil microbial biomass N were recorded in late April. Larger N values were again recorded under grass/clover, and although values were nearly always smaller under grazing than under the corresponding cut treatment the differences were not significant.Soil biomass N comprised a large reservoir of mobile N, and at any one time contained 11, 3 and 5 times more N than was present in the mineral N component of the soil, the standing crop or excretal returns, respectively. It did not appear to be responsive, within a season, to the considerable returns of C and N from grazing animals or to N fertiliser management.

The effects of grazing with and without excretal returns on the accumulation of nitrogen by ryegrass in a continuously grazed upland sward

AbstractRates of N accumulation were studied on sheep grazed grass swards maintained at a constant height of 5 cm for two growing seasons (1985 and 1986) and receiving no N fertilizer using a tiller tissue turnover technique. Grazing with normal excretal returns resulted in an 85‐105% increase in the estimated rates of N accumulation by laminae compared with similarly grazed swards where excretal returns were prevented. Generally, increases in tiller numbers in plots receiving excreta were mainly responsible for the increased rates of N accumulation, rather than increased rates of N accumulation per tiller. Rates of N remobilization from laminae and senescence (flux of N to standing‐dead litter pool) per tiller, and rates of leaf extension and leaf appearance/disappearance were unaffected by excretal returns, in urine patches increased tiller numbers and increased rates of accumulation per tiller both resulted in greater estimates of N accumulation compared with tillers not visibly affected by excreta. However, at any one time only about 11% of the plot area was affected by excreta and increases in N accumulation in excreta patches could not account for the overall plot increases in rates of N accumulation.The increased tillering in plots receiving excreta may have increased exploitation of the soil N. With an average stocking rate of 15 sheep ha−1, soil nitrate‐N, but not total N (Kjeldahl) nor bulk density, was increased during the winter of the second year as a result of excretal returns.

Effects of November–April grazing pressure on hill country pastures 3. Interrelationship with soil and pasture variation

Abstract Variations in soil moisture content, nutrient levels, and temperature were measured for a range of micro-sites located on a steep, north-facing hillside. Species distribution and plant responses to changing moisture conditions and different grazing treatments were related to these physical conditions. Soil nutrient levels (organic carbon; total, inorganic, and mineralised nitrogen; Olsen phosphorus; potassium) were highest in camp/old track areas reflecting nutrient transfer by grazing animals. Variation in nutrient level between other flat and sloping areas was low. Soil moisture holding capacities were similar for most areas, but sloping areas were consistently drier in the surface horizon (0–50 mm) because of less effective re-wetting compared with flatter areas. Maximum soil surface temperatures of 45–50°C were reached on clear days where low pasture cover existed on sloping areas. The effects of grazing treatments on ryegrass and browntop tiller number, white clover leaf number, and seedling establishment were similar across a wide range of micro-sites. However, pasture species content varied between micro-sites: ryegrass was dominant on camps and tracks; browntop increased with steepness of slope; white clover peaked on rolling and easy sloping areas; grass seedlings were most numerous on camps and tracks; and legume seedlings were most numerous on steeper slopes. Pasture type would appear to be determined more by nutrient fluxes (e.g., mineralisation rate, excreta return) and summer rewetting of the soil surface than by nutrient pool size and inherent water-holding capacity of the soil.

The comparative effects of defoliation, treading and excreta on a Lolium perenne-Trifolium repens pasture grazed by sheep

SUMMARYThe effects of treading and the return of excreta on a Lolium perenne-Trifolium repens sward defoliated by sheep set-stccked at high and low stocking rates were examined. Sward performance was measured inside ‘graze-through’ cages which allowed defoliation without treading and excreta return, and outside where sheep grazed either fitted with harness to prevent the return of excreta or unharnessed to allow the normal return of excreta. Live-weight gain was measured from excreta return and non-return swards. The treatments imposed had large effects on herbage growth and botanical composition.At a stocking rate of 25 yearling wethers/ha, sheep excreted about 1·1 kg N/ha/day, which increased soil N and led to an increase in herbage growth of about 26 %. The return of excreta increased ryegrass tiller density and this was partly responsible for a 26% reduction in the proportion of clover in the sward; the weight of clover was 13% loss where excreta were returned, and on this treatment stolon length at the end of the experiment was similar to that at the beginning. Doubling the stocking rate increased the N returned via excreta to about 1·3 kg N/ha/day, and this increased herbage growth by 53% but suppressed the proportion of clover by 21%, though not the weight of clover. Clover stolon length decreased during the experiment at this stocking rate, both with and without the return of excreta. Sheep live-weight change benefited from the stimulus to herbage growth where excreta were returned at the high stocking rate, but not at the low stocking rate.Treading by 25 sheep/ha increased soil compaction but had no significant (P > 0·05) overall effect on herbage growth and botanical composition. However, treading by double the number of grazing animals significantly reduced herbage growth by 10%, plant root weight by 47% and the proportion of clover in the sward by 11%.Differences in sward performance between stocking rates were due more to the difference in defoliation intensity between these stocking rates than to either treading or the return of excreta.

The Effects of Sheep Stocking Level on Invertebrate Abundance, Biomass and Energy Utilization in a Temperate, Sown Grassland

SUMMARY (1) Sixteen groups of large invertebrates were sampled at 42-day intervals over 3 yr from six grassland sites. The sites were grazed continuously with ten, twenty and thirty sheep per ha. Invertebrate collections were made from the herbage and litter and soil cored to 25 cm. (2) Stocking intensity affected the abundance and biomass of all invertebrates. The Hymenoptera (ant) group increased in numbers and biomass with each increase in sheep stocking; all other invertebrates were reduced substantially at the highest stocking level. Scarabaeid larvae and large Oligochaeta showed peak values for abundance and biomass at the intermediate stocking level. The abundance and biomass of the remaining groups were reduced with each increase in sheep numbers. (3) Base levels of invertebrate energy expenditure were determined from field censuses of abundance and mean fresh biomass, site measurement of habitat temperature and published respirometry data. A value of 0-50 for net tissue growth efficiency was derived from published studies and used to calculate additional heat production associated with growth. Data on assimilation efficiency and ratios of production to respiration were taken from the literature. (4) Invertebrate energy expenditure was apportioned between the activities of herbivory, decomposition and predation. Increases in sheep numbers resulted in a comparative decline in the activity of small decomposers. Scarabaeid larvae were the main invertebrate herbivores and large Oligochaeta and Collembola were the major decomposers. (5) Sheep were the dominant herbivores. Changes in energy expenditure with increased stocking level indicated that the sheep flocks were better able to derive energy from grazing than the invertebrate herbivores. There was no evidence that invertebrates reduced the wool production or biomass of the sheep at the low and intermediate stocking levels. (6) Approximate energy budgets were calculated for the total invertebrate communities. Energy values for the net annual residues of invertebrate excreta and corpses declined with stocking levels but the values exceeded the excretal returns from the sheep at the low and intermediate rates.

THE SIMULATION OF ANIMAL RETURNS IN GRASSLAND EXPERIMENTATION

ABSTRACTAn experiment was carried out on a grass/white‐clover sward at North Wyke to evaluate the use of mixtures of inorganic and organic nutrient sources to simulate the nutrient effect of animal excreta, both with and without overall PK fertilizer. Grazing with sheep and the return of excreta from caged sheep both increased herbage yields, as did artificial return treatments. Artificial return treatments giving 75% of the nutrient level returned by excreta gave yields comparable with grazing. The effect of the simulated return treatments was not influenced by PK application. Grazing gave a very different botanical composition to that from the treatments in wbich natural or simulated excreta were returned to cut swards.Mixtures simulating excreta may replace the nutrient effect of the grazing animal, but not its physical effect, in some forms of grassland experimentation. They are not recommended for fertilizer trials.

Chemical composition of pastures in relation to grass tetany in beef breeding cows

Abstract Pastures from 27 sites (19 farms), mainly in the Hawke's Bay district, were sampled during an outbreak of grass tetany in beef breeding cows. Pastures were generally ryegrass-dominant, with little clover at grazing height, and were mainly closely grazed. Chemical analyses gave the following results (mean value and range of values. %) :- Mg, 0.19 (0.14–0.25): Ca, 0.39 (0.29–0.61); K. 3.29 (2.0–4.0); Na. 0.06 (0.00–0.19); P, 0.50 (0.35–0.69); N. 5.28 (4.2–6.3); non-protein N. 0.94 (0.75–1.17); non-protein N as a percentage of total N, 18 (16–22); soluble carbohydrate. 9.7 (3.8–15.5); ratio K/(Ca + Mg). 2.45 (1.42–3.63). The magnesium levels fall within the range where occurrence of hypomagnesaemic tetany may be considered a possibility, and the over-all results suggest that the deficiency of magnesium in the animal is induced by a high-protein—low-energy intake. Possible contributory factors in the pasture are high potassium, low calcium, and low sodium. Since no fertiliser nitrogen or potassium was used, the high level of these elements is attributed mainly to luxury consumption from high-fertility patches resulting from the return of animal excreta.

AN INVESTIGATION INTO THE SIMULATION OF NUTRIENT RETURNS BY THE GRAZING ANIMAL IN GRASSLAND EXPERIMENTATION

An experiment is described that examined mowing with the return of excreta and mowing with the return of clippings as methods of simulating the return of nutrients by grazing animals in experiments where grazing is impracticable. These treatments were applied to a pure grass and to a grass/clover sward. Both methods gave herbage nearer in yield and composition to that resulting from natural grazing than did mowing with no return, but neither was suitable for use on sites outside experimental stations. Although the nitrogen returned in excreta was rather inefficiently used, it appeared to be the major factor in increasing yield on the grass sward and in changing the grass/clover balance on the mixed sward. The return‐treatments had a marked effect on the potassium nutrition of both swards and the results suggest that omitting the grazing animal from trials assessing potassium fertilizer requirements may invalidate the results.

The grazing animal and sward productivity

1. The results of a trial designed to investigate the effects of sheep excreta on sward growth and yield are described.2. The quantities of plant nutrients excreted, and their distribution, by the grazing animal are discussed. An assessment is made of the value of excreta to pasture growth in the light of the results gained.3. Under Boghall conditions, the return of excreta had little affect on sward output, the main effect was for the pasture to become progressively more grass dominant. In general, weather and soil nutrient limitation had a greater effect on nitrogen yields from the swards than did excreta. Recovery of excreta nitrogen would appear to be influenced by rainfall and the age of the sward.4. On a soil inherently low in available potassium, it was found that this element and nitrogen both affected the pattern of herbage growth and composition when returned in excreta. Phosphorus return by the sheep was, however, of no observable value in either the levels of the element in the soil or in the herbage. It was found that rainfall and the botanical composition influenced the contents of mineral elements in the herbages.5. Balance studies suggest that sheep grazed in small paddocks need adequate pre-conditioning before being moved into a trial. Only by this means can return of excreta reflect consumption of herbage. The limitations of small-scale animal grazing experiments are discussed.

SOME ESTIMATES OF THE AREAS OF PASTURE FOULED BY THE EXCRETA OF DAIRY COWS

Observations were made of the areas of herbage receiving the faeces of grazing dairy cattle and of the areas and relative palatability of herbage whose growth was affected by faeces and urine. The average area covered by faeces was 7·3 sq. ft./cow/day. Faeces dropped during grazing had a negligible affect on the utilization of herbage at that grazing, but each dung‐pat probably affected the growth and palatability of an area of herbage about six times as great at the next grazing. The area of herbage whose growth was affected by urine was equal to that affected by faeces, but unlike faeces, urine improved the palatability of the herbage to dairy cows. The data were used to calculate approximate areas of herbage likely to be affected by excreta at different levels of stocking, and it appeared that excreta return plant nutrients to a given pasture acreage more quickly than some other estimates suggest.

THE EFFECT OF SHEEP EXCRETA AND NITROGENOUS FERTILIZER ON THE BOTANICAL COMPOSITION AND PRODUCTION OF A LEY

Results are presented for the final two years of a previously described experiment.The return of dung and urine by sheep to a ryegrass/white‐clover ley was controlled by suitable harnesses to give four treatments (no dung or urine, dung, urine, dung and urine) which were combined in a replicated factorial design with four levels of nitrogenous fertilizer application (0, 52, 182, 312 1b. N per acre).Applied nitrogen and urine were the dominant factors affecting botanical composition. The percentage of ryegrass increased and that of clover decreased with the progressive increases in nitrogen application. Volunteer species (mainly Poa spp.) contributed up to 20 per cent by the final year, the maximum occurring under the medium‐high nitrogen treatment.Urine restricted the incursion of weed grasses.Combined with urine or the full return of excreta, high levels of applied nitrogen increased herbage production by up to 120 per cent. There was little response to dung except at the highest nitrogen level.The yield response to applied nitrogen was almost linear. In the absence of animal returns response was poor, partly due to shortage of potash. When both excreta were withheld the light nitrogen dressing depressed the annual production compared with the control; where both excreta were returned together with this dressing no reduction occurred in annual yield and the spring yield was improved (p <0.05).