Cultivated Organic Soils Research Articles

Modeling soil water dynamics of an intensively cultivated histosol

AbstractUnderstanding soil–water dynamics in cultivated organic soils (histosols) is crucial for sustainable agriculture, ecosystem preservation, and climate change mitigation. Data on the soil water retention curves (SWRCs) of these histosols in Canada are not readily available in the literature. The Hydrus‐1D model was used to predict SWRCs for a cultivated organic soil in Quebec. The model was validated with matric potential measured in a soil column at 10, 26, and 48 cm. The optimized hydraulic parameters in the Hydrus model resulted in field capacity moisture contents of 0.6, 0.696, and 0.49 cm3 cm−3 at the three depths, respectively. Wilting point moisture contents of 0.165, 0.107, and 0.14 cm3 cm−3 were obtained at the same depths. Model accuracy was confirmed with a Nash–Sutcliffe efficiency of 0.76, 0.91, and 0.78 for the three depths, respectively. These findings can inform decisions regarding water management practices such as irrigation and drainage requirements for intensively cultivated organic soils.

Principles and processes in conserving and restoring cultivated organic soils: promising avenues

Principles and processes in conserving and restoring cultivated organic soils: promising avenues

Discriminating stratigraphic layers of cultivated organic soils using proximal sensors

Discriminating stratigraphic layers of cultivated organic soils using proximal sensors

Relating soil properties to soil losses by wind erosion in a cultivated organic soil in the southwest of Quebec, Canada

Cultivated organic soils are known to be highly susceptible to wind erosion. The aim of this research was to explore the relationships between organic soil properties and measured soil height variation (SHV) in a cultivated organic soil and to analyze field soil erodibility (wind erodibility index: WEI) from known models. In the fall, 81 georeferenced soil samples were collected at a depth of 0–10 cm and analyzed in the laboratory to determine different soil properties. At the same time, soil height variations were measured over a 35-day period. Simple and multiple linear regressions were used to explore relationships between soil properties and analyze SHV and WEI. The average SHV across the farm was −0.19 mm per day, equivalent to a loss of 0.665 cm during the measurement period. Simple linear regression showed weak relationships with SHV. Nevertheless, the analysis showed that soil loss areas had a larger fraction of macro-aggregates. Conversely, deposition areas with low bulk density (BD) contained more fine material (organic matter [OM] and erodible material [EM]), suggesting wind erosion effects, i.e., deposition of fine matter. Many soil properties were found to correlate significantly with one another. Applying multiple linear regression with SHV and WEI as dependent variables and soil properties as independent variables produced the following results: a) 24% of the SHV was significantly explained by 6 soil properties (α=5%,p=0.001), BD, EM, mean weight diameter (MWD), elevation (Z), geometric mean diameter (GMD), and volumetric water (VW); and b) 75% of the variation in WEI was explained by 5 variables (α=5%,p=0.001), BD, VW, OM, MWD and GMD. This result shows that BD, VW, OM, MWD, EM, GMD, elevation Z are key soil properties in sustainable management of organic soil with >80% OM and will be used in a wind erosion risk model adapted to organic soils.

Mapping the maximum peat thickness of cultivated organic soils in the southwest plain of Montreal

Large organic deposits in the southwestern plain of Montreal have been converted to agricultural land for vegetable production. In addition to the variable depth of the organic deposits, these soils commonly have an impermeable coprogenous layer between the peat and the underlying mineral substratum. Estimations of the depth and thickness of these materials are critical for soil management. Therefore, five drained and cultivated peatlands were studied to estimate their maximum peat thickness (MPT)—a potential key soil property that can help identify management zones for their conservation. MPT can be defined as the depth to the mineral layer (DML) minus the coprogenous layer thickness (CLT). The objective of this study was to estimate DML, CLT, and MPT at a regional scale using environmental covariates derived from remote sensing. Three machine-learning models (Cubist, Random Forest, and k-Nearest Neighbor) were compared to produce maps of DML and CLT, which were combined to generate MPT at a spatial resolution of 10 m. The Cubist model performed the best for predicting both features of interest, yielding Lin’s concordance correlation coefficients of 0.43 and 0.07 for DML and CLT, respectively, using a spatial cross-validation procedure. Interpretation of the drivers of CLT was limited by the poor predictive power of the final model. More precise data on MPT are needed to support soil conservation practices, and more CLT field observations are required to obtain a higher prediction accuracy. Nonetheless, digital soil mapping using open-access geospatial data shows promise for understanding and managing cultivated peatlands.

Using cultivated organic soil depth to form soil conservation management zones

Cultivated Organic soils in Montreal's southwest plain are the most productive soils in the province of Quebec. After their initial drainage to enable farming, Organic soils are susceptible to many forms of degradation and soil loss. In this study, we characterized the physical, chemical, and pedological properties of 114 sites from five peatlands to form soil conservation management zones. We attempted to use the maximum peat thickness (MPT) as a soil degradation proxy. The MPT can be defined as the thickness of the layer of peat until coprogenous or mineral materials are reached. The latter are undesired growing media and are not considered in MPT calculation. A series of multivariate analysis of variance indicated that MPT was moderately related to soil degradation (optimal model's Pillai's trace = 0.495). Three soil degradation groups were defined, separated by two MPT thresholds: 60 and 100 cm. When looking at 17 different depth-property combinations, shallower sites (MPT < 60 cm) showed signs of soil degradation significantly higher than sites with an MPT above 60 cm. The second threshold was proposed for practical purposes. Then, these thresholds were used to separate the study area into spatially distinct management zones. Important spatial contrasts were found. This supports the theory that precision agriculture techniques are needed to target fields to optimize soil conservation interventions. The relationship between the MPT and soil degradation should be further explored to account for other degradation factors, and to better identify degraded soils and soils at risk.

Linking soil phosphorus pools to drainage water quality in intensively cropped organic soils

Higher than average fertilization rates, as applied to mineral soils, are often recommended for cultivated organic soils (>20% organic matter), which over time, have led to phosphorus (P) pollution into receiving water bodies via subsurface tile drainage. Limited studies have documented the P pools within organic soils or their link to tile drainage water quality. This study quantified the different soil P pools found in organic soils under two water management practices: controlled drainage (CD) and pump drainage (PD) systems. Phosphorus availability in these soils was assessed by measuring inorganic P (Pi) and organic P (Po) via sequential fractionation; available P via Bray-1 P testing; and microbial P, along with crop root total P uptake. Drainage water samples were also analyzed for total P (TP) and dissolved reactive P (DRP). The results identified calcium (Ca) bound P as the largest P pool in these organic soils. Its correlation with other P pools suggests that it acts as a P sink in these soils. The correlation analysis further suggests that aluminum (Al) and iron (Fe) bound P is a driving force for P movement in the soil, as it had the most significant relationship with the P parameters in both the soil and drainage water. The regression analysis of TP found that the fertilizer and root P content were significantly related to the changes in drainage water quality at both sites. A P balance indicated that more fertilizer was being applied each year than was being used by the crops or released into the water, causing an accumulation of legacy P in the soil. Overall, the soil P pools affect the fluctuations of P concentration in the tile drainage water quality, featuring the complex relationship of the soil-water P dynamic.

Phosphorus speciation in cultivated organic soils revealed by P K‐edge XANES spectroscopy

AbstractCultivated organic soils make a significant contribution to phosphorus (P) leaching losses from agricultural land, despite occupying a small proportion of cultivated area. However, less is known about P mobilisation processes and the P forms present in peat soils compared with mineral soils. In this study, P forms and their distribution with depth were investigated in two cultivated Histosol profiles, using a combination of wet chemical extraction and P K‐edge X‐ray absorption near‐edge structure (XANES) spectroscopy.Both profiles had elevated P content in the topsoil, amounting to around 40 mmol kg−1, and P speciation in both profiles was strongly dominated by organic P. Topsoils were particularly rich in organic P (P‐org), with relative proportions of up to 80%. Inorganic P in the profiles was almost exclusively adsorbed to surface reactive aluminium (Al) and iron (Fe) minerals. In one of the pro‐files, small contributions of Ca‐phosphates were detected.A commonly used P saturation index (PSI) based on ammonium‐oxalate extraction indicated a low to moderate risk of P leaching from both profiles. However, the capacity of soil Al and Fe to retain P in organic soils could be reduced by high competition from organic compounds for sorption sites. This is not directly accounted for in PSI and similar indices.Accumulation of P‐org in the topsoil may be attributable by microbial peat decomposition and transformation of mineral fertiliser P by both microbiota and crops. Moreover, high carbon–phosphorus ratio in the surface peat material in both profiles suggests reduced net mineralisation of P‐org in the two soils. However, advancing microbial peat decomposition will eventually lead to complete loss of peat horizons and to mineralisation of P‐org. Hence, P‐org in both profiles represents a huge potentially mobilised P pool.

Short‐Term Improvement in Soil Physical Properties of Cultivated Histosols through Deep‐Rooted Crop Rotation and Subsoiling

Core Ideas Short rotations showed small hydraulic conductivity improvement the year of rotation.Effects vanished the year after termination of the rotational crops.Pore continuity appears to be disrupted by tillage operations. The formation of a compacted layer in cultivated organic soils reduces water infiltration and can lead to the formation of a perched water table. To test the hypothesis that integrating deep‐rooted crops in a short‐term rotation could improve soil physical properties, a 3‐yr trial was conducted on two Histosols. A lettuce (Lactuca sativa L.) control and three crops combinations—corn (Zea mays L.) and common vetch (Vicia sativa L.), sorghum [Sorghum bicolor (L.) Moench] and faba bean (Vicia faba L.), and a mix of tillage radish (Raphanus sativus L.), ryegrass (Lolium perenne L.) and crimson clover (Trifolium incarnatum L.)—were planted for 2 yr, on subsoiled and not subsoiled plots. Then, lettuce was reintroduced on all plots the third year of the experiment. Measurements of soil penetration resistance (SPR), saturated hydraulic conductivity (Ks and Kfs), water table level, and matric potential were performed over time. Kfs improved in the compacted layer during the second year of the rotation compared with the lettuce control. Subsoiling improved SPR, Ks, and Kfs in some cases. Once tillage was used to reestablish lettuce in the third year, those effects disappeared quickly (<3 mo), likely due to tillage. No treatment differences in water table levels or soil matric potentials were observed at that time, indicating that the short‐term increase in Kfs did not improve deep drainage. Despite short‐term changes in the top horizons, the general drainage pattern was controlled mainly by the deeper organic layers rather than the shallow compacted layer originally identified.

Mapping of cultivated organic soils for targeting greenhouse gas mitigation

Cultivated organic soils can be a major source of GHG emissions in countries with high coverage of peat soils. Targeting mitigation measures based on mapping of cultivated organic soils would reduce these emissions and increase sustainability of agriculture. Different georeferenced datasets were combined to study the area trend and describe current agricultural use of organic soils. The area was also mapped regionally into classes based on intensity of cultivation and organic layer depth, and an example allocation of potential mitigation measures was made at the country scale. The area and proportion of cultivated organic soils have increased in Finland since 1990 but the clearance rate has decreased in recent years. More than half of the area retains a peat layer deeper than 0.6 m indicating long-lasting mitigation potential with measures capable of slowing peat decomposition. Sixty-five percent of the cultivated organic soil area was not considered a priority area for radical management changes, for various reasons, but there are 85,000 ha of field with more realistic potential for GHG mitigation. The mapping method was found to be a practical tool for depicting the GHG mitigation potential of cultivated organic soils. Significant reductions in agricultural GHG emissions can be expected with implementation of the suggested mitigation measures.

Strength and Permeability of Cultivated Histosols Characterized by Differing Degrees of Decomposition

Core Ideas Cultivated organic soils (Histosols) are highly productive but very sensitive to degradation and compaction. Penetration resistance and saturated hydraulic conductivity are two important parameters related to the degree of decomposition of Histosols. Penetration resistance could be used to assess the depth of the compact layer, as well as the degree of decomposition, of Histosols. Cultivated organic soils (Histosols) are an important part of the agricultural economy in Canada. However, problems of degradation and compaction affect this particular type of soil. The objective of this study was to characterize the soil penetration resistance and the saturated hydraulic conductivity (ksat) in cultivated organic soils that differed in their degree of decomposition. Three fields in the plain of Montreal, in southwestern Quebec, were selected to provide a gradient of degrees of decomposition. Site 1 was classified as a Limnic Fibrisol, Site 2 was classified as a Terric Mesic Humisol, and Site 3 was classified as a Terric Humisol. At each site, penetration resistance and ksat were measured directly in the field. Penetration resistance, particularly at the 25‐cm depth and deeper, was found to increase with increasing soil degradation. An inverse relationship was observed for ksat in the compact layer. The results presented in this study indicate that penetration resistance and ksat are both linked to the degree of soil decomposition. However, the relationship between both parameters is complex, and both parameters are to be measured to achieve a more accurate characterization of organic soils. Further work could assess the depth of the compact layer, as well as the degree of decomposition of organic soils at different spatial scales using penetration resistance. In Histosols, accurately mapping ksat would help in designing field drainage system, as this soil property is difficult to predict from other parameters.

The impact of cultivation on CO2 and CH4 fluxes over organic soils in Sweden

Cultivated organic soils are large contributors to global greenhouse gas emissions. We measured carbon dioxide (CO2) and methane (CH4) fluxes from two organic soil plots in central Sweden between 2012 and 2016 using the eddy covariance technique. One site was cultivated whilst the other was set aside with no cultivation occurring. The aim was to establish the impact that cultivation had on the carbon balance. Over the five year period the set aside field acted as a net carbon source whilst the cultivated site was seen to be a small carbon sink. The set aside was further seen to act as a small methane sink over a 36 month period, which reduced the CO2 source by ca. 10% in terms of CO2 equivalents. Considering exported biomass, both sites were carbon sources in terms of Net Biome Production (NBP).

Meta-analysis of lettuce (Lactuca sativaL.) response to added N in organic soils1

A soil test N (STN) is required to implement N fertilizer recommendations for vegetable crops in cultivated organic soils. A STN can be developed using the isometric log ratio (ILR) to balance soil C, N, and other soil components amalgamated into a filling value (Fv) and to derive a Mahalanobis distance (M2) as STN. Our objective was to conduct a meta-analysis of multi-year and multi-site N trials on lettuce (Latuca sativa L.) response to added N along a gradient of M2 values, and to develop an N recommendation model. Twenty-four N fertilization experiments were conducted from 2002 to 2006 in organic soils of southwestern Quebec. Each crop received four N rates from zero to 120–150 kg N ha−1 applied before seeding or in split applications. The relationship between N requirements by lettuce and STN was quadratic whether lettuce was seeded or planted. There were three STN fertility classes delineated by M2 values of 1 and 5.5. The N recommendation model and its uncertainty were valuable for M2 values up to ...

Mitigating greenhouse gas fluxes from cultivated organic soils with raised water table

Cultivated organic soils are a remarkable source of greenhouse gases (GHG) in many countries. Keeping the ground water table as high as possible could lower the mineralization rate of the peat and thus the emissions of carbon dioxide (CO2) and nitrous oxide (N2O) from these soils. We studied the effect of raised water table on the emissions of N2O, CO2 and methane (CH4) from undisturbed peat soil profiles of six different Finnish cultivated organic soils during a 5-week outdoor mesocosm experiment. The aim was to determine an optimum water table that would enable grass cultivation but lower the net gas balance of the soil. Raised water table decreased the GHG emissions from each peat type ranging from weakly decomposed Sphagnum peat to highly humified Carex peat. Based on the results, the optimum water table would be 30 cm below the soil surface. The average reduction of the total net emissions with a raise of water table from a typical drainage depth of 70 to 30 cm was 42 % in the outdoors mesocosm experiment and 23 % at a constant temperature (+6 °C). The emissions of both CO2 and N2O declined and the net consumption of CH4 changed to net production as the water table rose. The results were confirmed by long-term measurements at one of the sampled sites. As a conclusion, we see that promoting drainage systems enabling raising of the ground water table and cultivation of crops capable of producing good yields also in wet conditions would be beneficial for the GHG mitigation in agriculture.

Evaluating fluxes in Histosols for water management in lettuce: A comparison of mass balance, evapotranspiration and lysimeter methods

The evaluation of downward water fluxes in Histosols is critical for water budget and irrigation studies in natural and cultivated wetlands. By analyzing water fluxes in cultivated organic soils, our study aimed to (i) compare drainage water fluxes measured using in situ lysimeters to fluxes estimated by three indirect methods, specifically, a simplified water balance, a water balance including soil water storage changes, and a method based on the Buckingham–Darcy law; and (ii) investigate water flux mechanisms using a bromide tracer in the same lysimeters. In 2008–2009, three sites were each set up with four drainage lysimeters equipped with water content probes and tensiometers. Bromide was applied over each lysimeter at the beginning of the lettuce growing cycle. Daily outflow water volumes were measured and solute samples were collected. The results showed that measured cumulative drainage was very low (0–40.2mm) compared to water input (30–128mm). A rupture point in the unsaturated hydraulic conductivity at matric potentials around −4.5 to −6kPa, combined with the stratified profile of the organic layers, may in part explain these observations. The measured water fluxes were also significantly lower (by 1.2 to 1255.3 times) than the estimations made with the three indirect methods. Finally, the analyses of soil and outflow bromide concentrations confirmed the low fluxes through the lysimeters and revealed an accumulation at the surface layer interface (at a depth of about 0.3m), indicating that water perched in the profile and suggesting that preferential flow occurred, leading to episodic solute leaching. Direct evaluation of water and solute fluxes are needed in such soils, as all three methods presented important biases.

Strategies for carbon sequestration in agricultural soils in northern Europe

We present new and synthesize published results from long-term field studies exploring management options for carbon sequestration in cropland and grassland. Agricultural practices were evaluated within the framework set by global food demand and limited area available for agricultural production. Among options for higher C sequestration, we found minimizing the time with bare soil, improving recycling of organic materials and increasing yields through N fertilization to be efficient. Indeed, our results suggest that C stocks can increase with 1–2 kg C for each kg of mineral N fertilizer applied. Possibilities to decrease C emissions by reduced tillage were found to be limited under Nordic conditions. Options for reducing C emissions from drained cultivated organic soils are limited when used as cropland. Extensive production leads to lower soil C stocks and requires more land. Increasing photosynthesis at the global scale by intensification of crop production was found to be the most effective mitigation option and is a prerequisite for preventing further areal expansion of agriculture.

Spatial and seasonal variability of phosphorus risk indexes in cultivated organic soils

Guérin, J. É., Parent, L.-É. and Si, B. C. 2011. Spatial and seasonal variability of phosphorus risk indexes in cultivated organic soils. Can. J. Soil Sci. 91: 291–302. Many reports have attributed phosphorus (P) leaching from cultivated organic soils and the eutrophication of adjacent surface waters to P fertilization exceeding the P sorption capacity of the soil. The index of phosphorus saturation (IPS) using the Mehlich III method (M-III) has been proposed to define an agri-environmental threshold of P saturation in cultivated organic soils. The spatial and temporal variability of IPSM-IIImust be documented and related to the risk of P pollution to recommend more efficient fertilization practices. The objective of this research was to measure spatial and seasonal variation patterns of P in cultivated organic soils and to evaluate the losses of soil test extractable P between autumn and the following spring. Composite soil samples were taken on a 25-× 25-m grid within 7-ha areas in three representative types of cultivated organic soils of southwestern Quebec in fall 2006 and spring 2007. Soil P, iron, and aluminum were extracted in duplicate using the M-III and the acid ammonium oxalate methods (OX). The spatial analysis of organic soils showed that the PM-IIIand the IPSM-IIIwere spatially autocorrelated and that the experimental semivariograms can be described by linear to sill or spherical models with ranges of 68 to 168 m. There was a high seasonal variability among the PM-IIIand the IPSM-IIIvalues. The IPSM-IIIvalues were generally higher than the environmental threshold of 0.05 across sites and sampling periods. Losses of M-III and OX extractable P averaged 41 kg PM-IIIha−1and 84 kg POXha−1, respectively, between fall and the following spring, suggesting substantial contribution of cultivated organic soils to the pollution of downstream surface waters.

Influence of water table level and soil properties on emissions of greenhouse gases from cultivated peat soil

A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Orke, a typical cultivated fen peat with low pH and high organic matter content and Majnegarden, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, O29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO2, CH4 and N2O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO2 emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N2O emissions peaked in springtime and CH4 emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO2 equivalents m-2. The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates.

Exploring the Nature of the Relationships Among Total, Extractable and Solution Phosphorus in Cultivated Organic Soils*

Exploring the Nature of the Relationships Among Total, Extractable and Solution Phosphorus in Cultivated Organic Soils*

N2O emissions from an irrigated and non‐irrigated organic soil in eastern Canada as influenced by N fertilizer addition

Drainage and cultivation of organic soils often result in large nitrous oxide (N2O) emissions. The objective of this study was to assess the impacts of nitrogen (N) fertilizer on N2O emissions from a cultivated organic soil located south of Montréal, QC, Canada, drained in 1930 and used since then for vegetable production. Fluxes of N2O were measured weekly from May 2004 to November 2005 when snow cover was absent in irrigated and non‐irrigated plots receiving 0, 100 or 150 kg N ha−1 as NH4NO3. Soil mineral N content, gas concentrations, temperature, water table height and water content were also measured to help explain variations in N2O emissions. Annual emissions during the experiment were large, ranging from 3.6 to 40.2 kg N2O‐N ha−1 year−1. The N2O emissions were decreased by N fertilizer addition in the non‐irrigated site but not in the irrigated site. The absence of a positive influence of soil mineral N content on N2O emissions was probably in part because up to 571 kg N ha−1 were mineralized during the snow‐free season. Emissions of N2O were positively correlated to soil CO2 emissions and to variables associated with the extent of soil aeration such as soil oxygen concentration, precipitation and soil water table height, thereby indicating that soil moisture/aeration and carbon bioavailability were the main controls of N2O emission. The large N2O emissions observed in this study indicate that drained cultivated organic soils in eastern Canada have a potential for N2O‐N losses similar to, or greater than, organic soils located in northern Europe.