From the question "Has Mars supported life?" to "Can Mars support life?" - The answer seems to be an overwhelming "Yes." Although nitrates have yet to be detected, the Mars soil appears to have an alkalinity commonly found in terrestrial soils. At a pH of eight or nine, a zoo of bacteria and plants can live comfortably. Vegetables such as asparagus and turnips are farmed in soils to this degree of alkalinity.
says Universe Today