Bradford-reactive soil proteins and aggregate stability under abandoned versus tilled olive groves in a semi-arid calcisol

Glomalin, a substance produced by arbuscular mycorrhizal fungi, is reported to play a role in soil aggregation, but this role has been questioned in soils rich in calcium carbonate. We studied the relationship between aggregation stability and glomalin in a Haplic Calcisol comparing abandoned and active cultivation of olive groves. Abandonment was associated with increases in soil organic carbon, the percentage of water stable aggregates (WSA_1-2mm), and easily extractable and total Bradford-reactive soil protein. WSA_1-2mm was strongly positively correlated with both easily extractable and total Bradford-reactive soil protein. While easily extractable Bradford-reactive soil protein measured in both stable and unstable aggregates did not show any significant differences, Bradford-reactive soil protein was twice as high in stable than in unstable aggregates under both tillage and abandonment. Our results suggest that Bradford-reactive soil protein influences aggregate stability, even in soils with low organic matter and high calcium carbonate contents. However, more research is needed to elucidate the role of easily extractable Bradford-reactive soil protein in soil aggregation.     

The Chemical Composition of Precipitation in Madrid

The present study examines the chemical characteristics of first-fraction precipitation samples collected over a period of one year in Madrid, and patterns of temporal and spatial variation observed in their composition. One hundred and sixty-four samples of wet precipitation collected on an event basis were analysed for anions, cations, pH and electrical conductivity. Precipitation in Madrid was neutral, with only 3% of samples showing pH < 5.6. Dominant ions were calcium andsulphates. Calcium was the principal neutralizing agent, explaining 64% of all nitrates and sulphates. The marine influence did not appear to be relevant, while the soil seemed to play an important role in the composition of precipitation. Precipitation chemistry displayed seasonal differences, with higher concentrations of sulphates and chloride in autumn and winter and of calcium and sodium in the summer. There was an inverse relationship between concentrations and sample volumes; while the correlation between concentrations and the time elapsedsince the last rain event was positive, though poor for normalized concentrations. Four variables (sample volume, days elapsed since the last rain event, maximum wind gust direction and season) explained to a large extent (more than 90% for some sampling stations) the variability of certain chemical variables.