Relationships between soil biological and other soil properties in saline and alkaline arable soils from the Pakistani Punjab

In six regions of the Punjab forming a gradient in precipitation, soils differing in texture, salinity and sodicity were taken at 29 representative sites. The aim was to assess the effects of these interacting differences on microbial biomass C, biomass N, and biomass P in relation to their element-specific storage compartment, i.e. soil organic C, total N and total P. The soils formed three groups: five sites were non-saline, 16 sites were saline and nine sites were saline and sodic. The salt content of the soils showed a strong negative correlation with the sand content. Textural effects on salinity and sodicity clearly override direct precipitation effects. All soils were in the alkaline range, with a median soil pH of 9.2 ranging from 8.1 to 10.4. The soil pH had significant negative effects on soil organic C (r=−0.62, P<0.0001), but not on the microbial indices. Microbial biomass C and biomass N were closely correlated with r=0.69 (P<0.0001), but showed a strong variability between the four sampling subplots. The group-specific averages of microbial biomass C and biomass P varied without clear salinity and sodicity effects. In contrast, microbial biomass N, ergosterol and basal respiration declined by 20%, 31%, and 33%, respectively, comparing the group-specific maximum averages of the non-saline soils with the minimum values of the saline-sodic soils. The ratios microbial biomass C-to-soil organic C and microbial biomass N-to-total N declined by 19% and 35%, respectively, from maximum values of 2.6% and 3.1%. In contrast, the microbial biomass P-to-total P ratio remained unaffected by the salt content. A decrease in salinity and sodicity would improve the accessibility of soil organic matter to the soil microbial community. This implies a threat of further reduction in soil organic matter levels if the C input is not improved at the same time.