Annual weed distributions can be mapped with kriging

The authenticity of weed distribution maps prepared by the geostatistical estimation method, kriging, was investigated. We concentrated on the total number of weed plants and the dominant weed genus Veronica spp. in a 2.1-ha field of winter wheat. Different sampling distances were evaluated. Our analyses showed that kriging weed densities based on seedling counts collected in, 0.25.m² circles in a sampling grid of approximately 10 m × 10 m gave good agreement with actual observations. Reducing the sampling grid to 20 m × 30 m gave poor agreement. New sampling methods combined with positioning devices and injection sprayers are discussed with reference to site-specific weed management.     

Miocene stable isotope record: a detailed deep pacific ocean study and its paleoclimatic implications

Deep Sea Drilling Project site 289 in the western equatorial Pacific has yielded an extremely detailed record of the carbon and oxygen isotopic changes in the Miocene deep ocean. The isotopic record reflects major changes in paleoclimate and paleoceanography, probably dominated by a major phase of Antarctic ice-cap growth. The transition from a relatively unglaciated world to one similar to today occurred between 16.5 x 10(6) and 13 x 10(6) years before the present, with the greatest change occurring between approximately 14.8 x 10(6) and 14.0 x 10(6) years before the present.     

紫外分光光度法测定氟苯尼考及其注射液的含量

采用紫外分光光度法测定氟苯尼考原料药及其注射液的含量。实验结果表明,在0.05~0.5 mg/mL浓度范围内,氟苯尼考的吸光度与浓度呈现良好的线性关系(r=0.9997,n=6);与法定的高效液相色谱法检测结果无差异。     

Results of a thinning study in a black stain (Leptographium wageneri)‐infested Jeffrey/ponderosa pine forest in northern California

Black stain root disease (BSRD) caused by Leptographium wageneri var. ponderosum (Verticicladiella wageneri) is a destructive disease in many Jeffrey pine (Pinus jeffreyi) and ponderosa pine (P. ponderosa) forests of the western United States. Overcrowding is a pervasive problem in these forests, unless alleviated by thinning. In an overcrowded BSRD‐infested second‐growth Jeffrey/ponderosa pine forest in northern California, a large study (16.2 hr; 40 acres) was designed to determine the impact of thinning to four levels—6.9 m²/ha (30 ft²/acre), 13.8 m²/ha (60 ft²/acre), and 20.7 m²/ha (90 ft²/acre) of basal area and a control with no thinning—on the incidence of BSRD‐caused mortality. Ten years after this experiment was initiated, results indicate that thinning to any of these levels lowered the incidence of BSRD‐caused mortality as compared with BSRD‐caused mortality in unthinned control plots.