Inheritance of Resistance to Striga in Sorghum Genotype SRN39

Striga hermonthica (Del.) Benth., a parasitic weed of grasses, causes major yield reductions in the principal cereal crops of semi-arid Africa. Cultivar resistance is the most economic control measure, since adapted, resistant cultivars can be grown without additional input from the subsistence farmer. Information on the genetics of resistance to S. hermonthica is scant. This is partially attributable to the rarity of germplasms which exhibit stable resistance across geographical regions. The objective of this study was to determine if the stable resistance observed in sorghum [Sorghum bicolor (L.) Moench] cultivar SRN39 is heritable. Crosses were made between SRN39 and a susceptible parent, P954063. Parental, F₁, F₂ and backcross generations were grown in infested pots and development of both host and parasite was monitored. Significant variation among genotypes was observed for both host traits and effects on parasite populations. The F₁ did not differ significantly in Striga resistance from the susceptible parent, suggesting recessive inheritance. However, hybrid vigor was exhibited by the F₁ which yielded and developed as well as the resistant parent. Broad sense heritability ranged from 0.23 to 0.55 for host traits and from 0.10 to 0.43 for effect of genotypes on the Striga population. Joint scaling tests showed that observed variation in each host or parasite trait consisted of additive and dominance components, suggesting possible progress could be made with appropriate selection schemes.     

麦田杂草的图像识别技术的研究

主要研究了麦田杂草的图像识别技术,设计了麦田杂草识别系统.该系统包括使用数码相机进行麦田图像数据的采集,实现对图像的预处理;绿色植物与土壤背景的分割包括图像的灰度化与格式转换和图像的二值化;作物与杂草的分割包括作物中心行的识别和作物行的滤除,最后获取杂草图像.在滤除作物行的过程中确定边界阈值时采用通过先计算手工标定的作物行宽度与计算机自动检测的作物行宽度之间的相对误差,然后选定合适的对应最小误差的作物行边界阈值的方法.该系统全程使用MATLAB语言编程,系统最终目的是根据杂草和作物分布的位置特征滤除作物行,识别出杂草.     

基于机器视觉的田间杂草识别技术研究进展

田间杂草识别技术是实现变量喷洒除草剂以保护环境的关键所在。针对国内外在精细农业的杂草识别领域，全面、系统地分析了基于机器视觉的田间杂草识别技术的研究进展与应用状况，以促进该项技术在中国的应用和发展。分别阐述了利用植物和背景形状特征、纹理特征、颜色特征和多光谱特征识别田间杂草技术的理论依据、特征参数、研究状况和问题所在，并指出了实现田间实时识别的难点。     

长期不同施肥对玉米田间杂草生物多样性的影响

通过田间小区试验,研究了长期不同施肥对田间杂草总密度、优势杂草组成及生物多样性的影响。结果表明:综合施用N、P、K肥,不仅降低了田间杂草的总密度,降低了优势杂草在群落中的比重,而且有利于维持田间杂草的生物多样性;不施用N或P肥,田间杂草的总密度增大,优势杂草的比重也明显增强,但不利于维持田间杂草的生物多样性。所以,平衡施用N、P、K肥,有利于维持农田生态系统中的生物多样性,并能更好地进行杂草控制。     

Precise tillage systems for enhanced non-chemical weed management

Soil and residue manipulation can assist weed management by killing weeds mechanically, interfering in weed lifecycles, facilitating operations and enhancing crop establishment and growth. Current tillage systems often compromise these functions, resulting in heavy reliance on herbicides, particularly in no-till systems. Herbicides are an exhaustible resource, so new approaches to merge soil conservation and non-chemical weed management are needed. This paper broadly reviews various preventive and curative non-chemical weed management tactics. It also demonstrates how innovations can be derived from functional requirements of weed management operations, and from biological processes and weaknesses in weed's lifecycles. Mechanical weeding and enhancement of weed seed mortality are highlighted as examples. Major limitations with mechanical weeding include limited weed control in crop rows at early vulnerable crop stages, weather-dependent effectiveness, and difficulties in handling crop residues. Precise steering and depth control, improved seedbed friability and lighter tractors or controlled traffic could bring considerable improvements. To expose weed seeds to predators, position them for fatal germination, viability loss or low emergence may require completely different soil displacement patterns than those of current implements and systems. Controlled traffic and precise strip tillage offer good opportunities for implementing these weed management strategies in minimum-tillage systems.     

Contribution of fallow weed incorporation to nitrogen supplying capacity of paddy soil under organic farming

ABSTRACT

We studied soil nitrogen (N) management in a farmer’s organic rice farming in Japan, where the farmer applied no external N but incorporated gramineous fallow weeds and rice residues as in situ N sources. We focused on the effect of fallow weed incorporation on N-supplying capacity of the paddy soil by tracking decomposition of ¹⁵N-labeled fallow weeds after incorporation. The result fits well to the first order kinetics with the decomposition rate of 34.3% a year. A model of soil N accumulation and mineralization based on the first order kinetics showed that soil organic N originated from the incorporated weed would become saturated at the level 1.92 folds the annual input of weed N after several consecutive years of the incorporation. Mineralizable soil N (Min-N) of the weed origin would also become saturated after several years accounting for 21.2% of the total Min-N which includes the indigenous soil N from plow layer. We suspended weed incorporation (SWI) in a sub-plot of the fields for two consecutive years to compare Min-N therein with that in another subplot in the same fields subjected to continued weed incorporation (CWI). After 2 years of the suspension treatment, Min-N in SWI decreased to a similar extent as estimated with the soil-N model based on the first-order kinetics, with which we estimated that 16.9% of annual N uptake by the rice plants originated from the weed including 5.9% from the weed incorporated in the same year and 11.0% from that in the past years. N inflow to soil organic N from the weed was very close to N outflow attaining the steady state. The rice yield could thus be sustained by maintaining the soil N-supplying capacity via the internal cycling of fallow weed N.     

精确杂草控制技术的研究现状

农田杂草不仅与作物争光、争水、争肥、争空间，导致作物品质受损及产量下降，而且妨碍收获作业，增加生产成本，给农业生产造成了巨大危害。为此，阐述了精确杂草控制的意义；综述了国内外在该领域的研究进展；探讨了计算机杂草识别的方法；并指出了该技术在我国的应用前景和发展方向。     

基于计算机视觉的田间杂草识别方法研究

杂草对农作物的侵害一直是人们关注的问题。为此,利用计算机图像处理技术对复杂土壤背景下的田间杂草进行识别。研究中采用可变阈值法滤除了土壤背景,应用形态学方法识别出了杂草。同时,根据杂草投影中心的像素位置确定田间杂草的实际位置。实验结果表明,此方法可有效地从阔叶子植物中识别出窄叶子稗草。     

云南怒江干热河谷区旱地农田杂草及群落组成调查

首次报道了云南怒江干热河谷区旱地农田杂草分属34科共138种,和4个主要的群落组成:以热带果园、咖啡园为代表的,以竹节菜+三叶鬼针草+赛葵为主的群落;以果园成园前期、甘蔗田、台湾青枣截干后农田为代表的,以三叶鬼针草+皱果苋+马唐为主的群落;以冬蔬菜、香料烟等短期作物为代表的,以香附子+辣子草+蘩缕为主的群落;以闲置农田为代表的,以无芒稗+酢浆草+狗芽根+纱草+千金子+小飞蓬为主的群落。其中香附子、辣子草、竹节菜、狗牙根、三叶鬼针草为优势种。     

Effects of three management strategies on the seedbank, emergence and the need for hand weeding in an organic arable cropping system

The effects of three different weed management strategies on the required input of hand weeding in an arable organic farming system, the weed seedbank in the soil and the emerging weed seedling emergence were studied from 1996 to 2003. Strategies were based on population dynamic models and aimed for (1) control of weeds as carried out in standard organic farming practice, (2) control of all residual weeds that grow above the crop and (3) prevention of all weed seed return to the soil. Under all strategies, the size of the seedbank increased during the conversion from conventional to organic farming systems. The increase under strategy 3 was significantly smaller than the increase under the other strategies. From 1999 onwards, the weed densities in plots treated with strategy 3 became significantly lower than the weed densities in plots treated with the other strategies. The time needed for hand‐weeding required to prevent weed seed return, in addition to the time needed in standard organic farming practices, reduced during the course of the study. A management strategy aimed at the prevention of seed return (strategy 3) can reduce the size of the increase of the seedbank, which is usually observed after transition from conventional to organic farming. This study provides unique real‐world data that are essential for evaluating population dynamic models. The results may contribute to the development of weed management systems based on ‘no seed’ threshold strategies and to a further decrease in the dependence on herbicides.