Effect of organic soil amendments on carbon dynamics and productivity in saline and non-saline soils from Saskatchewan and Nigeria

Abstract

Carbon storage in salt affected and low organic matter (<3%) soils may be enhanced through the use of high carbon content soil amendments along with growing salt-adapted crops. To investigate and compare carbon dynamics in low organic matter, saline and non-saline soils, a field experiment was established in the Brown soil zone in southern Saskatchewan in the spring of 2017 to assess effects of three added amendments (leonardite, humic acid, and composted steer manure) and three crops seeded that spring (AC Saltlander green wheatgrass, Invigor canola and Tully Champion willow) on total soil organic carbon, carbon fractions and crop growth via randomized complete block design (RCBD) experiments conducted in saline and non-saline areas of a farm field. The soil samples collected in the spring of 2017 prior to establishment of treatments revealed similar organic carbon levels of 1.47% and 1.23% in the saline and non-saline sites, respectively. Soil samples taken in the fall of 2017 and spring of 2018 revealed that soils from the saline site amended with leonardite had significantly more light fraction organic carbon compared to unamended control plots. Furthermore, the total soil organic carbon mass in the 0-10 cm depth was significantly greater by 23% and 16% in the leonardite amended treatment compared to all other treatments in the non-saline and saline soils, respectively. The green wheatgrass had the largest impact on soil carbon fractions measured, increasing the concentration of water extractable organic carbon by 15mg C kg⁻¹ in the plots at the saline site. After one year, the total soil organic carbon in the 0-10 cm depth in the non-saline site treatments seeded to green wheatgrass was significantly higher than that found under canola and willow. Biomass production in the 2017 growing season was less on the saline than the non-saline soil, and the organic amendments did not significantly increase growth of any of the crops. To better understand the effect of the three amendments on short-term carbon turnover, a 29-day microbial respiration experiment was conducted using soils collected within 10 m of the two field sites. A low organic matter (0.61%) degraded tropical soil collected from an agricultural field in Ogbomosho, Nigeria was included in the incubation for comparison purposes. The saline soil had significantly higher cumulative CO2-C production compared to the non-saline and Nigerian soil, but organic amendment treatment had no influence on CO2-C production in the saline soil itself. In the non-saline and Ogbomosho soil, the composted steer manure produced significantly greater cumulative CO2-C emissions compared to the control and leonardite and humic acid treatments, respectively. The results suggest saline soils from southern Saskatchewan may not be lower in soil organic carbon content than non-saline comparable, and that under ideal moisture conditions, short-term carbon dioxide release through microbial respiration may be the same or higher than in non-saline soils due to an abundance of labile soluble organic carbon. Seeding saline and non-saline areas to salt tolerant green wheatgrass and applying 10 tonnes ha-1 of a high carbon content amendment like leonardite appears to be a relatively effective means of increasing the soil organic carbon content of the surface soil over a short time period.