Seasonal soil aggregate stability variation in relation to rainfall and temperature under Mediterranean conditions

Abstract

Aggregate stability, one of the main factors controlling soil erodibility, varies over time. Knowledge of its variation would help to identify better soil management practices. In 10 soils from central Greece devoted to cereal cropping, seasonal wet aggregate stability (WAS) fluctuations were investigated over a period of two successive years. The wet-sieving technique of airdried aggregates was used for WAS determinations, according to a test resulting in an instability index calculation. Over the first year, when typical Mediterranean climatic conditions dominated, WAS varied according to a nearly cyclic pattern, from a low in winter or early-spring months to a high in summer months. The instability index varied from a high between 123-152% of annual average to a low between 58-83% of annual average. Total monthly rainfall (TR) and mean monthly air temperature (MAT) strongly correlated with seasonal WAS. Their ratio (TR/MAT, ombrothermic ratio) has been proved to be a good predictor of structural stability throughout the year, for most of the soils studied. Possible mechanisms deteriorating aggregation seemed to be raindrop impact, repeated soil drying and wetting and repeated soil freezing and thawing, while possible mechanisms promoting aggregation seemed to be soil drying and warming and biological activity. Over the second year, severe climatic inconsistencies complicated the seasonal pattern of WAS response. From January to March, WAS unexpectedly increased, obtaining its maximum value for most of the soils in March, then it varied inconsistently until October and thereafter decreased, obtaining its minimum value in December for all soils. The instability index varied from a high between 130-196% of annual average to a low between 61-83% of annual average. Uneven seasonal distribution of climatic characteristics and extreme events decisively modified the typical for Mediterranean conditions seasonal WAS variation pattern.

A time for every season: soil aggregate turnover stimulates decomposition and reduces carbon loss in grasslands managed for bioenergy

“…Seasonal dynamics in soil aggregation are affected both by weather differences between the sampling years and by bioenergy system management. Dry periods increase aggregate stability (Dimoyiannis, ) and precipitation events can disrupt macroaggregates, which is consistent with our observations. In both years, corn systems experienced aggregate disruption between May and July sampling dates, with slight aggregate rebuilding in August.…”

Effects of permanent grass versus tillage on aggregation and organic matter dynamics in a poorly developed vineyard soil

“…The observed seasonal 311 dynamics in total aggregate loss seemed to be related to rainfall distribution with lower losses under 312 dry, summer conditions, and higher losses in spring and autumn with higher soil water content 313 (Figure 2, 4). This seasonal pattern was in line with numerous field studies where greater aggregate 314 stability was recorded in summer with respect to autumn and early spring (Bullock et al 1988;315 Blackman 1992;Chan et al 1994;Dimoyiannis 2009;Algayer et al 2014). 316…”

Short-term grazing exclusion has no impact on soil properties and nutrients of degraded alpine grassland in Tibet, China

“…In alpine grasslands, proportions of soil aggregates were generally influenced by both GST and GSP. Similar findings were also reported by Rillig et al (2002), who found that increasing temperature could decrease soil aggregate water stability by stimulating the role of arbuscular mycorrhizal fungi in soil aggregation in an annual grassland in northern California, USA, and by Dimoyiannis (2009), who reported that total monthly precipitation and mean monthly air temperature strongly correlated with seasonal soil aggregate stability in the Thessaly Plain, central Greece.…”

“…Soil pH affected by the climate factors has been found in many natural ecosystems (Barton et al, 1994), which is also confirmed in alpine grasslands in Tibet in the present study. Soil aggregate is a dynamic soil property, which varies over time, partially depending on climatic processes (Dimoyiannis, 2009). In alpine grasslands, proportions of soil aggregates were generally influenced by both GST and GSP.…”