Biochar, manure, and sawdust alter long-term water retention dynamics in degraded soil

Authors: Lentz, Rodrick; IPPOLITO, JAMES - Colorado State University; LEHRSCH, GARY - Retired ARS Employee

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2019
Publication Date: 10/31/2019
Citation: Lentz, R.D., Ippolito, J.A., Lehrsch, G.A. 2019. Biochar, manure, and sawdust alter long-term water retention dynamics in degraded soil. Soil Science Society of America Journal. 83(5):1491-1501. https://doi.org/10.2136/sssaj2019.04.0115.
DOI: https://doi.org/10.2136/sssaj2019.04.0115

Interpretive Summary: A critical component of a soil health and productivity is a soil’s ability to absorb and retain water for use by growing crops. Past cropping and irrigation practices and soil erosion in semiarid, farmlands have substantially compromised soils by decreasing the soil’s organic matter content, soil aggregate stability, infiltration rate, and water-holding capacity. A reduction in rainfall in some areas in response to global climate change will intensify the negative effects of this soil degradation. Biochar, a charcoal made by incomplete burning of organic material, and unburned organic byproducts such as manure and sawdust, are known to increase short-term soil water retention when added to soil; yet, their long-term, year-to-year effects on water retention are largely unknown. This study showed that a one-time application of either biochar, manure, or sawdust increased soil water retention in a degraded soil in each year during the 6-year study. However, the year-to-year water-retention effects differed by material, and a combined biochar+manure application produced the greater and most consistent benefit over time. This research is valuable because it identifies a superior soil additive (biochar and manure combined) that substantially improves long-term water availability in degraded soils, while simultaneously reducing atmospheric carbon dioxide, a greenhouse gas.

Technical Abstract: Biochars are porous but more recalcitrant that non-pyrolyzed organic materials, hence when biochar is added to soil it may cause more persistent alterations to soil water dynamics as compare to other materials. In this 6-yr, outdoor, large-pot study, we amended an irrigated calcareous silt loam with a single, one-time, 1 or 2% dry wt. (22.4, 44.8 Mg ha-1) application of either hardwood biochar, manure, sawdust, or acidified sawdust, a combined 1% biochar+2% manure treatment, and an untreated control. Each year the soils were hand-tilled and planted to a local crop. Soil water retention and plant available water (PAW, g H2O per g dry soil, being that retained between potentials of -10 to -1500kPa) were measured on spring soil samples. Across all years, the combined 1% biochar+2% manure produced the greatest PAW (0.262), with PAW in all treatments following the order of: 1% biochar+2% manure > all 2% rates > all 1% rates > control (0.222). In most years, the 2% treatments increased soil PAW relative to the control, i.e. their PAW ratios exceeded unity. The PAW ratios for 2% rates varied with amendment and year (P<0.0001). PAW ratios for: i) 2% manure peaked in yr 1 and declined to a minimum in yr 3; ii) 2% biochar, 2% sawdust, and 2% acid sawdust were least in yr 1 and peaked between yr 3 and 5; and iii) 1% biochar+2% manure was consistently near a maximum during the study period. Biochar effects on PAW were no more persistent than that of non-pyrolyzed amendments during the 6-yr study. Several factors influenced soil PAW development in addition to the quantity of the added highly porous amendment. Results suggest that water repellent properties and particle size distribution of the added organic material substantially influenced water retention dynamics in amended soils.