Interaction Effects Between Biochar and Fertilization Levels On Plant Production and N Losses.

Addressing the growing concern of nitrogen (N) pollution in vegetable production systems requires developing mechanisms to reduce N losses without compromising yields. In high input systems, such as in the production of lettuce (Lactuca sativa), N lost from the cycle contributes to environmental pollution in two ways: Nitrate leaching and nitrous oxide (N₂O) emissions. The incorporation of biochar in soils has been proposed as an approach to retain N. Biochar is a form of charcoal produced via pyrolysis of agricultural, forestry or animal wastes under low oxygen conditions. Biochar’s negatively charged surfaces and pores can sorb ions from soil. This property can potentially decrease N leaching and N₂O emissions; however, this response may be limited by the amount of N applied during the fertilization events. This study tests whether biochar reduces N losses and whether its effects on plant growth and N loss vary with fertilization rate. We investigated N losses by quantifying N in leachate and monitoring N₂O emissions during two growing seasons of lettuce. We carried out a bioassay under greenhouse conditions with two different biochar materials, a high temperature (900 ⁰C) walnut shell biochar (WS) and a moderate temperature (550 ⁰C) pine chip (PC) biochar, at rates equivalent to 10 tons of biochar per hectare, and five N fertilization treatments 0%, 25%, 50%, 75%, and 100% of 225 kg of N per hectare. Preliminary results show that the addition of biochar to soils does not promote plant production regardless of the fertilization rate. On a more positive note, our results show that biochars have the potential to decrease N losses and therefore have the potential for reducing environmental pollution of N.