Dehydrogenase activity and microbial biomass carbon in salt-affected soils of semiarid and arid regions

Excessive cunounts of salts present in the soil have an adverse impact on soil microbial population and their activities. Since microbial biomass represents an important reservoir of nutrients and is of crucial importance for long-term fertility of soils, the dehydrogenase activity (DHA) and microbial biomass carbon (MBC) were determined in typical saline, alkali, and saline-alkali sandy soils of northwestern India by collecting soil samples from the surface 0.30 m. In the 0-0.15 m soil layer, DHA declined by 71 % at electrical conductance (ECe) 28.0 and by 87% at ECe 40.8 dS m(-1) compared with ECe 18.0 dS m(-1) for the soil's saturation paste extract. The decrease in MBC was evident at ECe > 32.0 and 19 dS m(-1) in the 0-0.15 and 0.15-0.30 m soil layers, respectively. A reduction in pH of an alkali soil from 10.6 to 8.5 with gypsum application increased DHA from 2.5 to 10.4 mu g TPF g(-1) soil. In the saline-alkali sandy soil of an arid region (0-0.15 m), DHA was 5.3 mu g TPF g(-1) at ECe 33.4 dS m(-1), which increased to 16.0 mu g TPF g(-1) under the natural weed Luni (Suaeda spp.) at ECe 17.9 dS m(-1), and it was 8.3 mu g TPF g(-1) at ECe 24.4 dS m(-1) in the soil cropped with groundnut-wheat rotation. DHA and MBC decreased with increase in soil depth. DHA was negatively correlated with pH (r = -0.96 in barren alkali soil) and ECe (r = -0.767 in saline soil), while it was positively correlated with organic C (r = 0.812). Similarly, MBC was positively correlated with organic C (r = 0.593) and negatively correlated with ECe (r = -0.528). Saline soil dominated by NaCl and Na2SO4 salts had higher DHA than barren alkali and saline-alkali sandy soils, which was probably due to higher organic C content.