Significance of Sewage Sludge Amendments to Borrow Pit Reclamation With Sweetgum and Fescue

Sweetgum (Liquidambar styraciflua L.) and fescue (Festuca arundinocea Schreb.) were planted after subsolling and sludge applications to depths of 0, 0. 64, 1.27, and 2.54 em to reclaim a borrow pit In the Lower Piedmont of South Carolina. Sludge treatments in combination wi th subsoiling significantly improved establishment of fescue and growth of sweetgum, but all combi nations of fescue wi th sl udge significantly reduced first-year survival of sweetgum . Because survival was stabilized after the first growi ng season , allelopathy of fescue to sweetgum had little effect in this study . Fifth-year total height growth (0. 74 m) of sweetgum on the nonamended plots was rated not acceptable, but on P'lots amended at even the lowest rate of sludge , height growth (2.75 m) was acceptable. Total heights (ca 3.6 m) after 5 years on plots amended at the two highest sludge rates were equal to or greater than 5-year hei ghts reported for sweetgum on reforestation sites . The increase in total nitrogen avail able on the site after 5 years exceeded the amount initially pres ent in the sludge, which suggests either a si gnif icant atmospheric contribution or that organi c matter enhanced nitrogen fix at i on1. Keyword$: Llquidambar styracifl~a. Festuca ~­ dinocea, reforestation , hardwood plant1ng. Many const ruct i on projects , such as dams , hi ghways , and bui l dings , require extensive earth fil l to meet design crit er ia . When insuffi ci ent soil fi ll is avai lable on a construction site , it becomes necessary to bor row . soi 1 from another location . Generally , the result i ng borrow pits are excavations f rom which all of the A and B horizons 1Silv iculturi st , Institute of Mycorrhizal Research and Devel opment , Athens , GA , and Professor, Department of Forestry , Iowa State University. Ames , IA . \ r"". I' I ' ' <. l have been removed. Compared with other disturbed areas , such as surface mines , i ndividual borrow pits are often rela t i vely small . Borrow pits , however , do represent a significant amount of su rface area throughout the country . For example , the u.s. Department of Energy Savannah River ~ant (SRP) , Aiken, SC, where this research was conducted , covers approximately 81 , 000 ha , of which nearly 1 percent consists of borrow pits created during construction of plant facil i ties in the early 1950 ' s . Effectiveness of borrow pit recla mation varies from area to area, depending on existing soil types, slope , desired vegetation, climatic conditions , and other factors (Blauch 1978) . In general , however , a si ngle applicat i on of fer tilizer , scarifi cation of the surface soi 1 , and sowing grass seed or pl anting t ree seedl i ngs are not su ffic i ent to reclai m borrow pits (Ber ry and Marx 1980). Berry and Marx (1977 . 1980) and Berry (1979) have shown that deep subsoil i ng and organic amendments (sewage sl udge and bark) can signi f icantly improve borrow pit recl amat i on . Ber ry and Marx (1980) report ed t hat a combi nat i on of dr i ed sewage sl udge and subsoiling resulted in height growth of 3-year -old loblolly pi ne comparabl e to that attained by a 22-year -ol d plan tation where only surface scarifi cat i on and fertilizer were used init i ally in 1953 . Digitized by G oog I e -·I By the early 1970's, it was evident that the initial attempts at borrow pit rec 1 a mat ion at the SR P had not been suecessful. Active soil erosion was becoming increasingly severe as tree vigor continued to decline and tree mortality increased. These factors resulted in increasingly large openings in the pine plantation with little natural vegetation replacing the dying trees. This paper describes the long-range effects of subsoiling and sewage sludge application on the establishment and growth of Kentucky 31 fescue (Festuca arundinocea Schreb.) and sweetgum (Liquidambar styraciflua L.) planted on borrow pits at the SRP. Methods and Materials Twelve to 18 feet of borrow material were removed from this borrow pit site in 1951 and 1952. In the ori gina 1 soil survey, two soil series, occurring on this site were identified--Fuquay and Wagram. Reclamation was first attempted in 1953 by planting loblolly pine (Pinus taeda L.). In 1976, surviving pine trees were only 5 to 15 em in diameter and 2.5 to 5 m tall. The trees had chlorotic foliage and their roots were barely under the soil surface. Many surviving trees were windthrown and partly lying on the ground, while standing trees had such limited root development that they could readily be pulled from the soil by hand. Although a thin layer of litter was present under some trees, no understory was growing to retard rapid surface runoff. In the summer of 1975 all trees and 1 arge roots were removed and the entire site was subsoil ed by ripping furrows 0.9 m deep, spaced 1.2 m apart, in both north -south and east -west directions. The site was then double disked to break large clods of soil and to smooth ridges created by the subsoiling. Following disking, soil samples were randomly collected (0 to 17 em deep) from throughout the study area and were analyzed at the Soil Testing Center at the University of Georgia, Athens. These samp 1 es revea 1 ed the fo 11 owing soi 1 2 properties: organic matter, 0.4 percent; CEC, 1.39; pH, 4.6; and N, P, K, and Ca in p/m of 110, 5, 10, and 4, respectively. Forty plots, each 8.5 by 8.5 m, were laid out, separated by aisles 3m wide in one direction and 6 m wide in the other. Anaerobically digested, dried sewage sludge was broadcast by hand and incorporated by double disking. The rates of application were 0, 17, 34, and 68 metric tons of dried sewage sludge per hectare. These rates equaled 0, 0.64, 1.27, and 2.54 em of sludge evenly distributed over specific plots. The sludge, obtained from treatment plants in Athens, GA, contained about 2 percent N, 1 percent P, 0.5 percent K, and 50 percent organic matter by dry weight. Each treatment was randomly assigned to 10 different plots. In the fall of 1975, the entire borrow pit study area was seeded with Kentucky 31 fescue at a rate equ iva 1 ent to 34 kg/ha. Half-sib seedlings from two different mother trees were grown in the Whitehall experimental nursery near Athens, GA, during 1975 in raised beds. The beds had been heavily infested with the vesicular-arbuscular mYCorrhizal fungus Glomus mosseae (Nicol. ~ Gerd.) Gerdemann and Trappe by growing a crop of sorghum (Sorghum bicolor L. Moench. Shallu.) on the area in 1974. The seedlings were hand-lifted and out-planted in February 1976. A sampling (Kormanik and others 1980) showed that 75 percent of the feeder roots of these seedlings were heavily colonized by G. mosseae. Twenty-five test seed1 i ngs, five rows of five seedlings spaced at 1.2 by 1.2 m, were planted in each plot. A border row of comparable size nontest seedlings was planted around each plot. Initial root-collar diameters and heights of the seedlings were measured in March before bud break had occurred. Height growth, root-collar diameter, and survival were measured annually for 5 years. After each of the first three growing seasons, five root samples from each treatment plot were collected and assessed for mYCorrhizal development. At the end of the first, second, and third growing seasons, grass biomass samples were collected on each plot.