Dry Matter Production and Phosphorus Uptake of Juvenile Corn Grown in Soil Amended with Biochar.

Soil biochar amendments have been shown to sequester carbon and improve soil quality. Biochar may also enhance phosphorus (P) availability and improve P-use efficiency. To determine effects of legacy (2007) biochar, fresh biochar, and P fertilizer applications on soil P supply and early-season corn (Zea mays L.) growth, we conducted a laboratory/climate chamber experiment with a Clarion loam (Typic Haplaquolls) from central Iowa. Slow-pyrolysis hardwood biochar was added at 0 or 18 Mg ha^-1 to subsamples of unamended soil. Ammonium polyphosphate fertilizer was applied to provide 0 and 48 kg P ha^-1. Unamended soil served as a control. Following a four-week incubation, pre-germinated corn (Pioneer Brand 36V75) seedlings were planted, two per pot, and pots were placed in a controlled-climate chamber. Both biochar and P fertilizer amendments affected soil P supply and corn seedling growth during five consecutive production and harvest cycles. Relative differences in biomass (shoot and root dry matter) production observed at Harvest 1, 20 days after planting, tended to hold throughout the trial. Plants grown in soil amended with 48 kg P ha^-1 alone had the highest biomass production, while those grown in soil with legacy (2007) biochar without P fertilizer had the lowest values. Addition of 48 kg P ha^-1 increased biomass production, regardless of biochar amendment. Legacy biochar treatments had higher root:shoot dry weight ratios, suggesting that plants partitioned more resources to root growth. Although cumulative shoot dry matter production tended to be higher for the treatments without biochar, the overall agronomic efficiency (g DM g P^-1) of the P fertilizer was improved by biochar application. Further analysis of plant growth and nutrient uptake data should provide a clearer picture of the fertilizer value of the biochar, any biochar-fertilizer interactions, and whether legacy or fresh biochar affect the nutrition of juvenile corn in different ways.