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1.
Objective management of grazing livestock production systems needs monitoring of forage production at the managerial unit level. Our objectives were to develop a system that routinely estimates forage above-ground net primary production (ANPP) at the spatial and temporal resolution required by farmers in the Pampas of Argentina, and to facilitate adoption of the system by end users as a managerial support tool. Our approach was based on the radiation use efficiency (RUE) logic, which proposes that ANPP is determined by the amount of photosynthetically active radiation absorbed by the canopy (APAR), and the efficiency with which that energy is transformed in above-ground dry matter (radiation use efficiency, RUE). APAR is the product of incoming photosynthetically active radiation (PAR) and the fraction absorbed by the canopy (fPAR). We estimated fPAR as a non-linear function of MODIS normalized difference vegetation index (NDVI). RUE was empirically estimated for the two principal forage resources of the region, yielding the following relations: ANPP = 0.6 × APAR + 12, (R2 = 0.86; p < 0.001; n = 18) for the upland sown pastures, and ANPP = 0.27 × APAR + 26, (R2 = 0.74; p < 0.001; n = 18) for the lowland naturalized pastures, with ANPP in g/m2/60 days and APAR in MJ/m2/60 days. The models were able to predict independent ANPP values with acceptable accuracy. Computational procedures were automated and run in a Relational Data Base Manager System that stored and managed all the information. The system is currently monitoring 212,794 ha in 83 farms and provides monthly ANPP values for the previous month and a history of the last 6 years. The data so generated show ANPP differences between the two major forage resources, considerable variability of a given month’s ANPP among years and paddocks, and contrasting among-farm differences in the efficiency of conversion of ANPP and forage supplements into beef production. The system was well accepted by end users who utilize it mainly for making near real time decisions according to last month ANPP, and explaining results of previous production cycles by incorporating ANPP as an explicative variable. However, there were differences among farmers in the degree of utilization, apparently related to the advisor’s attitude toward this new technology. Our results indicate that (1) forage production of large extensions can be monthly monitored at the paddock level by a small laboratory with capabilities in geographic information systems, and (2) advisors and farmers apply this information to their managerial decisions.  相似文献   

2.
Information was obtained on the structure of the herds and flocks of a sample of 41 households on the three Maasai Group Ranches in Kenya. The purpose of the survey was to contribute to an intensive study of the livestock production system, and also to assess the amount of information that could be obtained from a herd structure study on its own. Differences in herd structure were related to the livestock wealth of the household, the stage of development of the Group Ranch as well as to the variation in climate, and production alternatives.Data from more than 5100 cattle revealed that Maasai herds contained less steers in 1982 (18%) than in 1968 (22%). The proportion of mature steers had also dropped from 5% (1968) to 2% (1982), with maximum valves of 3·2% on the most developed ranch and 2% for the wealthiest stratum of households. A high percentage of females had been retained (56%) giving a herd structure characteristic of subsistence production with milk as a primary output. This structure also caters for a strong market in immature animals and gives the herd a high potential for recovery after a drought. There appeared to be a trend towards increased use of introduced bulls, notably Sahiwal on the Small East African Zebu, with increased Group Ranch Development. However, this trend was confounded by a decreasing aridity gradient with increased development.On two of the ranches for which 1968 counts were available, cattle numbers were 119% of their previous value whereas small stock were 470%. The reason appears to be that increased sedentarisation without adequate range management has resulted in a severe reduction in grasses, and their replacement by forbs. These plants are more palatable to small stock which are better able to exploit the degraded habitat.Information from more than 2730 sheep and 2300 goats revealed that poor households preferred goats and richer households, sheep. The Small East African Goat was ubiquitous, but the most developed ranch had crossed Dorper onto Maasai sheep whereas the least developed and most arid ranch had introduced Somali Blackhead sheep. The Dorper crossbred catered for a market for mutton whereas the Blackhead was primarily for home consumption of fat.The conclusion is that Group Ranch Development has not projected the Maasai into commercial beef ranching as originally planned, but their production system has not stood still. A study of herd structures was a good way of demonstrating the evolution of the system. The method was simple but was dependent for its success on fairly involved and time-consuming sampling and data collection procedures.  相似文献   

3.
《Agricultural Systems》1999,60(2):87-98
This paper presents a series of Monte Carlo computer experiments designed to determine the effect of irrigation, stocking rate and lamb drafting weight on the profitability and productivity of a sheep grazing enterprise. The experiments were performed on a hypothetical farm in the Canterbury Plains of New Zealand. Pasture growth parameters were estimated based on a 21-year series of monthly measurements and were used to introduce production risk into the model. The paper demonstrates that, independently of the risk atittude of the producer, it is important to account for the stochastic nature of the environment in an agricultural management model.  相似文献   

4.
The contribution of wool to ewe output declines in relative terms as the number and value of lambs reared per ewe increases. This is illustrated by the spectrum of sheep production systems in Great Britain, from extensive hill production where wool accounts for 18% of ewe output, to intensive production out of the main lambing season, where wool only accounts for 6% of ewe output. The ratio of wool production to sheep meat production and their respective prices vary greatly between countries.In Great Britain, as technical efficiency increases, the relative, but not necessarily the absolute, contribution of wool to output declines. Changes in production systems and management, aimed at improving slaughter lamb output per hectare, will also bring about a consequential increase in wool production per hectare.Because wool represents an appreciably lower part of the output in meat producing systems than lamb sales, increases in wool prices have a relatively small effect on gross margins. In lowland flocks a 20% increase in wool prices only increases the gross margin per ewe by 3·1%.Although wool output is considerably less important than lamb sales in Britain it is, nevertheless, worthwhile for the producer to pay close attention to the fleeces produced in order to ensure that he receives the highest returns possible. This is illustrated by reference to the variation in wool returns per ewe between flocks.Fleece weights and quality have a high heritability and are rapidly improved by selection. However, the relative economic value of the annual genetic improvement in increasing the number of lambs reared per ewe is worth five times as much as the annual genetic improvement in fleece weight in lowland flocks; in hill flocks this falls to only twice the value.  相似文献   

5.
《Agricultural Systems》2007,92(1-3):223-239
Management of a game ranch is an important issue as many game ranches operate on meagre profits, and some even at a loss, as their part-time owners subsidize the ranches from other sources of income. In this paper, we address the sustainable game ranching problem in a South African context through an optimization model. To obtain a faithful picture of reality, the model includes conflicting objective functions, and takes into account the fact that annual rainfall is known only stochastically. An approach for solving the resulting multiobjective integer linear stochastic program is discussed and illustrated by means of a numerical example from a Northern Cape ranch.  相似文献   

6.
Pastoral communities in East Africa are facing considerable challenges arising from shifts in land tenure policy from communal to individual landholdings and high human population growth rates. Over the last 30 years, livestock-to-human ratios have generally declined to levels that will no longer support pure pastoralism. Many Maasai have thus diversified into cultivation, wage labour, and small businesses. Livelihood expectations are rising, with concomitant increases in the need for cash. We describe the modification of PHEWS, a simple rule-based model that tracks cash flow and calories in agro-pastoral households. We use it, coupled to Savanna, a sophisticated ecosystem model, to quantify some of the effects of subdivision and land fragmentation on household livestock numbers and on food security. For the group ranches simulated, model outputs indicate that subdivision results in substantial reductions in livestock numbers, partially because households have to sell more animals to generate the cash needed, with serious long-term consequences on herd sizes and food security. If subdivision occurs, even to parcels as large as 196 km2, livelihood strategies may need to be modified to maintain current levels of household well-being. Model results have been discussed in community meetings in southern Kajiado, but more work is needed on communication mechanisms to utilise more effectively the results of imperfect but useful integrated assessments of complex problems concerning land use and human well-being.  相似文献   

7.
Conventional ranching in Chiapas, Mexico typically includes annual pasture burns and agrochemical use that decrease the biodiversity and forest cover of ranch lands. Members of a holistic ranching “club” in the Frailesca region of Chiapas, Mexico have moved away from this conventional management by eliminating burns and agrochemicals from their systems after decades of use because they believed that the land and their production process were growing unhealthy; they were further motivated by extension courses on holistic ranching. They have also implemented sophisticated systems of rotational grazing and diversified the use of trees. For this study all seven holistic ranchers and 18 neighboring conventional ranchers were interviewed about their cattle ranches and production strategies. An emergy analysis was conducted to compare the resource use, productivity and sustainability of the conventional and holistic ranches. Holistic ranches were found to have double the emergy sustainability index (ESI) values of conventional ranches, and the emergy yield ratio was 25% higher in holistic systems. Government assistance programs were found to have a negative impact on the ESI and were variably administered among holistic ranchers during the year of emergy evaluation. Overall improved emergy sustainability did not decrease milk nor cattle productivity. Transformities and specific emergies, the emergy of one type required to make a unit of energy (transformity) or mass (specific emergy) of another type, did not differ between conventional and holistic systems. Transformities for milk production ranged between 3.4E5 and 1.2E7 solar emjoules/joule (sej/J). Specific emergy for cattle production ranged from 3.5E10 to 1.5E11 sej/g. To improve the ESI assistance programs could be re-targeted toward incentive programs for increased forest cover in ranching systems and startup costs for holistic ranching. The results from this study show that productivity can be maintained as the sustainability of rural dairy ranches is increased. These results also show that local knowledge and understanding of the surrounding ecosystem can drive positive environmental change in production systems.  相似文献   

8.
《Agricultural Systems》1999,61(3):207-221
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9.
《Agricultural Systems》2007,92(1-3):63-75
This article explores long-term land improvements (lime and phosphorus application) under land tenure insecurity on leased land. The dynamic optimisation problem is solved by a stochastic dynamic programming routine with known parameters for one-period returns and transition equations. The model parameters represent Finnish soil quality and production conditions. The decision rules are solved for alternative likelihood scenarios over the continuation of the fixed term lease contract. The results suggest that, as the probability for non-renewal of the lease contract increases, farmers quickly decrease investments in irreversible land improvements and, thereafter, yields decline gradually. The simulations highlight the observed trends of decreasing land improvements on land parcels that are cultivated under lease contracts.  相似文献   

10.
《Agricultural Systems》2007,92(1-3):295-317
The worldwide loss of utilisable rangeland in (semi-) arid areas results in huge economic and social costs. Only adaptive management strategies are able to cope with these systems, which are mainly driven by unpredictable and stochastic rainfall. The aim of the study was to investigate the relevance of rest periods as part of the management scheme in these non-equilibrium rangeland systems. The starting point of the analysis is an approved management system – the Karakul sheep-breeding Gamis-Farm (Namibia). The farmer applies a flexible strategy, which combines short-term adaptation of the stocking rate to the available forage and long-term adaptation by resting a third of the paddocks in years with sufficient rainfall.We developed a simulation model that focuses on the key dynamics of this non-equilibrium system. Beginning with the strategy used by the Gamis-Farm, a set of alternative grazing strategies was defined, all adapted to the available forage but differing in whether and when resting is granted for a part of the pasture. The effectiveness of these strategies was compared according to the long-term productivity of the pasture and the farmer’s livelihood.Our results reveal ecological settings during which resting is essential for the recovery of the vegetation in a fluctuating environment, as well as those during which it is not. The growth rates of both the vegetation and of the livestock are demonstrated to be highly influential. Rests during wet years are crucial for the regeneration of the pasture. We conclude that even though a non-equilibrium rangeland system is assumed, the application of pure opportunistic strategies – destocking in times of drought and fast post-drought restocking – are not always adequate to maintain the long-term productivity of the pasture. Rest periods are indispensable when vegetation has a low regeneration potential. On an applied level, the study emphasises that improved farming conditions (supplementary feeding, unrestricted options to purchase livestock) may run the risk of ecological as well as economic damages.  相似文献   

11.
Pasture-cropping is a novel approach to increasing the area of perennial forages in mixed livestock and cropping systems. It involves planting annual cereals directly into a living perennial pasture. There is interest in using subtropical grasses for pasture-cropping as they are winter dormant and their growth profile is complementary with winter crops. The ability of subtropical grasses to maintain feed quality in summer is likely to be an important attribute. However, a wide range of factors can affect the uptake of such systems. This paper evaluates the farm-system economics of subtropical grasses and pasture-cropping. The research question is: what factors affect the profitability of a new technology such as (1) subtropical grass and (2) subtropical grass that is pasture-cropped. The analysis uses the MIDAS model of a central wheatbelt farm in Western Australia. The results suggest the profitability and adoption of subtropical grasses is likely to be strongly influenced by the mix of soil types present on the farm; the feed quality of the subtropical grass; whether the production emphasis of the farm is for grazing or cropping, and the level of production in summer and early autumn. The same factors are relevant to pasture-cropping, with the addition of yield penalties due to competition between the arable crop and the host perennial. The results were less sensitive to changes in the winter production of subtropical grass. Pasture-cropping was more profitable and likely to involve a larger area of the farm when a meat rather than a wool-dominant sheep system was present. However, there was little difference between the meat and wool flocks in their sensitivity to other factors in this analysis.  相似文献   

12.
A computer program based on empirical relationships is described. It predicts daily energy and nitrogen utilisation repetitively for sheep of any age, before, during and after weaning; provision is also made for pregnancy, lactation and cold stress. Input information includes: intake, protein content and digestibility of the diet; age, empty body weight, fat content and feeding activity of the sheep; ambient temperature and wind speed; times of shearing and mating.Metabolisable energy from milk and/or dry feed is estimated and energy requirements for maintenance, including the cost of feeding activities and homeostasis in the cold, are deducted to obtain energy balance. The amount of amino acid nitrogen absorbed from the small intestine is estimated, and nitrogen balance in body tissues and wool is calculated from this, allowing for body weight and net energy intake. Potential wool growth is calculated from nitrogen and energy intakes, and potential conceptus growth or milk production is estimated primarily from stage of pregnancy or lactation. The use of nitrogen and energy for these products is assessed and balances of energy and nitrogen in body tissues are then obtained by difference. If achievement of the potential rates of production in pregnant or lactating animals would cause excessive loss of energy or nitrogen from body tissues, production of wool and conceptus or milk is reduced sufficiently to avoid this problem. Gain or loss of body fat and protein, and hence change of empty live weight, are finally derived and the animal parameters are incremented before proceeding to calculation for the next day.Evidence is presented that the model is stable in predicting lifetime performance, and that predictions of growth curves, body composition and various nutritional parameters are reasonably accurate in a variety of circumstances.  相似文献   

13.
《Agricultural Systems》2003,76(3):1183-1205
A generalised climate driven pasture growth model is described and evaluated by comparison to field observation. The model describes dry matter production and green-dead tissue flow dynamics for grazed temperate swards, especially perennial ryegrass (Lolium perenne). The model includes a unique feature to account for light interception by non photosynthetic tissue. Extrapolation across environments occurs by the interaction of climate variables with three parameters that tune the model to a site. These parameters reflect the influence of soil fertility and sward species composition on production patterns. They are: (1) the efficiency of radiant energy use for photosynthesis, (2) the timing of reproductive development and (3) the relative efficiency of radiant energy use in vegetative compared to reproductive swards. Initial parameter settings were derived from data from a sheep grazing experiment in New Zealand. In this paper the ability to describe pasture production under dairy grazing at a different site is confirmed. When the three available parameters were calibrated for the dairy site, all but two of the 42 seasonal estimates of pasture production were within the 95% confidence interval for mean measured production. The model is being used as a component of a whole-farm dairy production model.  相似文献   

14.
The ‘Mouton de Case’ is a small-scale stall-fed system of sheep fattening current in West Africa. Most fattened animals are males, kept for slaughter at the annual Moslem Feast of the Sacrifice (tabaski). More than 25% of total annual offtake in local sheep flocks occurs in relation to this feast. In two local agropastoral sub-systems more farmers kept stall-fed sheep in an irrigated rice sub-system (39%) than in a rainfed millet sub-system (24%). Farmers in both systems fed approximately two animals. Supplementary feed is mainly cut grass and tree leaves and some agricultural by-products. Average daily gains of Mouton de Case were, at 117 g, almost twice those of extensively reared animals (60 g) of the same type.  相似文献   

15.
田帅  王利军 《农业工程》2017,7(6):57-62
以1991、2004和2015年3个时相的TM/OLI遥感影像为数据源,利用基于归一化植被指数（NDVI）的像元二分模型估算保定市植被覆盖度,对其进行等级划分,并分析其时空变化特征。结果表明,1991—2015年,保定市植被覆盖度整体呈现下降的趋势,且不同区域存在差异现象。低植被与中低植被覆盖区面积整体呈增加趋势,而高植被覆盖区面积呈降低趋势。在4个研究分区中,保定市主城区植被覆盖度下降最为明显,1991—2015年的25年间,植被覆盖率下降了12.76%,平均每年下降约0.5%。研究发现,城市开发与建设及其导致的农用地减少等是植被覆盖度变化的主要原因。   相似文献   

16.
A computer model (NEMAT) of the life cycle of sheep nematodes and of the epidemiology of nematodiasis in sheep was constructed. Its purpose is to predict the development of nematodiasis in weaner sheep and to determine optimum nematode control programmes. It has been developed for use in western Victoria, Australia, but it should also be of use in other localities.NEMAT simulates the growth of perennial ryegrass (Lolium perenne) and subterranean clover (Trifolium subterraneum) pasture and weaner sheep and the development of populations of the sheep nematodes Ostertagia spp. and Trichostrongylus spp. The development and death rate parameters of the free-living stages of these nematodes were estimated by a direct search optimisation procedure specifically developed for this study. The death rates of the parasitic stages of Ostertagia spp. were determined in a field experiment and expressed as a function of the rate of infection and the time of exposure to infection. Other probability density functions and deterministic functions needed to complete the quantification of the sheep-nematode system were derived from published reports or personal communications.NEMAT was validated against data from two independent field experiments carried out in western Victoria. Predicted serial measurements of pasture availability, liveweights, total nematode counts, nematode eggs per gram of faeces and numbers of infective nematode larvae per hectare were compared with those actually observed. The predicted and observed measurements were subjectively similar and could not be differentiated statistically by spectral analysis.NEMAT was then used to evaluate some nematode control programmes in western Victoria. Using observed weather data, it simulated the continuous development of nematode populations during 1957–1976 on pastures set stocked on the 1st of January each year with recently drenched weaner sheep.If sheep were drenched in only one month of the year, the effect of this drench on liveweights and woolweights at the end of the year was greatest if it was given in February. There was a progressive decline in final liveweights and woolweights if it was given in subsequent months to December. If sheep were drenched in February and given a second drench in any one of the remaining months of the year, the effects of this second drench on final liveweights and woolweights was greatest if it was given at the autumn break. A drench in February and a drench and shift to ‘clean’ pasture (<104 nematode larvae per hectare) in July were always sufficient to limit the mean yearly effects of nematodiasis to 1 kg in liveweight and 0·1 kg in woolweight. When such a shift was not possible, a drench in February, another at the autumn break and 0–5 drenches in winter and spring were required to attain similar productivity. The number and timing of these drenches after the autumn break depended on the daily effects of weather on the nematode population and could be determined only by a model of the sheep-nematode system such as NEMAT.  相似文献   

17.
A simulation model which estimates the net primary production of the ground-storey component of the extensively grazed Acacia aneaura rangelands of semi-arid Queensland, Australia, was applied to the assessment of grazing capacity. The method described represents an alternative approach to the traditional method used by land administrators. Historic climatic records for a continuous period of 25 years were analyzed for one centre. Annual live herbage biomass production fluctuated widely in relation to both climate and grund-storey condition class. Herbage biomass carryover from year to year decreased significantly as the level of herbage utilization through animal consumption increased. At a conservative level of use, herbage biomass carryover provided an important reserve to supplement the smaller amount of live biomass produced in low rainfall years. Consequently, grazing capacity was related to the total herbage biomass available to the grazing animal at the end of each summer growing period. There were only small changes in the mean value of end-of-summer peak herbage biomass crop and sheep carrying capacity over the excellent to good ground-storey condition classes. However, there was a pronounced decline in these values as condition class decreased from moderate to poor.The implications of this method assessing grazing capacity for semi-arid rangeland management and administration are discussed.  相似文献   

18.
《Agricultural Systems》2001,68(1):69-91
The dynamic model of growth of an animal from conception through to maturity (Vetharaniam, 2001 A model of mammalian energetics and growth: model development. Agricultural Systems, 68, 55–68) is tested against data for sheep growth, to gauge its usefulness. The model is based on opposing forces of anabolism and katabolism, and does not include forcing functions for growth. The model gave good predictions of fetal and placental growth dynamics for sheep, including the differences between singleton and multiple offspring, as well as reproducing the post-natal growth patterns corresponding to rams with genetic merit similar to that of the fetuses. Although maintenance and fasting heat production are not explicit concepts in the model, the model was able to reproduce these through its mechanisms.  相似文献   

19.
A modelling approach is examined as a method of investigating alternative management strategies for improved systems of hill sheep production. In order to take account of the wide range in the quality of hill herbage and the ability of the hill sheep to select preferred components, herbage has been conceptually classified in terms of its digestibility; the digestibility classes are then grazed selectively by sheep. The model deals with herbage growth and deterioration, diet selection and the maintenance and liveweight change of wether sheep. Results produced by the model, in which wethers grazed Agrostis-Festuca at two stocking rates, are discussed.  相似文献   

20.
《Agricultural Systems》2004,82(1):45-56
Understanding processes of maize (Zea mays L.) growth and production of grain in high-yielding, irrigated conditions offers hope to understand yield potential in many other environments. In this study we investigated such processes at the plant level, and attempted to simulate maize yields at the field level and county level in the high yielding region of the High Plains of Texas. In addition, we used the normalized difference vegetation index (NDVI) from satellite data of year 2000 to update leaf area index for yield simulation in three counties. In the field study, we measured maize leaf area index (LAI), the fraction of photosynthetically active radiation intercepted (FIPAR), and the harvest index (HI) in irrigated plots near Dumas, Texas. The light extinction coefficient (k) for Beer's law was calculated with the FIPAR and the LAI. The radiation use efficiency (RUE) was determined with sequential measurements of the fraction of photosynthetically active radiation (PAR) intercepted and biomass harvests. The RUE was 3.98 g of above-ground biomass per MJ of intercepted PAR in 1999 and 3.41 in 2000 for three sampling dates prior to silking. These values are 106 and 93% of the expected RUE values at the measured vapor pressure deficits, using a previously published response function. The mean k value was −0.46 in 1999 and −0.47 in 2000, similar to the expected value of −0.43 reported in the literature for this row spacing. The mean HI measured in 2000 was 0.52, similar to values of 0.53 and 0.54 in the literature. Application of these parameters to maize simulation with the Agriculture Land Management Alternatives with Numerical Assessment Criteria (ALMANAC) model for 13 center pivot irrigated fields near Dumas in 1999 provided simulations within 1.0 Mg ha−1 with a mean error of 0.03 Mg ha−1 and a mean square error of 0.10. For five years of grain yields reported for each of four counties in this region of Texas, ALMANAC simulations were within 5% of the mean measured yields. Introduction of PAR interception, based on the satellite-derived normalized difference vegetation index (NDVI), into ALMANAC resulted in slight increases in accuracy of yield prediction for two counties and a slight decrease in accuracy in one county for year 2000. Consistency in values of RUE, k, and HI in this study as compared with values reported in the literature will aid modelers simulating maize growth and grain yields in similar high-yielding, irrigated conditions.  相似文献   

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