Location: Horticultural Crops Production and Genetic Improvement Research UnitTitle: Biochar alters hydraulic conductivity and impacts nutrient leaching in two agricultural soils
|GELARDI, DANIELLE - University Of California, Davis|
|AINUDDIN, A - California State University|
|PATINO, J - University Of California, Davis|
|ABOU NAJM, M - University Of California, Davis|
|PARIKH, SANJAI - University Of California, Davis|
Submitted to: Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/9/2021
Publication Date: 12/21/2021
Citation: Gelardi, D.L., Ainuddin, A., Rippner, D.A., Patiño, J.E., Abou Najm, M., Parikh, S.J. 2021. Biochar alters hydraulic conductivity and impacts nutrient leaching in two agricultural soils. Soil. 7(2):811-825. https://doi.org/10.5194/soil-7-811-2021.
Interpretive Summary: Nitrogen, in the form of ammonium and nitrate, is an important fertilizer and potential pollutant. Biochar, a material made by heating organic matter in the absence of oxygen, may influence the transport of ammonium and nitrate in soil systems. In the present study, biochars made from many different materials heated at many different temperatures were evaluated for their ability to keep ammonium and nitrate in the root zone of plants. All biochars limited ammonium mobility in soils. A pine biochar with high porosity was measured to limit nitrate mobility. This result means that this biochar could be used in agriculture to keep nitrogen in the root zone of plants, helping them grow.
Technical Abstract: Biochar is purported to provide agricultural benefits when added to the soil, through improvements in soil water holding capacity, hydraulic conductivity (Ksat), and nutrient retention through chemical or physical means. Despite increased interest and investigation, there remains uncertainty regarding the ability of biochar to deliver these agronomic benefits, due to differences in biochar feedstock, production method, production temperature and soil texture. In this project, a suite of experiments was carried out using biochars of diverse feedstocks and production temperatures, in order to determine the biochar parameters which may optimize agricultural benefits. Sorption experiments were performed with seven distinct, commercially available biochars to determine sorption efficiencies for ammonium and nitrate. Only one biochar effectively retained nitrate, while all biochars bound ammonium. The three biochars with the highest nitrate and/or ammonium binding capacity (produced from almond shell at 500 and 800 °C (AS500 and AS800) and softwood at 500 °C (SW500), were chosen for a series of column experiments. These biochars were amended to a sandy loam and a silt loam at 0 and 2% (w/w) and saturated hydraulic conductivity (Ksat) was measured. Biochars inhibited Ksat in both soils by 64-80%, with the exception of AS800, which increased Ksat by 98% in the silt loam. Breakthrough curves for nitrate and ammonium, as well as leachate nutrient concentration, were also measured in the sandy loam columns. All biochars significantly decreased the quantity of ammonium in the leachate, by 22 to 78%, and slowed its movement through the soil profile. Biochars had little to no effect on the timing of nitrate release, and only SW500 reduced decreased total quantity, by 27 to 36%. Together, this work sheds new light on the combined chemical and physical means by which biochar may alter soils to impact nutrient leaching and hydraulic conductivity for agricultural production.