1. ----------------- mg / kg dry soil ------------------
Assessing changes in soil microbial biomass
in grassland soils
Jessica Graça(1)(2), Rachel Creamer(1), Giulia Bondi(1), Achim Schmalenberger(2) and Karen Daly(1)
(1)Teagasc Research Centre, Johnstown Castle, Wexford, Republic of Ireland (2) Department of Life Science, University of Limerick, Republic of Ireland
RESULTS
QUESTIONS
How sampling season and soil drainage affects soil microbial biomass?
Which soil properties influence changes soil microbial biomass ?
MBC and MBN are affected by sampling season.
Soil MBP content was significantly higher in autumn in poorly drained soils.
INTRODUCTION
Soil microbes perform an important rule in nutrient cycle, acting as sink and source of available nutrients. Soil microbial biomass is known to be affected by season, soil properties and land management. In this study we aim to identify key drivers for soil microbial biomass in Irish grassland soils.
BIOCHEMICAL ANALYSIS
Microbial biomass carbon (MBC), nitrogen (MBN) and phosphorus (MBP) were measured by fumigation-extraction method in duplicates
Total carbon (TC), organic carbon (OC) and total nitrogen (TN) were determined by combustion; total phosphorus (TP) was determined by aqua-regia digestion
Figure 1. Effects of sampling season and drainage class for MBC, MBN and MBP. Symbols (*, **) indicate significant differences.
CONCLUSIONS
Spring
Autumn
MBC
MBN
MBP
-0,52*
0,69**
0,18
0,32
0,80**
0,36 C
-0,65**
0,61**
-0,12
0,41
0,28
0,40 N
-0,49*
0,52*
0,06
0,27
0,56*
0,22 P
0,17
0,05
0,67**
0,45
0,15 TC
0,14
-0,03
0,50
0,81**
0,20 TN
-0,04
0,12
0,71**
0,93**
0,48 TP
0,60**
0,55
-0,05
SOC
0,50*
0,31
-0,24
-0,22
Moisture
0,25
0,86**
0,76**
0,60*
Poorly drained soils presented higher microbial biomass (statistical significant for MBP) in autumn. Soil drainage class could have driven soil microbial biomass, potentially associated with their capacity to retain moisture.
The contribution of soil microbes to soil nutrient dynamics is potentially affected by grassland management in each season. The distinct behaviour of MBC and MBN content could indicate changes in soil nutrient status or even soil microbial communities.
Evaluation of microbial and soil nutrient ratios and identification of dominant grassland microbial communities should be performed.
SOILS DESCRIPTION
31 grassland sites were sampled in spring (May-June) and in autumn (September-October) of 2015 comprising two drainage classes: well drained soils and poorly drained soils
Season
Drainage
No. soils
Spring
Well 12
Poor 6
Total 18
Autumn 9 4 13
Table 3. Correlations between soil microbial biomass and soil properties. **Significant at p<0.01; *Significant at p<0.05
Table 1. Distribution of soils according to sampling season and drainage class.
Soil microbes seam to access distinct nutrient pools over the two studied sampling seasons.
Moisture appears to be a key driver for soil microbial biomass content in autumn.
Mean (± SD)
Max
Min
mg / kg dry soil
MBC
(± )
7985.7
720.0
MBN
211.1 (± 77.1)
383.82
100.7
MBP
19.8 (± 7.9)
41.35
8.9
Table 2. Descriptive statistics of MBC, MBN and MBP for the 31 sites. (± SD): standard deviation of the mean;
The authors acknowledge the Society for Applied Microbiology for funding this presentation.
This work is part of the Soil Quality Assessment Research Project (SQUARE), funded by the Department of Agriculture, Food and Marine and the Teagasc Walsh Fellowship Scheme.