Short-Term Impacts of Biochar Made from Different Feedstocks on Soil Quality and Water Holding Capacity of Arid Soils.

Soil additions of biochar offers the possibility for improving soil quality and water holding capacity of desert soils that are used for agricultural production. A study was conducted with two texturally different soils (clay loam and sandy loam) collected near Las Cruces, NM, to assess the effects of biochar made from different feedstocks (pecan shells, pecan wood trimmings, cotton gin trash and city yard waste) on soil quality and the available water capacity of the soil. Soil samples collected from the field, were air-dried and passed through a 2-mm sieve before they were used for this trial. Soil for each treatment was weighed and thoroughly mixed with biochar at a rate of 44.8 Mg ha^-1, after which the amended soils were slightly moistened and packed into cylindrical stainless steel soil cores (8 cm in diameter and 5 cm high), at a bulk density of 1.2 Mg m-³. Soil samples inside the cores were incubated for 3 weeks in a growth chamber set at 28^oC/20^oC (day/night) with soil moisture maintained at about 85% of the soil’s field capacity. After three weeks, the soil cores were brought to saturation and the soil water holding capacities of the amended soils were measured within each intact soil core using a combination of a Hyprop tensiometer and a Dewpoint potentiometer. After the soil water holding capacity measurements were concluded, the soils in the cylindrical cores were air-dried and analyzed for multiple soil indicator measurements including soil organic matter content, pH, electrical conductivity (EC), and available nutrients. Results showed the significant effect of the different biochar feedstock, with cotton gin trash biochar having the greatest impact on soil quality. Cotton gin trash significantly increased the soil organic matter and plant nutrient (P, K, Ca and Mn), but also led to elevated EC, raising salinity concern in the soil. Other biochar treatments significantly elevated soil salinity in clay loam soil, except for pecan shell biochar amended soil, which was not statistically different in EC from the control treatment. Sandy loam soil benefited more from the addition of biochar in terms of water holding capacity compared to a clay loam soil. This study shows that biochar can impact arid soils significantly even in short-term, and that there is need for further assessments of how biochar made from different feedstocks can impact the cropping systems of arid regions.