No abstract

Black mustard [Brassica nigra (L.) Koch.] contains watersoluble allelochemicals that inhibit the germination and growth of other species. This characteristic could be used in weed management programmes. Greenhouse and laboratory experiments were conducted to determine the effects on wild barley (Hordeum spontaneum Koch.) germination and seedling growth of (i) preceding crops, (ii) fresh black mustard residue incorporation, and (iii) black mustard leaf, stem, flower and root water extract concentrations. Growth of wild barley, as indicated by plant height and weight, was significantly reduced when grown in soil previously cropped to black mustard compared with that cropped to wild barley. Soil incorporation of fresh black mustard roots and both roots and shoots reduced wild barley germination, plant height and weight when compared with a no-residue control. In bioassays, black mustard extracts reduced wild barley hypocotyl length, hypocotyl weight, radicle weight, seed germination, and radicle length by as much as 44, 55, 57, 63 and 75 %, respectively, when compared with a water control. Increasing the water extract concentrations from 4 to 20 g per 100 ml of water of all black mustard parts significantly increased the inhibition of wild barley germination, seedling length and weight. Based on 8-day-old wild barley radicle length, averaged across all extract concentrations, the degree of toxicity of different black mustard plant parts can be ranked in the following order of inhibition: leaves > flowers > mixture of all plant parts > stems > roots. Key words: allelopathy -black mustard -Brassica nigra (L.) Koch. -Hordeum spontaneum Koch. -water extracts -wild barley U.S.

The effects of seeding rate (30, 60 and 90 seeds m−2), seeding date (14 January, 28 January and 12 February), seed weight (0.18 and 0.25 g seed−1), seeding depth (3 and 6 cm), and phosphorus fertilization rate (17.5, 35.0 and 52.5 kg P ha−1) and placement method (banded or broadcasted) on field pea (Pisum sativum L.) development and seed yields were investigated in irrigated field experiments conducted in northern Jordan in 2000 and 2001. Results and treatment responses were consistent in both years. Seeding rate, seeding date, seed weight and rate and method of phosphorus fertilization had significant effects on most traits measured; planting depth however did not affect any of the traits. Generally a positive correlation was observed between each factor and seed yield and yield components, with the exception of a negative correlation between seeding rate and yield components, and seeding date and yield and yield components. Increase in seeding rate from 30 to 90 seeds m−2, and increase in P fertilization from 17.5 to 52.5 kg ha−1 alone increased seed yields by 50 and 41 %, respectively. Each delay of 2 weeks for seeding from mid‐January resulted in reductions of 12 % in seed yields. Overall, the results revealed that a combination of early seeding (14 January), of large seeds at an high seeding rate (90 seeds m−2), with P fertilizer banding (52.5 kg P ha−1) maximize field pea yields in irrigated fields in semi‐arid Mediterranean environments. With such management pea seed yields can be as high as 2800 kg ha−1.

3 Lentil (Lenus culinaris Medik) is a major grain legume crop in many developing countries in West Asia, North Africa and many other areas of the world. The effects of sowing date (1 January, 15 January and 2 February), plant density (80, 100 and 120 plants m )2 ), phosphorus level (0, 17.5, 35.0 and 52.5 kg P ha )1 ) and ethephon application [(1500 p.p.m. 4 ethephon (2-chloroethel phosphonic acid) applied 30 days after sowing] were investigated in the semiarid region in the north of Jordan. High yields were obtained for early sowing (1 January), high plant density (120 plants m )2 ), and high phosphorus application rate (52.5 kg P ha )1 ). Yield and yield components were not affected by ethephon application 30 days after sowing.

The present study investigated the allelopathic effects of various black mustard ( Brassica nigra L.) plant parts on alfalfa germination and seedling growth. Aqueous extracts of black mustard ( Brassica nigra L.) leaf, stem, flower and root plant parts were made to determine their effects on germination and dry weights of hypocotyl, and radicle length of 5-day-old alfalfa seedlings over a range of extract concentrations. All aqueous extracts significantly inhibited alfalfa seed germination and seedling growth when compared with the distilled water control. Increasing the aqueous extract concentrations of separated Brassica nigra plant parts significantly inhibited alfalfa germination, seedling length and weight. Based on significant radicle length reactions to aqueous extracts, the toxicity may be classified in the following order of decreasing inhibition: flower, leaf, mixture of all plant parts, root, and stem. Increasing the concentration of aqueous flower extracts significantly inhibited the water uptake by germinated alfalfa seeds. The greatest inhibition in water uptake occurred at a 12 g kg -1 extract concentration for seeds soaked for 8 h.