Manure‐biochar blends effectively reduce nutrient leaching and increase water retention in a sandy, agricultural soil: Insights from a field experiment

Abstract Organic amendments are commonly applied singularly to soils to improve physical, biological and chemical properties, but their combination may be even more advantageous than when applied alone. In this study manure was applied singularly and in combination with biochar (90:10 and 50:50 ratios) to a drought prone agricultural Regosol in a field evaluation. Samples were collected twice a year for 2 years and subjected to testing for moisture retention, nutrient status and microbial activity whilst weed growth was monitored by drone. Substantial seasonal variability in all parameters measured was observed, though all amendments increased actual soil moisture content between 18 and 41% initially; without the addition of biochar (i.e., manure alone) this reverted back to reduced moisture content towards the second year of sampling. None of the tested amendment combinations significantly affected soil‐saturated hydraulic conductivity. Cation exchange capacity decreased as a result of manure addition alone, the addition of 10% biochar and 50% biochar increased this significantly (23%–54% increase). Though microbial biomass and enzyme soil health indicators showed no decisive changes as a result of amendment application, and plant biomass was variable by ground sampling, drone imagery proved that plant heights and health were generally increased as a result of biochar addition to manure, compared with manured soil alone. In summary, despite much field seasonal variability limiting the interpretation of the data, this study nonetheless demonstrates a useful maintenance of improved soil moisture achieved by adding biochar together with manure to a drought‐prone soil agricultural soil.