Changes In Other Soil Properties Research Articles

Representing soil health practice effects on soil properties and nutrient loss in a watershed-scale hydrologic model.

Watershed-scale hydrologic models are commonly used to assess the water quality effects of agricultural conservation practices that improve soil health (e.g., cover crops and no-till). However, models rarely account for how these practices (i.e., soil health practices) affect soil physical and functional properties such as water holding capacity and soil aggregate stability, which may, in turn, affect water quality. We introduce a method to represent changes in soil physical and functional properties caused by soil health practices in the Soil and Water Assessment Tool (SWAT) model. We used the SWAT model's default representation of winter cover crops and no-till and modified soil descriptive parameters to depict soil health practice effects on soil properties. We assumed that the soil health practices would increase soil organic carbon (SOC), a principal indicator of soil health, by 0.01g C g-1 of soil and then estimated changes in other soil properties (e.g., water holding capacity) using SOC-based predictive equations and preceding literature. Results indicated that our soil property modifications had statistically significant effects on simulated hydrology and nutrient loss, though outputs were more substantially affected by the model's default representation of cover crops and no-till. Results also indicated that soil health practices can reduce nitrogen and total phosphorus loss but may increase dissolved reactive phosphorus loss. Our representation of soil health practices provides a more complete estimate of practice efficacy but underscores a need for additional observational data to verify results and guide further model improvements.

Seasonal variations of soil phosphorus and associated fertility indicators in wastewater-irrigated urban aridisol

Use of wastewater is known to provide nutrients for crop plants, but its potential to improve phosphorus (P) availability in semi-arid regions is poorly understood. In this study, seasonal changes in soil P availability as well as associated phyiscochemical and biochemical indicators were investigated from the wastewater irrigated urban soils of Faisalabad, Pakistan. Soil sampling was carried out during summer and winter season from four wastewater irrigated sites of varied stream flow i.e. upstream wastewater (UWW), midstream wastewater (MWW), lowerstream wastewater (LWW) and downstream wastewater (DWW), and canal water irrigation (CWI) as a reference site. Across seasons, MWW site had significantly higher soil organic carbon (SOC), water extractable organic carbon (WEOC), microbial biomass carbon (MBC), microbial biomass phosphorus (MBP) as well as the availability of phosphorus i.e. NaHCO3–P and H2O–P compared to CWI site. In both sampling seasons, MWW site also recorded significantly higher soil enzyme activities compared to the rest of wastewater sites. Moreover, significantly higher total P and electrical conductivity (EC) of soil was noticed at DWW site across both summer and winter seasons. Biplot principle component analysis also indicated seasonally a stronger shift in soil total P and EC at DWW site. On the other hand, availability of P was closely related to soil active carbon pools at MWW site. However, buildup of soil salinity particularly at DWW site along with lower P availability and associated changes in other soil properties, call for careful assessment of wastewater use in these urban soils.

Transformation of Forest Ecosystems in Moscow Megapolis under Recreational Impacts

A comprehensive quantitative assessment of the state of vegetation, soil invertebrate complex, litter horizons, and soddy-podzolic soils (Albic Retisols) in Moscow forest parks (Bitsevskii Forest and Losinyi Ostrov) as dependent on the level of recreational loads is presented. The changes in the main components of forest ecosystems in the forest parks under study have a unidirectional character. At the fifth stage of the recreation-induced degradation, the portion of the trees in good condition decreases by 4–5 times; the canopy density, by 20–30%; and the abundance of undergrowth, by 3–4 times. This leads to an increase in illumination of the surface by more than 30 times. With an increase in recreational loads, the species diversity of herbs in the ground cover initially increases from 9–11 to 23 species owing to the invasion of forest-meadow, meadow, and ruderal plants; then, it decreases. The litter pool becomes lower, and its fractional composition changes: the portion of the active litter fractions decreases by 1.7–2 times, and the portion of mechanically comminuted fractions increases by 3.5–7 times. The density and biomass of mesopedobionts at this stage decreases by 2–2.5 times in the soil and by 4–7 times in the litter. The most pronounced changes in the soil properties take place in the uppermost mineral layer (0–5 cm); in the deeper horizons, they are weaker. According to the results of discriminant analysis, the major contribution to the discrimination of soils at different stages of the recreational degradation is made by the aggregation factor. Individual contributions of changes in other soil properties are small, though their cumulative effect of the discrimination of soils is significant.

Prediction of the glyphosate sorption coefficient across two loamy agricultural fields

Sorption is considered one of the most important processes controlling pesticide mobility in agricultural soils. Accurate predictions of sorption coefficients are needed for reliable risk assessments of groundwater contamination from pesticides. In this work, we aim to estimate the glyphosate sorption coefficient, Kd, from easily measurable soil properties in two loamy, agricultural fields in Denmark: Estrup and Silstrup. Forty-five soil samples in Estrup and 65 in Silstrup were collected from the surface in a rectangular grid of 15×15-m from each field, and selected soil properties and glyphosate sorption coefficients were determined. Multiple linear regression (MLR) analyses were performed using nine geo-referenced soil properties as variables to identify the parameters related with glyphosate sorption. Scenarios considered in the analyses included: (i) each field separately, (ii) both fields together, and (iii) northern and southern sections of the field in Silstrup. Considering correlations with all possible sets of the same nine geo-referenced properties, a best-four set of parameters was identified for each model scenario. The best-four set for the field in Estrup included clay, oxalate-extractable Fe, Olsen P and pH, while the best-four set for Silstrup included clay, OC, Olsen P and EC. When the field in Silstrup was separated in a northern and southern section, the northern section included EC, and oxalate-extractable Fe, Al and P, whereas the southern part included pH, clay, OC and Olsen P. The best-four set for both fields together included clay, sand, pH and EC. Thus, the most common parameters repeated in the best-four sets included clay and pH as also reported previously in the literature, but in general, the composition of the best-four set differed for each scenario, suggesting that different properties control glyphosate sorption in different locations and at different scales of analysis. Better predictions were obtained for the best-four set for the field in Estrup (R2=0.87) and for both fields (R2=0.70), while the field in Silstrup showed a lower predictability (R2=0.36). Possibly, the low predictability for the field in Silstrup originated from opposing gradients in clay and oxalate-extractable Fe across the field. Also, whereas a lower clay content in Estrup may be the limiting variable for glyphosate sorption, the field in Silstrup has a higher clay content not limiting the sorption, but introducing more variability in Kd due to changes in other soil properties.

Is bacterial moisture niche a good predictor of shifts in community composition under long‐term drought?

Both biogeographical and rainfall manipulation studies show that soil water content can be a strong driver of microbial community composition. However, we do not yet know if these patterns emerge because certain bacterial taxa are better able to survive at dry soil moisture regimes or if they are due to other drought-sensitive ecosystem properties indirectly affecting microbial community composition. In this study, we evaluated (1) whether bacterial community composition changed under an 11-year drought manipulation and (2) whether shifts under drought could be explained by variation in the moisture sensitivity of growth among bacterial taxa (moisture niche partitioning). Using 454 pyrosequencing of 16S rRNA, we observed shifts in bacterial community composition under drought, coincident with changes in other soil properties. We wet-up dry soils from drought plots to five moisture levels, and measured respiration and the composition of actively growing communities using bromodeoxyuridine (BrdU) labeling of DNA. The field drought experiment affected the composition of the active community when incubated at different moisture levels in the laboratory, as well as short-term (36-hour) respiration rates. Independent of history, bacterial communities also displayed strong niche partitioning across the wet-up moisture gradient. Although this indicates that moisture has the potential to drive bacterial community composition under long-term drought, species distributions predicted by response to moisture did not reflect the community composition of plots that were subjected to long-term drought. Bacterial community structure was likely more strongly driven by other environmental factors that changed under long-term drought, or not shaped by response to water level upon wet-up. The approach that we present here for linking niches to community composition could be adapted for other environmental variables to aid in predicting microbial species distributions and community responses to environmental change.

STUDY ON FRACTAL FEATURES OF SOIL AGGREGATE STRUCTURE UNDER NATURAL EVERGREEN BR OADLEAVED FOREST AND ARTIFICIAL REGENERATION IN SOUTHERN SICHUAN PROVINCE

Aims Fractal theory, a study tool popular in recent years, offers a new means to quantitatively investigate soil structure. Soil structure is the basis of soil fertility, which is the basic property of soil. It can be comprehensively reflected by soil physical, chemical and organism properties, and change of soil structure will result in changes in other soil properties. Fractal features of soil aggregate structure under natural evergreen broadleaved forest and regeneration of artificial systems is rarely studied. We chose to study natural evergreen broadleaved forest and three artificial plantations of Sassafras tzumu, Cryptomeria fortunei and Metasequoia glyptostroboides in southern Sichuan Province. Our objective was to determine a) effects of artificial regeneration on fractal features of soil aggregate structure, b) effects of different plantations on fractal dimension of soil aggregate structure, c) relationships between fractal dimension and soil physical properties, nutrient content and microbe number, and d) use of fractal dimension of soil aggregate structure for evaluating the water conservation, fertility and microbe activity of soil. Methods Soils were collected from each forest to determine a) fractal dimension of soil aggregate structure using Yang Peiling's approach and b) soil physical and chemical properties and soil microbe number. The relationship between fractal dimension and soil physical properties, nutrient content and microbe number was analyzed with regression analysis. Important findings Natural evergreen broadleaved forest and artificial regeneration resulted in increased fractal dimension of soil aggregate structure and percent of construction damage, poorer soil physical properties and reduced nutrient content and number of microbes. The higher the content of aggregates, water-stable aggregates and water-stable big aggregates in soil, the smaller the fractal dimension of soil aggregate structure. With wet sieving condition and decreased fractal dimension, the percent of construction damage decreased. There were close relationships between fractal dimension of soil aggregate structure and soil natural water content, bulk density, capillary porosity, non- capillary porosity, original infiltration coefficient, stable infiltration coefficient, content of organic matter, total-N, hydrolysis-N, total-P, available-P, total-K, available-K and the number of bacteria, fungi and actinomyces. Different stands had different effects for maintenance of soil structure, which resulted in changes of soil physical, chemical and organism properties under natural evergreen broadleaved forest and artificial regeneration, and changes of soil aggregate structure had an effect on the value of fractal dimension. This indicates that fractal dimension can be used as a comprehensive quantitative index to evaluate water conservation function, fertility states and microbe activity of soil for natural evergreen broadleaved forest and artificial regeneration. It provides a solid foundation for protecting natural evergreen broadleaved forest, choosing appropriate trees for its artificial regeneration, managing soil after artificial regeneration and choosing trees for converting farmland to forest.

Soil Structural Disturbance Effects on Crop Yields and Soil Properties in a No‐Till Production System

The development of well‐structured soils is a goal for achieving sustainable and productive agricultural systems. Nevertheless, the maintenance of soil structure in continuous no‐till (NT) soils has sometimes been thought to induce soil conditions that are detrimental to crop yields. The objectives of this research were to characterize the effects of periodic tillage disruption in otherwise NT systems on soil properties and the yields of winter wheat (Triticum aestivum L.), double‐cropped soybean [Glycine max (L.) Merr.], and maize (Zea mays L.) in rotation and to determine if soil structural changes occurring in tilled soils are independent of changes in other soil properties. A field experiment was established in 1992 on a Huntington silt loam soil (Fluventic Hapludoll) at the University of Kentucky Research and Education Center in Princeton (KY) under a NT crop sequence with two seedbed preparation methods for winter wheat, (a) NT or (b) chisel plus disk tillage (Till). In fall 2000, similar soil chemical properties were observed between disrupted and continuous NT systems over the 0‐ to 20‐cm layer. The geometric mean diameter of dry fragments and the soil water content retained between 0.0003 and 0.03 MPa water potential was greater in NT soils than in soils tilled for winter wheat. Tillage for winter wheat enhanced winter wheat yields (4.2% increase), mostly under low‐yielding conditions, but it resulted in a reduction of subsequent summer crop yields (i.e., 3.7% for soybean and 7.0% for maize). The yields obtained in our study translate to an economic benefit for the continuous NT system. Net returns per hectare were estimated to be $73 higher for the winter wheat/double‐crop soybean–maize rotation under NT than under Till treatments. The differences in maize yields between NT and tilled treatments were attributed to a better water supply in NT soil due to the maintenance of a larger number of mesopores and a great hydraulic conductivity. In the absence of significant changes in other physicochemical properties, periodic tillage appears to disrupt soil structure, which negatively affects crop productivity.

Nitrogen-fixation by Acacia dealbata and changes in soil properties 5 years after mechanical disturbance or slash-burning following timber harvest

Logging followed by slash-burning can result in large losses of Nitrogen from an ecosystem. Acacia dealbata (silver wattle) is the main N-fixing plant in Eucalyptus regnans (mountain ash) forest in Victoria, but its potential N-fixing capacity is uncertain. Losses of N and changes in other soil properties as a result of logging and slash-burning and inputs of N through N-fixation by A. dealbata were quantified in mountain ash forest near Tanjil Bren, Victoria. The study was based on four logging coupes harvested in 1988 (two burnt following harvest and two disturbed mechanically) and three areas of unlogged, 55-year-old regrowth. There was a 19% increase in concentration of potentially available N and a 48% increase in available P on burnt coupes relative to unburnt coupes, but a 12% decrease in total N and a 17% decrease in organic carbon. These differences were consistent with N and C being lost through burning and with an increase in fertility of surface soil due to the ash-bed effect. Wattles increased concentrations of potentially available N, total N and organic C and reduced bulk density of soil, but did not effect the amount of total N in soil. However, significant differences between the natural abundance of 15 N in A. dealbata and E. regnans and a significant inverse relationship between stocking of silver wattle and δ( 15 N) in soil indicated that N-fixation by A. dealbata trees had added substantial amounts of N to both vegetation and soil. At a stocking of 2500 stems ha −1 A. dealbata was estimated to contribute 40 kg ha −1 per year to total N in soil and 10 kg ha −1 per year to total N in vegetation through N-fixation over the first 5 years. This rate of N-fixation (50 kg ha −1 per year) is sufficient to replace an estimated loss of 430 kg N ha −1 due to timber harvesting and burning in 9 years.