In wheat fields, irrigated with treated sewage water, the performance of six herbicides: bromoxynil/MCPA; bentazon/ dichlorprop; diclofop-methyl; tralkoxydim; pendimethalin and bromophenoxim; and some their combinations were assessed at two different locations around the city of Riyadh. The common weeds include: Lolium spp.; Phalaris spp.; Avena spp.; Malva spp.; Chenopodium spp. and others. The best weed control treatments were: bentazon/dichlorprop followed by bromoxynil/MCPA for the broad-leaved, and diclofop-methyl followed by tralkoxydim for the grassy weeds. The combinations of bromoxynil/MCPA with either pendimethalin or tralkoxydim were far more effective against the broad-leaved weeds, and significantly improved the wheat growth and yield, compared with the single treatments. However, bromoxynil/MCPA combination with diclofop-methyl was less effective against the grassy and broad-leaved weeds than each of them. Bromophenoxim showed an effective control of the whole weeds, with appreciable improvement in the wheat growth and yield.
The effect of different shading densities on some chemical composition of the roots of two sugarbeet cultivars was studied out during 1984/1985 season. Plants were grown under 0, 37, 50 and 70 % shading treatments.
Results showed that the capacity of root tissue in production or storage of sucrose was not directly dependent on light intensity as all the shading treatments did not change the sugar percentage. Therefore, it was suggested that the sucrose percentage in the root was a genetically‐dependent character more than an environmental one.
Also, shading had no significant effects on the chemical composition (protein, fiber, fat, ash and dry matter) of fresh roots at maturity, except the fiber percentage which was significantly increased only under the 70 % shading treatment.
This study was carried out at the Agricultural Experiment Station of King Saud University near Riyadh (26° N, 46° E) during the 1984/85 season to study the effect of shading densities on the agronomic and growth parameters of sugarbeet. Two cultivars were grown under three shading nets with densities of 37, 50 and 70 % in addition to the control (0 % shading = normal sunlight condition).
The results indicated that shading affected the growth and the weight of sugarbeet plants and the effects were function of shading density. Root weights were drastically reduced by increasing shading density, whereas top weights were less affected.
Increasing shading density resulted in a significant increase in specific leaf area, leaf area ratio while it decreased leaf area index, root weight ration, net assimilation rate and crop growth rate for both cultivars. The interaction between shading densities and sampling dates was significant for most of the studied characters, while that between cultivars and shading densities was significant for root weight and crop growth rates only.
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