Moderation of nitrogen availability through the application of pyrolyzed and unpyrolyzed organic materials in saline water irrigated soil

Abstract

Soil application of pyrolyzed biomass (biochar) has been proposed as an effective strategy for managing degraded land, but its limitations as a sole nutrient supplier discourage its widespread application as a soil amendment. Excessive use of saline water for irrigation leads to buildup of salts and other toxic ions, which cause a decline in the availability of essential nutrients due to negative effects on the mineralization process. Therefore, a long-term incubation experiment was conducted for 52weeks to study the individual or combined impact of pyrolyzed [biochar derived from rice residue (RB)] and unpyrolyzed organic materials [rice residue (RR) and animal manure (AM)] on nitrogen (N) dynamics in soil irrigated with water of varying electrical conductivity (EC) (EC0.3 [non-saline canal water), EC10, and EC15 dS m-1 (saline)]. Increasing salinity had an adverse effect on N mineralization, reducing it by 20-70% during the incubation period. Irrespective of the EC, soil amended with AM showed greater and faster N mineralization than unamended control, while individual application of RB or RR showed immobilization of N during the early period of incubation. However, conjoint application of pyrolyzed (RB) and unpyrolyzed organic materials (RR or AM) showed enhanced mineralized N content (26-96%) compared with the sole biochar-amended soil irrigated with water of different EC levels. It was most likely due to the synergic effect of unpyrolyzed materials on the mineralization rate of biochar. On the other hand, the high cation exchange capacity, large surface area, and greater total porosity of the biochar may cause stronger adsorption of free NH4+-N released from the labile organic amendments, thereby moderating the N mineralization process under saline conditions. Therefore, it is recommended that biochar be used in conjunction with AM or RR to ensure the prolonged availability of N in a saline environment.