Influence of biochar and terra preta substrates on wettability and erodibility of soils
Smetanová, Anna; Dotterweich, Markus; Diehl, Dörte; Ulrich, Uta; Dotterweich, Nicola Fohrer
published: Mar 1, 2013
ArtNo. ESP023105701008, Price: 29.00 €
Biochar (BC) and terra preta substrates (TPS) have recently been promoted as soil amendments suitable for soil stabilization, soil amelioration and long-term carbon sequestration. BC is a carbon-enriched substance produced by thermal decomposition of organic material. TPS is composed of liquid and solid organic matter, including BC, altered by acid-lactic fermentation. Their effect on wettability, soil erodibility and nutrient discharge through overland flow were studied together for the first time, using laboratory experiments. At water contents between 0 and 100% BC is water repellent, while TPS changes from a wettable into a repellent state. The 5 and 10 vol% mixtures of BC and 10 and 20 vol% mixtures of TPS with sand remain mainly wettable during drying but repellency maxima are shifted to higher water contents with respect to pure sand and are mainly of subcritical nature. The runoff response was dominated by infiltration properties of the substrates rather than their wettability. Only the 20 vol% TPS mixture produced more runoff than sandy-loamy soil on a 15% slope at a rainfall intensity of 25 mm · h-1. The 10 vol% BC decreased runoff by up to ∼ 40%. At higher rainfall intensities (45 mm · h-1) the 10 vol% TPS7 was up to 27% less erodible than the 10 vol% BC. Nutrient discharge in sediment was significantly higher than in water. Despite the TPS containing more nutrients, nutrient discharge from mixtures was similar to sandy-loamy soils (except for P in TPS and C in BC) regardless of the slope gradient. Increased rainfall intensities (up to 55 mm · h-1) led to slight decline in enrichment ratios, while the nutrients concentrations remained comparable in the 10 vol% TPS and 10 vol% BC. The application of a 1 cm layer onto the soil surface instead of 10 vol% mixtures is not recommended due to high nutrient concentrations in the runoff and the wettability of pure substrates. The usage of 10 vol% BC in lowland areas with low frequency and low intensity precipitation and 10 vol% TPS7 in areas with higher rainfall intensities appears to be appropriate and commendable according to current results. However, together with reversibility of repellency, it needs to undergo further examination in the field under different environmental and land use conditions.