Biochar Mitigation of Allelopathy Induced Yield Loss in Continuous Maize.

Continuous maize yields are limited by the release of phytotoxic compounds as the previous year’s maize residue decomposes.  We tested the hypothesis that soil biochar applications could help mitigate maize autotoxicity and the associated yield depression. Eighteen small field plots (23.7 m²) were established in Fall 2010 by applying 0 to 112.1 Mg/ha of hardwood biochar and incorporating it to a depth of 30 cm using rotary tillage.  The site is on severely eroded Clarion soil with soil quality grading from the poorest in the southwest corner to the best in the northeast corner.  A pseudo Latin Squares experimental design was used to account for some of the spatial variability in soil quality.  Soil variability was also assessed by measuring total C, inorganic C, total N, CEC, pH and penetration resistance.  Maize residue (6.5 Mg/Ha) from the previous year’s crop was incorporated with the biochar and an additional 22.6 Mg/ha of maize residue was spread on the soil surface after tillage.  During the 2011 growing season, the plots received a total of 377 kg/ha of N fertilizer in a split application to mitigate the risk of N immobilization. Plant height (July 8) for residue amended plots were 33 to 65% of control plots that did not receive extra residue.  Grain yields ranged from 42 to 104% (4308 to 10,543 kg/ha) of the no residue controls.  Total aboveground biomass yields ranged from 44 to 99% (7.8 to 17.6 Mg/ha) of no residue controls.  Plant height, grain yield, and total biomass were all strongly influenced by both biochar and soil quality.  The biochar applications accounted for approximately 52% of the grain yield variability.  The results strongly suggest that biochar applications substantially mitigated the allelpathic inhibition of plant growth induced by 29.1 Mg/ha of maize residue.