Developing Strategies for Spatially Variable Nitrogen Application in Cereals, Part II: Wheat

For precision agriculture to provide both economic and environmental benefits over conventional farm practice, management strategies must be developed to accommodate the spatial variability in crop performance that occurs within fields. Experiments were established in crops of wheat (Triticum aestivum) over three seasons in two fields. The aim was to evaluate a set of variable rate nitrogen strategies and examining the spatial variation in crop response to applied N. The optimum N application rate in the field with three different soil series (predominantly calcareous silty clay loam over oolitic limestone) was uniform across the field. In contrast the other field with uniform soil type (slightly calcareous brown clay loam), provided a more variable response. Estimates of yield potential, produced from either historic yield data or shoot density maps derived from airborne digital photographic images, were used to divide experimental strips into management zones. These zones were then managed according to two N application strategies. The results from the historic yield approach, which is currently the most practical commercial system, based on 3 yr of yield data, were variable with no overall yield or economic advantages. It was concluded that that this approach may not provide a suitable basis for varying N rates. The shoot density approach, however, offered considerably greater potential as it takes account of variation in the current crop. Using this approach, it was found that there was insufficient variation in the shoot density in the field with diverse soil types. However, in the field with the uniform soil type, applying additional N to areas with a low shoot population and maintaining the standard N rate to areas with an average shoot population resulted in an average strategy benefit of up to 0·46 t ha⁻¹ compared with standard farm practice. It is necessary to combine the ‘real-time’ data on relative crop structure, obtained by remote sensing with ground truth assessments and absolute benchmark values to successfully adjust N input levels to maximise yield.     

Capture efficiency of a multi-species survey trawl for Snow Crab (Chionoecetes opilio) in the Newfoundland region

An experiment was carried out during September of 2001 to estimate the relative catching efficiency of the NAFC's (Northwest Atlantic Fisheries Centre) standard survey bottom trawl, the Campelen 1800 shrimp trawl, for Snow Crab (Chionoecetes opilio). Secondary trawls were mounted underneath the main trawl directly behind the footgear to estimate escapement of crab passing underneath the main trawl. Overall, the capture efficiency of the survey trawl was found to be much lower than 1.0 and highly variable, with variability being strongly related to substrate type and Snow Crab size. The probability of capture monotonically increased with crab size, and was higher on soft than on hard substrates. Three substrate-specific capture efficiency functions were defined; (1) efficiency was highest (about 0.73–0.95), and least dependent on crab size, on the softest mud substrate; (2) efficiency was lower (about 0.39–0.70) and linearly related to crab size throughout a soft mud–sand substrate; and (3) efficiency was lowest (about 0.05–0.33) on a variety of hard substrates within relatively shallow water. Our models over-estimated true efficiency because secondary trawls were not fully efficient, i.e., crab escaped underneath their footgear. Nevertheless, our experiment demonstrated that substrate type can affect capture efficiency and annual changes in trawl configuration or in Snow Crab distribution in relation to substrate type will affect survey biomass estimates. Additional studies using various approaches could provide a basis for standardizing survey catches for varying capture efficiency effects and refining survey-based estimates of biomass and exploitation rates of Snow Crab.     

Quantifying the effects of soil texture and weather on cotton development and yield using UAV imagery

Precision Agriculture - Quantification of interactions of soil conditions, plant available water and weather conditions on crop development and production is the key for optimizing field management...     

The Leucocytozoidae of South African birds: Passeriformes.

The leucocytozoids of ten families of Passeriformes--Estrildidae, Fringillidae, Laniidae, Nectariniidae, Passeridae, Ploceidae, Promeropidae, Pycnonotidae, Sturnidae and Zosteropidae--are reviewed. Leucocytozoon roubaudi from the Estrildidae, L. fringillinarum from the Fringillidae, L. balmorali from the Laniidae, L. gentili from the Passeridae, L. bouffardi from the Ploceidae, L. brimonti from the Pycnonotidae and L. zosteropis from the Zosteropidae are re-described. Leucocytozoon dutoiti, L. nectariniae, L. deswardti, L. pycnonoti and L. sturni are new species described from the Fringillidae (Carduelinae), Nectariniidae, Promeropidae, Pycnonotidae and Sturnidae respectively while L. monardi is considered to be a synonym of L. gentili and L. molpastis is considered to be a synonym of L. brimonti.     

CONTRAST PARANASAL SINUSOGRAPHY FOR EVALUATION OF DISEASE OF THE PARANASAL SINUSES OF FIVE HORSES

Positive-contrast paranasal sinusography was employed to evaluate 5 horses with disease of the paranasal sinuses. Diseases of the paranasal sinuses of these horses were progressive ethmoidal hematoma, bacterial sinusitis secondary to dental disease, and neoplasia. Positive-contrast sinusography allowed more complete evaluation of disease of the paranasal sinus of the horse than did survey radiographs.     

The application of island-biogeographic theory to forest tracts: Problems in the determination of turnover rates

Any change in the species-composition of birds on ‘islands’ may be described potentially by a number of models, one of which is the equilibrium island biogeographic model. The proper application of the equilibrium model requires that several conditions be met; the most important of which are: (1) the ability to identify true ‘colonists’; (2) balanced immigration and extinction rates; and (3) no large-scale environmental alterations causing changes in species-composition between sampling intervals. Failure to meet such conditions may lead to improbable or unrealistic interpretations of species change within the context of equilibrium island biogeographic theory. This problem is illustrated with some recent data on birds residing in a small forest patch.When the theory is used to determine the design characteristics of faunal reserves, the entire matter takes on added significance. Ecological justification for the preservation of large, contiguous areas cannot be gained from the equilibrium model. In addition, predictions of the model are virtually useless without an accompanying body of autecological information on the species intended to be preserved.