A model for recycling of feed nutrients in a crop,animal and biogas system in India

In northern India, with triple cropping intensity of fodder crops and recycling of feed nutrients in a milch animals and biogas system, from 1 ha of land it is possible to produce 82·63 GJ of energy and 906·11 kg of protein from milk; 263·93 kg of N; 148·93 kg of P₂O₅ and 90·94 kg of K₂O fertilizer from biogas slurry and 2897 kilowatts of power per annum for farm operation from biogas using the Kirloskar biogas engine. Traditional systems of wheat and rice cultivation can produce 93·87 GJ of energy and 654·25 kg of protein from food grain per hectare per annum. The recycling of feed nutrients in the available straws of rice and wheat crop can yield an additional 16·31 GJ of energy and 166·97 kg of protein from milk; 81·23 kg of N; 56·00 kg of P₂O₅ and 25·14 kg of K₂O fertilizer from biogas slurry and 1097 kilowatts of power per hectare annually from biogas.     

The yield,quality and profitability of annual forage,perennial pasture and perennial forage systems under irrigation

Intensive fodder production systems were compared under irrigation in western New South Wales. The three basic systems studied were:

• 1.(1) Annual forages (Sorghum bicolor × S. sudanense plus Avena sativa).
• 2.(2) Perennial pasture (Paspalum dilatatum).
• 3.(3) Perennial forage (Medicago sativa).

The first two systems included nitrogen fertilizer or legume options, while the last had the option of including a perennial sorghum.Dry matter production was highest in the annual forage system (maximum of 30·5 tonnes ha⁻¹ year⁻¹), although annual establishment costs were higher than for perennial systems. The perennial pasture yielded 21·5 tonnes ha⁻¹ year⁻¹ but, like the annual forage system, 250 kg N ha⁻¹ year⁻¹ was required to obtain this yield. The perennial forage yielded 19·8 tonnes ha⁻¹ year⁻¹ without nitrogen fertilizer. Furthermore, it yielded more digestible dry matter and nitrogen than any other system.Although the annual forage system was the most profitable when based upon a set price for hay, the best system for grazing was difficult to determine; factors relating to grazing management are discussed.     

Feed conversion efficiency and the efficiency of the UK food chain

The efficiency of transfer of food energy across various components of the human food chain is calculated for the UK. The processing and presentation stages have overall efficiencies of transfer of 0·75 and 0·93, respectively, with foods of animal origin mainly showing higher efficiencies of transfer through these processes. The efficiency of agriculture, related to a hypothetical maximum potential biomass production, is 0·026, with relatively lower efficiencies for the livestock industries. Yields of food energy from crops and livestock in the UK are calculated as 33 and 4 GJ per hectare, respectively. The factors affecting animal feed conversion efficiency are examined and it is shown that there is a potential conflict between high animal feed conversion and overall food chain efficiency. The consequences of this conflict—and possibilities for optimisation—are examined in terms of a simple resource allocation model.     

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.     

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 cultivation-cattle complex in Western Darfur

The agricultural/livestock system of a 40,000 km² area in western Sudan is described. Details of the three main components—traditional rainfed agriculture, small-scale irrigation and animal husbandry—are given. Data on crop yields and livestock production at both the unit level and the system level are provided. Millet is the main cereal crop overall but sorghum occupies an important place in the intensively cultivated alluvial zones. Cash crops, including groundnuts, chillies and okra for drying, are of some importance. Onions are the main winter irrigated crop while mangoes and citrus are important tree crops. The livestock sector is dominated by cattle which account for more than 75% of the livestock units present. Gross output of the area at 1976 prices was calculated at £Sud 14·8 to £Sud 16·2 million (US$ 41·4 to US$ 45·4 million) equivalent to £Sud 41·7 to £Sud 45·6 per head of population and £Sud 3·70 to £Sud 4·05 per hectare. Of these totals between 33 and 36% could be attributed to livestock production.     

An analysis of the nocturnal heat loss from a double skin plastic greenhouse

The rate of nocturnal heat loss from conventional single skin greenhouses is high because glazing materials provide low thermal resistance. A common method of increasing the thermal resistance of greenhouses is to add a second layer of glazing material—normally in the form of an inner liner of transparent plastic film. The extra convective resistance resulting from the air gap between the two sheets of glazing material results in a considerable reduction in heating requirements.It is possible to develop mathematical expressions for each of the energy transfer processes that contribute to the loss of heat, and thus develop a series of energy balance equations for the greenhouse cover. The solution of these equations yields the rate of loss of heat for any climatic condition, providing that the coefficient of convective transfer across the air gap is known. The method of analysis was applied in a series of 33 experiments in a double polyethylene greenhouse, and yielded a value of 3·85 W m⁻² K⁻¹ for the air gap convective coefficient. Energy savings averaging 32% were obtained compared with that required to heat a single skin greenhouse exposed to the same climatic conditions.     

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.     

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.     

Energy requirements for transport and surface application of liquid pig manure in Manitoba,Canada

The objective of this study was to conduct a thorough accounting of energy used to transport liquid pig manure from farm storage to the field and to surface-apply the manure. Energy consumption was determined using both energy data from the literature plus data from field-scale research. Energy consumption was compared between two manure application systems (the drag hose and the slurry wagon systems) and two application timing treatments (single vs. twice-annual manure application). The single annual application of liquid pig manure applied at 81.5 m³ ha⁻¹ and transported 1.8 km from storage to field consumed 2180 MJ ha⁻¹ with the drag hose system and 2185 MJ ha⁻¹ with the slurry wagon system. The twice-annual manure application regime used 2726 and 2209 MJ ha⁻¹ for the drag hose and slurry wagon systems, respectively. When energy use was calculated on the basis of MJ per kg of available N, liquid pig manure applied once annually with the slurry wagon system provided N at 17.76 MJ kg⁻¹ of available N, which was 33% of the energy cost of N from anhydrous ammonia and 23% of the energy cost of N from urea. Manure transport distance could be increased to 8.4 km before the energy cost per kg of available N from pig manure was equivalent to anhydrous ammonia, and up to 12.3 km before the energy cost of manure N was equivalent to urea N. Despite the high energy cost to deliver liquid pig manure from storage to field, the much lower cost per kg of available N compared to inorganic fertilizer N highlights the opportunities that exist for improving the energy efficiency of industrial agriculture by replacing inorganic fertilizers with manure.     

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.     

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.     

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.     

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.     

Impact of treated wastewater irrigation on quality attributes and contamination of tomato fruit

A field experiment was conducted in 1999 and 2000 to investigate the effect of different treatments of potable and treated wastewater on the quality of tomato fruit (Lycopersicon esculentum L. Mill) in Jordan. Tomato seedlings (cvs. GS₁₂ and RS₅₈₉₉₅₆) were furrow irrigated with different mixtures of potable and wastewater (1:0, 1:1, 1:3, and 0:1). The BOD, and SS of the treated effluent used were 34 and 35 mg/l, respectively. Irrigation with treated wastewater did not affect fruit pH, increased their size up to 2 cm in diameter, and weight up to 78.7 g. Additionally, a decrease of 1.5% in the SSC, 0.59 kg in firmness, and 5.1% in weight loss of tomato fruit were recorded. The 0:1 application of treated wastewater resulted in an increased microbial contamination (TC 1.56×10⁴ and 4.7×10² CFU/100 g; FC 3×10² and 130 CFU/100 g; TBC 188×10² and 205×10² CFU/100 g) on the surface of the fruit (skin) for GS₁₂ and RS₅₉₉₉₅₆ varieties, respectively. There was a negligible contamination on fruit scar, and nil in fruit flesh. Contamination increased exponentially with increasing the proportions of treated wastewater application. Since treated wastewater was highly contaminated with total coliform (up to 42.0 CFU/100 ml) and total bacterial count (up to 7.820 CFU/100 ml), hence, contamination was aggravated with increasing the percentage of treated wastewater. It is suggested that the treated wastewater can be used as an alternative for irrigation of tomatoes eaten after cooking, but not for those taken as raw provided that the effluent quality is continuously monitored to avoid contamination.     

A model for sericulture and milk production

With a view to increasing the annual output of edible nutrients (milk), employment generation and obtaining better economic returns per unit area under sericulture, a model was designed through the application of the integrated systems approach. By the application of this model, it is possible to produce 23·23 GJ edible energy and 266·33 kg edible protein from milk; 2975 man-days employment and Rs.30·11 profit per man-day labour input from 1 ha in a year. In contrast, the traditional system of rice cultivation in Southern India, with double cropping intensity, could generate 50·67 GJ energy and 244·00 kg protein from food grains, 288 man-days employment and only Rs.8·34 profit per man-day labour input from 1 ha in a year.     

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.