Temporal dynamics of microbial biomass- and mineral-N in legume amended soils from a spatially variable landscape

Abstract

The turnover of soil incorporated shoot biomass-N to soil mineral-N, SMN (nitrate plus ammonium), is basically a microbially mediated process. In spatially variable landscapes, microbial activity and consequently mineralization of soil incorporated shoot biomass may vary in space over time. In this incubation study we assessed the influence of spatially variable soil properties on the temporal dynamics of soil microbial biomass-N (MBN) and SMN. Soil samples were collected from five locations with the same cropping history from across a landscape. The soils were sieved (4 mm) and amended with red clover ( Trifolium pratense L.) shoot biomass. The amended and control treatments were compacted to two relative bulk densities (RBD) and incubated at −15 kPa for 70 d at 23°C. MBN and SMN were measured five times during incubation and the values were regressed with soil properties using stepwise analysis. RBD, the volume fraction of water-filled pores <1.5 μm ( S 1.5), clay, silt, and soil organic matter (SOM) contents accounted for 45 to 93% of the variation in MBN and SMN in the amended treatment at different times. In the control, SOM, cation exchange capacity (CEC), and S 1.5 accounted for 59 to 77% of the variability in MBN and SMN. The influence of spatially variable soil properties and pore characteristics on MBN and SMN was much stronger in the amended soil than the control. Pore characteristics are influenced by spatially variable textural characteristics and SOM, and management-induced changes in compaction, and were found to have large influence on the spatio-temporal dynamics of microbial biomass, i.e., MBN, and SMN.