David Buchan

Modeling Soil Moisture Effects on Net Nitrogen Mineralization in Loamy Wetland Soils

Nutrient dynamics in wetland ecosystems are largely controlled by soil moisture content. Therefore, the influence of soil moisture content on N mineralization should be explicitly taken into account in hydro-ecological models. The aim of this research was to establish relationships between N mineralization and soil moisture content in loamy to silty textured soils of floodplain wetlands in central Belgium. Large undisturbed soil cores were taken, incubated for 3 months under various moisture contents, and zero order and first order N mineralization rates were calculated. We used the percentage water-filled pore space (WFPS) as an expression of soil moisture because it is a better index for aeration dependent biological processes than volumetric moisture content or water retention. The relationship between the N mineralization rate and %WFPS was described by a Gaussian model. The optimum WFPS for N mineralization ranged between 57% and 78%, with a mean of 65% ± 6% WFPS. Expected annual net N mineralization rates at field temperature (9.7°C) and at optimal moisture content varied between 30 and 186 kg N ha-1 (0–15 cm depth) year-1, with a mean of 110 ± 42 kg N ha-1 (0–15 cm) year-1. The mean N turnover rate amounted to 2.3 ± 1.1 g N 100 g-1 N year-1. Multiple linear regressions between N mineralization and general soil parameters showed that soil structure has an overriding impact on N mineralization in wetland ecosystems.

Nematodes enhance plant growth and nutrient uptake under C and N-rich conditions

The role of soil fauna in crucial ecosystem services such as nutrient cycling remains poorly quantified, mainly because of the overly reductionistic approach adopted in most experimental studies. Given that increasing nitrogen inputs in various ecosystems influence the structure and functioning of soil microbes and the activity of fauna, we aimed to quantify the role of the entire soil nematode community in nutrient mineralization in an experimental set-up emulating nutrient-rich field conditions and accounting for crucial interactions amongst the soil microbial communities and plants. To this end, we reconstructed a complex soil foodweb in mesocosms that comprised largely undisturbed native microflora and the entire nematode community added into defaunated soil, planted with Lolium perenne as a model plant, and amended with fresh grass-clover residues. We determined N and P availability and plant uptake, plant biomass and abundance and structure of the microbial and nematode communities during a three-month incubation. The presence of nematodes significantly increased plant biomass production (+9%), net N (+25%) and net P (+23%) availability compared to their absence, demonstrating that nematodes link below- and above-ground processes, primarily through increasing nutrient availability. The experimental set-up presented allows to realistically quantify the crucial ecosystem services provided by the soil biota.

Changes in soil ergosterol content, glomalin-related soil protein, and phospholipid fatty acid profile as affected by long-term organic and chemical fertilization practices in Mediterranean Turkey

The present study examines the effects of different fertilization treatments (chemical fertilization, farmyard manure, plant compost, and mycorrhiza-inoculated compost) on the soil fungi under a crop rotation of wheat (Triticum aestivum L.) and corn (Zea mays L.) in a long-term field experiment established in Mediterranean Turkey in 1996. Soil samples were collected in May, August, and October 2009. Soil pH, organic carbon, plant-available nitrogen and phosphorus, mycorrhizal colonization, and a series of biochemical markers (phospholipid and neutral lipid fatty acid [PLFA and NLFA] profiles, soil ergosterol content, and glomalin related soil protein [GRSP] as indicators of abundance of bacteria, saprotrophic, and arbuscular mycorrhizal [AM] fungi) were assessed. No significant difference was observed in soil organic C and plant available N in relation to long-term fertilization treatments, but plant available P in soil changed significantly in relation to the fertilization treatment used and the sampling season (between 11.5–33.8 mg · kg−1 in spring, 10.4–28.6 mg · kg−1 in summer, and 10.5–33.2 mg · kg−1 in autumn). Mycorrhizal colonization patterns were similar for both plants. However, mycorrhiza-inoculated compost treatment exhibited higher root colonization (77.3%) over control (16.3%), chemical fertilization (10.0%), farmyard manure (19.3%), and plant compost (20.0%). No statistically significant change was observed in ergosterol content. The effect of long-term organic treatments on soil PLFA structure was statistically prominent; whereas seasonality only affected bacterial PLFAs. Organic fertilization increased GRSP (mean annual ranging from 0.91 to 2.46 mg · g−1 total GRSP) but long-term annual mycorrhizal inoculation had no significant effect on the soil GRSP pool.

Soil Quality under Different Farming Systems in Santa Clara, Cuba

In Cuba there is a strong differentiation in types of farming systems that operate at very different levels of management intensity. The aim of this research was to characterize differences in soil quality caused by different agricultural management systems and the effects of seasonality on soil chemical and biological indicators within representative farming systems in Santa Clara municipality, Villa Clara Province, Cuba. Two state farms, two cooperative farms, and three private farms, all located on brown calcareous soils, which differed in soil management and technological complexity were selected. Soil samples from two fields of each farm were collected to a depth of 20 cm. Laboratory analysis were performed to determine physical (aggregate stability, plasticity, and permeability), chemical (pH and organic matter), and biological (dehydrogenase and β-glucosidase activities) indicators of soil quality. We found significant differences in soil quality among the three farming systems, which were most pronounced between private and state farms, with respect to physical soil properties (aggregate stability and plasticity) and the activity of enzymes. Seasonality also exerted an important influence on the activities of dehydrogenase and β-glucosidase, which were greater in the rainy season. As a conclusion, we can say that the differences in soil management between the farming systems were reflected in consistent differences in soil quality indicators, notably between the state and private farms.