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FIELD experiment was conducted on a clayey soil at Sonnuris district, El-Fayoum Governorate, Egypt during the two successive seasons of 2010-2011 and 2011-2012 to evaluate the response of vegetative growth, nutritional status and yield of broccoli (Brassica oleracea L. var. Italica) as well as head quality to a partial substitution of 50% and 25% N-mineral from the recommended fertilizer rate by the N-bio-fertilizer, Azotobacter chroococcum (AT)and Azospirillium brasilense (AZ)[1:1] at one or two or three doses as compared with applying 100 % recommended dose of N-mineral fertilizer (120 kg N fed-1), hopping an alleviation of the possible reduces of chemical pollution for broccoli yield and environmental risks.
Data of the studied plant characters indicate that the greatest vegetative growth parameters of broccoli (i.e., leaf area plant-1, number of leaves plant-1, dry weight of leaves plant-1, dry weight of stem plant-1, leaf sugarand leaf nutritional status) were achieved by plants supplied with the combined treatment of 75 % recommended dose of N-mineral fertilizer + three doses of (AT+AZ). Such favourable conditions were reflected positively on the followed growth stages and gave the greatest total yield fed-1 (i.e., central head weight and lateral head weight), as well as better quality parameters of broccoli (i.e., central head weight, lateral head weight, number of lateral heads plant-1 and sugar head) during both two studied seasons. Such beneficial conditions were more attributed to the optimum soil case of the current experiment because of the renewed activity of bacteria in the soil by adding the three doses of (AT+AZ), which was achieved by ameliorated values of soil nutrients status.
The superiority of the applied N-mineral in combination with bio-fertilizer (AT+AZ) was mainly attributed to the later due to its ability to 1). Release some plant promoting substances, mainly IAA, gibberellic acid and cytokinin-like substances which stimulate plant growth. 2) Increasing the ability to convert N2 to NH4 and thus, make it available to plants. 3) Beneficial effects of (AT+AZ) bacteria on reducing soil pH by secreting organic acids (e.g. acetic, propionic, fumaric and succinic) and maintaining a suitable air-moisture regime, that finally leading to improve vegetative growth, chemical constituents and higher yield of broccoli with better quality heads. Moreover,the periodical application of such N- bio - fertilizer is
considered the best option not only for reducing the harmful effects of using chemical fertilizers but also for sustaining soil fertility status and help to alleviate the possible risks of environmental pollution on human health.