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Title: Cumulative and residual effects of repeated sewage sludge applications: Forage productivity and soil quality implications in South Florida, USA

Author
item Sigua, Gilbert
item ADJEI, MARTIN - UNIVERSITY OF FLORIDA
item RECHCIGL, JACK - UNIVERSITY OF FLORIDA

Submitted to: Environmental Science and Pollution Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/2005
Publication Date: 4/1/2005
Citation: Sigua, G.C., Adjei, M.B., Rechcigl, J.E. 2005. Cumulative and residual effects of repeated sewage sludge applications: Forage productivity and soil quality implications in South Florida, USA. Environmental Science and Pollution Research. 12(2):80-88.

Interpretive Summary: The cow-calf (Bos taurus) industry in subtropical United States and other parts of the world depends almost totally on grazed pastures. Establishment of complete, uniform stand of bahiagrass (BG) in a short time period is important economically. Failure to obtain a good BG stand early means increased encroachment of weeds and the loss of not only the initial investment costs, but also production and its cash value. Forage production often requires significant inputs of lime, N fertilizer, and less frequently of P and K fertilizers. Domestic wastewater sludge or sewage sludge, composted urban plant debris, waste lime, phosphogypsum, and dredged materials are examples of materials that can be used for fertilizing and liming pastures. We hypothesized that successive land application of sewage sludge for at least three years followed by no sewage sludge applications for at least two years would be a good practice economically and environmentally. In order to ensure that repeated sewage sludge applications are managed appropriately, there is a need to assess the cumulative and residual effects of sewage sludge on the soil and plant environment. For this reason, we initiated a field experiment on the long-term effects of repeated sewage sludge applications on BG production and soil properties at South Florida in 1997. Bahiagrass plots received sewage sludge to supply 90 or 180 kg total N ha/yr from 1997 to 2000. Land application of sewage sludge ceased in 2001 season. Under the intensive management condition of our study, bahiagrass maintained high forage yields through years with repeated biosolids applications and through years without biosolids application. Although the average BG forage yield in 2002 was slightly lower than in 2000, yield differences between the control and treated plots were indicative of a positive carry over effect of applied biosolids in 2002. Lime stabilized biosolids had the highest residual effects on BG forage yield and had enhanced overall soil characteristics. The carry over effect of these biosolids over the long term can be especially significant in many areas of Florida where only 50% of the 1 million ha of BG pastures are given inorganic nitrogen yearly. These biosolids if processed and applied according to USEPA rules have the potential to boost and maintain production because they are inexpensive, environmentally safe, and could act as liming and organic matter amendment as well. There is still much to be learned from this study and this investigation needs to continue to determine whether the environmental and ecological objectives are satisfied over the longer term.

Technical Abstract: Although biosolids supply some essential plant nutrients and provide soil property-enhancing organic matter, land-application programs still generate some concerns because of possible health and environmental risks involved. The objectives of this study were to evaluate the cumulative and residual effects of repeated applications of biosolids on (i) bahiagrass (BG, Paspalum notatum Flugge) production over years with (1997-2000) and without (2001-2002) biosolids applications during a 5-yr period, and (ii) nutrients status of soil that received annual application of biosolids from1997 to 2000 compared with test values of soils in 2002 (with no biosolids application) in South Florida. Bahiagrass plots received biosolids to supply 90 or 180 kg N ha-1 yr-1 from 1997 to 2000. Land application of biosolids and fertilizers ceased after 2001 harvest season. The experimental design was three randomized complete blocks with nine N-source treatments: ammonium nitrate, slurry biosolids of pH 7 or pH 11, lime-stabilized cake biosolids, and a non-fertilized control. Soil samples were taken from each plot in June 1997, June 1999, and in June 2002. Average soil test values in June 2002 exhibited: i) decrease in TIN (NO3-N + NH4-N), TP, K, Ca, Mg, Mn, and Fe; and ii) slight increase in Zn and Cu when compared with the June 1997 soil test results. Although the average BG forage yield in 2002 (2.3 Mg ha-1) was slightly lower than in 2000 (3.5 Mg ha-1), yield differences in 2002 between the control (1.2 + 0.2 Mg ha-1) and treated plots (2.3 Mg ha-1 to 3.3 Mg ha-1) were indicative of a positive carry over effect of applied biosolids. This study has shown that excessive build up of plant nutrients may not occur in beef cattle pastures that repeatedly received biosolids while favoring long-term increased forage yield of BG.