Pine Bark Alternatives

Could Cotton residuals be a “Wrinkle Free” Choice?

Currently, the N.C. State Substrates Research Group are evaluating several alternative substrate components that could improve pine bark based substrates by increasing water holding capacity and reduce loss of air filled porosity overtime. Work continues with pine tree substrate. Pine tree wood chips and pine bark are frequently used as base substrate components for blending with other potential potting mix components. We think cotton residuals (stalks and gin trash) may offer a new “wrinkle free” choice in potting substrates. Cotton is a major agronomic crop in the southern U S. In no-till cotton fields, stalks and residue remaining in the field after harvest are very woody and do not easily decompose. When stalks are bush hogged, the mulch may persist for several seasons and eventually the accumulation will interfere with planting and application of fertilizer and herbicides. Cotton gin trash is another by-product of the cotton industry that has found no real economic market. Current research at N.C. State is focused on blending pine bark and pine tree chip components with cotton stalks or cotton gin trash. Objectives in our studies include maintaining or increasing growth of nursery crops in test substrates, but also to extend the longevity and acceptable physical properties of potting mixes so if plants have a birthday in the container, they are not in dire risk of drowning. Proof of results are determined using growth studies and laboratory analyses. Physical properties are determined initially at the beginning of studies as well as at the end of the study or after a selected period of time such as one calendar year. Ratio’s of substrate components are manipulated to achieve optimal air filled porosity and available water content characteristics initially and through the production cycle of the crop. Our results demonstrate that blending stable components to pine bark based substrates is important to offset decomposition of organic components during the growing season.