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Summary: The effects of reduced‐cultivation Systems on weeds in cereals are reviewed. Increasing dependence of these Systems upon Chemical weed control together with changes in the soil physical environment are expected to modify existing weed floras. Annual‐grass weeds are likely to remain a problem with the use of minimal cultivations, particularly when early drilling is practised, while hitherto unimportant species may become more prevalent, e.g. Bromus spp. Furthermore, reduced cultivations may encourage the establishment of wind‐disseminated species. However, annual dicotyledonous species characteristic of arable land are expected to continue to decline.

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Relations between yield, water use and pre-anthesis growth were analysed for crops of barley grown for three seasons at several sites in northern Syria. The relations obtained were compared with those for other cereal crops grown in similar regions of Mediterranean climates.Phosphorus fertilizer application increased the rate of crop development from emergence to floral initiation and advanced anthesis by up to 11 days. Grain and total shoot dry-matter yields were increased by fertilizer (nitrogen + phosphorus) applications at all sites in all years, in most cases without increasing total evapotranspiration. The increased dry matter at anthesis was produced without having used a larger proportion of the total evapotranspiration in the whole season. Consequently, the ratio of grain yield to total above-ground dry-matter yield (harvest index) and kernel weight were also relatively stable between sites and years, despite some very low amounts of post-anthesis water use. Grain yield appeared to be largely determined by anthesis and there were strong linear relationships between grain yield or total dry-matter yield and number of kernels. Differences in water use efficiency of crops given fertilizer between sites and years were closely related to the differences in amounts of winter growth. Some responses differed from those predicted from models of growth, water use and yield developed in other regions with similar climates. It is concluded that agronomists and breeders should increase amounts of early growth thereby increasing grain and dry-matter yields. Future research emphasis should also be on the development of dynamic simulation models of pre-anthesis growth and water use.

Summary Seeds of tomato and oats were subject to hydration‐dehydration treatments at various times during germination. Desiccation has little harmful effect if carried out before cell division and enlargement has commenced. Some advancement of the onset of germination was apparent due probably to slight changes in the seed covering and also to the initiation of metabolic events which could withstand the dehydration, e.g. the increased protease activity was maintained in the dried seed. Dehydration can be done more than once. The effects are only truly accumulative if the prior imbibitions are of substantial duration. Physical changes associated with hydration are fairly easily reversed but some of the chemical changes beginning in oat within 8–12 hours of imbibition cannot be returned to the original dry seed condition by desiccation. Once embryo growth is apparent, embryo damage of some sort usually results.

Summary Seeds of Alopecurus myosuroides, Bromus sterilis, Capsella bursa‐pastoris, Papaver rhoeas, Stellaria media, Veronica arvensis, Veronica persica and Viola arvensis were sown in soil at depths of 0, 25 and 150 mm. Seeds buried at 150 mm were exhumed at intervals of 3, 6, 12 and 15 months and incubated at an alternating temperature regime of 10/20 °C (16/8 h) or irradiated with light of various wavelengths prior to incubation. In general, shallow burial (25 mm) reduced seedling emergence except in the case of B. sterilis, which also germinated at a depth of 150 mm but failed to emerge. Cyclic changes in dormancy of buried seeds were observed. Although sensitivity to light was enchanced by burial, germination and response to light quality varied between seasons. Dormancy of most species, including the winter annuals A. myosuroides, Veronica persica and Viola arvensis, was least in autumn and most in summer. Papaver rhoeas was least dormant in spring and S. media was least dormant in summer. Generally, red light promoted germination whereas far‐red light or darkness was not stimulatory. However, A. myosuroides was more sensitive to far‐red light in autumn than at other times of the year. Natural day‐light promoted germination of A. myosuroides, S. media and Veronica arvensis. Germination of B. sterilis was delayed in natural daylight. Transfer of A. myosuroides, Papaver rhoeas, Veronica arvensis and Viola arvensis from darkness to daylight increased germination above that obtained under natural daylight. Germination of freshly collected seeds of Alopecurus myosuroides, Arrhenatherum elatius, Poa annua, Poa trivialis, Plantago major and Viola arvensis was promoted by short irradiations of red light. Dry‐storage did not affect germination of Alopecurus myosuroides, Poa annua, Plantago major or Viola arvensis, but did affect dormancy and light requirement of Poa trivialis. Burial of seeds of Alopecurus myosuroides, Poa trivialis and Plantago major increased their sensitivity to far‐red light. It is concluded that cyclic changes in seed dormancy and associated light sensitivity are determined seasonally and result from changing environmental factors and that they are of adaptive importance for survival.

Summary. The adsorption capacity for paraquat of the following materials was examined: three peat soils; two peaty layers below a turf; a commercial sphagnum peat; grass; Begbroke soil; Fullers’ earth; humic acids isolated from a peat soil; lignin isolated from hardwood sawdust; cellulose powder. The Strong Adsorption Capacity (SAC) of these adsorbents was examined first using a chemical method of analysis and then with the more sensitive Lemna bioassay. Peat soils had an appreciable SAC for paraquat even when measured with the bioassay (88–165 kg/ha 2–5 cm depth, 750–1000 ppm), > 10 times that of Begbroke soil (14 kg/ha, 50 ppm). Humic acids had a higher adsorption capacity (k = 42, 000) than lignin (k = 2600), while cellulose adsorbed very little paraquat (k = 64). The adsorption of paraquat decreased as the ratio of soil to water increased. Temperature appeared to have very small effects on adsorption in organic soils. Results were consistent with calcium competing for adsorption sites. Paraquat sprayed on the surface of a peat soil up to 36 kg/ha remained in the top 7 mm after leaching with 305 mm of natural rainfall over a period of 4 months. Paraquat adsorbed on commercial sphagnum peat could transfer to clays after incorporation and be inactivated. Adsorption et mobilité du paraquat sur diffétrents sols et constituents du sol Résumé , La capacityé d'adsorption du paraquat par les milieux suivants a étéétudiée: 3 sols tourbeux, 2 assises tourbeuses sous un gazon, une tourbe commerciale de sphagnum, une tourbe, un sol de Begbroke, une terre à foulon, un acide humique extrait d'un sol tourbeux, une lignine extraite d'une sciure de bois dur, de la poudre de cellulose. La capacityé brute d'adsorption (CBA) de ces adsorbants a été examinée, au moyen d'une méthode chimique d'analyse puis avec la méthode biologique plus sensible utilisant Lemna. Les sols tourbeux montrèrent une CBA appréciable pour le paraquat même lorsqu'elle fut mesurée par la voie biologique (88/165 kg/ha 2,5 cm de profondeur, 750–1000 ppm), plus de 10 fois celle du sol de Begbroke (14 kg/ha 50 ppm). Pour les acides humiques, la capacityé d'adsorption fut plus éievée (k = 42 000) que pour la lignine (k = 2600) alors que la cellulose n'adsorba que très peu de paraquat (k = 64). L'adsorption du paraquat diminua à mesure que le rapport sol/eau augmentait. La temperature n'eut que de très faibles effets sur l'adsorption dans les sols organiques. Les résultats furent en accord avec la concurrence du calcium pour les lieux d'adsorption. Le paraquat appliquéà la surfaee d'un sol tourbeux jusquà la dose de 36 kg/ha resta dans les 7 premiers millimètres après lessivage par 305 mm de pluie natureile péndant une période de 4 mois. Le paraquat adsorbé sur une tourbe commerciale de sphagnum put être transféréè des argiles aprtè avoir été incorporé et inactiveée. Adsorption und Beweglichkeit von Paraquat in verschiedenen Böden und Bodenbestandteilen Zusammenfassung. Die Adsorptionskapazität von Paraquat wurde für folgende Materialien untersucht: 3 Torfböde...