Evaluación de técnicas de defensa y de la densidad en el cultivo de una nueva hortaliza : Cucúrbita pepo var. vegetable spaghetti

El zapallo Spaghetti, cultivo vigoroso de clima templado, constituye una alternativa productiva interesante y novedosa para nuestro país. El objetivo de este estudio fue evaluar el efecto del mulching y de la densidad sobre el rendimiento total, el peso medio y el calibre de los frutos. El estudio se llevó a cabo en Azul sobre un suelo Argiudol típico en camellones de 0,80 m de ancho con diferentes densidades de siembra. Se realizó una fertilización profunda en bandas de 0,80 m con fosfato diamónico, controlando las malezas en forma química, manual y mecánicamente, y las plagas haciendo aplicaciones preventivas de insecticidas y fungicidas. La siembra manual se efectuó el 2 de noviembre y los tratamientos fueron: densidades de siembra de 20, 15, 10 y 5 mil pl/ha (D1, D2, D3 y D4), con y sin mulching. Se trabajó con 32 parcelas y cada una tenía tres surcos de seis metros de longitud separados entre si por 2m. Se realizaron cuatro cosechas al llegar a la madurez completa (15/2, 29/2, 7/3 y 3/4). Los calibres evaluados fueron: (1) 2,2 kg, (2) 1,7 kg; (3) 1,3 kg y (4) 0,8 kg / fruto. Para el análisis de los datos se utilizó un modelo de bloques completamente aleatorizados con parcelas sub-divididas. En la parcela principal se evaluó el efecto del mulching, en la subparcela la densidad y la interacción de mulching por densidad, y en la subsubparcelas las diferentes cosechas. La cosecha total mostró diferencias significativas para el efecto del mulching, obteniéndose 71,90 t/ha (a) (con mulching) y 62,02 t/ha (b) (sin mulching); para cada densidad se detectaron diferencias significativas para el efecto mulching: D1: 84,45 t/ha (a), D2: 76,47 t/ha (ab); D3: 65,14 t/ha (b) y D4: 61,55 t/ha (b). Se observaron diferencias significativas en el número de frutos cosechados: con mulching (51.667 frutos/ha) y sin mulching (44.167 frutos/ha), y para las diferentes densidades: D1: 54.167 (a); D2: 50.000 (ab); D3: 47.700 (ab) y D4: 40.833 (b) t/ha. La composición de calibres de frutos cosechados fue el mismo para todos los tratamientos y cosechas.

The Influence of Formulation, Buffering, pH and Divalent Cations on the Activity of Endothall on Hydrilla.

Endothall has been used as an aquatic herbicide for more than 40 years and provides very effective weed control of many weeds. Early research regarding the mechanism-of-action of endothall contradicts the symptomology normally associated with the product. Recent studies suggest endothall is a respiratory toxin but the mechanism-of-action remains unknown. To further elucidate the activity of endothall, several endothall formulations were evaluated for their effects on ion leakage, oxygen consumption and photosynthetic oxygen evolution from hydrilla shoot tips. The influence of pH, buffering and divalent cations was also evaluated. (PDF contains 6 pages.)

Fish production from aquatic weeds

Irrigation in the eleven River Basin Authorities and in particular in the South Chad Irrigation Project and the Baga Polder Project is increasing and demands high yearly investments for aquatic weed control in canals and drains. If the weeds are biologically controlled by the grass carp (Ctenopharyngodon idella Val.), the costs will be turned into profit, particularly when the fish production (resident fish plus grass carp) is harvested and sold for food. The use of irrigation canals and drains for aquaculture in the form of fish polyculture may be a wise step towards increased fish production. This paper highlights the concept of fish production from aquatic weed control and concludes that it is a proven profitable venture in several countries

Utilization of some aquatic macrophytes in Nigeria in-land water bodies: a review

Aquatic vegetation is an essential component of the aquatic ecosystem with both positive and negative implications on the water body. Efforts are always made to curtail the excessive growth of aquatic plants in order to prevent them from becoming a nuisance in the ecosystem. One of the ways of solving such problem is the positive economic use of such plants. Utilization as a method of weed control within the aquatic ecosystem is considered to be one of the safest methods of weed control as this provides the riparian communities double advantages in terms of save environment and personal benefits of the plant. The flora diversity of freshwater and brackish environments posses a great potential to both man and higher animals alike. Due to this fact, this paper attempt to review the exploited and unexploited aquatic plants resources of many of our water bodies in Nigeria both economica/ly and socially, to the populace. Recommendations are also advanced for further studies that will enhance sound management of the resources for maximum benefits and sustainability

Cultura de tecidos e análise fitoquímica de Arachis repens HANDRO.

Os representantes do gênero Arachis são conhecidos como amendoim, e suas sementes possuem grande quantidade de óleos e proteínas, podendo ser consumidas cruas. A espécie mais cultivada do gênero é Arachis hypogaea, que possui grande importância comercial. Outras espécies são também utilizadas para controle das ervas daninhas e cobertura do solo, assim como ornamentais e na alimentação. Arachis repens, popularmente conhecida como grama amendoim, é utilizada como planta ornamental, na formação de pastagens, como forragem e para cobertura do solo em substituição a várias espécies comuns de grama. Diversas substâncias bioativas têm sido identificadas em A. hypogaea. Contudo, estas substâncias ainda não foram descritas em outras espécies do gênero. O objetivo deste trabalho foi o estabelecimento de sistemas de cultivo in vitro para Arachis repens, visando à micropropagação e à análise comparativa da produção de resveratrol em extratos alcoólicos dos materiais produzidos in vitro, em comparação com as plantas in vivo. Segmentos nodais, internodais e foliares foram excisados de plantas in vitro e inoculados em meio MS suplementado com diferentes concentrações de BAP, TDZ, AIA e KIN, utilizados isoladamente ou em combinação. Os explantes apresentaram respostas distintas de acordo com o regulador de crescimento utilizado. Na presença de BAP foi observada a formação de calos compactos, com formação de brotos em diferentes taxas. Na presença de TDZ, segmentos nodais e internodais formaram calos compactos em todas as concentrações. Segmentos nodais cultivados na presença de diferentes concentrações de AIA em combinação com KIN apresentaram a formação de calogênese. Foi também realizada uma avaliação da atividade antioxidante e a presença de fenóis totais em extratos de diferentes materiais in vivo e produzidos in vitro. Nas análises por meio de CLAE, foi possível detectar a presença de resveratrol tanto nos materiais in vivo, quanto os produzidos in vitro. Dessa forma, o trabalho forneceu resultados preliminares sobre as possibilidades de utilização de A. repens para a produção de metabólitos especiais.

Monitoring report: sand dune reconstruction and restoration, at the Moss Landing Marine Laboratories

The Plan for Sand Dune Reconstruction and Restoration (and Biological Assessment) at Moss Landing Marine Laboratories (ABA Consultants, April 1, 1992) described reconstruction of dune contours and biological restoration with native dune plants to be carried out over the 8 acre site formerly occupied by the marine labs (prior to the Loma Prieta earthquake of October 1989). The plan called for annual reports in letter form which would present data on plant abundance, a short narrative description of changes on the site, progress towards recovery of the plant community, and assessment of progress based on restoration goals and further steps to be taken. This monitoring report [dated April 25, 1994] addresses those points and also contains a summary of other activities integral in dune restoration -- education, public participation, school and conservation organization field trips, as well as the associated activities of restoration, plant collecting, propagation, and weed control.

Management of water hyacinth, Eichhornia crassipes, in Lake Victoria Basin

Water hyacinth is a free-floating waterweed native to the Amazon River Basin in South America. In its native range, water hyacinth is not an environmental problem, although the weed is one of the most invasive alien plants in freshwater environments. Water hyacinth has the potential to become invasive through fast vegetative reproduction and rapid growth to accumulate huge biomass and extensive cover in freshwater environments. Over the last 150 years water hyacinth has invaded most countries in the tropics and sub-tropics, introduced by man, mainly for ornamental purposes. Such introductions led to the infestation of most freshwater-ways in the southern United States of America, parts of Australia, the pacific islands, and most countries in Asia and Africa. The extensive tightly packed mats of water hyacinth are often associated with devastating socio-economic and environmental impacts. Invasion by the weed has, therefore, often generated urgent costly problems associated with the weed biomass and its management. A classic example of such problems was triggered by the invasion and proliferation of water hyacinth in the Lake Victoria Basin during the 1980s (Freilink 1989, Taylor 1993, Twongo et al., 1995). The weed infestation marked the beginning of a decade of intensive and systematic campaign by the three riparian states (Kenya, Tanzania and Uganda) to bring weed proliferation under control. The discussions in this Chapter span over ten years of dealing with the challenges paused by the imperative to manage infestations of water hyacinth in the Lake Victoria Basin. The challenges included the need to understand the dynamics of water hyacinth infestation; its distribution, proliferation and impact modalities; and the development and implementation of appropriate weed control strategies and options. Most specific examples were taken from the Ugandan experience (NARO, 2002).

The potential for further proliferation of water hyacinth in Lakes Victoria, Kyoga and Kwania and some urgent aspects for research

Shore environments of Lakes Victoria and Kyoga with potential for the establishment and proliferation of water hyacinth were identified. They are characterised by: (i) shelter from violent off-shore and along-the-shore wind and wave action (ii) flat or gentle slope under relatively shallow water, and (iii) a muddy bottom rich in organic matter. Such environments are strongly associated with emergent macrophytes of papyrus, Vossia sp and, at times Typha sp where Pistia stratiotes, species of ceratophyllum, myriophylum and nymphaea also occur. In Lake Kyoga association with Vossia sp facilitated establishment of water hyacinth even along wind-swept shores and promoted extension of mats of the two machrophytes into the open lake. Urgent research on water hyacinth is proposed in the areas of nutrient relations, weed biology and on its impact on the biodiversity resource, with particular emphasis on the fishery component. Findings from the research could facilitate formulation of weed control options and alternative resource management strategies. A regional approach to address the water hyacinth menace is highly recommended.

瑞香狼毒（Stellera chamaejasme L.）对高寒草甸系统生长和非生长季节碳氮循环的影响及其花粉化感效应

瑞香狼毒（Stellera chamaejasme L.）是瑞香科（Thymelaeaceae）狼毒属的一种多年生野草，有毒。据调查，从20 世纪60 年代开始至今，狼毒在青藏高原东缘的高寒草甸上不断蔓延、密度不断变大，在一些地段甚至成为优势物种。有关狼毒在高寒草甸蔓延的生态系统效应的研究尚未见报道。本文从系统碳、氮循环的角度，分别研究狼毒在生长和非生长季节对高寒草甸生态系统的影响。同时，从花粉化感的角度，深入研究狼毒对当地同花期物种有性繁殖的影响。系统地研究高寒草甸生态系统物质循环过程，特别是非生长季节微生物和土壤碳氮库的动态变化，有助于揭示狼毒在系统物质循环方面的“物种效应”以及这种效应的季节变化，为丰富有关高海拔生态系统，特别是其非生长季的物质循环的科学理论做出贡献。同时，碳氮循环和花粉化感的研究还有助于深刻地理解狼毒作为一种入侵性很强的杂草的特殊的蔓延机制，从而为狼毒的有效防治、高寒草甸的科学管理提供依据。 针对狼毒在青藏高原高寒草甸上蔓延的生态系统碳氮循环方面的影响，开展以下2 方面的研究：（1）在生长季，研究松潘县尕米寺附近（北纬32°53'，东经103°40'，海拔3190 m）的两种地形（平地和阳坡）条件下狼毒对土壤碳氮循环影响及可能的原因。狼毒和其它几个主要物种（圆穗蓼（Polygonummacrophyllum D. Don var. Macrophyllum），草地早熟禾（Poa pretensis L.），四川嵩草（Kobresia setchwanensis Hand.-Maizz.），鹅绒委陵菜（Potentilla anserina L.var. anserine）和鳞叶龙胆（Gentiana squarrosa Ledeb.）的地上凋落物产量以及地上凋落物和根的化学组成被测量。在有-无狼毒斑块下，各种土壤的库（比如，铵态氮、硝态氮、无机磷和微生物生物量）和周转率（包括净矿化、净硝化、总硝化、反硝化和微生物呼吸速率）被测量和比较。（2）在非生长季节，尤其是春季冻融交替期，选取了两个研究地点——尕米寺和卡卡沟（北纬32°59'，东经103°41'，海拔3400 m），分别测定有狼毒和无狼毒斑块下土壤微生物生物量碳和氮、可溶性有机碳和氮以及铵态氮和硝态氮的动态变化。同时，分别在上述两个地点有-无狼毒的样地上，研究6 个主要物种（狼毒、圆穗蓼、草地早熟禾、四川嵩草、鹅绒委陵菜和鳞叶龙胆）从秋季开始、为期1 年的凋落物分解过程。 针对狼毒花粉化感对同花期其它物种可能的花粉化感作用开展以下工作：在实验室中，用一系列浓度的狼毒花粉水浸提液对与它同花期的其它物种以及自身花粉进行测试，测定花粉萌发率；在野外自然条件下的其它物种的柱头上施用上述浓度的狼毒花粉水浸提液，观测种子结实率，同时，观察狼毒花粉的种间花粉散布数量。 生长季节的研究结果表明，狼毒地上凋落物氮含量比其它几个主要物种更高，而木质素-总氮比更低。狼毒显著地增加其斑块下表层土壤中有机质的含量，而有-无狼毒的亚表层土壤在有机碳和总磷方面没有显著差异。狼毒表土中硝态氮含量在平地和阳坡比无狼毒土壤分别高113%和90%。狼毒表土中微生物生物量碳和氮量显著高于无狼毒表土。无论是平地还是阳坡，狼毒土壤的总硝化和微生物呼吸速率显著高于无狼毒土壤；而它们的反硝化速率只在平地有显著的差异。狼毒与其它物种间地上凋落物的产量和质量的差异可能是导致有-无狼毒土壤碳氮循环差异的原因。我们假设，狼毒可能通过增加贫氮生态系统土壤中的有效氮含量提高其入侵能力。 非生长季的研究结果表明，在青藏高原东缘的高寒草甸上，土壤微生物生3物量在11 月的秋-冬过渡期达到第一个峰值；在春季的冻融交替期，微生物生物量达到第二个峰值后又迅速降低。无机氮以及可溶性有机碳氮与微生物生物量有相似的变化过程。微生物碳氮比呈现显著的季节性变化。隆冬季节的微生物生物量碳氮比显著高于生长旺季的微生物碳氮比。这种变化可能暗示冬、夏季微生物的群落组成和对资源的利用有所不同。有-无狼毒斑块下土壤微生物和土壤碳、氮库一般只在秋-冬过渡期有显著差异，有狼毒土壤微生物生物量和土壤碳、氮库显著高于无狼毒土壤；而在之后的冬季和春季没有显著差异。所有6 个物种凋落物在非生长季分解率为24%-50%，均高于生长季的10%到30%。其中在秋-冬过渡期，凋落物开始埋藏的两周时间内，分解最快，达10%-20%。不同物种凋落物全年的分解率和分解过程有显著差异。圆穗蓼在全年的分解都较缓慢（非生长季26%，生长季15%），草地早熟禾和四川嵩草等全年的分解速率比较均匀（非生长季和生长季均为30%，非生长季略高），而狼毒在非生长季分解较快（约50%），而在接下来的生长季分解变得缓慢（约12%）。所有物种的凋落物氮含量在非生长季下降，而在随后的生长季上升。 实验室的花粉萌发试验证明，狼毒花粉对自身花粉萌发没有自毒作用，而其它受试的所有物种（圆穗蓼，秦艽（Gentiana macrophylla Pall. var. fetissowii），湿生扁蕾（Gentianopsis paludosa (Hook. f.) Ma var. paludosa），鳞叶龙胆，椭圆叶花锚（Halenia elliptica D. Don var. elliptica），蓝钟花（Cyananthus hookeri C. B.Cl. var. grandiflorus Marq.），小米草（Euphrasia pectinata Ten.），川西翠雀花（Delphinium tongolense Franch.），高原毛茛（Ranunculus tanguticus (Maxim.)Ovcz. var. tanguticus）和鹅绒委陵菜）的花粉萌发率随着狼毒花粉浸提液浓度的增加呈显著的非线性降低。大约3 个狼毒花粉的浸提液就可以抑制受试的多数物种的50%的花粉萌发。在鳞叶龙胆和小米草柱头上狼毒花粉的数量分别为5.76 个和3.35 个。狼毒花粉散布数量的差异最可能的原因在于是否有共同的传粉昆虫。花的形状（辐射对称VS 左右对称）、植株或花的密度以及花期重叠性可以部分解释这种差异。在野外试验中，我们发现6 个物种（秦艽、湿生扁蕾、鳞叶龙胆、椭圆叶花锚、蓝钟花和小米草）的种子结实率随狼毒花粉浸提液浓度的增加呈显著的非线性降低。鳞叶龙胆和小米草柱头上狼毒花粉的数量（分别是5.76 个和3.35 个）分别达到了抑制它们63%和55%种子结实率的水平。因此，狼毒对鳞叶龙胆和小米草可能存在明显的花粉化感抑制作用。狼毒周围的物种可能通过花期在季节或昼夜上的分异避免受到狼毒花粉化感的影响或者通过无性繁殖来维持种群繁衍，因此狼毒通过花粉化感作用对其周围物种繁殖的影响程度还需要进一步地研究。如果狼毒的花粉化感抑制作用确实存在，那么它可能成为一种自然选择压力，进而影响物种的进化。 Stellera chamaejasme L., a perennial toxic weed, has emerged and quicklydominated and spread in the high-frigid meadow on the eastern Tibetan Plateau ofChina since the 1960s. In the present study, effects of S. chamaejasme on carbon andnitrogen cycles on the high-frigid meadow on the eastern Qinghai-Tibetan Plateau ingrowing and non-growing season, and its pollen allelopathic effects on the sympatricspecies were determined. The present study that focused on carbon and nitrogencycles, especially on microbial biomass and pools of carbon and nitrogen innon-growing season, could profoundly illuminate plant-species effects on carbon andnutrient cycles and its seasonal pattern and help to understand spread mechanism ofS. chamaejasme as an aggressive weed. The present study also contributed to furtherunderstand carbon and nutrient cycles on alpine regions in non-growing season andprovide a basis on weed control of S. chamaejasme and scientific management in thehigh-frigid ecosystem. Effects of S. chamaejasme on carbon and nitrogen cycles on the high-frigidmeadow on the eastern Qinghai-Tibetan Plateau were determined. The study couldbe divided into two parts. (1) In the growing season, we quantified the effects of S.chamaejasme on carbon and nitrogen cycles in two types of topographic habitats, theflat valley and the south-facing slope, where S. chamaejasme was favored to spreadlitter and root were measured to explain the likely effects of S. chamaejasme on soilcarbon and nutrient cycles. The sizes of various soil pools, e.g. nitrite, ammonium,inorganic phosphorus and microbial biomass, and turnover rates including netmineralization, gross nitrification, denitrification and microbial respiration weredetermined. (2) In the non-growing season study, microbial biomass carbon andnitrogen, soluble organic carbon and nitrogen, ammonium and nitrate weredetermined through the non-growing season, especially in the processes offreeze-thaw of spring in two high-frigid sites, i.e. Kaka valley and Gami temple, onthe eastern Qinghai-Tibetan Plateau. Meanwhile, litter decomposition of six commonspecies, including Stellera chamaejasme L., Polygonum macrophyllum D. Don var.Macrophyllum, Poa pretensis L., Kobresia setchwanensis L., Potentilla anserina L.var. anserine and Gentiana squarrosa Ledeb., were also examined under theabove-mentioned experimental design through one whole-year, which began in theautumn in 2006. In the study of pollen allelopathy, several work, including in vitro study oneffects of extract of pollen from S. chamaejasme on sympatric species and pollenfrom itself, field experiments on effects of pollen extract with the same regime ofconcentrations on seed set and field observation on heterospecific pollen transfer ofS. chamaejasme to six of those sympatric species has been done. The results in the growing season showed that aboveground litter of S.chamaejasme had higher tissue nitrogen and lower lignin: nitrogen ratio than thoseco-occurring species. S. chamaejasme significantly increased topsoil organic matter,whereas no significant differences were found for organic C and total P in subsoilbetween under-Stellera and away-Stellera locations. The nitrate in Stellera topsoilwas 113% and 90% higher on the flat valley and on the south-facing slope,respectively. Both microbial biomass C and N were significantly higher in Stelleratopsoil. Gross nitrification and microbial respiration were significantly higher inStellera topsoil both on the flat valley and on the south-facing slope, whereassignificant differences of denitrification were found only on the flat valley. Thedifferences in the quantity and quality of aboveground litter are a likely mechanismresponsible for the changes of soil variables. We assumed that S. chamaejasme couldenhance their spread by increasing nutrient availability in N-deficient ecosystems. The results in the non-growing season showed that microbial biomass achievedthe first summit in late autumn and early winter on the eastern Qinghai-TibetanPlateau. In the stages of freeze-thaw of spring, microbial biomass firstly achieved thesecond summit and subsequently sharply decreased. Inorganic nitrogen, solubleorganic carbon and nitrogen had a similar dynamics with that of microbial biomass.Ratio of microbial biomass carbon and nitrogen had an obviously seasonal pattern.The highest microbial C: N were in the non-growing season, which weresignificantly higher than those in the growing season. The seasonal pattern inmicrobial biomass C: N suggested that large changes in composition of microbialpopulation and in resources those used by microbes between summer and winter.Generally, microbial biomass and pools size of carbon and nitrogen in Stellera soilwere significantly higher than those under adjacent locations in late autumn andearly winter, but there were not significant differences in winter and in spring. Litterof all the focal species (Stellera chamaejasme L., Polygonum macrophyllum D. Donvar. Macrophyllum, Poa pretensis L., Kobresia setchwanensis Hand.-Maizz.,Potentilla anserina L. var. anserine and G. squarrosa Ledeb.) decomposed about24%-50% in the non-growing season, which were higher than those in the growingseason (ranged from 10% to 30%). Litter decomposed 10%-20% within the first twoweeks in late autumn and early winter. Significant differences in the whole-yeardecomposition rate and in the processes of decomposition were found among species.Polygonum macrophyllum decomposed slowly through the whole year (26% and15% in the non-growing season and in the growing season, respectively). Certainspecies, such as P. pretensis L. and K. setchwanensis, decomposed at a similar rate(30% both in the non-growing and in the growing season, slightly higher in the8growing season than those in the growing season), whereas S. chamaejasmedecomposed more rapidly (about 50%) in the non-growing season and subsequentlydecomposition became slow (about 12%) in the growing season. Litter nitrogencontents of all the focal species firstly decreased in the non-growing season and thenincreased in the growing season. In vitro experiments of pollen allelopathy, the results showed that pollen from S.chamaejasme was not autotoxic, whereas pollen germination in all the sympatricspecies (Polygonum macrophyllum D. Don var. Macrophyllum, Gentianamacrophylla Pall. var. fetissowii, Gentianopsis paludosa (Hook. f.) Ma var. paludosa,Gentiana squarrosa Ledeb., Halenia elliptica D. Don var. elliptica, Cyananthushookeri C. B. Cl. var. grandiflorus Marq., Euphrasia pectinata Ten., Delphiniumtongolense Franch., Ranunculus tanguticus (Maxim.) Ovcz. var. tanguticus andPotentilla anserina L. var. anserina) decreased nonlinearly as the increasingconcentrations of extract of pollen from S. chamaejasme. Pollen Extract of threepollens from S. chamaejasme generally inhibited 50% pollen germination of most ofthe focal species. 5.76 and 3.35 pollens from S. chamaejasme were observed in fieldon stigmas of G. squarrosa and E. pectinata, respectively. Differences inheterospecific pollen transfer of S. chamaejasme could be attributed to the primaryreason whether they shared common pollinators. Flower morphology (e.g.zygomorphic or actinomorphic), plant or floral density and concurrence in floweringphonologies could explain, in part, the differences in heterospecific pollen transfer.In field experiments, the results showed that seed set in six sympatric species(Gentiana macrophylla Pall. var. fetissowii, Gentianopsis paludosa (Hook. f.) Mavar. paludosa, Gentiana squarrosa Ledeb., Halenia elliptica D. Don var. elliptica,Cyananthus hookeri C. B. Cl. var. grandiflorus Marq. and Euphrasia pectinata Ten.)decreased nonlinearly as the increasing concentrations of extract of pollen from S.chamaejasme. According to the nonlinear curves, the amounts of pollens from S.chamaejasme on stigmas of G. squarrosa and of E. pectinata (i.e. 5.76 grains and3.35 grains, respectively) could reduce 63% and 55% seed set of G. squarrosa and ofE. pectinata, respectively. Thus, allelopathic effects of S. chamaejasme on G.squarrosa and E. pectinata could be realistic. The sympatric species of S.chamaejasme could avoid pollen allelopathy of S. chamaejasme to sustainthemselves. This highlights the need to study how much pollen allelopathy in S.chamaejasme influences the sympatric species through divergence in seasonal ordiurnal flowering phonologies or through asexual reproduction. If pollen allelopathyin S. chamaejasme was confirmed, it could be as a pressure of natural selection andthus play an important role in species evolution.

Eficacia de distintos herbicidas residuales en malezas de barbecho

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El tabaco negro en Colombia competitividad de la cadena productiva

En el presente trabajo de investigación se pretende establecer, los factores que se consideran claves en el desarrollo competitivo de la cadena agroproductiva del tabaco negro en Colombia, en primera instancia realizando una aproximación a los actores que integran la cadena, constituida por: Los proveedores de insumos, productores de tabaco, comercializadores y entidades de apoyo; se realiza una descripción del proceso del cultivo del tabaco desde la selección de las semillas, los semilleros o bandejas flotantes, fertilización, el suelo cuyas características deben satisfacer los requerimientos mínimos de calidad, el riego, el control de malezas, recolección de hojas y por último el proceso de secado o curado con las variaciones necesarias según corresponda al tipo de tabaco. Posteriormente se realizan los análisis del sector a nivel nacional, en el cual se consideran cinco factores como son: El político, económico, social, tecnológico e institucional; y el estudio comparativo a nivel internacional para el cual se identificaron siete países de mayor volumen de exportación como Brasil, Malawi, Zimbabwe, Estados Unidos, Argentina, La Unión Europea y China; considerando los factores principales tales como: Sistema de producción, perfil del productor, aspectos de asociatividad, industria y políticas estatales. Para tener un mayor acercamiento del posicionamiento de la industria del tabaco a nivel mundial, se realizó el análisis de competitividad que demuestra que a pesar de estar por encima del promedio mundial, está muy por debajo de los países que están liderando, la industria del tabaco a nivel mundial. El análisis pretendió identificar las mejores prácticas en cada país, y a partir de dicho análisis se formularon bases de estrategia para mejoramiento de la competitividad del sector tabacalero en Colombia.

The role of weeds in supporting biological diversity within crop fields

Weeds are major constraints on crop production, yet as part of the primary producers within farming systems, they may be important components of the agroecosystem. Using published literature, the role of weeds in arable systems for other above-ground trophic levels are examined. In the UK, there is evidence that weed flora have changed over the past century, with some species declining in abundance, whereas others have increased. There is also some evidence for a decline in the size of arable weed seedbanks. Some of these changes reflect improved agricultural efficiency, changes to more winter-sown crops in arable rotations and the use of more broad-spectrum herbicide combinations. Interrogation of a database of records of phytophagous insects associated with plant species in the UK reveals that many arable weed species support a high diversity of insect species. Reductions in abundances of host plants may affect associated insects and other taxa. A number of insect groups and farmland birds have shown marked population declines over the past 30 years. Correlational studies indicate that many of these declines are associated with changes in agricultural practices. Certainly reductions in food availability in winter and for nestling birds in spring are implicated in the declines of several bird species, notably the grey partridge, Perdix perdix . Thus weeds have a role within agroecosystems in supporting biodiversity more generally. An understanding of weed competitivity and the importance of weeds for insects and birds may allow the identification of the most important weed species. This may form the first step in balancing the needs for weed control with the requirements for biodiversity and more sustainable production methods.

Proof of concept of automated mapping of weeds in arable fields

The project investigated whether it would be possible to remove the main technical hindrance to precision application of herbicides to arable crops in the UK, namely creating geo-referenced weed maps for each field. The ultimate goal is an information system so that agronomists and farmers can plan precision weed control and create spraying maps. The project focussed on black-grass in wheat, but research was also carried out on barley and beans and on wild-oats, barren brome, rye-grass, cleavers and thistles which form stable patches in arable fields. Farmers may also make special efforts to control them. Using cameras mounted on farm machinery, the project explored the feasibility of automating the process of mapping black-grass in fields. Geo-referenced images were captured from June to December 2009, using sprayers, a tractor, combine harvesters and on foot. Cameras were mounted on the sprayer boom, on windows or on top of tractor and combine cabs and images were captured with a range of vibration levels and at speeds up to 20 km h-1. For acceptability to farmers, it was important that every image containing black-grass was classified as containing black-grass; false negatives are highly undesirable. The software algorithms recorded no false negatives in sample images analysed to date, although some black-grass heads were unclassified and there were also false positives. The density of black-grass heads per unit area estimated by machine vision increased as a linear function of the actual density with a mean detection rate of 47% of black-grass heads in sample images at T3 within a density range of 13 to 1230 heads m-2. A final part of the project was to create geo-referenced weed maps using software written in previous HGCA-funded projects and two examples show that geo-location by machine vision compares well with manually-mapped weed patches. The consortium therefore demonstrated for the first time the feasibility of using a GPS-linked computer-controlled camera system mounted on farm machinery (tractor, sprayer or combine) to geo-reference black-grass in winter wheat between black-grass head emergence and seed shedding.

Final report on research project PS2010, proof of concept of automated mapping of weeds in arable fields

Many weeds occur in patches but farmers frequently spray whole fields to control the weeds in these patches. Given a geo-referenced weed map, technology exists to confine spraying to these patches. Adoption of patch spraying by arable farmers has, however, been negligible partly due to the difficulty of constructing weed maps. Building on previous DEFRA and HGCA projects, this proposal aims to develop and evaluate a machine vision system to automate the weed mapping process. The project thereby addresses the principal technical stumbling block to widespread adoption of site specific weed management (SSWM). The accuracy of weed identification by machine vision based on a single field survey may be inadequate to create herbicide application maps. We therefore propose to test the hypothesis that sufficiently accurate weed maps can be constructed by integrating information from geo-referenced images captured automatically at different times of the year during normal field activities. Accuracy of identification will also be increased by utilising a priori knowledge of weeds present in fields. To prove this concept, images will be captured from arable fields on two farms and processed offline to identify and map the weeds, focussing especially on black-grass, wild oats, barren brome, couch grass and cleavers. As advocated by Lutman et al. (2002), the approach uncouples the weed mapping and treatment processes and builds on the observation that patches of these weeds are quite stable in arable fields. There are three main aspects to the project. 1) Machine vision hardware. Hardware component parts of the system are one or more cameras connected to a single board computer (Concurrent Solutions LLC) and interfaced with an accurate Global Positioning System (GPS) supplied by Patchwork Technology. The camera(s) will take separate measurements for each of the three primary colours of visible light (red, green and blue) in each pixel. The basic proof of concept can be achieved in principle using a single camera system, but in practice systems with more than one camera may need to be installed so that larger fractions of each field can be photographed. Hardware will be reviewed regularly during the project in response to feedback from other work packages and updated as required. 2) Image capture and weed identification software. The machine vision system will be attached to toolbars of farm machinery so that images can be collected during different field operations. Images will be captured at different ground speeds, in different directions and at different crop growth stages as well as in different crop backgrounds. Having captured geo-referenced images in the field, image analysis software will be developed to identify weed species by Murray State and Reading Universities with advice from The Arable Group. A wide range of pattern recognition and in particular Bayesian Networks will be used to advance the state of the art in machine vision-based weed identification and mapping. Weed identification algorithms used by others are inadequate for this project as we intend to collect and correlate images collected at different growth stages. Plants grown for this purpose by Herbiseed will be used in the first instance. In addition, our image capture and analysis system will include plant characteristics such as leaf shape, size, vein structure, colour and textural pattern, some of which are not detectable by other machine vision systems or are omitted by their algorithms. Using such a list of features observable using our machine vision system, we will determine those that can be used to distinguish weed species of interest. 3) Weed mapping. Geo-referenced maps of weeds in arable fields (Reading University and Syngenta) will be produced with advice from The Arable Group and Patchwork Technology. Natural infestations will be mapped in the fields but we will also introduce specimen plants in pots to facilitate more rigorous system evaluation and testing. Manual weed maps of the same fields will be generated by Reading University, Syngenta and Peter Lutman so that the accuracy of automated mapping can be assessed. The principal hypothesis and concept to be tested is that by combining maps from several surveys, a weed map with acceptable accuracy for endusers can be produced. If the concept is proved and can be commercialised, systems could be retrofitted at low cost onto existing farm machinery. The outputs of the weed mapping software would then link with the precision farming options already built into many commercial sprayers, allowing their use for targeted, site-specific herbicide applications. Immediate economic benefits would, therefore, arise directly from reducing herbicide costs. SSWM will also reduce the overall pesticide load on the crop and so may reduce pesticide residues in food and drinking water, and reduce adverse impacts of pesticides on non-target species and beneficials. Farmers may even choose to leave unsprayed some non-injurious, environmentally-beneficial, low density weed infestations. These benefits fit very well with the anticipated legislation emerging in the new EU Thematic Strategy for Pesticides which will encourage more targeted use of pesticides and greater uptake of Integrated Crop (Pest) Management approaches, and also with the requirements of the Water Framework Directive to reduce levels of pesticides in water bodies. The greater precision of weed management offered by SSWM is therefore a key element in preparing arable farming systems for the future, where policy makers and consumers want to minimise pesticide use and the carbon footprint of farming while maintaining food production and security. The mapping technology could also be used on organic farms to identify areas of fields needing mechanical weed control thereby reducing both carbon footprints and also damage to crops by, for example, spring tines. Objective i. To develop a prototype machine vision system for automated image capture during agricultural field operations; ii. To prove the concept that images captured by the machine vision system over a series of field operations can be processed to identify and geo-reference specific weeds in the field; iii. To generate weed maps from the geo-referenced, weed plants/patches identified in objective (ii).

The effect of the year of wheat variety release on productivity and stability of performance on two organic and two non-organic farms

Nineteen wheat cultivars, released from 1934 to 2000, were grown at two organic and two non-organic sites in each of 3 years. Assessments included grain yield, grain protein concentration, protein yield, disease incidence and green leaf area. The superiority of each cultivar (the sum of the squares of the differences between its mean in each environment and the mean of the best cultivar there, divided by twice the number of environments; CS) was calculated for yield, grain protein concentration and protein yield, and ranked in each environment. The yield and grain protein concentration CS were more closely correlated with cultivar release date at the non-organic sites than at organic sites. This difference may be attributed to higher yield levels with larger differences among cultivars at the non-organic sites, rather than to improved stability (i.e. similar ranks) across sites. The significant difference in the correlation of protein yield CS and cultivar age between organic and non-organic sites would support evidence that the ability to take up mineral nitrogen (N) compared to soil N has been a component of the selection conditions of more modern cultivars (released after 1989). This is supported by assessment of green leaf area (GLA), where more modern cultivars in the non-organic systems had greater late-season GLA, a trend that was not identified in organic conditions. This effect could explain the poor correlation between age and protein yield CS in organic compared to non-organic conditions where modern cultivars are selected to benefit from later nitrogen (N) availability which includes the spring nitrogen applications tailored to coincide with peak crop demand. Under organic management, N release is largely based on the breakdown of fertility-building crops incorporated (ploughed-in) in the previous autumn. The release of nutrients from these residues is dependent on the soil conditions, which includes temperature and microbial populations, in addition to the potential leaching effect of high winter rainfall in the UK. In organic cereal crops, early resource capture is a major advantage for maximizing the utilization of nutrients from residue breakdown. It is concluded that selection of cultivars under conditions of high agrochemical inputs selects for cultivars that yield well under maximal conditions in terms of nutrient availability and pest, disease and weed control. The selection conditions for breeding have a tendency to select cultivars which perform relatively better in non-organic compared to organic systems.