An approach for using general soil physical condition-root growth relationships to predict seedling growth response to site preparation tillage in loblolly pine plantations
Tree seedling root growth rate can be limited by any one of three soil physical factors: mechanical resistance, water potential or soil aeration. All three factors vary with soil water content and, under field conditions, root growth rate will depend on the soil water content as a result of its relationship to each factor. For a specific site, the relationship between soil water content and each factor can be developed from periodic measurement in the field or estimated from intact soil core samples. A STELLA™ model of first-year pine seedling growth response to soil tillage was developed using previously established relationships between root growth and these growth-limiting factors. The model predicts reductions in root growth below optimal conditions from soil water content. Accumulated root length is then used to estimate aboveground size from an available allometric relationship. Model predictions were compared to results from a site preparation tillage study on an upland site for which soil water content had been measured bi-weekly. Treatments used for this comparison were: no tillage, bedded, subsoiled and bedded plus subsoiled. Seedling height predicted by the model differed from measured mean seedling height by 1 to +14% with absolute differences in height of 0.1 m or less. Predicted aboveground biomass was 12 to +41% of mean measured biomass. Our results suggest that this modeling approach is useful for integrating results from controlled greenhouse experiments with field results and may prove useful for predicting soil tillage response in young loblolly pine plantations.