Effect of soil compaction and water-filled pore space on soil microbial activity and N losses
Abstract
Soil compaction is a significant production problem for agriculture because of its negative impact on plant growth, which in many cases has been attributed to changes in soil N transformations. A laboratory experiment was conducted to study the effect of soil compaction and water‐filled pore space on soil microbial activity and N losses. A hydraulic soil compaction device was used to evenly compress a Norfolk loamy sand (fine‐loamy, siliceous, thermic Typic Kandiudults) soil into 50 mm diameter by 127 mm long cores. A factorial arrangement of three bulk density levels (1.4, 1.6, and 1.8 Mg/m) and four water‐filled pore space levels (60, 65, 70, 75%) was used. Fertilizer application of 168 kg N/ha was made as 1.0 atom % N as NH4NO3. Soil cores were incubated at 25°C for 21 d. Microbial activity decreased with both increasing water‐filled pore space and soil bulk density as measured by CO2‐C entrapment. Nitrogen loss increased with increasing bulk density from 92.8 to 334.4 g N/msoil at 60% water‐filled pore space, for 1.4 and 1.8 Mg/m, respectively. These data indicate that N loss and soil microbial activity depends not only on the pore space occupied by water, but also on structure and size of soil pores which are altered by compaction.
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- Hence moisture content should be considered as potential driver for both the microbial biomass as well as for contrast between community structures. Also soil porosity has been shown to increase soil microbial biomass and activity [40]. Indeed, in our soils soil porosity was positively correlated with bacterial and fungal biomass and the contrasts between the microbial communities.
[Show abstract] [Hide abstract] ABSTRACT: Human activities such as land use and -management may strongly affect the soil's ability to provide ecosystem services, in which microbes are playing a key role. Because sampling is usually restricted to the topsoil, little is known about effects of land use on ecosystem functioning down the soil profile. The present study assessed the effects of different land use types (arable, forest, grassland) on soil microbial biomass, activity and community structure at different soil depths (A, AC, C horizons), under the same climatic and pedological conditions, in the Danube Floodplain in Austria. Microbial biomass was 4–5 times lower in the arable field than in forest and grassland in the upper horizons. Additionally, both microbial biomass and activity decreased 3–4 fold with soil depth in forest and grassland. However, up to 30% of total microbial biomass was found in the C horizon in the arable field. We found a differentiation of microbial community structure between land use types and with soil depth: i.e. strong differences in the topsoil between land uses, whereas community structure in the C horizon was similar. This study confirms that land use exerts strong effects on soil microbes in the topsoil and that microbial biomass and activity decrease with soil depth. However, considerable microbial biomass and activity are found below 30 cm depth which is usually not included in samplings. In the deeper soil horizon effects of land use disappear, with microbial community structure and functioning becoming similar in similar pedological conditions.- In general, soil compaction may reduce soil respiration (e.g., Conlin and van den Driessche, 2000). This is primarily due to restricted gas diffusion (Xu et al., 1992; Goutal et al., 2012), causing an accumulation of CO 2 concentration inside the soil (Conlin and van den Driessche, 2000; Goutal et al., 2012), reduced microbial activity and reduced root respiration by increasing anaerobic spaces (Torbert and Wood, 1992). However, several studies reported no significant effect of soil compaction on the respiration rate of forest soils (Ponder, 2005; Busse et al., 2006).
[Show abstract] [Hide abstract] ABSTRACT: In recent decades, the use of heavy machinery in forest management has significantly increased, causing the compaction of forest soils and potentially affecting seedling survival and establishment. We thus investigated the effects of soil compaction on soil physical parameters, microarthropod biodiversity, soil respiration, as well as growth and physiology of Pedunculated Oak (Quercus robur) seedlings in an experimental field in central Italy (coarse loamy soil). Two levels of soil compaction were simulated, i.e. 10 tractor passes vs. 25 tractor passes. The larger number of tractor passes increased soil bulk density (+27%) and penetration resistance (+46%), while porosity declined (−11%). Compaction decreased the qualitative biodiversity of soil microarthropods (−13%), the number of growth flushes (−22%) and of leaves (−22%), shoot biomass (−26%), the shoot/root ratio (−10%), the main root length (−24%) and the longest first-order later root length in the top 10 cm of soil (−31%). The decreased growth of seedlings in the soil compaction treatment was accompanied by lower photosynthetic rate (−34%) and leaf nitrogen content (−27%). We concluded that limited access and acquisition of nutrients and water due to the shorter length of main root likely played a key role for growth and physiological responses to soil compaction in Q. robur seedlings. http://www.sciencedirect.com/science/article/pii/S0378112716308374- The moisture content of the soil causes the soil to compact. Studies had shown that the compact soil had significantly lower biomass C (38% decrease) and lower enzyme activities (decrease in range from 41-75%) than the un-compacted soil [21][22][23]. The total activity and AWCD was obtained in the following decreasing order, BNS > KNS > DPC > MC >DNS> PC > AC > DC > OC > VC (data of AWCD not shown).
[Show abstract] [Hide abstract] ABSTRACT: All living beings of various trophic levels in ecosystem depend on the soil as a source of nutrients and depend on soil organisms to release and recycle key nutrient elements by decomposing organic residues. Microbiota of soil plays critical role in the maintenance of soil health and quality by secreting important enzymes, which are capable of function even after being released by the cell. Comparing various types of soils, salinity is profoundly observed in coastal and desert region. Study of such type of soil may give insights for understanding the variations in microbial community and effect of various abiotic factors like, salt concentrations on the same. Studying diversity at the ecosystem level is important to understand range of processes and complexity of interactions. Polyphasic approach of studying microbial community by C source utilization profiling and soil enzyme activity measurement was employed in this study to compare desert and costal ecosystems. Functional diversity was studied by CLPP method using Ecoplate®. Six different soil enzyme activities were investigated. In some samples protease, urease and L-asparaginase activity were not detected at all. β-glucosidase and L-asparaginase showed significant positive correlation with all functional diversity indices, most of the microbial groups and temperature while negatively correlated with moisture and pH respectively. Alkaline phosphatase activity negatively correlated with temperature. PCA analysis based on enzyme activity showed that samples were grouped together geographically or according to the source of origin.- where SWC is the volumetric water content (cm 3 cm -3 ), BD is the soil bulk density (g cm -3 ), and PD denotes the soil particle density, which was assumed to be 2.65 g cm -3 (Torbert & Wood 1992, Breuer et al. 2002).
[Show abstract] [Hide abstract] ABSTRACT: Numerous studies have documented that soil respiration and nitrogen cycling show a distinct seasonal dependence regulated by environmental factors (e.g., soil temperature and soil water content). The mechanisms controlling the seasonal dependence of these two key ecosystem processes have rarely been linked to both soil microbial community and soil environmental factors. Here, we present results on the seasonal patterns of soil respiration and gross nitrification rates in three subtropical plantations of Pinus massoniana, Castanopsis hystrix and Erythrophleum fordii over a period of 11 months. Turnover rates were measured with the Barometric Process Separation technique (BaPS). We elucidated how soil respiration and gross nitrification are controlled by the soil microbial community and by soil environmental factors. Soil respiration and gross nitrification showed strong seasonal dynamics, although no significant differences were observed among plantations. The turnover rates were the highest during the wet season and the lowest during the dry season. Microbial biomass, total phospholipid fatty acids (PLFAs), fungal PLFAs and bacterial PLFAs peaked during the dry season. Both soil respiration and gross nitrification rates were positively correlated with soil temperature and soil water content. Microbial biomass decreased with increasing turnover rates. Our findings highlight that carbon and nitrogen turnover rates were mostly controlled by soil temperature and soil water content.- Hence moisture content should be considered as potential driver for both the microbial biomass as well as for community structure. Also soil porosity has been shown to affect soil microbes (Torbert and Wood, 1992), and indeed, soil porosity in our soils was significantly correlated with bacterial and fungal biomass as well as with the scores of the microbial communities on the first PC-axis. However, the correlations with soil moisture and soil porosity were less strong compared to the correlations of microbial biomass and microbial community structure with TOC and TN.
- Increased quantity and quality of organic matter inputs from residues and roots fuel microbial biomass and activity by contributing substrate and nutrients (Doran 1980; Dick 1992 ). In contrast , the negative correlation between bulk density and biological soil properties reflects the direct and indirect effects of the physical soil environment on microbial dynamics (Torbert and Wood 1992). Although SQIs are often correlated with each other within a given data set, each SQI in the SMAF represents a unique set of important soil functions (Andrews et al. 2004), and the minimum data set used to assess soil quality must be diverse to capture the complexity of soil function across varied management systems (Doran and Parkin 1996 ).
[Show abstract] [Hide abstract] ABSTRACT: Kristen S. Veum is a research soil scientist, Rob-ert J. Kremer is a soil microbiologist (retired), Kenneth A. Sudduth is an agricultural engineer, Newell R. Kitchen and Robert N. Lerch are soil scientists, and Claire Baffaut is a research hydrol-ogist at the USDA Agricultural Research Service (ARS) Cropping Systems and Water Quality Unit in Columbia, Missouri. Diane E. Stott is the national soil health specialist with the USDA Natural Resources Conservation Service in West Lafay-ette, Indiana. Douglas L. Karlen is a supervisory research soil scientist at the USDA ARS National Laboratory for Agriculture and the Environment in Ames, Iowa. E. John Sadler is the research leader at the USDA ARS Cropping Systems and Water Quality Unit in Columbia, Missouri. Abstract: The Conservation Effects Assessment Project (CEAP) was initiated in 2002 to quantify the potential benefits of conservation management practices throughout the nation. Within the Central Claypan Region of Missouri, the Salt River Basin was selected as a benchmark watershed for soil and water quality assessments. This study focuses on two objectives: (1) assessing soil quality for 15 different annual cropping and perennial vegetation systems typically employed in this region, and (2) evaluating relationships among multiple measured soil quality indicators (SQIs). Management practices included annual versus perennial vegetation , and varying grass species composition (cool-season versus warm-season), tillage intensity (no-till versus mulch-till), biomass removal, rotation phase, crop rotation (corn [Zea mays L.]–soybean [Glycine max L. Merr] versus corn–soybean–wheat [Triticum aestivum L.]) and incorporation of cover crops into the rotation. Soil samples were obtained in 2008 from 0 to 5 cm (0 to 2 in) and 5 to 15 cm (2 to 6 in) depth layers. Ten biological, physical, chemical, and nutrient SQIs were measured and scored using the Soil Management Assessment Framework (SMAF). Across SQIs, biological and physical indicators were the most sensitive to management effects, reflecting significant differences in organic carbon (C), mineralizable nitrogen (N), β-glucosidase, and bulk density. In the 0 to 5 cm layer, perennial systems demonstrated the greatest SMAF scores, ranging from 93% to 97% of the soil's inherent potential. Scores for annual cropping systems ranged from 78% to 92%: diversified no-till, corn–soybean–wheat rotation with cover crops (92%) > no-till, corn–soybean rotation without cover crops (88%) > mulch-till corn–soybean rotation without cover crops (84%). Conversely, in the 5 to 15 cm layer, no-till cropping systems scored lower for overall soil function (58% to 61%) than mulch-till systems (65% to 66%). In the 0 to 5 cm layer, biological soil quality under the diversified no-till system with cover crops was 11% greater than under no-till without cover crops, and 20% greater than under mulch-till without cover crops. The effect of rotation phase was primarily reflected in 64% lower mineralizable N following corn relative to soybean. Additionally, soil nutrient function was significantly affected by biomass removal. The results of this study demonstrate that the benefits of conservation management practices extend beyond soil erosion reduction and improved water quality by highlighting the potential for enhanced soil quality, especially biological soil function. In particular, implementing conservation management practices on marginal and degraded soils in the claypan region can enhance long-term sustainability in annual cropping systems and working grasslands through improved soil quality.
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