# Biochar Amended Soils and Water Systems: Investigation of Physical and Structural Properties
## 1 Introduction  
Meeting increasing global demand for food in the context of constrained resources and changing climate means that our agricultural systems must be both more productive and resilient. From 2009 to 2020 FAO's climate change portfolio has expanded and more than 300 programs and projects addressed the problems caused by climate variability and extremes in the agriculture sectors were developed in response to increasing demands [1]. Innovative tools are required to help deal with these complex challenges, which have increase interest in biochar as a potential soil amendment to improve soil quality and crop productivity [2]. Using thermal decomposition of plant-derived biomass in partial or total absence of oxygen it is possible to obtain biochar (BC). BC is a C-rich organic material characterized by a stability in soil environments has well known up to 1000 years [3, 4]. Since the organic carbon produced in biochar is very stable, addition of BC to the soil has the potential to improve soil quality. Considering variations in key BC properties such as pH, electrical conductivity, bulk density, and surface area, those depending on the feedstocks and productionconditions, BC increased soil pH and improved its electrical conductivity, aggregate stability, water retention, micronutrient contents and also sequester carbon, which is important for mitigation of excessive carbon dioxide in the atmosphere [5,6]. Scientific literature [7, 8, 9] fully revised the impacts of biochar amendments in soil. Yield crop increase has been demonstrated by the increasing of soil pH [10] nutrient use efficiency [11], and enhanced soil hydraulic properties [4,12] due to the BC application in different environments. The use of BC to ameliorate soil physical properties has emerged after identifying its general high porosity [13] and large inner surface area [14]. The improved physical properties in BC amended soils have been related to the lower particle density of BC, compared to that of soil minerals, and to the prevalence of micro-pores [15,16]. BC can contribute to improving water storage in soil modifying a specific portion of the pore size distribution associated with aggregation and water storage in soil systems [17]. Porosity (P), soil water retention (SWR), and plant available water (PAW) are all fundamental soil physical properties and the latter, being the amount of water between the water content at the field capacity and at the wilting point, can be improved. BC physico-chemical properties delineate its structural influence on the soil and are related to the feedstock material and pyrolysis thermal parameters like as final pyrolysis temperature and heat rate ramps [18, 19, 20]. BC produced by using high pyrolysis temperature (\(\geq\)500 \({}^{\circ}\)C) is more expected to increase soil physical properties considering the higher aromaticity, surface area, pH, and ash contents [21, 22, 23]. Lower pyrolysis temperature (\(<\)500 \({}^{\circ}\)C) during the BC production will contribute to the changes of nutrient status and bioavailability in soil systems [21, 23, 24]. Overall, most of the improvements of biochar-amended soils principally depend on the modifications of pore configuration, aggregate and surface properties in the amended biological systems [25, 26, 27, 28]. Given the high stability of BC in soils [29], long-term effects are expected in the context of soil water holding capacity and other physical properties. However, BC amelioration effects on soils can vary depending on soil C content [30], on soil textural differences [31], as well as on the rate of amendment. BC amendment has been found to improve the amount of PAW in coarse textured soils [31], or in soils with large amounts of macropores [22,28]. [PERSON] et al.