Hani Z. Ghosheh

Allelopathic effects of Pinus halepensis and Quercus coccifera on the germination of Mediterranean crop seeds

Agroforestry is a leading alternative for food security and forest conservation. A full understanding of positive and negative, i.e. allelopathic, interactions between crops and forest trees is necessary for producing crops and conserving forests especially within the threatened Mediterranean forest ecosystems. The present study explored the allelopathic effects of green and senescent leaf and soil extracts of two agroforestry trees—Pinus halepensis and Quercus coccifera—on the germination of wheat, barley, lentil, chickpea, and fababean as the major grain crops of Jordan. Results revealed that allelopathic effects reduced seed germination of these crops. Germination reduction reached a maximum of 75% in fababean treated with green extracts of Q. coccifera and differed among crops and extract sources, but not between tree species. Comparing between green and senescent leaf and soil extract, regarding their effect on germination percentage, it was noticed that these effects were similar in some crops and were different in others. Germination responses were generally different between cereals and legumes where cereals tend to be less affected by allelopathic influences than legumes, especially fababean. We suggest using cereals such as wheat and barley in agroforestry practices in the Mediterranean region of Jordan.

Utilization of Alfalfa (Medicago sativa L.) as a Smother Crop in Field Corn (Zea mays L.)

ABSTRACT Field experiments were conducted at two locations in Jordan to investigate the effects of alfalfa grown as a smother crop on corn and weeds. The two locations were characterized by semi-arid conditions. Treatments were; (1) a mixture of alfalfa-corn with alfalfa clipped once; (2) a mixture of alfalfa-corn with alfalfa clipped twice; (3) a mixture of alfalfa-corn with alfalfa clipped three times; (4) a mixture of alfalfa-corn with alfalfa clipped four times; (5) weed-free corn; (6) weedy corn; (7) weed-free alfalfa; and (8) weedy alfalfa. Results indicated that alfalfa reduced corn grain yield more than total above ground dry biomass. Grain yield reductions ranged from 23 to 53% of amounts harvested in weed-free corn plots. Yields were comparable or greater than amounts harvested from weedy check plots, indicating that alfalfa imposed equivalent or less competition on corn than the prevailing weeds of the two sites. Alfalfa harvested from frequently clipped plots was 48 to 57% of quantities harvested from weed-free alfalfa plots. Effectiveness of alfalfa in suppressing weeds was not obvious and varied between locations and cutting frequencies. Results of these experiments encourage corn producers to replace polyethylene mulches with alfalfa smother crop to maximize their utilization of scarce water resources available for Mediterranean agriculture. Possible economic advantages arise from lowering the initial costs of polyethylene mulches and additional returns from producing a high-quality forage crop, thus compensating for any reductions in corn grain yields.

Influence of weeds and onion thrips, Thrips tabaci (Thysanoptera: Thripidae), on onion bulb yield in Jordan.

Abstract Field experiments were conducted in two seasons to investigate the effects of weeds and onion thrips on onion bulb yield grown under irrigation. Treatments were combinations of three levels of weed infestation and two onion thrips infestation levels. Weed interference was found to severely reduce bulb yield, whereas reductions from onion thrips infestations were of lower magnitude. Hand weeding was more effective in weed control than a single oxyfluorfen application. No significant interactions were detected in this investigation between weeds and onion thrips infestations, which could be attributed to the strong preference of onion thrips towards the crop over the weeds.