Results 1 - 10 of 749
Results 1 - 10 of 749. Search took: 0.039 seconds
|Sort by: date | relevance|
[en] To restore a degraded pasture of Brachiaria decumbens, located in Sao Carlos - SP, southeastern Brazil, under altitude tropical climate, an experiment was carried out to study the effects of limestone, buried or not buried in the soil, and fertilizer use on mineral content and forage yield, after 3 years of treatment. Limestone and phosphorus were applied once, one month before starting. NK were applied after each cutting, for fertilized plots, four to five times a year. Experimental design was a random block (100 m2), with 6 replications and 4 treatments. Each block received 4 t/ha of limestone, except the control. Forage samples were collected 14 cm above soil surface. Instrumental neutron activation analysis (INAA) followed by gamma-ray spectrometry was the analytical method used to determine the mineral contents. Dry matter yield was affected positively with liming when compared with the limestone control, but the effect of limestone use was more pronounced with the concomitant use of NK fertilizer. The contents of Ca, Cs, Fe, La, Mg, Rb, Sc, Sm and Th in forage were negatively affected with the NK use, perhaps due to a dilution effect, while a reverse were observed for K, Cl, perhaps due to input of KCl, besides Br, Mn and Se. It seems that limestone is not a key input to restore degraded tropical pastureland, grown on acid soils, when nitrogen is lacking. INAA allowed the monitoring of some not routine elements that may be under observation to avoid potential plant nutritional disorders in production systems with high limestone and fertilizer use. (author)
[en] The study was conducted at National Agricultural Research Centre (NARC) Islamabad during 2002-03 to asses the effect of nitrogen fertilizer and harvesting intervals on the forage yield and nutritional value of elephant grass. Four nitrogen levels i.e. 0, 40, 80 and 120 kg N ha/sup -1/ in the form of Urea were applied with three harvesting intervals i.e. 30, 45 and 60 days. The study revealed that the highest Dry Matter yield was obtained by harvesting elephant grass at 60 days interval with 80 or 120 Kg N ha/sup -1/ fertilizer level while the lowest Dry Matter was obtained at 30 days harvesting interval. The results showed that crude protein decreased with longer harvesting intervals in elephant grass. The higher crude fiber was noted in plants harvested after longer interval of cutting, 45 or 60 days interval contained CF as 30.0 and 32.7, respectively. The plants harvested at 45 days interval gave good total ash than other intervals while nitrogen fertilizer had slight effect. (author)
[en] Slime mold Physarum polycephalum optimizes its foraging behaviour by minimizing the distances between the sources of nutrients it spans. When two sources of nutrients are present, the slime mold connects the sources, with its protoplasmic tubes, along the shortest path. We present a two-dimensional mesh grid memristor based model as an approach to emulate Physarum’s foraging strategy, which includes space exploration and reinforcement of the optimally formed interconnection network in the presence of multiple aliment sources. The proposed algorithmic approach utilizes memristors and LC contours and is tested in two of the most popular computational challenges for Physarum, namely maze and transportation networks. Furthermore, the presented model is enriched with the notion of noise presence, which positively contributes to a collective behavior and enables us to move from deterministic to robust results. Consequently, the corresponding simulation results manage to reproduce, in a much better qualitative way, the expected transportation networks. (paper)
[en] The study was conducted at the National Agricultural Research Centre, Islamabad, Pakistan to investigate the impact of mixing low palatable grasses namely Heteropogon contortus, Desmostachya bipinnata, Sorghum halepense and Chrysopogon aucheri with tree leaves of Leucaena leucocephala (Ipil ipil) in the ratio of 75:25, 50:50, 25:75, along with sole species on their chemical composition. Samples were analyzed for proximate parameters (crude protein (CP), crude fiber (CF), total ash and ether extract (EE)). The results revealed that there were significant differences in dry matter (DM) among different grasses. DM content of low palatable grasses was generally high (70-75%) as compared to Ipil ipil leaves (45-55%). DM content among mixtures was also variable. For the treatment grass 75% + Ipil ipil 25%, DM range was 65-70%, for grass 50% + Ipil ipil 50%, it was 60-65% and for grass 25% + Ipil ipil 75%, it was 55%. The CP value of the treatments showed significant variation ranging from less than 10% in grasses to almost 30% in pure Ipil ipil leaves. The mixtures had CP content corresponding to proportions of grasses and legume tree leaves. The CF values also varied significantly among the treatments. Grasses had in general higher CF content than legume leaves. It can be concluded that addition of Ipil ipil leaves to grasses improved overall nutrition especially CP of the feed. (author)
[en] Anthropogenic noise is rapidly becoming a universal environmental feature. While the impacts of such additional noise on avian sexual signals are well documented, our understanding of its effect in other terrestrial taxa, on other vocalisations, and on receivers is more limited. Little is known, for example, about the influence of anthropogenic noise on responses to vocalisations relating to predation risk, despite the potential fitness consequences. We use playback experiments to investigate the impact of traffic noise on the responses of foraging dwarf mongooses (Helogale parvula) to surveillance calls produced by sentinels, individuals scanning for danger from a raised position whose presence usually results in reduced vigilance by foragers. Foragers exhibited a lessened response to surveillance calls in traffic-noise compared to ambient-sound playback, increasing personal vigilance. A second playback experiment, using noise playbacks without surveillance calls, suggests that the increased vigilance could arise in part from the direct influence of additional noise as there was an increase in response to traffic-noise playback alone. Acoustic masking could also play a role. Foragers maintained the ability to distinguish between sentinels of different dominance class, increasing personal vigilance when presented with subordinate surveillance calls compared to calls of a dominant groupmate in both noise treatments, suggesting complete masking was not occurring. However, an acoustic-transmission experiment showed that while surveillance calls were potentially audible during approaching traffic noise, they were probably inaudible during peak traffic intensity noise. While recent work has demonstrated detrimental effects of anthropogenic noise on defensive responses to actual predatory attacks, which are relatively rare, our results provide evidence of a potentially more widespread influence since animals should constantly assess background risk to optimise the foraging–vigilance trade-off. - Highlights: • Anthropogenic noise disrupts response to surveillance calls in dwarf mongooses. • Foragers more vigilant in anthropogenic noise. • Partly driven by noise itself. • Also a result of partial acoustic masking. - Anthropogenic noise decreases response to sentinel's surveillance calls through partial masking and the direct influence of anthropogenic noise on perceived risk.
[en] Dry seeds of sorghum × sudan were carried into space by satellite Shijian No.8 and the mutagenic effects of space condition on the seeds vigor and agronomic traits in SP1 generation were studied. The results showed that the space condition slightly damaged these seeds with slight depression of germination vigor and germination rate, and had no effects on phenophase, plant height, node diameter and leaf area, but the tiller and leaf number were effected greatly, and two typical useful mutation type were found, multi-leaf and multi-tiller identified. Further study indicated that the multi-leaf mutant was only physiological damage and the multi-tiller mutant were genetically stable mutation. By direct selection and purification with several generations, an excellent parent material with multi-tiller, high ratio of leaf to stem, and high only matter content was obtained, which could be propagated by seeds. (authors)
[en] Interception and retention in pasture grass of nuclides in ionic form and of labelled particles (40-63, 63-100, 100-200 μ in size) were studied experimentally during 1968-70. The results obtained are compared with data from grazing experiments during 1970-72. The data showed that the relative amount of material intercepted by the vegetation decreased markedly in the following order: wet-deposited nuclides > wet-deposited particles > particles dry-deposited on grass wet rain > particles dry-deposited on grass superficially wet > particles dry-deposited on dry grass, and small particles > larger particles. At high relative humidity of the air much more of a deposition could be intercepted than at low relative humidity. The retention of intercepted material was influenced by type of material and by precipitation. Intense rains shortened the half residence time considerably. Dry-deposited materials intercepted in grass suffered marked losses by falloff during the first few days after deposition, which was followed by a phase with a longer half residence time. (author)
[en] Constructing models of living organisms locating food sources has important implications for understanding animal behavior and for the development of distribution technologies. This paper presents a novel simple model of stochastic differential equations for the foraging behavior of fish schools in a space including obstacles. The model is studied numerically. Three configurations of space with various food locations are considered. In the first configuration, fish swim in free but limited space. All individuals can find food with large probability while keeping their school structure. In the second and third configurations, they move in limited space with one and two obstacles, respectively. Our results reveal that the probability of foraging success is highest in the first configuration, and smallest in the third one. Furthermore, when school size increases up to an optimal value, the probability of foraging success tends to increase. When it exceeds an optimal value, the probability tends to decrease. The results agree with experimental observations. (paper)
[en] This paper outlines the chief design and performance features of a forage drying installation which makes use of locally available geothermal energy. The heat exchange is accomplished through a water-air exchanger directly fed by 59 degrees C geothermal springs. Two 80,000 cubic meter/hour ventilators, making use of this energy (58 to 38 degrees C heat exchange), raise the drying air temperature by 16 degrees C, while providing an overall drying capacity of 43,200 kg/day. The balance of available 38 degrees C geothermal energy is being employed by a local aquaculture farm. The paper comments on the economic and environmental benefits being derived from this direct utilization of geothermal energy
[en] Highlights: • Heavy metals in nectar deterred nectar robbing. • Heavy metals in nectar shortened foraging time but increased visitation rate of pollinators. • Heavy metals in nectar might indirectly enhance female fitness of Hosta ensata mediated by pollinators and nectar robbers. Plants growing in heavy-metal-rich soils can accumulate metals into their nectar. Nectar chemical composition can alter foraging behavior of floral visitors (including pollinators and floral antagonists) and further affect plant reproductive fitness. The role of nectar heavy metals in deterring pollinators (e.g., shortening foraging time) has been recently studied, but their effects on plant reproduction via changes in behaviors of both pollinators and floral antagonists (e.g., nectar robbers) are less understood. We experimentally manipulated four nectar heavy metals (Zn, Cu, Ni, and Pb) in a native ornamental plant, Hosta ensata F. Maekawa, to investigate the effect of nectar metals on plant reproductive success. We also recorded nectar robbing as well as foraging time and visitation rate of pollinators to assess whether nectar metals could alter the behavior of antagonists and mutualists. Although metals in nectar had no significant direct effects on plant reproduction via hand-pollination, we detected their positive indirect effects on components of female fitness mediated by pollinators and nectar robbers. Matching effects on female plant fitness, nectar robbers responded negatively to the presence of metals in nectar, robbing metal-treated flowers less often. Pollinators spent less time foraging on metal-treated flowers, but their visitation rate to metal-treated flowers was significantly higher than to control flowers. Moreover, pollinators removed less nectar from flowers treated with metals. Our results provide the first direct evidence to date that heavy metals in nectar are capable of deterring nectar robbers and modifying pollinator foraging behavior to enhance plant reproductive fitness.