Increasing Stocking Rate Research Articles

Native grassland management: a botanical study of two native grassland management options on a commercial cattle property

Variations in the botanical composition of two native grasslands, each managed differently, were investigated on a commercial cattle property in northern NSW. One grassland had not been fertilised, whilst fertiliser and subterranean clover had been applied by aerial application to the other grassland. Soils in both treatments had the same Bray 1 phosphorus level when the study was conducted. The fertilised grassland was stocked at triple the rate of the other grassland. Although more native species were recorded in the fertilised grassland many species had a lower frequency than in the unfertilised grassland; and introduced species tended to have a higher frequency in the fertilised grassland. ground cover was significantly higher in the fertilised grassland in spite of the greatly increased stocking rate.

Development of Smallholder Dairy Systems in the Kenya Highlands

Kenya is recognized among developing countries for its success in integrating dairy into smallholder farming systems, particularly in the highland areas. The major determinants of this success were colonial history, its favourable agroecology and supportive agricultural policies, and the importance of milk in rural and urban diets. In response to agricultural policies, market opportunities and human population pressure on land, smallholders have changed their farming systems by introducing the Friesian and Ayrshire breeds, keeping smaller herds with fewer heifers but more cows, increasing stocking rates through stall-feeding, growing fodder, purchasing feeds and becoming more dependent on external inputs and services. As a result, they can sell more milk. This increasing intensification, here defined as the use of external inputs and services to increase the output quantity and/or value per unit input, has ensured that more people are maintained per unit of land through increased returns per ha of family land. Because the level of intensification varies with the agroecological potential for cropping and dairying and with the level of milk market access and household resources, recommendations for production practices supporting intensification will be site-specific. Identifying appropriate recommendations will require a thorough understanding of farmers' objectives for keeping cattle.

Alfalfa leafcutting bee (Hymenoptera: Megachilidae) pollination of oilseed rape (Brassica napus L.) under isolation tents for hybrid seed production

In this 3-yr field study, the activities of alfalfa leafcutting bees (Megachile rotundata Fabricius) (LCB) at varying stocking levels were monitored in shade cloth isolation tents containing male-sterile and male-fertile rows of oilseed rape Brassica napus L. to determine optimum conditions for hybrid seed production. Bumble bees, Bombus impatiens Cresson, were similarly tested in 1 yr; their pollination activities were minimal, and weight of seed produced on female lines in tents containing bumble bees was similar to that in tents without pollinators. Leafcutting bee activity, as measured by the number of female bees at the entrance to tunnels in the hive, at first increased, then decreased with increasing stocking rate. Duration of time spent visiting flowers did not vary with stocking rate, but was longer on male-fertile than on male-sterile flowers. Production of hybrid seed within tents varied with leafcutting bee stocking rate, with the highest seed yield achieved at stocking rates equivalent to three charges at weekly intervals of 400 000 leafcutting bees per hectare. At optimum LCB stocking rates, the method described provided sufficient seed quantity for small-plot multi-location field evaluation of oilseed rape hybrids. Key words: Megachile rotundata, alfalfa leafcutting bee, Bombus impatiens, Brassica napus, oilseed rape, hybrid seed production, isolation tents

Economics of increasing the persistence of sown pastures: costs, stocking rate and cash flow

Poor persistence of sown pastures, trends of low pasture resowing rates and a substantial decline in carrying capacity of non-crop areas bring into question the basis of the philosophy of pasture improvement by sowing pasture species. If graziers are to adopt grazing strategies or stocking rates that are more ecologically sustainable, then clearly they must also be cost-effective in either increasing income or reducing costs so that they are economically sustainable. This paper describes the use of an interactive spreadsheet model developed to assist graziers and their advisers with assessing the long-term profitability of pasture management and/or improvement (and therefore pasture persistence). The model provides a comparative cash flow for different levels of inputs (fertiliser, herbicides and feed supplements) over a 15-year period. Results clearly show that at the same stocking rate, different animal enterprises have markedly different profitabilities over a 15-year period. Further, for native, improved and sown pastures, the most profitable pastures are those that can sustain increased stocking rates for long periods of time, without the need for resowing.

Optimized dairy grazing systems in the northeast United States and New Zealand. II. System analysis.

Factors that optimize milk production from Northeast United States and New Zealand grazing systems are compared using a linear programming model. The objective function maximized gross margin per hectare of land farmed. The experimental design compared the optimum characteristics of each system over a range of milk prices. The Northeast has a shorter grazing season and lower cropping costs than New Zealand. The optimum pasture area was 49% of the farm for Northeast systems. Gross margins declined rapidly above 55% or below 36% pasture area. The optimum stocking rate was 1.13 cows/ha, or 2.3 cows/ha of pasture. Optimum per cow production was higher for Northeast [7105 kg of fat-corrected milk (FCM)] than New Zealand (5710 kg of FCM) systems. This was related to lower grain relative to milk prices in the Northeast. New Zealand, all-pasture systems gave the lowest cost per unit of milk but also gave the lowest gross margin across all milk price scenarios. The best use of purchased feed in New Zealand systems was to support increased stocking rate rather than per cow production. Optimum grazing management practices were similar for supplemented New Zealand and Northeast systems. All-pasture New Zealand systems are characterized by short lactations and long autumn rotations to transfer pasture in situ for winter feeding. Higher costs per unit of milk produced will be an inevitable consequence of maximizing gross margin at high milk prices in New Zealand systems.

Urea Placement and Nitrification Inhibitor Effects on Growth and Nitrogen Accumulation by No‐Till Winter Wheat

Reduced forage production, grain yield, and visual N deficiency symptoms in no‐till winter wheat (Triticum aestivum L.) prompted this study. Our objectives were to determine the effect of urea placement and two nitrification inhibitors—nitrapyrin [2‐chloro‐6 (trichloromethyl) pyridine] (NP) and dicyandiamide (DCD)—on aerial dry matter and N accumulation. A 4‐yr field study was conducted on a Renfrow silt loam soil (fine‐silty, mixed, thermic Udertic Paleustoli) silt loam near El Reno, OK. The seven treatments included urea fertilizer (60 kg N ha−1) with and without the two inhibitors, surface broadcast or banded 3 to 4 cm below the seed row, and an unfertilized control. Aerial dry matter accumulation during autumn was higher for banded urea plus DCD (22%) and broadcast urea plus DCD (25%), than for broadcast urea without an inhibitor. Whole plant N content during autumn also was higher for banded urea plus DCD (28%) than for broadcast urea without an inhibitor. Neither inhibitor nor placement affected total dry matter accumulation measured at tillering, but differences were noted at spike emergence, gainful, and final harvest. At spike emergence in 1991, when climatic conditions were favorable for early season wheat growth, N content was greater for broadcast urea plus nitrapyrin than for broadcast urea or banded urea without inhibitor. At final harvest, both DCD treatments exhibited greater N content than all other N treatments. In 1993, when dimatic conditions were favorable for leaching, DCD was effective in slowing nitrification and increasing N uptake, regardless of fertilizer placement. Our results suggest that fall application of DCD with urea can potentially increase autumn forage production and N content, thus prolonging the grazing season or accommodating increased stocking rates.

Carbon (13C) uptake and allocation in pasture plants following field pulse-labelling

The allocation of carbon (C) to plant roots and conversion to soil organic matter is a major determinant of the size of the terrestrial C pool in pastoral ecosystems. The aim was to quantify C allocation to roots in contrasting pastoral ecosystems. Pastures on long-term research sites in Canterbury, New Zealand were pulse-labelled using 13CO2 within portable gas-tight enclosures. Sites included Winchmore (with or without superphosphate fertiliser, and with or without irrigation) and Tara Hills (low, medium or high grazing intensity with continuous or alternating grazing). Separate micro-plots were labelled in late spring, summer and autumn at Winchmore and in spring at Tara Hills. Herbage label 13C recoveries were greatest one hour after pulse labelling and declined by 21 days, whereas in roots they were initially lower but generally continued to increase until 21 days. The greatest recoveries of 13C in roots, one hour and 21 days after labelling, were in summer and autumn respectively. The proportion of label 13C allocated to roots by 21 days was 0.50 in the absence of superphosphate and 0.41 in the superphosphate treatment, and was 0.39, 0.43 and 0.51 respectively in spring, summer and autumn. Irrigation had no significant effect on root allocation. The low stocking rate at Tara Hills, which had the greatest herbage biomass, also had greater total 13C, tussock herbage 13C and root 13C recoveries than the higher stocking rate treatments. Inter-tussock root recovery and allocation of 13C to roots increased with increasing stocking rate, whereas tussock root allocation was greatest in the high and least in the medium stocking rate treatment. By 21 days there was a greater inter-tussock and tussock root recovery and lower inter-tussock herbage recovery in the continuous than in the alternating grazing management treatment. The root allocation was generally greater in the continuous than in alternating grazed treatments, except for tussocks one hour after labelling where the reverse was the case. In conclusion the 13C pulse labelling showed pasture plants allocate more C to roots with low soil fertility, high grazing intensity, continuous grazing, and in autumn.

Herbage Characteristics and Performance of Steers Grazing Old World Bluestem

Old World bluestem (OWB; Bothriocloa spp.) are popular in the southern Great Plains but little is known about the relationships between forage characteristics and animal productivity. The influence of differences in herbage mass and sward height of OWB on rate of gain during the summer grazing season was examined during 2 years at El Reno, Okla. Soils were fine, silty Pachic Haplustolls of the Dale series. Swards of caucasian [B. caucasica (Trin.) C. E. Hubb.] and 'Plains' [B. ischaemum var ischaemum (L.) Keng.] OWB were maintained at different levels of forage mass (low, medium, and high) by continuous variable stocking and were grazed from mid- May to late September by steers with an initial weight of about 225 kg. Weight gains were depressed in late August, but in 1985 gains recovered due to late season rains. Season-long gains averaged 0.61 kg day-1 in 1984 and 0.69 kg day-1 in 1985. Daily gains of steers increased linearly with increased herbage mass (P < 0.05), but slopes were different due to a year X species interaction. Daily gains peaked at a herbage height of 41 cm in 1984, but increased linearly throughout the range of the data (75 cm) in 1985. Individual animal gains decreased linearly with increasing stocking rate such that maximum gain per hectare was achieved at about 5 animals ha-1 (standard 500 kg). The data suggest that maintaining higher herbage mass and height of OWB forage improves animal performance and support the practice of intensive early grazing and removing cattle by late July when rate of gain declines.

Steer Performance and Nutritive Values for Continuously and Rotationally Stocked Bermudagrass Sod-Seeded with Wheat and Ryegrass

Considerable research has been conducted comparing animal and plant responses between rotational and continuous stocking, but more studies are needed to evaluate intensive, multi-paddock rotational stocking for managing forages in the southeastern USA. A 2-yr study was conducted with bermudagrass [Cynodon dactylon (L.) Pers.] pastures that were drill-planted with wheat (Triticum aestivum L.) and ryegrass (Lolium multiflorum Lam.) to compare steer performance and forage nutritive values between continuous stocking, 3-paddock low-intensity and 11-paddock high-intensity rotational stocking systems for both the cool-season annuals and warm-season perennial. In vitro dry matter digestibility (IVDMD) and crude protein (CP) were similar (P > 0.10) between continuous stocking and averages of pregraze, midgraze, and postgraze sample times for both rotation systems. There were decreases (P 0.10) by the grazing treatments in either season. Higher stocking rates were achieved (P 0.10) during the warm season. Thus, there was higher (P 0.10) during the warm season. Results of the study indicate that rotational stocking can enhance steer liveweight gain per acre because of increased stocking rate on wheat-ryegrass, but not on bermudagrass. Also, the more intensive 11-paddock system was not more productive than the 3-paddock system in either season.

The performance of grazing sheep in relation to stocking rate and exposure to nematode infections

The effect of nematode infections on the performance of sheep grazing at different stocking rates was investigated. Six groups of four ewes per group, each having twin lambs, grazed six paddocks at 9, 13 and 17 ewes/ha for two seasons. Three infected groups grazed paddocks contaminated with nematodes, while three control groups grazed parasite-free paddocks. Paddocks received 0, 80 or 160 kg N fertilizer ha −1 year −1 to compensate for increasing stocking rate. Ewes were withdrawn at the end of July. The serum albumin levels were markedly depressed in infected ewes and lambs ( p<0.001), and especially depressed in lambs at higher stocking rates ( p<0.001). Higher stocking rate and infection with nematodes resulted in marked reductions in weight gains of lambs ( p<0.001). Weight gains of lambs were more affected in males than in females, and the postweaning interaction of stocking rate, infection and sex was marginally significant ( p<0.06). The detrimental effect of nematode infections on slaughter carcass value was more pronounced at higher stocking rates ( p<0.0001). In the second year, the value of product per hectare increased with stocking rate in control paddocks, but decreased in infected paddocks. The study indicated that the loss in productivity associated with nematode infections in sheep may increase with increasing stocking rates.

Long-term fertiliser application and fertility of hill soils

Application of phosphatic fertiliser to legume/grass pastures, and increased stocking rate, is commonly assumed to increase soil organic matter (estimated from soil carbon) content, to lower soil pH, and to increase soil Olsen P status. Changes in these variables in soils derived from sedimentary parent material were monitored over 16 years, in a longterm grazing experiment on southern North Island hill country. There were 2 fertiliser treatments, principally high (capital applications followed by 375 kg/ha/year) and low (125 kg/ha/year) superphosphate application. There was a net loss of soil C of approximately 200 kg/ha/year in both treatments, although annual C inputs to the soil were greater (by 1000 kg/ha) in the high fertiliser soils. Soil pH increased slightly; and Olsen P status reflected P application, although it was less responsive to P application (13 kg P/ha applied above maintenance for 1 Olsen P unit increase) than has commonly been assumed is the case (4-7 kg P/ha per unit). The most likely reason for net loss of soil C is increased decomposer activity in the soil, and the greater proportion of plant-fixed C ingested by grazing animals as a result of intensification. The lack of a decline in soil pH may have been related to the declining soil organic matter level lowering hydrogen ion-supplying power. The lower-than-expected responsiveness of Olsen P to fertiliser P application was probably because the experimental area had a very poor fertiliser application history, in comparison with previous experiments against which Olsen P was calibrated. Keywords: carbon, fertiliser application, hill country, Olsen P, organic matter, pH, soils

A comparison of growth rates and carcass quality of steers receiving maize silage as a supplement to annual pasture or as a component of a feedlot ration

Summary. We tested the hypothesis that liveweight gain per hectare could be doubled in beef steers grazing irrigated annual pastures by increasing stocking rate from 2.5 to 5.0 steers/ha and supplementing the heavier stocked treatments with maize silage offered at either 2.4 or 5.6 kg dry matter/steer. day to replicated groups of 4 steers. During an average period on feed of 172 days, liveweight gain was substantially increased, from 245 kg/ha to either 464 or 576 kg/ha, when maize silage was fed to steers at 2064 or 4816 kg dry matter/ha, in association with an increase in stocking rate from 2.5 to 5.0 steers/ha. However, such production systems increased the chance of feed shortages, particularly in exceptionally wet winters such as the one experienced in the experiment. Increasing the rate of supplementary feeding without increasing stocking rate may not be economically viable. Other strategies, such as lot feeding steers, were also tested. Diets where maize silage constituted either 46% dry matter (with the balance of the diet comprising wheat grain, cottonseed meal, urea, bentonite, vitamins and minerals) or 97% dry matter (with the balance of the diet comprising urea, vitamins and minerals) led to steers achieving liveweight gain of 1.34 and 0.93 kg/steer. day respectively. Carcasses from steers eating maize silage fed at pasture or maize silage as a component of lot-fed diets had at least as adequate fat cover and as good eating quality as carcasses from steers grazing at 2.5 steers/ha.

Grazing management of oversown tussock country 3. Effects on liveweight and wool growth of Merino wethers

The liveweight performance, wool production, and wool characteristics of Merino wethers under nine different grazing management regimes for oversown tussock pasture on a steep (30°), south‐east facing hillside (760–930 m altitude, 500 mm annual rainfall) in New Zealand was measured for six consecutive years. Continuous stocking, alternating (two paddock), and rotational (six paddock) grazing were each compared at low, medium, and high stocking rates (1.9, 3.0, and 4.1 SU/ha/year, respectively). By the sixth year, alternating grazing at the medium stocking rate gave maximum liveweight gain/ha. An interaction was demonstrated, with advantage to alternating and rotational grazing over continuous stocking strengthening with increasing stocking rate. Liveweight gain for alternating and rotational grazing was similar at all stocking rates, showing an advantage in animal performance over that from continuous stocking can be achieved with a minimal amount of subdivision fencing. The advantage to alternating and rotational grazing over continuous stocking was most obvious during late spring/early summer, suggesting that in practical terms runholders need to consider such management for ewes in late lactation with lambs still at foot. Wool growth/ha increased linearly with increased stocking rate, with advantage to alternating and rotational grazing evident at high stocking rates. In contrast to the lowland experience with Romneys, the rate of Merino wool growth declined as the grazing season progressed. Fibre diameter was 1.5 μm less at the high than at the low stocking rate. Practical application is discussed, with emphasis on achieving a realistic balance between objectives to maximise wool production and those to sustain pasture production and maintain desired animal liveweight.

Cause for the Decline of Large Rainbow Trout in a Tailwater Fishery: Too Much Putting or Too Much Taking?

We studied causes for the decline of large (>40 cm total length, TL) rainbow trout Oncorhynchus mykiss and the transition from put–grow–take to put-and-take conditions in Lake Taneycomo, a popular tailwater in Missouri. In this fishery, rainbow trout densities have been sustained against increasing fishing pressure over the last 30 years mainly by increasing stocking rates of catchable-size fish (23–33 cm TL). Short residence times of rainbow trout resulting from heavy fishing pressure and high vulnerability to angling are generally considered the main reason for this speciesˈ limited growth after stocking in cold tailwaters. However, we found that increasing stocking rates in Lake Taneycomo have been paralleled by food base degradation, leading to submaintenance consumption rates for rainbow trout (i.e., poor growth conditions). A less prominent role of residence times was evident in the decline of poststocking growth and fewer large fish. In contrast to resident brown trout Salmo trutta, high diet similarity was observed across all sizes of rainbow trout collected during the 3-year study, hinting that this species may have a relatively limited capacity to partition food resources intraspecifically in some cold tailwaters. This limitation may contribute to the tendency of rainbow trout to fail to reach large sizes in these environments. Our findings indicate that when poststocking growth of rainbow trout is desired in cold tailwaters, greater attention to energetic conditions is warranted.

Vegetation Response to Increasing Stocking Rate under Rotational Stocking

This 10-year study was designed to evaluate vegetation response to increasing stocking rates under rotational stocking (3 days graze, 51 days rest) and long-term rest. The 4 stocking rate treatments ranged from the recommended rate for moderate continuous grazing to 2.7 times the recommended rate. Common curly-mesquite [Hilaria belangeri (Steud.) Nash] increased (P = 0.05) in all grazed treatments and decreased in the livestock exclosure. Sideoats grama [Bouteloua curtipendula (Michx.) Torr.] along with other midgrasses decreased (P = 0.07) in all grazed treatments and increased in the livestock exclosure. Because the midgrasses were palatable species and not abundant, they were defoliated too intensively and too frequently. Rotational stocking was not able to sustain initial species composition at any of the stocking rates tested.

Rotational vs. Continuous Stocking of Beef Cows and Calves on Mixed Endophyte-Free Tall Fescue-Bermudagrass Pasture

Endophyte-free tall fescue (Festuca arundinacea Schreb.) furnishes better animal performance than endophyte- infected grass but is less persistent under grazing, especially in mixture with common bermudagrass [Cynodon dactylon (L.) Pers]. Rotational (RS), compared with continuous (CS), stocking of endophyte-free tall fescue may improve persistence when grown with an aggressive warm season perennial grass. Four 40-acre bermudagrass pastures no-till seeded witb endophyte-free 'AU Triumph' tall fescue were used, allowing two replications to compare CS and RS methods. Rotationally stocked pastures were divided into 12 paddocks to allow 2 d of grazing and 22 d of rest. Twenty Hereford (Bos taurus)x Brangus (B. indicus x B. taurus) beef cows/40-acre pasture were maintained year around for 3 yr with additional cows added in spring and summer to maintain similar forage availability. Grazing method had no effect on cow weight change, pregnancy rate, or calf weaning weight. Pasture stocking rate and calf weaning weight per acre were 38 and 37% higher (P < 0.10), respectively, and winter hay consumption was 31% lower from rotationally stocked pastures because of better tall fescue persistence and forage availability. Crude protein (CP) and in vitro dry matter digestibility of available forage generally exceeded 8 and 50%, respectively, throughout the year. Rotational stocking appears to be useful in maintaining stands of endophyte-free tall fescue in bermudagrass pastures.

A comparison of growth, survival rate, and number of marketable fish produced of swordtails, Xiphophorus helleri Heckel (Family Poeciliidae), between two types of culture systems

To test the effect of stocking density on growth, survival rates and size distribution of juvenile swordtails, Xiphophorus helleri Heckel, under different environmental conditions, fish were stocked at rates of 1, 3 and 6 fish I−1. Growth was monitored over a 14-week period. Fish were weighed in six groups of 20 fish per tank. Size variation was determined at the end of the growth period by measuring the total length of each fish to the nearest mm. Fish were stocked in two different systems at three stocking densities (1, 3, and 6 fish I−1) in replicate. The systems were an indoor aquarium system and a tunnel system under semicommercial conditions. In each system, increasing stocking rates resulted in a significant reduction of growth rates. In the aquarium system, survival rate was not related to stocking density, whereas in the tunnel system, fish at the highest stocking density had a lower survival rate than those kept at the two lower stocking densities. The number of marketable fish above a set size limit of 40 mm total length was not higher in fish stocked at 6 fish I−1 than at 3 fish I−1 at the end of the study. Therefore, a stocking rate of 3 fish I−1 would be optimal. At the end of the study, fish were categorized into males, females and immature fish. Fish with a clearly visible gonopodium were classified as males, those with typical female characteristics as females, and small fish that were not yet differentiated as immature fish. The ratio of females to males was highly skewed in both systems, favouring a higher percentage of females. As stocking density increased, the female:male ratio was significantly reduced, which would result in a greater number of saleable pairs at increased stocking density. The implications of these results for the management of intensive production of swordtails are discussed.

The influence of stocking rate on gastrointestinal nematode infections of sheep over a 2-year grazing period

Six groups of four ewes with twin lambs grazed six paddocks during two consecutive seasons from May to September in a two-factorial study on stocking rate (9, 13 and 17 ewes ha −1) and infected (designated I-low, C-medium and I-high) versus clean pasture (C-low, C-medium and C-high). All animals were treated with anthelmintic at turn-out and the C-groups were further treated fortnightly. The two sets of paddocks received 0, 80 and 160 kg N fertilizer ha −1 annually with increasing stocking rate. Ewes were withdrawn at the end of July, and all lambs were slaughtered at the end of the grazing season for total worm counts. Nematode infections were subclinical during the first year. The second year, diarrhoea and soiled hindquarters were present from early August onwards in all I-groups with highest incidence at high stocking rate. The faecal egg counts of I-ewes were similar the first year but were substantially higher in I-medium and I-high compared with I-low in the second year. The lambs had differences in faecal egg counts related to stocking rate both years ( P<0.05) and group I-high had faecal egg counts ten-fold higher than I-medium and I-low at the end of the second year. A significant effect of the interaction of stocking rate times ± infection was found in serum-pepsinogen levels in lambs ( P<0.05). Worm burdens (predominantly Trichostrongylus vitrinus, Ostertagia circumcincta and Nematodirus filicollis) were not related to stocking rate in lambs at the end of the first year whereas there was a significant effect of stocking rate on T. vitrinus burdens the second year. Pasture larval counts and results of tracer lambs indicated a positive relationship between stocking rate and pasture infectivity. It is concluded that the level of ovine nematode infections, especially Trichostrongylus spp., in weaned lambs increased with increasing stocking rate even though pasture production was enhanced by increased rates of fertilizer application.

Financial viability - a long-term view

Farm profitability is under pressure, with depressed product prices and a rising exchange rate combining to reduce farmer incomes. While exchange rate movements do affect short-term profitability, longterm trends have a much greater effect upon farm profits. While commodity prices are cyclical, over time they fail to keep up with inflation. An analysis of international commodity prices from 1949 to the present day demonstrates a reduction in real terms for all agricultural commodities. An analysis of prices received by New Zealand farmers since the 1950s shows a similar trend. The efficiency of sheep production, measured as lambing percentage and wool weights, has not demonstrated the improvements achieved by other sectors. Milkfat production per cow has doubled over the past 80 years, broiler chicken feed conversion efficiency has doubled over the past 20 years, wheat yields are two and a half times greater now than 70 years -ago, while lambing.percentage and wool weights hXVc not-significantly-improved-since-I-950.Sheep. and beef farms maintained profitability by increasing stocking rate and stock numbers per labour unit, and diversifying .into more profitable stock, such as deer. The pressures facing farmers in the mid 1990s are being faced by other farmers elsewhere in the world, and have existed since intensive farming began in New Zealand. To farm profitability today, as in the past, farmers need to continue to capitalise on technology, and modify farm outputs to match market demand, at a greater rate than?%tip~titEK -~~ - Keywords: agricultural profitability, agricultural production, commodity prices, New Zealand

Factors influencing the yield of brown trout, Salmo trutta m. lacustris L., in northern Finnish lakes

Abstract Lake‐to‐lake variation in brown trout, Salmo trutta m. lacustris L., yield from stocking was examined in 34 lakes in northern Finland. The trout were mainly stocked as 2–3‐year‐old fish. Catch statistics were compiled with information on water quality, water level fluctuations, fishing effort and lake geomorphology. Absolute brown trout yields (kgha‐1) increased with increasing stocking rate, but there was an indication of non‐linearity at higher stocking densities. Relative yields (kg per thousand trout released) were highest at low stocking rates. Stepwise multiple regression analysis was used to determine the best predictive model for lake‐to‐lake variability in brown trout yields. Seventeen measured regressands were used initially, and then replaced with scores obtained in a principal component analysis of highly correlated water quality variables and species‐specific fish yields. Three major determinants of brown trout yields in these lakes were found in both analyses: fish community, stocking rate and fishing effort. Brown trout yields from stocking were higher in lakes with proportionally high yields of vendace or vendace and whitefish and proportionally low yields of pike.