It is well known that trophic interactions between plant cover and soil organisms are key factors in
ecosystems balance. In present study, the effect of combination among mineral, organic and bio-fertilizers on
quality and productivity of lettuce under drip irrigation conditions have been studied. The combination effect of
fertilizers on soil microbial enzyme activities also was studied. The highest total yield of lettuce is 31.96 and
31.84 Mg ha-1, respectively during the two growing seasons. The best yield components were obtained with
using combination of mineral, organic and bio-fertilizers (50 % mineral + 50 % organic + biofertilizers).
Whereas, the using of organic and biofertilizer treatments recorded the lowest content of nitrate in leaves 0.82
and 0.81 g kg-1 DW, respectively, were observed in both seasons. The highest soil dehydrogenase, alkaline
phosphatase and nitrogenase activities were 64.2 and 51.0 μg TPF g-1 dw h-1, 22.3 and 19.9 μg ρNP g-1 h-1 and
83.7 and 81.2 μL C2H4 g-1 dw h-1 respectively in both seasons and after 30 days from lettuce transplanting were
achieved by using of the combination of fertilizers (50 % mineral + 50 % organic + biofertilizer). The results of
this study suggest that, it could be depended on the biological or organic farming to produce a better food and
the integrated fertilization program should be followed in agriculture under drip irrigation even in clay loam
soil.