Response of Onion (Allium Cepa,L.) Plants and Associated Weeds to Biofertilization under Some Plant Mulches and Associated Weeds

Two field experiments were carried out to study the effect of multi strains biofertilizer (phosphate dissolving bacteria, Azospirillum spp. and Pseudomonas spp.) with different levels of NPK fertilizer (50 and 75% of recommended rate) under different weed control treatments, including 4 plant mulches (sawdust, rice straw, clover weed or cogongrass) as well as hand hoeing and butralin herbicide with one hoeing on onion plants and associated weeds. Counts of Azospirillum spp. in biofertilized rhizosphere recorded higher densities with 50% NPK application, while counts of phosphate dissolving bacteria and Pseudomonas spp. showed higher populations with 75% NPK application under different weed control treatments. Generally, hand hoeing treatment recorded higher counts of tested microorganisms in onion rhizosphere as compared to unweeded check, butralin herbicide and applied different plant mulches except clover weed mulch treatments. Numbers of broad- leaved weeds were significantly decreased by increasing the rate of NPK fertilizer, in the presence and absence of biofertilization, while the grassy weed was increased. Broad-leaved weeds were more susceptible than grassy weed to mulching treatments. Application of hand-hoeing (trice), sawdust mulch, rice straw mulch, clover weed mulch, cogongrass mulch and butralin herbicide + one hoeing decreased significantly the total dry weight of weeds at 75 days from transplanting and produced higher bulb yields over unweeded by 143.2, 127.2, 118.1, 151.6, 123.1 and 133.3 % respectively. No significant difference in marketable bulb yield was detected between biofertilizer + 75% NPK and 100% NPK application, under different weed control treatments. The highest values of N and P content in onion bulbs were obtained as a result of combined action of biofertilizer and 75% NPK under different weed control treatments. However, sawdust mulch treatment recorded the greatest value of N-content in the presence of biofertilizer + 50% NPK, while Zn and Fe contents reached their highest values under 100% NPK applicatio