Field application of pelletized biochar: Short term effect on the hydrological properties of a silty clay loam soil

• The addition of pelletized biochar suddenly increases soil water retention.
• The use of pelletized biochar is effective as conditioner in a fine-textured soil.
• The incorporation of pelletized biochar creates functional accommodation pores.
• The amount of biochar directly influences AWC of amended soil.
• The pyrolysis process influences biochar AWC.

The field application of pelletized biochar is seldom employed and its effect on soil hydrological behavior scarcely investigated. Biochar is usually added in powdered or granular form to improve the homogeneity of distribution, meanwhile favoring its interaction with soil matrix. In this paper we evaluated the possibility of applying pelletized biochar as soil conditioner during a single cropping season of a tomato cultivation. For that purpose, the water retention curves (WRCs) were determined three months after the addition of two differently pyrolysed biochars (B1 and B2), at the rate of 14 Mg ha−1, to a silty clay loam soil prone to compaction. Starting from the WRCs the pore size distribution was determined. The gravimetric water content at both field capacity (FC) and wilting point (WP) was also measured on biochar samples to assess their available water capacity (AWC).In both the treatments, soil bulk density (BD) was significantly lower compared to control (Co), apparently as direct consequence of the addition of low density pellets. Actually, excluding the intrinsic biochar porosity from soil bulk density calculation, BD values of the treated soils remain lower of around 10% over Co. Such findings suggest that a modification of soil structural characteristics might have been induced by pellet addition. Data of the SWRCs indicate a significant increase in transmission (500–50 μm), storage (50–0.5 μm) and AWC pores (30–0.2 μm) for the amended soils. The pyrolysis process seemed to differentiate the extent of direct biochar contribution expressed by AWC values The addition of pelletized biochar was able to enhance the soil water retention properties even in the short term, and such improvement might be correlated to both the inherent biochar retention capacity and to a more functional rearrangement of soil aggregates/particles with pellets.