PERFORMANCE OF FREE LIVING N2-FIXERS BACTERIA, COMPOST TEA AND MINERAL NITROGEN APPLICATIONS ON SOME SOIL PROPERTIES, PRODUCTIVITY AND QUALITY OF ONION CROP (Giza red vr.).

Abstract

A field experiment was carried out at the Experimental Farm of Sakha Agricultural Research Station in Kafr El-Sheikh Governorate at North Nile Delta Region. The experiments were conducted to study the response of onion to nitrogen fertilizer levels under different bio-organic fertilizers (compost tea and N2-fixing bacteria) as well as their interaction, on some soil properties and the growth and onion bulbs yield and its quality during the two successive winter seasons of 2009/2010 and 2010/2011. A split-split plot design with three replicates was used in this study. The main plots were designated to the three mineral nitrogen fertilizer levels (60, 90 and 120 kg N fad.-1), whereas foliar spraying treatments with compost tea at the same dose, 20 L fad.-1 (spraying with water; foliar spraying at 40 days after transplanting (DAT); foliar spraying at 40 and 60 DAT; foliar spraying at 40, 60 and 80 DAT and soil application, 30 DAT at rate of 30 L fad.-1) were randomly distributed in sub plots. While uninoculation and inoculation with di-nitrogen fixing bacteria (Azotobacter Chroococum and Azospirilium Brasilense) were randomly distributed in the sub-sub plots. The obtained results could be summarized as follow: The highest increase in soil available nutrients (N, P and K), organic matter percentages and total bacterial counts were increased significantly and recorded in the plots treated with compost tea as soil application batches and/or inoculation at nitrogen fertilizers level 90 kg N fed-1 (N2B4C2) while the lowest were recorded in the uninoculated plots treated with N fertilizers at 60 kg N fed-1 without both compost tea and bacterial inoculation. With inoculation and mineral nitrogen applications, soil salinity and pH were decreased in compost tea treatment under soil application as compared with others compost tea applications. The experimental results confirmed that the combination of compost tea, inoculation by di-nitrogen fixing bacteria and mineral nitrogen fertilizers could improve soil fertility. Growth and onion bulbs yield and their quality were highest due to application of compost tea on thrice than twice batches at the same dose and other treatments. The effect of bio-fertilizer in plant height, leaves dry weight/plant, bulb dry weight, plant dry weight, bulb diameter and bulb weight as well as bulb quality was evident in both seasons. In general, inoculation with Azotobacter chroococcum and Azospirilium brasilense positively increased all the previous characters. Based on the results of the current study, the combinations of medium dose of mineral N and compost tea or biofertilizers could be considered as an integrated nutrient management to improve soil bio-physical properties and the growth and yield of onion plants. It also confirmed that compost tea can be used as organic substrate additives in plant cultivation and substitute for chemical nitrogen fertilizers.