<p num="16">FIELD: agriculture.</p> <p num="17">SUBSTANCE: invention relates to agriculture, in particular to vegetable growing, and can be used in growing leaf lettuce in closed agrobiotechnological systems. Biopreparation Niva, containing a number of microorganisms, humic components and a complex of micro- and macroelements without lipids, is used in closed agrobiotechnical system in amount of 5 vol.% of aqueous solution once as a foliar top dressing on 18–20th day of vegetation of leaf lettuce.</p> <p num="18">EFFECT: method ensures increase of crop capacity and quality of grown products.</p> <p num="19">1 cl, 2 tbl</p>