Evaluation of microbial biomass C and N content of the soils cultivated with vetch (Vicia sativa L.) and alfalfa (Medicago sativa L.)

Abstract

Legume forage crops have the ability of retaining free nitrogen in the air through symbiotic Rhizobium bacteria found in their roots. Additionally, microbial biomass (MB)-an essential living component of soil and a significant factor influencing plant nutrient dynamics-is considered to be accurate indicator of soil's biological condition. Given the aforementioned aspects, soil MB C (C-mic) and MB N (N-mic) of different legume forage crops were investigated in this study. Soil samples were taken in order to identify certain physical and chemical characteristics of the soil using volume cylinders (0 - 6.5 cm depth) from Vicia sativa L. (VSP) and Medicago sativa L. planted (MSP) areas. To determine the C-mic and N-mic contents, topsoil samples were also taken from 0 - 6.5 cm depth. C-mic and N-mic contents were identified using chloroform - fumigation - extraction method. There was no statistical significance for particle density, bulk density, electrical conductivity, CaCO3 %, and decomposition ratio (C-org/ N-total) of the VSP and MSP soil (P > 0.05). However, some other soil characteristics such as temperature, porosity, sand, silt and clay contents, pH, organic C and total N differed significantly (P < 0.05). Compared to VSP soil, the C-mic contents were determined to be 27 % higher (P < 0.05) in MSP soil. In VSP soil, the soil N-mic content ranged from 83.38 mu g g(-1) to 124.67 mu g g(-1), while it ranged from 91.62 mu g g(-1) to 187.07 mu g g(-1) in MSP soil. The N-mic content of the MSP soil was observed to be approximately 35 % higher than VSP soil, and a statistically significant difference (P < 0.05) was noticed between the two. Moreover, a significant positive correlation was found not only between the C-mic and organic C contents (r = 0.667; P < 0.05) but also between the N-mic and total N contents of MSP and VSP soil (r = 0.881; P < 0.01). The results of the study revealed that soil C-mic and N-mic values differ as the types of planted legume forage crops change. Furthermore, the obtained soil C-mic and N-mic results indicate that soil MSP soil is more fertile than VSP soil.