Biochars Effects on Water Consumption by Soybean on Claypan and Cultivated Alfisols from Central Missouri

Biochars were produced by slow pyrolysis between 400-600°C. The air-dried biomass included corn stover (Zea mays), giant miscanthus (Miscanthus giganteus), switchgrass (Panicum virgatum), cedar (Juniperus virginiana), white pine (Pinus strobus) and willow (Salix alba). All biochars were crushed to pass a 12 mm sieve before mixing with soil samples (2% and 5% by weight). Soil samples were from a claypan layer and the top 20 cm of another cultivated Alfisol from Central Missouri. Greenhouse experiments were conducted to determine water utilization with soybean as test crop and were terminated after 60 days when plants were in the R5 growth stage. The soil water content was adjusted to FC level periodically and water use (WU) was recorded. Biochars affected both evaporation and transpiration at different rates. At 5% AR, miscanthus, switchgrass and willow biochars reduced WU by plants growing on claypan soil by 37%, 23%, and 33% respectively. On the other hand, at this AR, corn stover and cedar biochars saved only 18% and 17% water, respectively. At 2% rate, WU was reduced to 9.5% (miscanthus), 18% (switchgrass), 17% (willow), corn stover (7%) and cedar (5%). Some biochars significantly increased soybean growth on the sandy loam Alfisol resulting in more transpiration and increased WU. With some exceptions, at the 5% AR, biochars reduced water usage compared to control pots at the following rates: miscanthus (10%), pine (9%), switchgrass (16%), and willow (9%). Corn stover biochar, however, increased water usage by 4% (at 5% AR) and 6% (at 2% AR). At 2% AR, miscanthus and switchgrass biochars also increased WU by 2% and 6%, respectively. This experiment indicates that use of biochars to combat drought should be approach with thorough knowledge of soils, water potential fluctuations, biochars and plants.