NOVELTY - A compost cover (20) has an intermediate layer (24) including microporous membrane layer(s) having variable porosity and surface area for condensing and retaining water vapor within the membrane layer and a top layer (28) of predetermined water and air permeability for controlling the degree to which water is admitted to the composting structure through the cover.    USE - Compost cover for controlling the emission of odorous substances from a composting mass or structure in the form of compost assemblage, compost mass, compost biomass, compost heap, compost hill, compost pile, compost windrow, open windrow, open pile, open stack or similar having a flat or truncated top or upper surface and at least two sloping sides arranged to extend longitudinally with the lengthwise extending central axis (claimed).    ADVANTAGE - The compost cover can control the emission of odorous substances from a composting mass or structure that produces the odorous substances during composting operation.    DETAILED DESCRIPTION - A compost cover (20) comprises a base layer (22) being a low moisture retention layer having a predetermined water and air permeability for transmitting a portion of water vapor/moisture produced by composting of the composting structure to an intermediate layer. The intermediate layer includes microporous membrane layer(s) having variable porosity and surface area for condensing and retaining water vapor within the membrane layer and a top layer of predetermined water and air permeability for controlling the degree to which water is admitted to the composting structure through the cover where the compost-derived water condensed within the intermediate layer through or by the base layer is retained in the intermediate layer to interact with the vapor of the odorous substances to convert the malodorous substance to a less unpleasant substance to reduce the amount of odorous substance emitted from the composting structure through the top layer to reduce the emission of odors from the compost structure. INDEPENDENT CLAIMS are included for:    (1) a method of composting to reduce the emission of odorous substances from a composting structure comprising forming a compost structure, applying a composting cover to the composting structure, controlling the amount of moisture admitted to the cover from the composting structure by trapping a proportion of the moisture produced by the composting structure within an intermediate layer of the cover where some of the odorous substance produced during composting of the composting structure is converted to a less odorous material so that less odorous substance is emitted through the cover to externally of the cover; and    (2) an engineered composting system for reducing the emission of odorous substances from a composting structure comprising a compost structure capable of undergoing composting to produce a odorous substance, and a compost cover capable of partially enveloping the compost structure where the compost cover has a first layer for selectively allowing water vapor/moisture produced by composting of the compost structure to permeate through the first layer to limit the transmission of water vapor/moisture to a second layer of the compost cover, where the second layer being arranged to retain some of the water obtained from condensation of the water vapor/moisture transmitted through the first layer so that the retained water in the second layer assists in converting the odorous substances to less odorous materials so that the less odorous substance is available for transmission through a third layer of the compost cover to atmosphere outside the compost cover and/or structure to reduce the amount of odorous substance released for the compost structure when fitted with the compost cover.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic sectional view through cross-section of the compost structure having compost cover.    Compost cover (20)    Base layer (22)    Intermediate layer (24)    Top layer (28)    Convection ventilation panel (30)