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排序方式: 共有1479条查询结果,搜索用时 15 毫秒
1.
Nooshin Shahbazi Ken C. Flower J. Nikolaus Callow Ajmal Mian Michael B. Ashworth Hugh J. Beckie 《Weed Research》2021,61(1):25-34
Weeds and weed control are major production costs in global agriculture, with increasing challenges associated with herbicide‐based management because of concerns with chemical residue and herbicide resistance. Non‐chemical weed management may address these challenges but requires the ability to differentiate weeds from crops. Harvest is an ideal opportunity for the differentiation of weeds that grow taller than the crop, however, the ability to differentiate late‐season weeds from the crop is unknown. Weed mapping enables farmers to locate weed patches, evaluate the success of previous weed management strategies, and assist with planning for future herbicide applications. The aim of this study was to determine whether weed patches could be differentiated from the crop plants, based on height differences. Field surveys were carried out before crop harvest in 2018 and 2019, where a total of 86 and 105 weedy patches were manually assessed respectively. The results of this study demonstrated that across the 191 assessed weedy patches, in 97% of patches with Avena fatua (wild oat) plants, 86% with Raphanus raphanistrum (wild radish) plants and 92% with Sonchus oleraceus L. (sow thistles) plants it was possible to distinguish the weeds taller than the 95% of the crop plants. Future work should be dedicated to the assessment of the ability of remote sensing methods such as Light Detection and Ranging to detect and map late‐season weed species based on the results from this study on crop and weed height differences. 相似文献
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植被盖度是刻画陆地生态系统植被覆盖的重要生态参量。以当雄县Landsat-8OLI为数据源,从10种常用植被指数中筛选出适合反演高寒草地生长季/非生长季草地植被盖度的植被指数,引入像元三分法确定端元特征值,通过不同植被指数基于像元二分模型反演植被盖度的对比分析,确定适合生长季/非生长季植被盖度最优植被指数,根据反演结果分析了研究区草地生长季/非生长季植被盖度的时空变化特征。结果表明:1)由可见光-近红外波段构建的植被指数适用生长季植被盖度反演,由短波红外构建的植被指数适用于非生长季植被盖度反演。2)基于MSACRI的像元二分模型适合非生长季植被盖度反演,基于NDVI的像元二分模型则最适用于生长季植被盖度的反演。3)研究区草地植被盖度随海拔增加呈现先增加后减少的单峰变化格局,草地集中分布于海拔4300~5100 m处。生长季植被盖度主要集中于20%~80%,非生长季绝大部分的草地盖度小于40%。研究结果可为草地生态系统碳存储、植被生产力、土壤侵蚀、生态水文等研究提供参考依据。 相似文献
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Tcia Gomes Bergstein‐Galan Romildo Romualdo Weiss Luiz Ernandes Kozicki 《Reproduction in domestic animals》2019,54(2):401-407
Multiple ovulation and embryo transfer (MOET) is an important tool in the sheep industry for increasing numbers of genetically superior individuals. The objective of this study was to evaluate the effect of semen source (frozen or fresh), the number of embryo collection procedures for each donor (NECP), the season in which embryo transfer and collection was performed, and the age and breed of the donor, on the number of recovered embryos and pregnancy rates after embryo transfer. The Alamos Genetics’ flushing station database was used. This consisted of 140 embryo collection procedures, from 53 Dorper and White Dorper sheep donors, aged between one and eight years, totalling 1,200 collected embryos. Neither the number of retrieved embryos nor the pregnancy rate was affected by the semen preservation method (fresh or frozen), NECP or the age and breed of donor. The season did not affect the number of collected embryos but had a significant effect (p < 0.05) on the recipient pregnancy rate, with higher pregnancy rates reported in the winter (65.57% ± 25.33%) compared with spring (37.11% ± 33.27%), summer (29.95% ± 28.33%) or autumn (35.03% ± 31.66%). There is an estimated increase of 98.4% and 71.5% of embryos recovered in the spring and summer seasons, respectively, when winter is used as reference. The survival of embryos is significantly higher when implanted during the breeding season, more specifically in winter. Embryo collection can be carried out throughout the year in sheep, but there may be a marginal advantage in the use of superovulation and fresh embryo transfer programmes in the autumn and winter. 相似文献
6.
[目的]为了探讨张家口坝下地区寒冷季节育肥牛舍内外光照和风速的变化规律,以期发现该地区寒冷季节这两项指标的变化规律。[方法]在张家口怀安县某肉牛场进行了入冬后不同月份牛舍内外光照和风速的研究,在试验前对开放式肉牛育肥舍的后窗进行了封堵,测试时间为2018年11月至2019年5月,每个月的11日、12日和13日进行测定并记录数据。[结果]结果表明,坝下地区中午时间段光照强度大,育肥牛舍内外与密闭舍对比均有不同程度差异显著性(P<0.05或P<0.01);育肥舍及舍外风速也存在不同程度的差异显著性(P<0.05)变化或差异极显著变化(P<0.01)。[结论]该结果为在张家口坝下地区冬季养好育肥牛,科学合理地修缮及改造牛舍提供理论依据和技术参数。 相似文献
7.
Thresholds,sensitive stages and genetic variability of finger millet to high temperature stress 下载免费PDF全文
R. A. Opole P. V. V. Prasad M. Djanaguiraman K. Vimala M. B. Kirkham H. D. Upadhyaya 《Journal of Agronomy and Crop Science》2018,204(5):477-492
Finger millet [Eleusine coracana (L.) Gaertn.] is an important coarse cereal crop grown in the arid and semi‐arid regions and often experiences high temperature (HT) stress. The objectives of this research were (i) to quantify effects of season‐long HT stress on physiological and yield traits, (ii) to identify the developmental stages most sensitive to HT stress and (iii) to quantify the genetic variability for HT stress tolerance in finger millet. Research was conducted in controlled environment conditions. HT stress decreased the chlorophyll index, photosystem II activity, grain yield and harvest index. Maximum decrease in number of seeds per panicle and grain yield per plant was observed when stress was imposed during booting, panicle emergence or flowering stages. Maximum genotypic variation was explained by panicle width and number of seeds per panicle at optimum temperature (OT) and grain yield per plant at HT and number of seeds at HT. Based on the stress response and grain yield, tolerant or susceptible genotypes were identified. Finger millet is sensitive to HT stress during reproductive stages, and there was genotypic variability among the finger millet genotypes for number of seeds per panicle and grain yield under HT, which can be exploited to enhance stress tolerance. 相似文献
8.
Effect of system of lamb rearing and season on early post‐partum fertility of ewes and growth performance of lambs in Katahdin sheep 下载免费PDF全文
S. Rastle‐Simpson K. D'Souza A. Redhead D. Singh‐Knights Q. Baptiste M. Knights 《Journal of animal physiology and animal nutrition》2017,101(5):e21-e30
The effect of season (S), lamb rearing system (RT) and grain supplementation (GS) on post‐partum fertility in Katahdin ewes and growth in Katahdin lambs was evaluated. Katahdin ewes were bred to lamb in fall (n = 36) or spring (n = 56) and at approximately 2.5 months post‐partum were randomly assigned to be permanently separated or to continue to suckle their lambs for an additional 3 months. All ewes were joined with rams following treatment to synchronize oestrus. Weaned (W, n = 84) and continuously suckled lambs (CSK, n = 88) were fed forage only (n = 84; hay and pasture for fall‐ and spring‐born lambs respectively) or were supplemented (n = 88; 18% crude protein ration ad libitum) and all weighed biweekly. Ewes rebred in the fall had a shorter ram introduction to lambing interval (p < 0.05), higher prolificacy (p = 0.001) and higher lambing rates (p = 0.02); however, the proportion of ewes lambing was not affected by season. The first service lambing rate was lower in ewes continuously suckling lambs in the spring, but not in the fall breeding season (S × RT, p = 0.03). Lambs that continuously suckled their dams and were supplemented grew quicker and gained more (p < 0.001) than their weaned and unsupplemented counterparts. The effect of CSK on growth rate of lambs was greater in the spring (RT × S; p = 0.05), and the effect of supplementation on growth rate of lambs was greater in the fall (GS × S; p < 0.0001). In conclusion, Katahdin lambs achieved higher weight gains from continuous suckling and grain supplementation. Moreover, Katahdin ewes are capable of early rebreeding post‐partum while suckling their lambs, which makes them suited for use in accelerated lambing programmes. 相似文献
9.
Simulating bimodal tall fescue growth with a degree‐day‐based process‐oriented plant model 下载免费PDF全文
J. R. Kiniry S. Kim A. S. Williams T. R. Lock R. L. Kallenbach 《Grass and Forage Science》2018,73(2):432-439
Plant growth simulation models have a temperature response function driving development, with a base temperature and an optimum temperature defined. Such models function well when plant development rate shows a continuous change throughout the growing season. This approach becomes more complex as it is extended to cool‐season perennial grasses with a dormant period and bimodal growth curves. The objective of this study was to develop such a bimodal growth model for tall fescue (Schedonorus arundinaceus (Schreb.) Dumort) in the Midwest USA based on multiyear measurement trials. Functions for bimodal growth were incorporated into the ALMANAC model and applied to tall fescue using published tall fescue yields for a variety of sites and soils. Fields of cultivars “Kentucky 31” and “BarOptima Plus E34” were divided into paddocks and sampled weekly for dry‐matter accumulation. These biomass estimates were used to derive weekly growth values by differences between sequential weekly samplings. The measured values were compared to a single tall fescue simulation each year on one soil. Using these results, the ALMANAC model was modified and tested against mean reported tall fescue yields for 11 sites, with one to three soils per site. When we introduced midsummer dormancy into ALMANAC, we assumed dormancy began on the longest day of the year and lasted until the photoperiod was 0.68 hr shorter than the longest. ALMANAC simulated previously reported tall fescue yields well across the range of sites. Thus, ALMANAC shows great promise to simulate bimodal growth in this common cool‐season grass. 相似文献
10.
Seasonal Changes in the Milt Quality of Waigieu Seaperch,Psammoperca waigiensis: Implications for Artificial Propagation 下载免费PDF全文
Milt quality of Waigieu seaperch was sampled at the beginning, the middle, and the end of the spawning season to assess if the sampling season has an effect on milt quality parameters. The milt volume and total sperm production were higher at the middle of the spawning season while the sperm concentration in milt was significantly higher at the beginning and the end of the spawning season. Sperm morphology and the major parameters of seminal plasma (pH, total protein, Mg2+, or Ca2+ concentrations) did not differ throughout the spawning season. The concentrations of Na+ and the osmolality increased throughout the spawning season. The percentage of motile cells did not differ during the spawning season while the duration of sperm motility (swimming duration) and velocity (swimming speed) were significantly different during the spawning season. The fertilization rate (75.7 ± 6.8%) and hatching rate (56.5 ± 3.1%) at the middle of the spawning season were higher than at the beginning and end periods. Results indicated that milt quality parameters and fertility success in the middle of the spawning season were higher compared to earlier and later sampling dates. Thus, we recommend collecting milt during this time for maximal fertilization and hatching success. 相似文献