Alkaline Biochar Amendment Increased Soil pH, Carbon, and Wheat-Pea Yields.

Alkaline biochar amendment to arable soils has been proposed as one effective countermeasure to increase soil pH, improve soil fertility and water retention, increase soil organic carbon (SOC) stock, and enhance crop productivity. However, there is limited information on the integrated effects of biochar amendments in combination with chemical N-fertilizer in cropping systems of the PNW. This study investigated the effects of alkaline biochar on soil pH, SOC, and crop yields of direct-seeded winter wheat (Triticum aestivum L.)–spring pea (Pisum sativum L.) rotation in northeastern Oregon. Biochar was applied at the onset of the experiment in 2013. Both phases of the rotation were present every year, which received fertilizer N rates of 94 kg ha^-1 in wheat and 18 kg ha^-1 in pea at planting. The treatments were recommended-N plus biochar rates of (i) 0 Mg ha^-1 (B₀N_R), (ii) 11.2 Mg ha^-1 (B₁N_R), (iii) 22.4 Mg ha^-1 (B₂N_R), and (iv) 44.8 Mg ha^-1 (B₃N_R), and (v) 18 kg fertilizer-N ha^-1 in wheat only with no biochar as control (B₀N_c). Grain yields of both phases were determined every year (2014-2016), while soils were tested in the fall of 2016 after crop harvest. Application of B₀N_R slightly declined surface 0-10 cm soil pH as compared to control treatment (B₀Nc). On the contrary, biochar treatments (B₁N_R, B₂N_R, and B₃N_R) significantly increased soil pH and SOC over the fertilizer-N alone treatments (B₀Nc and B₀N_R) at 0-10 cm soil. Soil pH and SOC increments observed with biochar treatments increased with biochar rate. Mean (2014-2016) grain yields of both wheat and pea were higher with biochar treatments than fertilizer-N alone treatments. Pea yields were similar across biochar rates, whereas wheat yields increased in B₂N_R compared with B₁N_R by 28 kg ha^-1 or with B₃N_R by 17 kg ha^-1 treatments. Overall, the study showed that alkaline biochar has potential to increase crop yields through its positive effect on soil health.