Concentrated animals feeding operations (CAFOs) often pose a negative environmental impact due to the uncontrolled spreading of manure into soils that ends up in the release of organic matter and nutrients into water bodies. Conventional aerobic methods treating CAFOs wastewater require intensive oxygenation, which significantly increases the operational costs. The alternative proposed in this research is the application of micro-algae based systems by taking advantage of the cost-effective in situ oxygenation via photosynthesis. A 4.9 L enclosed tubular biofilm photo-bioreactor was inoculated with an algal-bacterial consortium formed by the micro-algae Chlorella sorokiniana and a mixed bacterial culture from an activated sludge process. C. sorokiniana delivers the O(2) necessary to accomplish both organic matter and ammonium oxidation. The reactor was fed with diluted swine wastewater containing 180, 15 and 2,000 mg/L of NH(4) (+)-N, soluble P and total COD, respectively. The photo-bioreactor exhibited good and sustained nutrient removal efficiencies (up to 99% and 86% for NH(4) (+) and PO(4) (3-), respectively) while total COD was removed up to 75% when the biofilm was properly established. Liquid superficial velocities up to 0.4 m/s (achieved by culture broth recirculation) hindered the formation of a stable biofilm, while operation at velocities lower than 0.1 m/s supported stable process performance. The high shear stress imposed by the centrifugal recirculation pump disintegrated the large aggregates detached from the biofilm, which resulted in a poor settling performance and therefore poor COD removal efficiencies. Enclosed biofilm photo-bioreactors therefore offer a potentially more economical alternative to conventional tertiary treatments process.

been removed from the soil by leaching or via harvested crops (Granados et al., 1993). Acidic soils, therefore, Soil acidity reduces maize (Zea mays L.) yields by up to 70% on generally have a low pH, contain toxic levels of Al and 8 million hectares in developing countries. Several breeding programs have produced populations better adapted to these conditions. TheMn, and are deficient in Ca, Mg, P, K, and Mo. These objectives of this study were to evaluate these populations for both characteristics limit the fertility of acid soils and inhibit per se cultivation and the development of new breeding germplasm. root development, leading to low water and nutrient up-To do so, we generated a diallel cross design, which included six acid take and low maize yields (Duque-Vargas et al., 1994). soil-tolerant and five susceptible populations with high yield potential Soil amendments (the application of lime and fertilizor tolerance to other stresses. Populations and crosses were evaluated ers) have been used to bring acid soils under agricultural in five environments, on acidic Al-toxic soils and in comparable limed production. However, such solutions may not be envisoils in Guadeloupe, Cameroon, and Colombia. Soil acidity decreased ronmentally friendly, have only a temporary effect, and grain yield by 46 to 73%, depending on the location and year. Signifiare too expensive for poor farmers in developing councant genotype ϫ soil condition interactions were observed for grain tries (The et al., 2001). The use of acid soil-tolerant maize yield. Mid-parent heterosis for yield was significantly higher in acid soils (32%) than in nonacid soils (20%). This suggests that the develop-cultivars provides an environmentally friendly, inexpenment of variety crosses between acid soil-tolerant populations could sive, and permanent solution, contributing to sustainbe used to increase maize yields in acid-soil cropping systems. The able crop production on acid soils (Granados et al., observed high general combining ability (GCA) for yield variation of 1993). the crosses in acid soil and its close relationship to per se performance Considerable genetic variation in acid-soil tolerance suggest that parental populations of variety crosses could be efficiently has been reported in maize. Early studies demonstrated screened on the basis of per se performance in acid soil.

germplasm. For instance, Iowa Stiff Stalk Synthetic is considered a source population of inbreds with above-Breeders need more information on selecting testers to identify average performance for combining ability (Hallauer lines for formation of synthetics and need more user-friendly methods to study general combining ability (GCA) and specific combining and Miranda, 1988). Lonnquist (1961) defined a synability (SCA) of genotypes. Forty-three lines were crossed to two thetic as an open-pollinated population formed by internarrow-based (S3 line and S3 ϫ S3 hybrid) and two broad-based crossing lines and maintained subsequently by mass setesters, which were open-pollinated varieties (OPVs). Topcrosses lection. In this paper, synthetics are defined as OPVs (line ϫ tester, L ϫ T) were evaluated in eight acid soil environments. formed by recombining lines with high GCA and main-The additive main effect and multiplicative interaction (AMMI) and tained from one generation to the next by open pollithe site regression (SREG) models were used to study the GCA of nation. the testers and lines and the SCA of the L ϫ T interaction. The SREG The use of testers in a maize recurrent selection probiplot contains the effect of the lines plus the L ϫ T interaction and gram has been well documented (Jenkins and Brunson, displays both GCA and SCA, whereas the AMMI biplot contains the 1932;Matzinger, 1953;Rawlings and Thompson, 1962; effect of the L ϫ T interaction and displays only the SCA. One synthetic was developed by recombining six lines identified as superior Allison and Curnow, 1966, Hallauer, 1975; Hallauer and by each tester. The four synthetics were evaluated in 12 acid and nine Miranda, 1988;Russell et al., 1992, Menz et al., 1999. nonacid soil environments. The synthetic developed with the S3 lineThese authors concluded that choice of a suitable tester as tester yielded the highest and the one developed with an OPV as should be based on simplicity in its use, its ability to tester yielded the lowest. The AMMI and SREG models seem to classify the relative merit of lines, maximize genetic gain, provide an effective tool to visualize and study GCA and SCA of geand enhance the expected mean yield of a population notypes.

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