Energy requirements of hand tools for wood cutting

The axe and the matchet are the traditional wood cutting tools in Nigeria. This paper compares the human energy requirements of these tools in wood cutting with that of a medium-sized power chain saw. The energy requirements were measured by the indirect open circuit method using the heart rate as the measured parameter. Four subjects used for the tests were calibrated with a bicycle ergometer. The heart rates measured in the field during cutting were used to determine the work rates from calibration graphs. The trials were carried out in three seasonal environments encountered in Northern Guinea Savanna of Nigeria. The results show that the power chain saw could cut over 10 times more surface area of wood per minute with a lower energy demand of 3·8 kJ/min than the traditional tools which demanded high energy ranging from 5 to 9 kJ/min. Of the three seasonal environments in which the trials were made, Harmattan (temperature 21 to 23°C, relative humidity 15 to 19%) demanded the least in human energy. The energy requirements increased at higher temperatures and humidities.     

Tillage Tool Design by the Finite Element Method: Part 2. Experimental Validation of the Finite Element Results with Soil Bin Test

Laboratory soil bin tests of subsoiler cutting in a sandy loam soil were carried out in order to validate the results obtained from the finite element calculations reported in Part 1 of this study. Measured results of subsoiler draught force and soil failure dimension taken on the surface were presented for four combinations of the subsoiler shank rake angle and chisel angle. Soil bin tests also measured the variation of draught force with subsoiler displacement. It was observed that the angle of both the subsoiler parts affected the dimensions of the surface soil failure and the magnitude of subsoiler draught force.Finite element method predictions of the subsoiler draught force as well as the extent of surface soil failure agreed well with measurements made in the soil bin. The predicted draught force for all subsoiler types exceeded the measured ones. The overprediction error ranged from 11·76 to 20·04%. The finite element model provided a good approximation to the maximum upward soil movement for the experiments. Better finite element method predictions of the front soil failure was obtained for the two subsoiler designs with a small chisel angle of 15° than for the designs with chisel angles of 23 and 31°. Among the four investigated subsoiler types the best subsoiler design was devised, which required the lowest draught and developed good soil loosening qualities as estimated by soil volume change. This subsoiler had a shank of 75° rake angle and an inclined chisel of 15° angle. Keeping a good soil loosening performance was attributed to the smaller shank rake angle of 75°, which indicated that the shank played an important role for the determination of the quality of soil loosening.     

Emission of Nitrous Oxide and other Trace Gases during Composting of Grass and Green Waste

The emission of trace gases during composting of green waste from land maintenance (fresh cuttings of mixed herbage from fallow land) were studied. Concentrations of nitrous oxide and other trace gases were measured in experimental compost heaps by means of an infrared gas analyser and a high-resolution FT-IR spectrometer. It was verified that the maintenance of aerobic conditions is essential to keep emissions of methane and nitrous oxide at a low rate. Estimates made using a simple air transport model, indicated that the emission of nitrous oxide during composting of green waste from land maintenance was about 0·5% of the total nitrogen content of the initial material. Carbon monoxide was also detected in the compost air and its emission during biodegradation corresponded to about 0·04% of the initial carbon content of green waste.For a detailed evaluation of the findings during field experiments, laboratory apparatus for measuring the composition of compost air was developed. The measurements were performed at a temperature of 35°C and at different ventilation rates. Moistened plant material (dry cuttings of mixed herbage from fallow land) amended with lime saltpetre was used as compost substrate. At a ventilation rate of 100 cm³/min of air per kg of substrate, the maximum emission rate of nitrous oxide was 2·2 mg/h per kg of substrate. The maximum emission rate increased to 13·3 mg/h kg, when the ventilation rate was lowered to 20 cm³/min kg. The emission rate of carbon monoxide was about 40 μg/h per kg of substrate at the low ventilation rate and rose above 200μg/h kg at the higher ventilation rate.     

Force-Time Behaviour of Flat Tines in Dry Sand

Studies conducted in a laboratory soil bin filled with dry sand indicated that the nature of soil reactions on tines of 90° rake angle were cyclic for tine aspect ratios (width/depth) of 0·6 and greater. For tine aspect ratio of four, soil reactions were observed to be cyclic for all the tine rake angles studied (15-140°), These variations were found to be closely related to the observed soil failure patterns. Wave ratio (wave length/tine depth) for tines with a rake angle of 90° increased with increase in tine aspect ratio up to four. The amplitude of cyclic variations in draught increased with tine width for a rake angle of 90°.     

Monitoring Milk Flow as an Aid to Management in Automatic Milking Systems

The milking of animals in automatic milking systems requires the development of sensor-based feedback control. This paper proposes the use of milk flow as a method of monitoring the correct performance of the milking machine and examines the repeatability of this measure through lactation. The milk flow was defined by the let down time (the time from attachment of teat cups until a steady flow of milk begins), the peak flow rate and the stripping time. Peak flow rate was the rate at which the first 75% of milk was extracted. Stripping time was the time to extract the last 25% of milk removed. The milk flow profile of four goats was recorded at morning and evening milking once each week for 30 weeks. The mean let down time was constant throughout lactation at 12·1 s (S.D. 0·45 s), while the mean stripping time was 25·7 s (S.D. 7·76 s) indicating the variability of milk flow towards the end of milking. Peak milk flow for individual animals varied little throughout lactation. A method of deriving peak flow rate automatically was developed and this can be used to check that milking is progressing correctly.     

Replacement policy in dairy herds on farms where heifers compete with cows for grassland: Part 2-Experimentation

Replacement policy is not easy to determine on dairy farms where heifers compete with cows for grassland. Using a computer simulation model of this farm situation, two factorial experiments were conducted to evaluate quantitatively the effect of different replacement rates on profitability and herd improvement.The variables changed in herds of average health and very good health were replacement rate (0·14, 0·22, 0·30), age at first calving (36, 24 months), calving index (13, 12 months) and AI sire merit (standard, premium). Initially, the experimental herd had average health, a replacement rate of 0·22, a calving index of 13 months, calved its heifers at 36 months and had been using standard bulls for many years.After 15 years, the increase in the level of a sinking fund when the age at first calving was reduced was between three and five times greater than when premium bulls were used, calving index was reduced or herd health was improved. There was a major interaction between replacement rate and age at first calving.Yield per cow was significantly reduced (P≤0·001) by reducing the age at first calving and significantly increased when premium bulls (P≤0·001) were used or when herd health was improved (P≤0·05).Some treatments were not tested as expected due to the restraining effect of a 13-month calving interval on the availability of cows for breeding pure in a seasonally calving herd.     

The effect of air speed changes on the group postural behaviour of pigs

A group of 26 pigs were housed in 2 pens in a specially designed building. The animals were subjected to air speeds varying from 0·3 to 1·0 m/s, which, using a theoretical model for lower critical temperature (LCT), gave departures from LCT of between −2·4 and +2·8°C. The response of the pigs in terms of variations in group postural behaviour was measured from photographs. The measurements indicated that the contribution due to air speed was accurately taken into account in the theoretical model. Statistical analysis of the data showed significant variations in group postural behaviour with liveweight.     

Estimation of Moisture Diffusivity Coefficient and Thermal Properties of Alfalfa Pellets

Heat and mass transfer characteristics of alfalfa pellets are needed in the optimization of coolers for freshly-made pellets and in managing storage schedules of the pellets in silos and bins. Moisture diffusivity and thermal properties are important parameters used to characterize the heat and mass transfer ability of a material. In this study, experimental thin-layer data on (a) moisture desorption, (b) moisture absorption and (c) rate of heating of alfalfa pellets were collected. By applying the inverse theory and using second order mass transfer and heat transfer equations in cylindrical coordinates, the moisture absorption and desorption data were used to estimate the moisture diffusivity as a function of moisture content of the pellets while the heating rate data were used to estimate the thermal properties (thermal conductivity and specific heat) as a function of pellet temperature.Better estimates were obtained when moisture diffusivity of the pellets was exponentially related to moisture content in comparison with a linear relation between moisture diffusivity and moisture content. Moisture diffusivity during desorption (2·40×10^-9to 4·12×10^-9 m²/s) was about three times that of the values of diffusivity during moisture absorption (7·50×10^-10to 1·26×10^-9 m²/s). A good fit to the experimental heating rate data was obtained when thermal conductivity and specific heat of the pellets were linearly related to temperature. Over a temperature range of 2 to 110°C, estimated particle thermal conductivities and specific heats of the pellets were in the range of 0·04 to 0·19 W/m K and from 962 to 2114 J/kg K respectively.     

High-rate anaerobic digestion of screened dairy manure

Laboratory-scale fixed-film reactors were used for the high rate production of methane from screened dairy manure under mesophilic temperatures. The active biomass, growing on the support structures, enabled the reactors to withstand high organic loadings as well as very short hydraulic retention times down to 1 h. Screened dairy manure (3·25% VS) was added intermittently at loading rates ranging from 2·25 to 778 gram volatile solids per litre per day (g VS 1⁻¹ d⁻¹) for fixed-film reactors. The maximum methane production rate was 6·20 litre methane per litre reactor per day (6·20 1 CH₄ 1⁻¹ d⁻¹) when operated at a loading rate of 259 g VS 1⁻¹ d⁻¹ with a 3 h hydraulic retention time. The fixed-film reactor was capable of sustaining a loading rate of 778 g VS 1⁻¹ d⁻¹ (1 h hydraulic retention time). The data illustrated the advantages of fixed-film reactors. The results obtained with reactors of varying sizes, and different fixed-film support materials are discussed.     

Optimization of the Design of Subsoiling and Pressurized Fluid Injection Equipment

There are two different design objectives for subsoilers with pressurized fluid injection, for use as pan-breakers or injectors respectively. A large soil failure is desirable when it is used as a pan-breaker and little soil failure is advantageous when it is used as an injector. This paper determines optimum shapes of pan-breaker and injector, where the draught can be reduced by injecting pressurized air (about 1·2 MPa at the air tank) from a nozzle port at the tip of the chisel.The results show that the optimum pan-breaker with fluid injection should have a rake angle of 45 to 60°, a chisel thickness of 50 × 50 mm, and a heel position at 100 mm. The optimum injector with fluid injection should have a rake angle of 90°, a shank thickness of less than 15 mm, a chisel length of 250 mm, a chisel thickness of 30 × 30 mm, and a heel position at 100 mm.     

Chemical Composition and Energy Value of Maize Silage Made on Farms in England and Wales 1984-92

The chemical composition of 960 samples of maize silage, made on commercial farms in England and Wales between 1984-1992, is described. The average composition was 302 g/kg dry matter (d.m.), pH 3·78, ammonia-N 60 g/kg N, 87 g/kg d.m. crude protein (CP), 292 g/kg d.m. modified acid detergent fibre (MADF), 678 g/kg d.m. neutral-detergent cellulase digestible organic matter (NCDG) and 301 g/kg d.m. starch. The predicted mean metabolizable energy content was 10·5 MJ/kg d.m. There was significant year-to-year variation for each variable. Ammonia-N and ash contents were negatively correlated and starch and metabolizable energy content were positively correlated with silage d.m. content.The results indicated that in recent years maize silage has consistently been made with d.m. contents above 300 g/kg, which should produce little or no effluent, and will lead to high silage intakes by animals.     

基于CFD-DEM的秸秆还田机碎秆运动特性分析与试验

为明确玉米碎秆在粉碎室内运动机理,基于CFD-DEM耦合分析不同粉碎刀轴转速碎秆运动过程和受力变化规律。仿真结果表明,当转速为1900、2000r/min时,碎秆-粉碎室壁面平均相互作用力波动较为剧烈,2300r/min时稳定在（175.228±19.08）N,且碎秆平均能量大幅增加。当转速为1900、2000、2300r/min时,碎秆间平均作用力最大分别为10.61、7.78、18.76N,〖JP2〗碎秆-粉碎刀轴壁面平均作用力分别稳定在（112.36±8.32）N、(101.15±8.02)N和（107.25±4.97）N,碎秆抛撒均匀度分别为(85.40±4.77)%、(78.52±5.56)%和(75.17±5.32)%。粉碎刀轴转速增大,使得碎秆-碎秆及碎秆-粉碎室壁面平均相互作用力增大,导致碎秆间及碎秆与粉碎室壁面的碰撞次数增多,加剧了碎秆能量的损耗,过大转速不利于碎秆抛撒均匀度提升。为验证仿真结果,进行田间试验验证。结果表明,当转速为1900、2000、2300r/min时碎秆抛撒均匀度分别为（82.35±6.57）%、（76.14±7.18）%和（74.22±5.65）%。田间试验和仿真结果表明在碎秆长度达标后,增大粉碎刀轴转速不利于抛撒均匀度提升,且作业功耗上升较大,同时验证了仿真的准确性。该研究可为玉米秸秆还田机设计和优化提供支撑。     

Mesophilic anaerobic digestion of high solids cattle waste in a packed bed digester

A mixture of manure and straw (26·3% total solids) obtained from the overwintering of dairy cattle was anaerobically digested in a 10 litre packed bed reactor, through which liquor (which provided the inoculum) was continuously recycled. The system was operated as a batch process (Digester A) for retention times of 40 and 70 days. A mean gas yield of 0·215 m³/kg VS added was obtained with a mean gas composition of 62·6% methane, together with a mean volatile solids reduction of 31% and cellulose reduction of 57%. To improve the efficiency of the process, a digester containing fresh solid material (C) was linked in series with a digester (B) which had operated for 40 days by recycling liquor between digesters B and C. This resulted in a gas yield of 0·264 m³/kg VS added in digester B, an increase of 18·6% in gas yield compared to digester A over the same period. The gas production in digester C was comparable to a batch digestion operating over the same period of time.     

Physical and Hygroscopic Properties of Makhana

Makhana is the popped expanded kernel of the gorgon nut (Euryale ferox) and is used as a delicious food in India. Presently, it is sorted, graded and used as an ingredient of various ready-to-eat products. High volumetric expansion of makhana increases transport cost and makes it too expensive in distant places. Makhana thus requires further processing to get some value-added products of minimum volume. To develop any kind of product and mechanized system for their production, physical properties are required. Furthermore, since makhana is a seasonal and regional crop its storage conditions are also needed for keeping it appropriately at processing centres. Physical properties of makhana at moisture contents ranging from 5 to 20% (dry basis) and equilibrium moisture content at relative humidities ranging from 11·2 to 88% at temperature 30°C were determined using standard techniques. Physical properties were found to be: test weight (weight of 1000 makhana) 286 to 384 g; bulk density 56·5–84·6 kg/m³; particle density 105–240·6 kg/m³; porosity 29·4–48·9%; angle of repose 33–35·6°; and static coefficient of friction 0·596–0·82 and 0·493–0·684 on galvanized iron and stainless steel, respectively. The equilibrium moisture content of makhana was found to be between 11·5 and 58·9% (dry basis) within the ranges of variables studied.     

The effect of plant spacing on water runoff,soil erosion and yield of maize (Zea mays L.) on a steep slope of an ultisol in Trinidad

The amount of water runoff and soil loss from a bare soil of 45–50% slope gradient and from the soil cropped with maize at 2 plant populations were measured for 20 storms. The lower population (wide spacing) of 41,500 plants/ha is the population currently in use and the higher population (close spacing) was 62,500 plants/ha.Maize at each of the 2 plant spacing significantly reduced runoff and soil loss. The closer planting did not only significantly reduce soil loss but also produced significantly more ears than the wide spacing. The most severe storm caused a disproportionate amount of soil loss. The runoff/rainfall ratio for storms of different amounts varied between 0·01 and 0·73 for close spaced maize, 0·01 and 0·83 for wide spaced maize and 0·02 and 0·92 for the bare soil. The ratio was highest for the largest storms.     

Kleingrass growth and utilization by growing steers

A model of kleingrass (Panicum coloratum L.) growth and utilization by steers is presented. The model included stochastic inputs of climatological characteristics, water retention at different soil depths, rainfall runoff, potential evapotranspiration, forage growth, forage intake and steer performance. The model was used in a 2 × 3 × 4 factorial experiment where the factors were energy systems (ARC, 1965 versus NRC, 1976), stocking rates (2·47 head per hectare, 4·32 head per hectare and 6·18 head per hectare), and four management options. Individual steer weights by months were not significantly affected by the use of either energy system. Steer weights at the end of the grazing season were affected (F = 0·06) by energy system, the NRC system predicting 7·2 kg per head more liveweight gain than the ARC system. The light stocking rate had greater (P = 0·01?0·13) daily gains over months than the heavier stocking rates. The heavy stocking rate resulted, however, in greater (P < 0·05) production per hectare per year than the lighter stocking rates. Season-long production per hectare favored (P < 0·1) management options that removed steers immediately after forage was consumed rather than anticipating rainfall and new forage growth. The light stocking rate had the least mean seasonal production per hectare (P < 0.·05) but also had the least year-to-year variability. The heavy stocking rater yielded the greater (P < 0·05) mean seasonal production per hectare but the year-to-year variation was much greater. It was emphasized that the use of such probabilities of production could aid the grazier in making stocking rate and related decisions.     

Tillage Tool Design by the Finite Element Method: Part 1. Finite Element Modelling of Soil Plastic Behaviour

The finite element method calculations of draught and vertical forces, soil deformation and normal pressure distribution on subsoiler face were reported for four subsoiler types. A non-linear, three-dimensional, finite element analysis of the soil cutting process by a standard medium-deep subsoiler based upon the Drucker–Prager elastic-perfectly plastic material model was used. The mathematical construction of the Drucker–Prager model was presented. The material non-linearity of soil was dealt with using an incremental technique. Inside each step, the Newton–Raphson iteration method was utilized. The geometrical non-linearity was solved by using the small strain assumption. A comparison of subsoiler forces for calculations made with the small strain assumption and the updated Lagrange formulation of large displacement was reported for subsoiler cutting in a sandy soil. It was shown that the small strain assumption was more convenient for solving the geometrical non-linearity of a soil tilled down to relatively deep horizons.The theoretical results showed that a well coordinated angle combination of the two parts of the subsoiler made a large reduction in the draught and vertical forces of the subsoiler with a shank angle of 75° and a chisel angle of 15°. On the soil surface in front of the shank, the soil was deformed to produce a wedge-shaped soil upheaval. A maximum upward surface movement of 23·7 cm was calculated when soil tilling was performed with this design of subsoiler. For all the geometrical types of subsoiler studied, concentrations of normal pressure at the outer linking edges between the two parts of the subsoiler, as well as on the bottom corners of the chisel, indicated that during manufacturing these parts should be better supported against wear and deformation. The smallest chisel angle of 15° reduced considerably the pressure values at these two parts, whereas changing the shank rake angle from 90 to 75° only assisted in reducing the pressure values at the outer linking edges.     

Measurements of the Effect of Animals on Airflow in an Experimental Piggery

Airflow and animal activity are important factors influencing the distribution of pollutants in livestock housing. In order to investigate the effects of the animals on commonly measured characteristics of airflow, an ultrasonic anemometer was used to determine air velocities in the occupied zone of an experimental slot-ventilated piggery with near-isothermal, rotary airflow. The determinations were made at eight points at 20 or 40 cm from the floor. Four situations were considered: when the piggery was empty, when it housed unheated models of pigs, and when it housed pigs either in an active or quiet state. Mean air speed and relative turbulence intensitiesI_t, defined here as the standard deviation of the local air speed divided by the mean local air speed, were calculated. In the empty building, air speeds around 0·7 m/s were measured at 20 cm and in the range of 0·3–0·6 m/s at 40 cm, ranges of relative turbulence intensities being 0·15–0·19 and 0·07–0·17, respectively. In comparison, in the vicinity of either models or pigs, the average air speeds of 0·3–0·5 m/s were lower (p<0·05), withI_tvalues of 0·25–0·54.The results indicate that the occupants of livestock housing affect the airflow around them, and will have substantial effects on the characteristics of airflow in these buildings. This has implications for research carried out in model buildings or empty full-scale buildings.     

The Influence of Cement Content and Water/Cement Ratio on the Durability of Portland Cement Concretes exposed to Silage Effluent

This paper outlines the findings of a study on the influence of cement content (275–425 kg/m³) and water/cement ratio (0·45 to 0·75) on the durability of concrete exposed to silage effluent. The test facility exposed concrete specimens to a controlled flow of effluent such that the volume of effluent in each 28 day cycle of exposure simulated one year's volume and expected period of effluent flow at the front of a well-drained 200 t horizontal silo. The relative performance of the concrete mixes was assessed over 10 cycles through measurement of saturated mass loss and surface depth change. The saturated mass loss measurement gave more consistent results. Optimum performance was recorded in concretes of cement content 325 and 375 kg/m³with water/cement ratios of 0·55 and 0·50, respectively. The studies indicate that water/cement ratio is a more critical variable than cement content. Deterioration increased significantly when the water/cement ratio exceeded 0·5. Increasing the cement content beyond the minimum recommended value in current national specifications (350 kg/m³) did not lead to a reduction in mass loss rate. The benefits of high cement content concretes is questioned, therefore, not least because of the increased risk of early-thermal cracking. It is postulated that specifications should limit the maximum water/cement ratio and both maximum and minimum cement content.     

An experimental investigation into factors influencing the soil injection of sewage sludge

Injection techniques for applying sewage sludge to grassland were investigated. The results have shown injection to be a viable technique for the application of sewage sludge under UK conditions. The technique is also suitable for the application of agricultural slurry, since the physical characteristics of both sewage sludge and slurry are similar.Research has shown an acceptably uniform grass response can be obtained from 280 mm wide winged times operating at a depth of 150 mm and spacing of 650 mm, when the soil is in the moist friable to plastic consistency state. Immediate rolling of the injected zone improved the crop response in the vicinity of the injector path, provided surface contamination was avoided.Injection on sloping land should be conducted downslope, rather than across, to ensure adequate machine stability, providing that maximum application rates are not exceeded. Sludges with dry solids contents in excess of 6% can be injected at application rates of 140 m³/ha into slopes of 12°, without down-slope seepage occurring. Rates should, however, be reduced for sludges with lower dry solids content, depending upon field slope.Increasing the injector leg rake angle reduced surface disturbance, with little effect on the resulting draught and vertical forces, until rake angles in excess of 100° were reached. Vibration of the injector tine using a rotating eccentric mass reduced the draught force under dry, brittle soil conditions, but not under more plastic field conditions.