Use of Deep-Row Biosolid Applications to Grow Forest Trees: A Case Study

Deep-row application of biosolids on reclamation sites is a unique alternative method of land application that solves many of the problems associated with surface application techniques. When combined with the growth of nitrogen-demanding hybrid poplar trees, it provides a natural recycling system that utilizes nutrients on-site, produces forest products and wildlife habitat, and reduces erosion while reclaiming abandoned, biologically dead soils created by sand and gravel operations. In the Washington, DC/Maryland area, environmentally sound, cost-efficient utilization of biosolids has created constant challenges since the passage of the Clean Water Act of 1972. Presently, biosolids are distributed on farmland, marketed for compost, and incinerated; however, the most cost-effective methods of biosolids management are either application to agricultural land or burial in landfills. Biosolids production for 1995 in Maryland (MDE 1997) was 857,355 Mg of which 672,129 were utilized in-state as follows: agricultural land (59%), landfill disposal (5%), distributed and marketed (21%), incinerated (10%), and marginal land applications (5%). The data fail to acknowledge the fate of the remaining 190,653 Mg (22%) of the total which was hauled out of state, most likely a portion going to large landfills. Also, the District of Columbia produces an average of 362,872 Mg per year—a large percentage of which is currently disposed of out of Maryland. More current figures to show the fate of biosolids are not available; however, the percentage sent to landfills versus other land application methods is known to increase with excess landfill capacity in a region and associated lower tipping fees (ENR 1997). Difficulty in siting new landfills and possible future restrictions on out-of-state hauling may result in restriction and/or increased cost of landfill disposal of biosolids. Current agricultural land application of municipal biosolids can boost soil productivity for field crops and improve soil textural characteristics. However, regular broadcast applications once every 1–3 years, necessary to provide crop nutrient requirements, can cause logistical, safety, and economic concerns due to transportation cost, poor weather, frozen soils, availability of labor, and other problems. Resentment by rural landowners and offensive odors in developing areas has resulted in many local application restrictions. There are also developing concerns over phosphorus pollution in receiving waters from repeated applications. The developing drawbacks of landfill and agricultural land application point to the need for alternative disposal technologies (Sikora and Colacicco 1979, 1980). Land application of biosolids on native forests, reclamation sites, and plantations through regular broadcast applications has been used in other parts of the country, with significant growth responses documented (Cole et al. 1986, Heilman et al. 1995, Sopper 1993, Aschmann 1988, Purkable 1988). Burying biosolids in deep-rows covered by a soil overburden, known as deep-row application, is a promising disposal technology that was researched in the early 1970s (Sikora and Colacicco 1980, Taylor et al. 1978). While the production of annual corn