The use of associative diazotrophs with different rates of N fertilisation and compost to enhance N2 fixation and growth of wheat

Abstract

In this work the influence of inoculation with single and double-mixed strains of diazotrophs on the growth and N2 fixation of wheat was studied. For this purpose a field trial was conducted on a sandy soil of West-Samalout, Minia, Egypt, during the 1996 growing season under sprinkler irrigation with different levels of compost from potato leaves (0, 16 and 32 tons ha-1), and the rational mineral nitrogen rate. The 15N-isotope method was used to estimate N2 fixation; 15N ammonium sulfate (1% atom excess) was applied at a rate of 100 kg N ha-1. Inoculation resulted in different 15N atom excess. The highest values were recorded with the uninoculated plants. Straw, grain, N yield, % Ndfa, N2 fixed and % N recovery responded positively to both inoculation and N fertilizer application. Irrespective of N fertilization, increases in both total dry matter (11.1%-17.8%) and total N2 fixed (247.8%-331.3%) were achieved with the highest level of dual inoculation. Total dry matter production after single-strain inoculation with Azospirillum brasilense (24.5% increase) was superior to Herbaspirillum seropedicae. On the other hand, total N2 fixed by Herbaspirillum seropedicae was 19.4% over that of Azospirillum brasilense. Irrespective of inoculation, the maximum increases in straw, grain and N yields and N recovery were obtained when compost was applied at the rate of 32 tons ha-1 whereas % Ndfa and N2 fixed were inhibited at such high level of application. Maximum increases in total % Ndfa (86.2%) and total N2 fixed (43.7 kg N ha-1) were observed when the rational N level was applied in organic form (16 tons ha-1 equivalent to 190.4 kg N ha-1). The maximum values of total dry matter, total N-yield, total N-recovery were recorded when dual inoculum of diazotrophs was combined with 32 tons ha-1 compost. Estimates of % Ndfa and N2-fixed were maximum when dual inoculation was combined with a compost rate of 16 tons ha-1.