Roel Merckx

N dynamics and sources of N2O production following pig slurry application to a loamy soil

Abstract Carbon (C) and Nitrogen dynamics and sources of nitrous oxide (N2O) production were investigated in a loamy soil amended with pig slurry. Pig slurry (40000kgha–1) or distilled H2O was applied to intact soil cores of the upper 5cm of a loamy soil which were incubated under aerobic conditions for 28 days at 25°C. Treatments were with or without acetylene (C2H2), which is assumed to inhibit the reduction of N2O to dinitrogen (N2), and with or without dicyandiamide (DCD), which is thought to inhibit nitrification. Volatilization of ammonia (NH3), pH, carbon dioxide (CO2) and N2O production, and ammonium (NH4+) and nitrate NO3–) concentrations were monitored. The pH of the pig slurry amended soil increased from an initial value of 7.1 to pH 8.3 within 3 days; it then decreased slowly but was still at a value of 7.4 after 28 days. Twenty percent of the NH4+ applied volatilized within 28 days. Sixty percent of the C applied in the pig slurry evolved as CO2, if no priming effect was assumed, but only 38% evolved when the soil was amended with DCD. Pig slurry significantly increased denitrification and the ratio between its gaseous products, N2O and N2, was 0.21. No significant increases in NO3– concentration occurred, and N2O produced through nitrification was 0.07mg N2O-N kg–1 day–1 or 33% of the total N2O produced. C2H2 was used as a C substrate by microorganisms and increased the production of N2O.

Genotypic differences in the uptake and distribution of radiocaesium in plants

Abstract137Cs uptake rates and distribution within the plant were investigated for clover, maize, sunflower and radish under five different nutritional scenarios. Nutritional scenarios differed in cationic composition only: K+ concentration ranged from 0.25 to 5 mM, Ca2+ from 1.89 to 3.60 mM. 137Cs uptake and distribution depended both on species and on the ionic composition of the growth medium. Differences between the species were maximal at the lowest K+ concentration. Ranking of the species with respect to 137Cs level in the plant was also dependent on the external K+ concentration. It is concluded that crop selection as a measure to reduce 137Cs contamination of the food chain should not occur without taking into consideration the external K+ concentration.

Evaluation of the intrinsic methyl tert-butyl ether (MTBE) biodegradation potential of hydrocarbon contaminated subsurface soils in batch microcosm systems.

Eleven soil samples (contaminated and non-contaminated top soils and aquifers) from seven different locations in Belgium were examined in lab-scale batch microcosms simulating in situ conditions for their indigenous capacity to biodegrade methyl tert-butyl ether (MTBE). The effect of implementing nutrients or additional oxygen and of the presence of co-contaminants on MTBE degradation was investigated. All soils showed rapid degradation of benzene. On the other hand, only one site, historically contaminated with oxygenated fuel, provided soil samples showing relatively fast MTBE biodegradation. These soil samples originated from four different depths from the vadose and saturated zone. MTBE degradation kinetics differed between the samples of the saturated and non-saturated zone and depended on the implemented conditions. MTBE-biodegradation in the samples from the non-saturated zone started after a very short lag-phase (<7 days), while long lag-phases (up to 270 days) were obtained with the other samples. Addition of extra nutrients stimulated MTBE degradation kinetics in microcosms containing the saturated soil samples while inhibiting effects were seen in the case of non-saturated soil samples. In contrast, implementing dissolved oxygen concentrations of 9.5 and 11.5 mg l(-1) led to lower degradation kinetics compared to 8 mg l(-1) in microcosms containing saturated soil samples, while stimulating effects were seen with the non-saturated soil samples. Addition of an extra carbon source like benzene or propane did increase in general the MTBE first order degradation rate constant. Differences in the eubacterial community composition between these depth samples were confirmed based on denaturing gradient gel electrophoresis (DGGE) patterns of PCR-amplified 16S rRNA gene fragments. The results of the presented study indicate that an aerobic MTBE biodegradation potential is not omnipresent in Belgian sub-soils.

Effect of short-term exposure to methyl-tert-butyl ether and tert-butyl alcohol on the hatch rate and development of the African catfish, Clarias gariepinus

Methyl tert-butyl ether (MTBE), a synthetic chemical used as a fuel additive, has been detected more frequently in the environment than previously. In this study, we examine the effects of MTBE (up to 100 mg/L) and its primary metabolite tertbutyl alcohol (TBA) (up to 1,400 mg/L) on the hatch rate and larval development of the African catfish Clarias gariepinus. Exposure to higher MTBE concentrations resulted in deformed eyes, mouthparts, and spinal cord and in increased larval mortality. Methyl tert-butyl ether exposure had no significant impact on egg viability, whereas TBA induced a decline of hatch rate. The MTBE can be regarded as a pollutant with toxicological effects on catfish larvae at concentrations above 50 mg/L. Although such concentrations greatly surpass present-day concentrations found in surface water (0.088 mg/L), concentrations up to 200 mg/L have been detected in groundwater.

Balanced Nutrient Management System Technologies In The Northern Guinea Savanna Of Nigeria: Validation And Perspective

Based on experimental evidence that combining mineral fertilizers with organic matter may address poor soil fertility status and result in added benefits, farmer-managed demonstration trials were initiated in 9 villages in the northern Guinea savanna (NGS) of northern Nigeria. The trials had four treatments: (i) a farmers control in which the farmer grows maize according to his usual practice, (ii) the maize technology being promoted by the NGO Sasakawa-Global2000 (SG2000), involving hybrid seeds, proper plant density and fertilizer application practice, and fertilizer application rates that are relatively high for the region (136 kg N, 20 kg P, and 37 kg K ha-1), (iii) the Balanced Nutrient Management Systems (BNMS) manure technology that follows the SG2000 package for maize, except that part of the fertilizer quantity is replaced by animal manure; and (iv) a soybean-maize rotation, again with reduced fertilizer rate to the maize.