Nitrogen fixation by white clover in pastures grazed by dairy cows: Temporal variation and effects of nitrogen fertilization

Effects of rate of nitrogen (N) fertilizer and stocking rate on production and N₂ fixation by white clover (Trifolium repens L.) grown with perennial ryegrass (Lolium perenne L.) were determined over 5 years in farmlets near Hamilton, New Zealand. Three farmlets carried 3.3 dairy cows ha^–1 and received urea at 0, 200 or 400 kg N ha^–1 yr^–1 in 8–10 split applications. A fourth farmlet received 400 kg N ha^–1 yr^–1 and had 4.4 cows ha^–1.There was large variation in annual clover production and total N₂ fixation, which in the 0 N treatment ranged from 9 to 20% clover content in pasture and from 79 to 212 kg N fixed ha^–1 yr^–1. Despite this variation, total pasture production in the 0 N treatment remained at 75–85% of that in the 400 N treatments in all years, due in part to the moderating effect of carry-over of fixed N between years.Fertilizer N application decreased the average proportion of clover N derived from N₂ fixation (P_N; estimated by ¹⁵N dilution) from 77% in the 0 N treatment to 43–48% in the 400 N treatments. The corresponding average total N₂ fixation decreased from 154 kg N ha^–1 yr^–1 to 39–53 kg N ha^–1 yr^–1. This includes N₂ fixation in clover tissue below grazing height estimated at 70% of N₂ fixation in above grazing height tissue, based on associated measurements, and confirmed by field N balance calculations. Effects of N fertilizer on clover growth and N₂ fixation were greatest in spring and summer. In autumn, the 200 N treatment grew more clover than the 0 N treatment and N₂ fixation was the same. This was attributed to more severe grazing during summer in the 0 N treatment, resulting in higher surface soil temperatures and a deleterious effect on clover stolons.In the 400 N treatments, a 33% increase in cow stocking rate tended to decrease P_N from 48 to 43% due to more N cycling in excreta, but resulted in up to 2-fold more clover dry matter and N₂ fixation because lower pasture mass reduced grass competition, particularly during spring.     

Waterbird assemblages and associated habitat characteristics of farm ponds in the Western Cape, South Africa

Natural freshwater wetlands are among the most threatened habitats on Earth. Effective wetland biodiversity conservation can not, however, be evaluated without fully understanding the roles of artificial waterbodies as refuges for water-dependent plants and animals. Waterbird assemblages were examined on 59 farm ponds in the Elgin and Caledon districts of the Western Cape, South Africa. This study examines the relationship between waterbird use and habitat characteristics of farm ponds. Patterns of temporal and spatial variation of waterbird species richness and abundance were quantified in relation to the habitat characteristics of each pond. Cluster analysis and multiple regression analyses identified surface area of the farm ponds as an important variable determining the presence and abundance of many waterbird species. Structural diversity in terms of vegetation in and around the ponds was especially important in determining their usage by waterbirds. These variables were evaluated in terms of creating a mosaic of habitat types (by varying vegetation structure and pond topography), which may be a useful way to enhance waterbird diversity at farm ponds. This study concludes that the high number of farm ponds in the transformed habitat matrix of the Western Cape plays an important role in conserving waterbirds.     

Impact of nitrogen cycling on stream water quality in a basin associated with forest, grassland, and animal husbandry, Hokkaido, Japan

The direct discharge of wastes from agricultural fields and livestock feedlots increases the concentration of nitrogen (N) in streams. This study was conducted to determine the impact of farm N budgets on stream water quality. In 1999–2000, we investigated an experimental livestock farm of 457 ha in the Kepau River watershed in Shizunai, Southern Hokkaido, Japan, where grasslands and maize fields account for 33% of the farm's total area. Annual N flow was calculated on the basis of the farm's land management records. Livestock was supplied with 15.2 t N yr⁻¹ from agricultural lands, which made the farm 81% self-sufficient. Livestock excreta produced 17.2 t N yr⁻¹, of which 4 t N yr⁻¹ was lost, probably by ammonia volatilization during decomposition. Apart from manure, the major N inputs were 9.1 t N yr⁻¹ of chemical fertilizers, 6.4 t N yr⁻¹ of atmospheric deposition, and 12.6 t N yr⁻¹ biological N fixation. The major outputs were uptake by forest vegetation of 11.0 t N yr⁻¹, denitrification of 1.5 t N yr⁻¹, and livestock feed production. Consequently, the annual surplus N on the whole farm was estimated to be 12.7 t N yr⁻¹, which corresponds to 28 kg N ha⁻¹ of agricultural land.The annual N load from the farm to the Kepau River was measured at 14.4 t N yr⁻¹. Ninety percent of this load, however, occurred during rainfall and spring snowmelt. Within one 2-week snowmelt period, 5.0 t N was discharged, which corresponds to 35% of the annual load. Although the average N concentration of stream water below the farm was 2.8 mg N L⁻¹, the maximum concentration recorded during the snowmelt season was 13.5 mg N L⁻¹. The N concentration of the stream water increased and the silica (Si) concentration decreased as the stream flow rate increased. Consequently, the molar ratio of Si/N frequently dropped below 2.7, the critical level for the occurrence of eutrophication. The large N load during rainfall and snowmelt could be ascribed to open ditches, which collect tile drainage and surface runoff from the fields, discharging it directly to the river, bypassing the forested riparian zone.     

Monoculture and mixed-species algal farms on a coral reef are maintained through intensive and extensive management by damselfishes

Algal farms maintained by different species of territorial herbivorous damselfishes vary in size, algal biomass, and species composition. To determine the factors that affect the structure of these farms, we compared farming behavior and intensity between two sympatric damselfish species, Stegastes nigricans (Lacepède) and S. obreptus (Whitley), which maintain two different types of farms in the Okinawa Islands, southern Japan. By weeding of indigestible algae and prompt exclusion of herbivorous fishes and grazing sea urchins, S. nigricans manage relatively small farms largely dominated by one algal crop species, Polysiphonia sp. In contrast, by delayed exclusion of herbivores, S. obreptus maintain larger farms invaded by diverse indigestible algae, such as Chondria sp. and Padina sp. As a result of intensive management, S. nigricans attains a higher algal biomass per area than does S. obreptus. This study provides a new perspective, as it suggests that damselfishes practise both intensive and extensive farming. The former results in small and highly productive monoculture farms of one palatable alga, while the latter leads to large, species-rich, mixed-culture farms.     

不同海拔高程梯度下鄱阳湖典型草洲植物群落物种-多度分布格局的模型拟合

基于恒湖农场茶叶港草洲4个样带、19个样地（5 m×5 m）沿海拔高程（高高程-湖边、中高程-洲滩中间、低高程-洲滩边缘）调查得到的植被数据,用4种生态位模型拟合研究该区域不同海拔高程段植物种-多度分布格局。结果表明：（1）随着海拔高程下降,群落偶见种不断减少,且平均盖度均较低;常见种数目保持不变,其中优势种灰化薹草（Carex cinerascens Kukenth）平均盖度、平均高度持续升高,在群落中保持较高的优势地位;（2）3个高程段内生态位优先占领模型对群落物种-多度分布格局有较高的拟合优度（P < 0.05,AIC值分别为-149.41、-61.11、-25.63）,断棍模型、重叠生态位模型、优势优先模型总体上拟合效果较差（P < 0.05,但AIC值均较大）。为研究区植物群落生物多样性的保护和构建机制的探索提供了一定参考。     

Technical note: fate and transport of jet fuel (JP-8) in soils with selected plants

Remediation of soil and groundwater contaminated by leaking fuel storage tanks may be assisted by plants, although plant effects on abiotic and biotic removal processes remain unclear. The objectives of this study were to investigate abiotic and biotic removal of JP-8, a kerosene-based jet fuel, in soils with plants, and to determine the effects of plant-induced water movement. Loss of JP-8 in a dry-soil, control column was 25% after 5 months, primarily due to volatilization and gas-phase diffusion. By comparison, managed treatments with simulated surface spills averaged 86% mass reduction at 5 months, indicating an important contribution of biodegradation. Overall JP-8 mass reduction was similar in surface and subsurface-irrigated systems, indicating water content, not mode of water application, influences bioremediation in near-surface systems. The JP-8 concentration reductions in soil columns contaminated above a simulated watertable were 36% after 3 months and 50% after 12 months for vegetated columns compared to 26% and 34% in unplanted columns. Downward movement of JP-8 in unplanted columns was double that in planted columns. Near the groundwater table, JP-8 persists longer than near the soil surface. Plants promote upward movement of water and help draw spilled JP-8 to aerobic near-surface soil.     

A Bird and Small Mammal BACI and IG Design Studies in a Wind Farm in Malpica (Spain)

Wind farms have shown a spectacular growth during the last 10 years. As far as we know, this study is the first where the relationship between wind power and birds and small mammals have been considered. Before–after control impact (BACI) study design to birds and Impact Gradient (IG) study design to small mammals to test the null hypothesis of no impact of a wind farm were used. In the BACI model Windfarm Area and a Reference Area were considered. Distance from turbines was considered in the IG model. Windfarm installations did not clearly affect bird and small mammal populations. Flight height of nesting and no nesting birds did not show a clear tendency. Small mammals populations suffered high variations in numbers through times by intrinsic population factors. There are many practical problems of detection of human influence on abundances of populations so sampling in the long run can be suggested.     

Effects of species, culture history, size and residency on relative competitive ability of salmonids

The relative competitive ability of juvenile farm and wild salmonids was investigated to provide insight into the potential effects of introduction of cultured salmon on wild Pacific salmonid ( Oncorhynchus ) species. Aquarium experiments involving equal contests ( i.e. size matched, simultaneously introduced individuals) indicated that two wild coho salmon Oncorhynchus kisutch populations were competitively equal to a farm coho salmon population. In equal contests between farm Atlantic salmon Salmo salar (Mowi strain) and these wild coho salmon populations or coastal cutthroat trout Oncorhynchus clarki clarki , Atlantic salmon were subordinate in all cases. When Atlantic salmon were given a residence advantage, however, they were competitively equal to both wild coho salmon populations, but remained subordinate to coastal cutthroat trout. When Atlantic salmon were given a 10–30% length advantage, they were competitively equal to one wild coho salmon population but remained subordinate to the other. In equal contests in semi-natural stream channels, both wild coho and farm Atlantic salmon grew significantly more in the presence of the other species than when alone. It appears that coho salmon obtain additional food ration by out competing Atlantic salmon, whereas Atlantic salmon were stimulated to feed more in the presence of coho salmon competitors. These results suggest that wild coho salmon and cutthroat trout should out compete farm Atlantic salmon of a similar size in nature. As the relative competitive ability of Atlantic salmon improves when they have a size and residence advantage, should feral populations become established, they may exist on a more equal competitive footing owing to the long freshwater residence of Atlantic salmon.     

Changes in demersal wild fish aggregations beneath a sea-cage fish farm after the cessation of farming

Demersal, non-cryptic, wild fishes were counted in replicate 100 m² transects beneath a floating sea-cage fish farm and two nearby sandy locations at Gran Canaria (Canary Islands, eastern Atlantic) four times before and after the cessation of farming. Cessation of farming involved the removal of farmed fishes and ceasing of the daily feeding, although farm structures (cages and moorings) remained. A 'beyond-BACI' sampling design provided the framework to detect the effect of the cessation of farming, which produced qualitative and quantitative changes in the composition and structure of the fishes assemblages beneath the sea-cage fish farm compared with two nearby controls. The aggregative effect on wild fishes due to the existence of the farm decreased from c. 50 times compared to nearby controls when the farm was in full operation to less than two times when only the farm structures remained. Abundances of particulate organic matter feeders (large-sized mugilids), large benthic chondrichthyid rays and Pagellus spp. declined markedly at the fish farm after the cessation of farming, suggesting that the removal of daily feeding was responsible for their disappearance. In contrast, abundances of herbivores, benthic macro- and meso-carnivores were similar beneath the fish farm both before and after the cessation of farming. Benthic macro-carnivores, however, were more abundant beneath the sea-cages compared to control locations, supporting the hypothesis that the increase in the physical structure beneath farms plays a role in aggregating these species. Sparids occurred beneath the sea-cages only after the cessation of farming, while the two natural control locations did not show differences from before to after the cessation of farming. Overall, the results show that the wild fish assemblage beneath the farm partially changed after the cessation of farming to a more natural state, approaching the assemblages observed at the control sites.     

Flora diversity of farm forestry plantations in southeast Queensland

Summary Plant species composition in plantation monoculture of the native Gympie Messmate (Eucalyptus cloeziana F. Muell.) was assessed and compared with native eucalypt forest and cleared grazing land in southeast Queensland, Australia. A total of 18 sites (11 in the plantations, four in native eucalypt forests and three on cleared grazing land) were surveyed. The four plantation age classes during the 18‐month survey period were 0.3–1.8 (very young), 2.1–3.8 (young), 15–16.5 (mid‐aged) and 38–40.5 (old) years of age. Significantly more native plant species were recorded in the plantations, regardless of their age, than on cleared grazing land. The number of native plant species in the old plantations was not significantly different from the native eucalypt forests. Native tree and shrub species richness increased significantly with plantation age. Two species (Ricinocarpos speciosus Muell. Arg. and Xanthostemon oppositifolius F. M. Bailey) listed as Vulnerable and one species (Alyxia magnifolia F. M. Bailey) listed as Rare were recorded in the old plantations. Two Rare species (A. magnifolia and Acianthus amplexicaulis (F. M. Bailey) Rolfe) were recorded in the native eucalypt forests. Exotic plant species, consisting mainly of herbs, grasses and shrubs in the plantations, were significantly more abundant in the very young and young plantations. However, the number of exotic species decreased significantly with increasing age of the plantations. The results suggest that even small‐scale plantation can increase landscape heterogeneity and help protect biodiversity.