Rosa Calvo

Carbon mineralisation kinetics of poultry manure in two soils

Soil has an important role in the greenhouse effect as a net source or net sink of greenhouse gases. This study compared CO2 emission from broiler poultry manure (PMB) and hen poultry manure (PMH) in two different soils. A laboratory experiment was conducted to evaluate the decomposition of poultry manure by analysing carbon mineralisation. Jars were filled with soil, sealed, and placed in an incubator for 60 days, with periodic CO2 analysis. Higher emissions were found in soil amended with PMH; cumulative carbon released as CO2 was 800 mg C/kg in soil amended with PMH, and 600 mg C/kg with PMB. Data for cumulative CO2-C released from unamended and amended soils were fitted to four different kinetic models. With poultry manure, there were significant differences in the model parameters that represent the amount of total potentially mineralisable carbon and the mineralisation rate constant. After 60 days, the percentages of organic carbon mineralised for PMH were 40% and 26% for each soil, whereas the percentages were 20% and 12% for PMB.

Biomass Production and Development of Native Vegetation Following Biowaste Amendment of a Degraded, Semi-Arid Soil

Water erosion is a worrying environmental problem affecting many Mediterranean soils, which are subject to progressive degradation due mainly to the loss of organic matter. To promote the restoration of an abandoned, degraded soil with a semi-arid climate, sewage sludge (SS) and municipal solid waste (MSW) were surface-applied once only to field plots with an 8–12% slope at four different rates: 0, 40, 80, 120 Mg ha−1. The growth of native plants was enhanced by the addition of these organic wastes. Total plant biomass and canopy cover increased significantly and remained higher in all the biowaste treatments over the 5-year study period. An estimated maximum biomass of 550 g m−2 was obtained when 80 Mg ha−1 of SS were applied; for MSW, a maximum estimated value of 361 g m−2 was obtained with the 40 Mg ha−1 rate. Native plant species richness decreased with an increasing biowaste application rate. Differences in the composition of native plant communities were observed among treatments, but with a reduction in perennial and an increase in annual plants seen in all biowaste-treated plots. This was more remarkable in the plots in which SS was applied, and was seen throughout 5 years of the study. Increasing biowaste rates resulted in somewhat increased nutrient concentrations, mainly nitrogen; this effect was less evident in the last years. All plant heavy metal concentrations determined were below those considered hazardous.

Impact of Sewage Sludge Compost Utilization on Chemical Properties of Olive Grove Soils

Field experiments were conducted for four years, between 1998 and 2002, in two olive grove soils of adult olive orchards (Olea europaea L. cv. Cornicabra) in a clay loam soil in Seseña (Toledo, Spain) and in a sandy loam soil in Aranjuez (Madrid, Spain). There were four treatments, sewage sludge compost (SSC), sewage sludge compost plus urea (SSC+U), urea (U) and control (C). Each treatment was replicated four times and two depths were studied (0-15 and 15-30 cm). Once a year, before spreading sewage sludge compost, soil samples were taken at depths of 0 to 15 cm and 15 to 30 cm. Organic matter, total Kjeldhal nitrogen, phosphorus availability, pH, and electric conductivity were measured. No differences were found between treatment on organic matter and electric conductivity after four years of application of sewage sludge compost to two olive grove soils. In relation to nitrogen content, sewage sludge compost, only in Seseña, produced higher nitrogen soil content than the traditional urea treatment. Sewage sludge compost applied on olive grove soils improved the Phosphorus availability for the olive tree. In Aranjuez, the use of sewage sludge compost increased the pH of the soil with respect to Urea and Control plots. In Seseña, the reverse effect was found.