The potential of biochar and anaerobic digestate use in a temperate conventional wheat production system

Interest in the use of waste products as soil amendments, derived from renewable energy technologies, has grown of late as they offer the potential to reduce fertiliser costs and, in the case of biochar, promote carbon storage. This study examined the efficacy of two such waste products, digestate, produced by anaerobic digestion and biochar, produced from pyrolysis, in comparison and in combination with a commercial synthetic fertiliser. The arable field trial was located on a sandy soil in a commercial farm setting. Four treatments were tested; digestate alone, digestate with biochar, commercial fertiliser alone and commercial fertiliser with biochar. The biochar and digestate was applied on one date and the commercial fertiliser applied on four dates, but in either case the rate of Total Nitrogen (TN) applied was the same. Digestate produced the same level of above ground biomass (t/ha), grain yield (t/ha), grain protein and TN off-take (kg/ m2) as the commercial fertiliser with no statistically significant differences found (P>0.05). Leaf Soil-Plant Analyses Development (SPAD) readings were taken by a SPAD-502 chlorophyll meter (Minolta Camera Co., Japan) throughout the trial indicating chlorophyll levels. Both the commercial fertiliser only and commercial fertiliser and biochar produced leaf SPAD readings that were, on certain dates, significantly higher (P>0.05) than digestate alone, and in combination with biochar. However, just before harvest all readings on all treatments converged on the same SPAD level. Critically, treatments which included biochar resulted in lower aboveground biomass (t/ha), grain yield (t/ha), grain protein and TN off-take in all cases. It is clear that biochar may have negative effects on yield, even when combined with additional fertilisation and, as biochar use increases and its presence in soil would be of long duration, it is therefore vital that further studies are conducted in this area.