الفهرس 
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Abstract
This investigation was carried out at the greenhouse of soil Dept. Faculty of Agric., Moshtohor, Benha University.
The aim of this study was to investigate the effect of biofertilization on N-use efficiency (NUE) by maize plants grown on the alluvial and calcareous soils.
Two surface soil samples were collected namely, alluvial soil which collected from Faculty of Agric. Farm at Moshtohor and the other sample was collected from El-Nobareia region.
Maize plants were grown for 60 days on both soils under investigation.
Basic application of phosphorus and potassium as well as micronutrients as nutrient solution were applied at recommended levels.
Labeled 15N fertilizer in the form of (NH4)2SO4 was applied at 6 rates, namely 0 kg N / fed., 15 kg N / fed. in the form of chicken manure(CM) , 15 kg N / fed in the form of ammonium sulphate (AS), 30, 60 and 90 kg N / fed. in the form of AS+CM (half dose from each of them).
Maize grains were inoculated prior to sowing with N2-fixing bacteria either singly Azotobacter chrococcum or Azospirillum brasilense as well as a mixture of them.
Maize plants were grown for 60 days from sowing after that shoot plants were harvested just above the soil surface, dried at 70°C and ground .Subsamples of 0.2 g dried material were digested using mixture of sulphuric and perchloric acids (1: 1). The digested solution were prepared and analysed for total N, P and K according to the standard methods.
The following parameters were determined.
1-Dry weight of maize plants.
2-Uptake of N, P and K.
3-NUE (nitrogen use efficiency ) by maize plants.
4-The percentage of N derived from fertilizer (%Ndff), from soil (% Ndfs) and from air (%Ndfa).
5-Microbiological activity which represented by :
a-Nitrogenase activity.
b-Dehydrogenase activity.
Obtained results could be summarized as follows:
- Values of maize dry weight and uptake of N, P and K increased due to nitrogen fertilization either in the form of mineral or organic form as compared to control (without fertilization).
2- The abovementioned values increased as a result of maize inoculated with N2-fixing bacteria either with nitrogen fertilization or without. Moreover inoculation of maize grains with dual-strains (A.chroococcurn + A.brasilense) produced the highest values of dry weight, uptake of N, P and K followed by inoculation with A. chroococcum then A. brasilense inoculants.
3 Values of NUE increased due to biofertilizer inoculation. dual inoculation induced the highest values as compared to individual inoculation.
4• Values of Ndfa increased due to inoculation with N2-fixing bacteria and the highest values were obtained with dual-strains inoculants as compared to inoculation with individual inoculants. As well as A.chroococcum was more effective than A. brasilense.
5• Increasing the rate of applied N up to 30 kg N/fed. decreased activity of N2-fixing bacteria, whereas lower rates of applied N increased the activity of such organisms.
6-Inoculation with N2-fixing bacteria minimized the dose
of applied N, therefore this investigation proved that the
economic doses of nitrogen fertilizer varied from 15 to
30 kg N/fed. in the presence of biofertilization and
organic manure.
7-Calcareous soil induced lower values of dry weight and
uptake of N, P and K as compared to alluvial soil.This
result may be due to the low fertility of calcareous soil.
The main recommendation of this study could be summarized in the important role of biofertilization especially at the lowest dose of applied nitrogen to increase plants growth and their uptake of nutritive elements at suitable rates. This approach may assist low income farmers in increasing their cereal production with less fertilizer N. Also, considerable reduction in N losses would be obtained by N-fertilizer management and application of such approach (bio-fertilization). Consequently, the potential for contamination of both surface and ground water must be minimized.