Physical properties of gram

The dependence of physical properties of gram on moisture content was determined. The best approximate shape was found to be a prolate spheroid. At 10·9% moisture content d.b., the measurements yielded an average 1000 grain weight of 0·173 kg, a mean surface area of 133·4 mm², and sphericity and roundness of 74% and 70% respectively. In the moisture range from 9·64 to 31·0% d.b., studies on rewetted gram showed that the bulk density changed from 780 to 708 kg/m³, kernel density from 1311 to 1257 kg/m³; porosity from 40·5 to 43·7% and static coefficient of friction from 0·384 to 0·651 over surfaces of different materials. The angle of repose was observed to change from 25·5° to 30·4° in the moisture range from 8·62 to 17·6% d.b.     

Some Physical Properties of Lentil Seeds

Several physical properties of lentil seed were evaluated as a function of moisture content. The average diameter, thickness, unit mass and volume of seed were 6·64 mm, 2·65 mm, 0·070 g and 49·08 mm³respectively at 6·5% m.c.d.b. Studies on rewetted seed showed that as moisture content increased from 6·5 to 32·6% d.b., bulk density decreased from 1190 to 935 kg/m³, porosity increased from 27·4 to 32·0%, projected area increased from 56 to 82 mm²and terminal velocity increased from 10·95 to 12·06 m/s. The static and dynamic coefficients of friction of lentil seed against galvanized sheet metal, plywood and rubber surfaces increased with moisture content in the range from 6·5 to 32·6% d.b. The largest coefficient of friction was against a rubber surface, ranging from 0·374 to 0·532. The effect of moisture content was as great as or greater than the difference between the surfaces.     

Physical Properties of Pumpkin Seeds

Several physical properties of pumpkin seeds and kernels were evaluated as functions of moisture content. The average length, width, thickness and unit mass of the seed were 16·91 mm, 8·67 mm, 3·00 mm and 0·203 g respectively. Corresponding values for the kernel were 14·62 mm, 6·89 mm, 2·50 mm and 0·160 g respectively. In the moisture range from 4 to 40% d.b., studies on re-wetted seed showed that the bulk density increased from 404 to 472 kg/m³, true density decreased from 1179 to 1070 kg/m³, porosity decreased from 65·73 to 55·46% and terminal velocity increased from 4·7 to 6·5 m/s. For the kernel, the corresponding values changed from 481 to 554 kg/m³, 1080 to 1143 kg/m³, 55·46 to 51·53% and from 4·27 to 5·25 m/s respectively. In the moisture range of 4 to 27% d.b. the static coefficient of friction varied from 0·41 to 0·76 for seed and from 0·34 to 0·65 for kernel over different material surfaces, while angle of repose varied from 30 to 52° for seed and 34 to 42° for kernel.     

Equilibrium Moisture Content of Cotton Plant Components

Equilibrium moisture contents for cotton plant parts (leaves, sticks and burs), all trash, were obtained at temperatures ranging from 5 to 80°C in a moving air stream (flow rate of 3×10^-4 m³/s) and relative humidity ranging from 0 to 98%. The temperatures used were 5, 20, 35, 50, 65 and 80°C. Data were obtained for both absorption and desorption for each temperature and plant part tested. The data showed that temperature had a small effect on the moisture content for absorption, but there was a more noticeable effect for desorption. The results showed an almost linear increase in equilibrium moisture content between 20 and 70% relative humidity followed by an exponential rise as the relative humidity approached 100%. Two equations (the Modified-Oswin and a functional relationship developed by the author) were found to give acceptable fits to the experimental results. Data from the literature showed slightly higher equlibrium moisture contents for the same humidity conditions. This information will be used in conjunction with absorption and desorption rate curves to estimate the moisture content of harvested seed cotton during various phases of cotton processing.     

Compressibility of Some Trinidadian Soils as Affected by the Incorporation of Peat

The effect on compressibility of incorporating peat into four remoulded Trinidadian agricultural soils was investigated over a range of stresses from 0 to 1000 kPa using a compression machine. Air-dry peat was applied at four levels (0, 4, 8 and 12% by mass) to the soils (two sandy loams, clay loam and clay) and tested at three moisture contents close to the Proctor optimum moisture content of the soils. Compression curves (bulk density versus log applied stress) for each soil at the moisture levels tested were almost linear and parallel over the range of stresses from about 100 to 1000 kPa.Mean values of dry bulk density declined significantly at 0.001 level with increasing peat content from 1·23 to 0·87 Mg m^-3. Mean bulk density values increased significantly at 0·001 level with increasing applied stress and moisture content and declined with increasing clay content. Significant interaction effects were observed between soil type and peat content and between peat content and moisture content. Peat incorporation resulted in greater soil compression, but the increases were less evident in clay than in sandy loam soils. Soil compression refers to the decrease in soil volume with the application of external load. The compression index, C (slope of the dry bulk density versus log applied stress relationship), increased significantly at 0·05 level from 0·21 Mg/m³ in one sandy loam soil to 0·38 Mg/m³ in the clay soil. While the C value did not differ significantly with increasing peat content in the sandy loams and the clay loam, it decreased significantly at 0·01 level in the clay soil. An equation expressing C as a function of initial soil bulk density before compression and a strain parameter was developed in order to explain the variation of C in the soils tested. A method is described that can be adopted to quantify the effect of peat on soil compressibility.     

Thermal properties of gram

Values of specific heat, thermal conductivity and thermal diffusivity of rewetted whole grain were found. The specific heat of the grain shows a nonlinear relationship both with temperature and moisture content in the range of 292 to 308 K and 12·4 to 32·4% d.b. respectively, resulting in a second-order multiple regression equation. Bulk thermal conductivity increases both with increase in temperature and moisture content in the ranges 283 to 312 K and 11·5 to 27·2% respectively and was found to vary from 0·114 to 0·247 W/m K. Thermal diffusivity increases with increase in moisture content and decreases with increase in temperature in the temperature and moisture ranges of 293 to 307 K and 12·5 to 26·5% respectively, and its value lies between 9·46 × 10⁻⁸ to 16·35 × 10⁻⁸ m²/s.     

The performance and economics of a dairy refrigeration heat recovery unit

The results of a series of experiments on a refrigeration heat recovery unit designed to provide 300 1 of 60°C water from a 2·25 kW refrigeration system cooling 21001 of milk per day are presented. The unit was inserted between the compressor and condenser of the refrigeration plant and tested with two condenser systems (air and water), four condenser pressures (6·5 bar, 7·5 bar, 10 bar and 12 bar), two milk inlet temperatures (23°C and 18°C), and two milk final temperatures (4°C and 7°C). In addition, tests on receiver pressure and suction superheat were performed to determine their effect on the overall system performance.Increasing condenser pressure caused the gross heat recovery to rise from 15·1 MJ (4·2 kWh) d⁻¹ m⁻³ to 29·2 MJ (8·1 kWh) d⁻¹ m⁻³ of milk for the water cooled system, while water outlet temperatures rose from 45°C to 64°C. The corresponding ranges for the air cooled condenser were 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ to 23·8 MJ (6·6 kWh) d⁻¹ m⁻³, and 38°C to 55°C. Changing milk inlet and final temperatures gave a proportional change in cooling times and total heat recovery, but had no effect on C.O.P. or heat recovery rates. Suction superheating increased the total heat recovery by approximately 3·2 MJ (0·9 kWh) d⁻¹ m⁻³, and water outlet temperatures by 5°C. Although increasing condenser pressure resulted in an increase in gross heat recovery, these gains were offset by the additional compressor power required. The net heat recovery varied between 13·7 MJ (3·8 kWh) d⁻¹ m⁻³ at 6·5 bar, to 19·1 MJ (5·3 kWh) d⁻¹ m⁻³ at 12 bar for the water cooled system. For the air cooled condenser system the net heat recovery remained fairly constant at approximately 11·5 MJ (3·2 kWh) d⁻¹ m⁻³.Based on these figures, the annual savings have been calculated under various conditions. At 10 cents per kWh, the heat recovery unit used in a system with a water cooled condenser operating at 12 bar, with suction superheat, on a farm producing 2100 1 per day, could save $NZ453 per annum. For a 210 cow dairy farm, such a system would cost around $NZ5000 (including the cost of the water cooled condenser), making the installation marginally uneconomic. However, heat recovery systems on larger farms are likely to be more attractive financially, because the increase in return is not matched by a similar increase in cost. The optimum operating conditions may vary if the electricity tariffs are altered. Methods of increasing the net heat recovery are considered and other techniques for reducing hot water power consumption are discussed.     

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.     

Temperature-compensated and Density-independent Moisture Content Determination in Shelled Maize by Microwave Measurements

Moisture content of shelled maize,Zea maysL., was correlated with the attenuation and phase shift of electromagnetic waves travelling through a layer of grain. Several calibration equations are presented in the paper that are based on measurements taken at 15·2 GHz for various grain densities, moisture contents and temperatures. Validation of the calibration equations indicated that moisture content can be predicted with an uncertainty less than ±0·72% moisture content w.b. at the 95% confidence level. Moisture predictions are largely independent of bulk density variations at temperatures from 4 to 45°C and moisture contents from 9 to 19% w.b. By following one approach described, the grain bulk density can be determined from the same measurements with an uncertainty of less than 25 kg/m³. With another approach, the grain bulk density cannot be determined, but moisture content is determined independent of the material bulk density and compensated for temperature. No differences among three maize hybrids were observed in the measured data.     

Experimental Evaluation,Simulation and Optimization of a Commercial Heated-Air Batch Hay Drier: Part 1, Drier Functional Performance,Product Quality,and Economic Analysis of Drying

This paper considers the engineering design, operation, functional performance, product quality, and economic analysis of a natural gas heated-air batch hay drier that operates with an automatic bale wagon. The automatic bale wagon and a track are used for loading and off-loading stacks of alfalfa and timothy hay en masse to and from the drier. The newly developed batch hay drier has two identical drying units in a gable roof building, and each drying unit has a large axial flow fan which forces about 450 m³/min of air by negative pressure through 22-32 t (a maximum of five stacks) of small rectangular hay bales placed to dry on the perforated extended metal grate floor of the drier. Top plenum swing-away frames, with attached polyethylene curtains, were used for effectively sealing the vertical sides and one end of the hay stacks.Batches of hay, initially at about 25-40% moisture content wet basis (w.b.) were successfully dried to 12-15% final moisture content in 17-37 h at moderate drying air temperatures of 45±5°C. The drying capacity was 1·0 t dried hay/h, specific fuel consumption 26 m³/t, specific energy consumption 4790 kJ/kg water evaporated, and drying energy cost Canadian $5·82/t when hay was dried from an initial moisture content of 30% w.b. to a final value of 15% w.b. The hay produced by the drier was of high quality with an attractive green color.     

A dairy refrigeration heat recovery unit and its effects on refrigeration operation

Concern about increased energy costs prompted an investigation into refrigeration heat recovery as one conservation alternative for reducing water heating costs on farm dairies. A theoretical energy balance was conducted, from which the potential for recovery of refrigeration condenser heat was estimated to be up to 60% of the water heating energy requirements.Preliminary tests with heat exchangers led to the development and testing of a tube-in-tube, counter flow heat exchanger, with fins on the refrigerant side and cores on the water side to improve the heat transfer characteristics. The exchanger, designed to provide 300 l of water at 60°C from a 2·25 kW refrigeration system which cooled 2100 l of milk per day, had a surface area on the refrigerant side of 0·84 m², and an overall thermal conductance of 750 W m⁻² °C⁻¹. It was inserted between the compressor and the condenser of the refrigeration plant and tested with two condensing systems (air and water), together with varying conditions of condenser pressure and milk temperatures at inlet and final cooling. In addition, tests on the receiver pressure and suction superheat were performed to determine their effect on the overall system performance.Increasing the condenser pressure from 6·5 bar to 12 bar increased cooling times. In extreme circumstances the system failed to comply with the New Zealand milk cooling regulations. The average coefficient of performance (C.O.P.) of the refrigerator (with the heat exchanger in the circuit) decreased with increasing pressure, varying from 3·0 to 2·3 over this range of pressures for the water cooled condenser system. Values for the air cooled condenser system were 0·3 to 0·4 lower due to fan power consumption.     

Effect of Peat on the Compactibility of Some Trinidadian Soils

The effect on compactibility of incorporating peat into four Trinidadian agricultural soils before compaction was investigated in a laboratory experiment. A factorial experiment was used to study the effect of peat applied at four levels (0, 4, 8 and 12% by mass) on the maximum dry bulk density (MDBD) and optimum moisture content (OMC) of the four soils (two sandy loams, clay loam and clay) compacted using 5, 15 and 25 Proctor hammer blows. The compaction tests were carried out at different moisture contents which varied according to the values of the plastic limits of the soils.Results showed that while the mean values of MDBD of the soils declined significantly (p = 0.001) from 1·51 to 0·92 Mg m^-3 with increasing peat content, the mean values of OMC increased from 24·2 to 42·6%. While MDBD increased, OMC decreased with increasing compaction levels. This applied to all the soils tested. The clay soils had significantly lower values of MDBD and greater values of OMC than the sandy loam soils. There were significant interaction effects between soil type and level of added peat and between compaction level and level of added peat. These interactions were used to describe the effect of peat on soil compactibility. Multiple linear regression equations based on compactive effort, sand content, clay content and percentage peat content, were generated for predicting values of MDBD and those of OMC of compaction of the soils used in this study. There was reasonable agreement between the equation for predicting MDBD and a similar equation derived for Nigerian soils in previous work. A good negative relationship obtained between MDBD and OMC is also similar to the one derived from previous research.     

Prediction of Kernel and Bulk Volume of Wheat and Canola during Adsorption and Desorption

Information don the shrinkage of grain both in bulk and as individual kernels is important in postharvest processing of these materials. The mass and volume of samples of wheat and canola seeds exposed either to humid or dry air were measured during adsorption or desorption cycles. When the grains were exposed to 90% r.h. at 40°C, the bulk density of wheat decreased almost linearly from 790 to 686 kg/m³as the kernel moisture content increased from 8% to 22% w.b. The bulk density of canola descreased by 11 kg/m³, from 672 to 661 kg/m³as the kernel moisture content increased from 5% to 19% w.b. The laws of mixtures were used to develop the following equations to predict grain kernel (v_k)and grain bulk volume (v_b)respectively as functions of moisture adsorption or desorption:v_k/v_k0=[1-M₀/1+(γ-1)M₀] [1+(γ-1)M/1-M]andv_b/v_b0={[1-(M₀-M)][1+(γ-1)M]/[1+(γ-1)M₀]} (1-ϵ₀)/(1-ϵ)wherev_kandv_k0are the kernel volumes,v_bandv_b0are the bulk porosities at the kernel moisture contents ofMandM₀respectively;γis the dry kernel density and is assumed to be a constant for each grain. Compared with experimental data, the kernel volumes of both wheat and canola, adequately predicted by the first equation. The second equation gave an adequate prediction of the bulk volume of canola by assumingϵ= ϵ₀,but not for wheat unlessϵwas expressed as a polynomial function of kernel moisture content.     

Dependence of dielectric properties of whole-grain wheat on bulk density

Samples of hard red winter wheat were conditioned to moisture contents ranging from 3·4 to 24·2%, wet basis. A subsample from each conditioned sample was manually adjusted to various bulk densities and the dielectric properties of the subsample were measured. Moisture content and bulk density influenced dielectric properties measured at frequencies of 1, 18, 300, and 2450 MHz. A calibration equation for estimating moisture content from dielectric constant and bulk density, and an empirical equation for estimating the loss factor from bulk density and moisture content were developed.     

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.     

Prediction of the fractional rate of outflow of water from the rumen of sheep

The fractional outflow rate of water from the rumen, measured as the rate of disappearance of the chromium complex of ethylenediamine tetra-acetic acid, was related to a number of dietary factors. A multiple regression equation was derived which expressed fractional outflow rate as a function of the intakes of dry matter, ash, acid-detergent fibre and crude protein.The data analysed consisted of 243 observations for sheep on 59 diets, including forage, concentrate and mixed diets. The ranges covered by the data were: fractional outflow rate 0.7–3.6 day^?1; dry matter intake 560–1400g/day; ash 4–30%, acid-detergent fibre 7–41%, crude protein 5–26 % of dry matter; there were no observations for sheep of less than 34 kg liveweight.The equation accounted for 56·3 % of the total variance. Between-sheep variance could not be calculated for the whole of the data but was undoubtedly substantial since, for a sixth of the data, it was known to account for 38 % of the total variance.     

Dynamics of plant and animal production of a subterranean clover pasture grazed by sheep: Part 1—Field measurements for model calibration

A grazing system with Merino sheep and subterranean clover pasture was studied in a 550 mm rainfall, mediterranean climate in Western Australia.Changes over twelve months in seed, the quantities of green and dry herbage, soil moisture, animal intake and liveweight, wool growth and body composition were measured. Six paddocks, representing two soil types, were grazed continuously at 8·75 sheep per hectare. The system was also simulated and the actual results were compared with those from the simulation model.From a seed pool in March of 300 kg ha^?1, 80% of which was soft and non-dormant, 4000 clover seedlings per square metre became established; subsequent drought reduced this to 1450 plants per square metre. From measurements of soil moisture it was shown that this population survived at available moisture levels as low as 0·5 mm in the main root zone in gravelly sandy loam. Pasture growth rate reached a spring peak of 102 kg ha^?1 day^?1 and total growth (estimated from pasture grazed for 26 weeks) was 6700 kg ha^?1 for 500 mm of rainfall between germination and maximum biomass. At maturity, burr and seed made up 57% of the plant residues on offer, with a seed pool of 1160 kg ha^?1. During the summer this biomass decreased at 5 kg ha^?1 day^?1 without grazing and 19 kg ha^?1 day^?1 under grazing.The liveweight losses and gains of the sheep were atypical, no liveweight gain until 1200 kg ha^?1 of gree herbage was available—about treble the expected amount. Measurements of food intake indicate a gross inefficiency in energy utilisation during the winter and a low intake of energy in the spring.Total green and dry plant residues showed general agreement between actual and simulated results for most of the growing season. However, the field data highlighted error in the pasture sub-model which were corrected and are reported elsewhere.     

不同硬脂酸添加量下大豆分离蛋白/海藻酸钠膜特性研究

为改善大豆分离蛋白/海藻酸钠复合膜的耐水性,通过添加不同添加量（0、2%、4%、6%、8%、10%）硬脂酸制备大豆分离蛋白/海藻酸钠/硬脂酸三元复合膜,探究硬脂酸对大豆分离蛋白/海藻酸钠复合膜的机械性能、阻水性能和微观结构的影响,最终明确不同硬脂酸添加量对耐水性变化的影响规律。结果表明：与大豆分离蛋白/海藻酸钠二元复合膜相比,添加6%和8%硬脂酸后,复合膜的断裂伸长率、水蒸气透过率显著下降,并且对其含水率及水溶性也有显著影响。当硬脂酸添加量为8%时,三元复合膜的水蒸气渗透性最低,水蒸气透过系数为（2.95±0.49） g·mm/（m²·h·kPa）,接触角最大,为91.68°±9.02°。通过傅里叶变换红外光谱和扫描电子显微镜分析可知,大豆分离蛋白和海藻酸钠通过共价交联形成网络结构,加入的硬脂酸则分布在网络结构的缝隙中,当硬脂酸添加量为8%时,膜的表面较为光滑平整,内部结构致密,能够形成良好的网络结构,键与键之间结合较强,能有效提高复合膜的阻水性能。     

Mapping the total volumetric irrigation water requirements in England and Wales

The net volumetric (m³) irrigation water requirements for the main crop categories currently irrigated in England and Wales have been calculated and mapped within a geographic information system (GIS). The procedure developed by Knox et al. (1996, Agric. Water Manage., 31: 1–15) for maincrop potatoes (Solanum tuberosum) was extended to cater for the other crops currently irrigated. The annual irrigation needs (mm) for the eight major irrigated crop categories, grown on three contrasting soil types at 11 representative weather stations, were determined using a daily water balance irrigation scheduling model. The results were correlated with existing national datasets of climate, current land use, soils and irrigation practice, to generate volumetric (m³) irrigation water requirement maps at 2 km resolution.The total net volumetric irrigation water requirements for a UK ‘design’ dry year (defined as the requirement with a 20% probability of exceedance) are estimated to be 140 × 10⁶ m³ for the eight main crop categories currently irrigated and the 1994 cropping pattern. Previous theoretical dry year demand estimates, using scheduling models and large agroclimatic areas, were 109 × 10⁶ m³ and 222 × 10⁶ m³. The irrigation demand for other crops grown in the open would typically add another 4%.The procedure has been validated nationally, by comparing the calculated dry year demand for 1990 against government irrigation survey returns for 1990, for each crop category, and regionally against National Rivers Authority (NRA) abstraction records for 1990, for each NRA Region. The estimates obtained agree well with the reported distribution between crops and between regions.The most recent actual ‘dry’ year for which comparative data are available is 1990. It is estimated that the dry year requirements for the 1990 land use would have been 148 × 10⁶ m³. Although farmer demand, actual abstractions and crop requirements are not necessarily the same, irrigation survey returns to the Government indicated that 134 × 10⁶ m³ were actually applied, and the NRA estimated from meter returns that 138 × 10⁶ m³ were abstracted. It is noted, however, that some abstraction restrictions were in force, the scope of the data is slightly different and all figures contain inaccuracies. Potential applications for improving irrigation demand management and water conservation at regional and catchment levels are discussed with reference to two contrasting regions.     

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.