Juan Carlos García-Gil

Long-term effects of municipal solid waste compost application on soil enzyme activities and microbial biomass

A long-term field experiment utilising barley received four different treatments prior to sowing: municipal solid waste (MSW) compost at either 20 t ha 21 (C20) or 80 t ha 21 (C80); cow manure (MA) at 20 t ha 21 ; mineral fertilizer (MIN) or NPK (400 kg ha 21 ); and NH4NO3 (150 kg ha 21 ). The effects of these applications on soil enzyme activities and microbial biomass at crop harvest were measured after nine years. In comparison with the control (no amendment) MSW addition increased biomass C by 10 and 46% at application rates of 20 and 80 t ha 21 , respectively, while MA treatment increased microbial biomass C by 29%. The ratio of soil microbial C to soil organic C was the lowest at the high rate of MSW application. Oxidoreductase enzymes, such as dehydrogenase and catalase, were higher in the MSW treatments by 730 (C20) and 200% (C80), respectively, and by 993 and 140% in MA treatments than in the unamended soil, indicating an increase in the microbial metabolism in the soil as a result of the mineralization of biodegradable C fractions contained in the amendments. The addition of MSW and MA caused different responses in hydrolase enzymes. Phosphatase activity decreased with MSW (^62% at both rates) and MA (^73%), to less than those in the mineral fertilization and the control treatments. Urease activity decreased by 21% (C20) and 28% (C80), possibly being affected by the heavy metals contained in the MSW. However,b-glucosidase and protease-BAA increased in all the organic treatments, especially with MA (by 214 and 177%, respectively). This is attributed to the microbial stimulation by the organic C and is correlated with the increase in dehydrogenase Or 2 a 0:882U and catalaseOr 2 a 0:654U activities. q 2000 Elsevier Science Ltd. All

Habitat Fragmentation can Modulate Drought Effects on the Plant-soil-microbial System in Mediterranean Holm Oak (Quercus ilex) Forests

Ecological transformations derived from habitat fragmentation have led to increased threats to above-ground biodiversity. However, the impacts of forest fragmentation on soils and their microbial communities are not well understood. We examined the effects of contrasting fragment sizes on the structure and functioning of soil microbial communities from holm oak forest patches in two bioclimatically different regions of Spain. We used a microcosm approach to simulate the annual summer drought cycle and first autumn rainfall (rewetting), evaluating the functional response of a plant-soil-microbial system. Forest fragment size had a significant effect on physicochemical characteristics and microbial functioning of soils, although the diversity and structure of microbial communities were not affected. The response of our plant-soil-microbial systems to drought was strongly modulated by the bioclimatic conditions and the fragment size from where the soils were obtained. Decreasing fragment size modulated the effects of drought by improving local environmental conditions with higher water and nutrient availability. However, this modulation was stronger for plant-soil-microbial systems built with soils from the northern region (colder and wetter) than for those built with soils from the southern region (warmer and drier) suggesting that the responsiveness of the soil-plant-microbial system to habitat fragmentation was strongly dependent on both the physicochemical characteristics of soils and the historical adaptation of soil microbial communities to specific bioclimatic conditions. This interaction challenges our understanding of future global change scenarios in Mediterranean ecosystems involving drier conditions and increased frequency of forest fragmentation.

Dynamics and model fitting of nitrogen transformations in pig slurry amended soils

Abstract To optimize the efficient use of nutrients in pig slurry by crops and to reduce the pollution risks to surface and groundwater, a full knowledge of the fate of nitrogen (N) in amended soils is needed. A 120 day laboratory incubation experiment was conducted to study the effects of pig slurry application on soil N transformations. Pig slurry was added at the rates of 50 and 100 g kg−1. A nonamended soil was used as a control treatment. Soil samples were taken after 0, 7, 14, 30, 45, 60, and 120 days of incubation and analyzed for NH4 +‐N and NO3 −‐N. Initially, the application of pig slurry produced significant increases in NH4 +‐N, especially at the highest application rate, whereas NO3 −‐N content was not affected. Nitrification processes were active during the entire incubation time in the three treatments. In the control soil, the net N mineralization rate was highest during the 1st week (5.7 mg kg−1 d−1), followed by a low‐steady phase. Initially, net N mineralization rate was slower in soil with the lowest slurry rate (2.7 mg kg−1 d−1), whereas in the treatment with the highest slurry rate, a net N immobilization was observed during the 1st week (4.8 mg kg−1 d−1). Mineral‐N concentrations after 120 days were 180, 310, and 475 mg kg−1 in soils amended with 0, 50, and 100 g kg−1 of pig slurry, respectively. However, when results were expressed as net mineralized N, the opposite trend was observed: 74, 65, and 44 mg kg−1. Of the six kinetic models tested to describe the mineralization process, a two‐component, first exponential model (double model) offered the best results for all treatments.