The quantitative relationship between weed emergence and the physical properties of mulches

Mulches on the soil surface are known to suppress weed emergence, but the q uantitative relationships between emergence and mulch properties have not b een clearly defined. A theoretical framework for describing the relationshi ps among mulch mass, area index, height, cover, light extinction, and weed emergence is introduced. This theory is applied to data from experiments on emergence of four annual weed species through mulches of selected material s applied at six rates. Mulch materials, in order from lowest to highest su rface-area-to-mass ratio, were bark chips, Zea mays stalks, Secale cereale, Trifolium incarnatum, Vicia villosa, Quercus leaves, and landscape fabric strips. The order of weed species' sensitivity to mulches was Amaranthus re troflexus > Chenopodium album > Setaria faberi > Abutilon theophrasti, rega rdless of mulch material. The success of emergence through mulches was rela ted to the capacity of seedlings to grow around obstructing mulch elements under limiting light conditions. Mulch area index was a pivotal property fo r quantitatively defining mulch properties and understanding weed emergence through mulches. A two-parameter model of emergence as a function of mulch area index and fraction of mulch volume that was solid reasonably predicte d emergence across the range of mulches investigated.