Microbial Response to Sodic Soils Amended with Flue-Gas Desulfurization Gypsum, Sugar Beet Processing Byproduct Lime, and Langbeinite.

In the Northern Great Plains, about 10 million ha of agricultural land is mapped as sodic and generally have low productivity indexes. Amendments are commonly used to alleviate the poor physical and chemical conditions related to the presence of sodium. However, information on how microbial activity responds to amendments is not well known. The objective of this research was to compare the microbial response of three amendments added to sodic soils by measuring the CO₂ efflux to determine the impact that soil and amendments have on CO₂ respiration. The amendments used included flue-gas desulfurization gypsum (FGDG) and sugar beet processing byproduct lime at rates of 11.2, 33.6, and 67.2 Mg ha^-1, langbeinite at rates of 2.2, 5.6, and 11.2 Mg ha^-1, and a control with no amendments added. Surface soil (0 – 15 cm) was collected from two Aberdeen-Ryan complexes, both series mapped as “natric”, combined with the amendments, placed in microcosms, and replicated four times. The cores were maintained at 20 percent gravimetric water content and incubated for 11 weeks at 25 C, measuring the CO₂ efflux weekly using a soil respiration CO₂ system. The control released 76.9 g CO₂-C m^-2, where the sugar beet processing byproduct lime treatments released 119, 161, and 223 g CO₂-C m^-2, respectively. These cumulative fluxes were much greater than those exhibited by the FGDG (65.2, 68.2, and 84.8 g CO₂-C m^-2, respectively), and the langbeinite which revealed to be lower than the control at all three rates (57.7, 64.3, and 59.3, respectively). The sugar beet processing byproduct lime had positive effects on microbial activity whereas the langbeinite restricted respiration, likely due to the increase in electrical conductivity. Although the sugar beet processing byproduct lime enhanced soil respiration, its solubility is about 35 times less than the solubility of gypsum so time to amelioration must also be considered.