Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: November 20, 2004
Publication Date: June 20, 2005
Citation: Sigua, G.C. 2005. Use of dredged materials for pasture establishment: Forage productivity and ecological implications. In: Cannizzaro, P.J., editor. Proceedings of the 31st Annual Conferences on Ecosystems Restoration and Creation. Tampa, Florida. p.117-128. Interpretive Summary: 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 (SBS11, CBS) 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. Successive land application of biosolids for at least three years followed by no biosolids application for at least two years would be a good practice economically and environmentally because it will boost and/or maintain sustainable forage productivity and at the same time minimize probable accumulation of nutrients, especially heavy metals. Consecutive applications of biosolids may result in build up of toxic metals in some other states with initial high metallic content, but in this study no detrimental effects on soil chemical properties were detected. The possibilities for environmentally and economically sound application strategies are encouraging, but more and additional research is required to find optimal timing and rates that minimizes negative impacts on the environment. For proper utilization of biosolids, knowledge of the biosolids' composition, the crop receiving it, are absolutely crucial, so that satisfactory types and rates are applied in an environmentally safe manner. 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 Flügge) 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 ± 0.7 Mg ha-1) was slightly lower than in 2000 (3.5 ± 1.2 Mg ha-1), yield differences in 2002 between the control (1.2 + 0.2 Mg ha-1) and treated plots (2.3 ± 0.5 Mg ha-1 to 3.3 ± 0.6 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.