The long‐term economic benefits of `patch' spraying are likely to be related to the initial spatial distribution of the target weeds, the demographic characteristics of the species and the weed control and crop husbandry practices to which they are subjected. This paper describes a stochastic simulation model developed to investigate the interaction between weed seed dispersal and patch spraying. Simulated weed plant and seed populations are generated and compared with data from field observations. Lloyd's Patchiness index is used to quantify the patchiness of the weed density distribution, and the parameter k of the negative binomial distribution is used as a measure of distribution shape. A method of assessing the spatial scale of weed aggregation is proposed, in which spatial weed density information is transformed into the frequency domain, using a discrete two‐dimensional Fourier transform. In this paper, we simulate `on/off' patch spraying (full or zero herbicide application rate). A quantitative analysis of the effects of sprayer resolution and weed seed dispersal range on the herbicide reduction and yield benefits from patch spraying is performed for three initial spatial seedbank distributions. The model is parameterized for the grass weed Alopecurus myosuroides Huds. Herbicide is applied in square areas (whose size is defined by the spatial resolution of the sprayer) in which mean weed density is greater than or equal to one plant m–2. For a system conforming to this specification we show that for the control of A. myosuroides, it is unlikely that patch spraying would be profitable in the long term if the control area is larger than 6 m × 6 m. In some circumstances higher resolution may be required.
Airborne multispectral imaging has been used to map patches of Avena spp. (wild‐oats) in a field of seedling triticale (X Triticosecale, Wittmack). Images of the target field were acquired using a four‐camera airborne digital imaging system, recording in the infrared, red, green and blue wave‐bands. Spectral information derived from images of 0.5‐, 1.0‐, 1.5‐ and 2.0‐m spatial resolution were correlated with detailed on‐ground weed density measurements to investigate the effect of image resolution on mapping accuracy. Comparisons between normalized‐difference vegetation index (NDVI) or soil‐adjusted vegetation index (SAVI) images and weed data achieved correlations of up to 71%. The highest correlation was achieved with the 0.5‐m‐resolution images and the lowest with the 2.0‐m‐resolution images. At 0.5‐m resolution, NDVI images could not reliably discriminate weed populations of less than 28 weeds m–2 from weed‐free regions, while SAVI images could not discriminate populations of less than 17 weeds m–2. At 1.0‐, 1.5‐ and 2.0‐m resolution, SAVI images could not discriminate populations of less than 23 weeds m–2, while NDVI images again demonstrated a higher discrimination threshold. Results suggest that airborne multispectral imaging could be used as part of a stratified weed sampling system.
This study assessed the diversity and distribution of trees and shrubs in a 16 ha disturbed plot in the Takamanda Rainforest. Linear transects (8) were laid in the field which radiated from the centre of the plot. The girth of the trees and shrubs were measured and species identified. A total of 99 species (72 trees and 27 shrubs) belonging to 87 genera and 34 families were recorded. Caesalpinaceae was the most represented tree family (9 species) while Rubiaceae was the most represented among shrubs (9 species). Baphia nitida recorded the highest tree density (143.75 individual's ha
α-Glucosidase inhibitory potential of selected anti-diabetic plants has been studied. The study evaluated α-glucosidase inhibition using α-glucosidase from Saccharomyces cerevisiae and pnitrophenyl α-D-glucopyranoside as substrate. The result showed that the extract of Albizzia chevalieri leaf, Khaya senegalensis stem bark, Zizypus spina-christi stem bark, Arachis hypogea seed varieties and Mangifera indica leaf had significant (P < 0.05) α-glucosidase inhibitory effect in a concentration dependant manner as compared to acarbose. Cardiac glycosides, alkaloids, saponins, flavonoids and tannins were identified in the extracts. The study concludes that the plant extract contain bioactive compound that may be source(s) of lead compounds with α-glucosidase inhibitory potentials and may explain their hypoglycaemic effects.
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