CT Soils Research Articles

Effect of Tillage and Crop Establishment Methods on Physical Properties of a Medium-Textured Soil under a Seven-Year Rice−Wheat Rotation

Rice−wheat (Oryza sativa L.−Triticum aestivum L.) rotation is the major production system in Asia, covering about 18 million ha. Conventional practice of growing rice (puddled transplanting) and wheat (conventional till, CT) deteriorate soil physical properties, and are input- and energy-intensive. Zero-tillage (ZT) along with drill-seeding have been promoted to overcome these problems. A 7-yr permanent plot study evaluated various tillage and crop establishment (CE) methods on soil physical properties with an aim to improve soil health and resource-use efficiency. Treatments included transplanting and direct-seeding of rice on flat and raised beds with or without tillage followed by wheat in CT and ZT soil. Bulk density (Db) of the 10- to 20-cm soil layer was highest under puddled treatments (1.74–1.77 Mg m−3) and lowest under ZT treatments (1.66–1.71 Mg m−3). Likewise, soil penetration resistance (SPR) was highest at the 20-cm depth in puddled treatments (3.46−3.72 MPa) and lowest in ZT treatments (2.51–2.82 MPa). Compared with conventional practice, on average, water-stable aggregates (WSAs) > 0.25 mm were 28% higher in ZT direct-seeding with positive time trend of 4.02% yr−1. Infiltration was higher (0.29–0.40 cm h−1) in ZT treatments than puddled treatments (0.18 cm h−1). The least-limiting water range was about double in ZT direct-seeding than that of conventional practice. Gradual improvement in soil physical parameters in ZT system resulted in improvement in wheat yield and is expected to be superior in long-run on system (rice+wheat) basis. Further research is needed to understand mechanisms and requirements of two cereals with contrasting edaphic requirements in their new environment of ZT direct-seeding.

Fungal colonization in soils with different management histories: modeling growth in three-dimensional pore volumes

Despite the importance of fungi in soil functioning they have received comparatively little attention, and our understanding of fungal interactions and communities is lacking. This study aims to combine a physiologically based model of fungal growth with digitized images of internal pore volume of samples of undisturbed soil from contrasting management practices to determine the effect of physical structure on fungal growth dynamics. We quantified pore geometries of the undisturbed-soil samples from two contrasting agricultural practices, conventionally plowed (chisel plow) (CT) and no till (NT), and from native-species vegetation land use on land that was taken out of production in 1989 (NS). Then we modeled invasion of a fungal species within the soil samples and evaluated the role of soil structure on the progress of fungal colonization of the soil pore space. The size of the studied pores was > or =110 microm. The dynamics of fungal invasion was quantified through parameters of a mathematical model fitted to the fungal invasion curves. Results indicated that NT had substantially lower porosity and connectivity than CT and NS soils. For example, the largest connected pore volume occupied 79% and 88% of pore space in CT and NS treatments, respectively, while it only occupied 45% in NT. Likewise, the proportion of pore space available to fungal colonization was much greater in NS and CT than in NT treatment, and the dynamics of the fungal invasion differed among the treatments. The relative rate of fungal invasion at the onset of simulation was higher in NT samples, while the invasion followed a more sigmoidal pattern with relatively slow invasion rates at the initial time steps in NS and CT samples. Simulations allowed us to elucidate the contribution of physical structure to the rates and magnitudes of fungal invasion processes. It appeared that fragmented pore space disadvantaged fungal invasion in soils under long-term no-till, while large connected pores in soils under native vegetation or in tilled agriculture promoted the invasion.

Effects of tillage and crop rotation on soil microbial residues in a rainfed agroecosystem of northeast China

Agricultural management has significant impacts on soil microorganisms, which in turn influence soil relevant processes including soil organic matter (SOM) turnover. Amino sugars, as a microbial residue biomarker, are highly involved in microbial-mediated SOM cycling. However, the response of microbial-derived amino sugars to changes in soil management practices is poorly characterized in the arable soils (Typic Hapludoll, USDA Soil Taxonomy) in northeast China. The objective of this study was to assess the effects of soil tillage (conventional tillage CT vs. no tillage NT) and crop rotation (continuous corn ( Zea mays L.) monoculture vs. corn–soybean [ Glycine max (L.) Merr.] rotation) on the accumulation of amino sugars in this region. The following hypotheses were tested: (1) in an agroecosystem, tillage and crop rotation influence the accumulation of microbial residues in soils; (2) responses of fungal and bacterial cell wall residues to the practices are different, i.e., fungal-derived cell wall residues more benefited by no-tillage practices than bacterial. Implementation of no-tillage practices for 6 years significantly increased soil total amino sugars with an increase of 59% as compared with conventionally tilled plots ( P < 0.05). This highlights the positive effects of NT that promotes the accumulation of microbial-derived organic matter. The ratios of glucosamine to muramic acid in the NT soils across three soil depths significantly exceeded those in the respective CT soils due to a higher enrichment of glucosamine. This confirms our hypothesis that the microbial community shifted towards fungal dominance under NT and the phenomenon was more pronounced within the 0–5 cm layers. When NT systems were evaluated, the type of crop rotation used had a significant influence on the soil amino sugar content. Significant enrichment of total amino sugars (1042–1317 mg kg −1 soil) occurred in the continuous corn monoculture system as compared with the corn–soybean rotation field (943–1112 mg kg −1 soil) in the soil layers from 0 to −20 cm. Data obtained suggest that NT practices combined with continuous high C inputs can be adopted as an effective strategy to improve the cropland SOM in northeast China. Our results also indicate that it is possible to use amino sugars as an indicator to assess the changes in microbial community within a given ecosystem.

Macro-porosity and leaching of atrazine in tilled and orchard loamy soils

Atrazine is the most commonly detected herbicide in the groundwater. Leaching of atrazine largely depends on soil management practices. The aim of this study was to examine leaching of atrazine in tilled and orchard silty loam soils. The experimental objects included: conventionally tilled field (CT) with main tillage operations including pre-plow (10 cm) + harrowing, mouldboard ploughing (20 cm), and a 35 year-old apple orchard (OR) with a permanent sward. To determine leaching of atrazine soil columns of undisturbed structure were taken with steel cylinders of 21.5 cm diameter and 20 cm high from the depth of 0–20 cm. All columns were equilibrated at water content corresponding to field capacity (0.21 kg kg −1). Atrazine suspended in distilled water was dripped uniformly onto the surface of each column. Then water was infiltrated and breakthrough times of leachates were recorded. Atrazine concentration in the leachates was determined by means of HPLC Waters. Macro-porosity and percolation rate were higher in OR than CT soil. Cumulative recovery % of the atrazine applied was 1.267% for OR and approximately one third more from the CT soil but the rate of leaching (per unit of time) was greater from the OR soil. The lower leaching under OR than CT can be due to a greater SOM and the presence of earthworm burrows with organic burrow linings that could adsorb atrazine and contribute to preferential flow allowing solutes to bypass parts whereas the greater rate of leaching due to a greater infiltration rate.The results indicate potential of management practices for minimizing atrazine leaching.

A comparison of 2D vs. 3D thresholding of X-ray CT imagery

Non-destructive soil constituent analysis has advanced from resin impregnation of intact samples to the utilization of non-destructive imaging devices (i.e., CT scanners) for 3D composition. A difficulty of CT scanning is the finite resolution of such devices and the resulting non-definitive boundaries. Isolation of voxels that contain a single constituent (i.e., low variance voxels) allows for improved segregation of 3D data by histogram thresholding. The results from proposed 2D and 3D low variance voxel segmentation techniques were compared to establish whether or not 3D consideration should be used when analyzing CT and intact soil columns. It was determined that 2D processing in single orientation and as a multiplicative orthogonal process produced dissimilar results to 3D processed data. The authors encourage further exploration of 3D investigation in soil science, particularly related to soil composition and arrangement. Key words: Computed tomography, threshold, segmentation, soil, 3D

Fate of nitrogen applied to maize on conventional and minimum tilled Nitisols in Western Ethiopia

Maize production in western Ethiopia is practiced mainly on Nitisols inherently low in N. Neither conventional nor minimum tilled maize reaches its full yield potential without fertilization. A large amount of applied N usually escapes from the soil-crop system and this may exert harmful effects on the environment in addition to yield losses. Hence, the objective was to quantify the fate of labelled urea applied to conventional and minimum tilled maize. The study was conducted in 2004 on selected plots of experiments started in 2000 at three sites. At each site, the experiment was laid out in a randomized complete block design with three replications. Three tillage systems (MTRR = minimum tillage with residue retention, MTRV = minimum tillage with residue removal and CT = conventional tillage) and three N fertilization levels (recommended rate of 92 kg N ha−1 and 25% less and 25% more than this rate) were combined in complete factorial arrangement. Only the CT and MTRR plots fertilized at the recommended rate were used for this study. A micro plot of 2.4 m2 was demarcated in the center of every selected 24 m2 macro plot where labelled 15N @ 5 atom % urea was applied instead of unlabelled urea. The grain, stover and total biomass N derived from fertilizer was consistently higher for CT than MTRR. Conversely, the grain, stover and total biomass N derived from soil was consistently higher with MTRR than CT. Therefore, the fertilizer N recorded in the MTRR soils was higher than in the CT soils and mainly confined to the upper 450 mm. The fate of fertilizer N was in MTRR: 47% recovered by maize, 17% remained in the soil and 36% unaccounted for and in CT: 54% recovered by maize, 12% remained in the soil and 34% unaccounted for.

Net Global Warming Potential and Greenhouse Gas Intensity in Irrigated Cropping Systems in Northeastern Colorado

The impact of management on global warming potential (GWP), crop production, and greenhouse gas intensity (GHGI) in irrigated agriculture is not well documented. A no-till (NT) cropping systems study initiated in 1999 to evaluate soil organic carbon (SOC) sequestration potential in irrigated agriculture was used in this study to make trace gas flux measurements for 3 yr to facilitate a complete greenhouse gas accounting of GWP and GHGI. Fluxes of CO2, CH4, and N2O were measured using static, vented chambers, one to three times per week, year round, from April 2002 through October 2004 within conventional-till continuous corn (CT-CC) and NT continuous corn (NT-CC) plots and in NT corn-soybean rotation (NT-CB) plots. Nitrogen fertilizer rates ranged from 0 to 224 kg N ha(-1). Methane fluxes were small and did not differ between tillage systems. Nitrous oxide fluxes increased linearly with increasing N fertilizer rate each year, but emission rates varied with years. Carbon dioxide efflux was higher in CT compared to NT in 2002 but was not different by tillage in 2003 or 2004. Based on soil respiration and residue C inputs, NT soils were net sinks of GWP when adequate fertilizer was added to maintain crop production. The CT soils were smaller net sinks for GWP than NT soils. The determinant for the net GWP relationship was a balance between soil respiration and N2O emissions. Based on soil C sequestration, only NT soils were net sinks for GWP. Both estimates of GWP and GHGI indicate that when appropriate crop production levels are achieved, net CO2 emissions are reduced. The results suggest that economic viability and environmental conservation can be achieved by minimizing tillage and utilizing appropriate levels of fertilizer.

Impact of Soil Sorption Characteristics and Bedrock Composition on Phosphorus Concentrations in two Bohemian Forest Lakes

Phosphate (PO4-P) sorption characteristics of soils and bedrock composition were determined in catchments of two mountain lakes, Plesne Lake (PL) and Certovo Lake (CT), situated in the Bohemian Forest (Czech Republic). The aim was to explain higher terrestrial P export to mesotrophic PL compared to oligotrophic CT. Concentrations of Al and Fe oxides were the dominant parameters affecting soil ability to adsorb PO4-P. Depending on concentrations of Al and Fe oxides, P sorption maxima varied from 9.7 to 70.5 mmol kg−1 and from 7.4 to 121 mmol kg−1 in organic and mineral soil horizons, respectively. The catchment weighted mean PO4-P sorption capacity was 3.4 mol m−2 and 11.9 mol m−2 in the PL and CT soils, respectively. The higher PO4-P sorption capacity in the CT catchment was predominantly associated with higher pools of soil and Fe oxides. The CT bedrock (mica schist) released one order of magnitude less P than the PL bedrock (granite) within a pH range of catchment soils (pHCaCl2 of 2.5–4.5). The higher ability of PL bedrock to release P and the lower ability of PL soils to adsorb PO4-P thus contributed to the higher terrestrial P loading of this lake.

Carbendazim sorption–desorption in Vietnamese soils

Four Vietnamese soils (denoted AG, CT, ST and TG) which differed with respect to pH (pH 2.9–5.4), clay (17–50%) and organic matter (0.3–9.8%) content, were selected for sorption and desorption studies of carbendazim using the batch equilibration technique. Sorption increased with increasing organic carbon (OC) and clay content. K d values for carbendazim sorption on AG, CT, ST, TG soils at initial concentration of 20 μg/g were 12.5, 127, 8.1 and 9.6 ml/g, respectively. The OC partition coefficients ( K oc) for AG, CT, ST and TG were 1140, 1300, 2700 and 960 ml/g, respectively. Carbendazim was strongly sorbed and the binding was less reversible in the acid sulfate soil (CT), than in the other soils. The CT soil had both the highest OC content (9.8%) and the highest clay content (49.8%). The influence of pH on carbendazim sorption was studied in the ST and CT soils. Sorption of carbendazim by the sandy ST soil (OC 0.3%; clay content 26.3%) increased as the pH decreased, while sorption of carbendazim by the CT soil decreased as pH decreased.

Soil organic carbon and fractions of a Rhodic Ferralsol under the influence of tillage and crop rotation systems in southern Brazil

Soil organic matter (SOM) and its different pools have key importance in optimizing crop production, minimizing negative environmental impacts, and thus improving soil quality. The objective of this study was to evaluate the soil C and N contents in bulk soil and in different SOM pools (light and heavy fractions) of a clayey Rhodic Ferralsol after 13 years of different tillage and crop rotations in Passo Fundo, State of Rio Grande do Sul, Brazil. Soil samples were collected from no-tillage (no soil disturbance except for sowing; NT) and conventional tillage (disc plough followed by light disc harrowings; CT) applied to wheat/soybean (W/S) and wheat/soybean–vetch/maize (W/S–V/M) rotations. As reference, soil was sampled from a non-cultivated area adjacent to the field experiment. The greatest soil C and N contents were found in non-cultivated soils in the 0–5 cm depth (45 g C kg −1 soil and 3.6 g N kg −1 soil). Crop cultivation led to a decrease in SOM content which was higher for CT soils (approx. 60% decrease in C and N contents) than NT soils (approx. 43% decrease in C and N contents) at 0–5 cm. Tillage had the greatest impact on soil C and N storage. Soils under NT did not contain higher C and N storage than CT soils below 5 cm depth. Significantly, higher amounts of organic carbon of FLF in CT (0.5–0.7 g C kg −1 soil) than in NT soils (0.2 g C kg −1 soil) at 10–20 cm depth were also observed and the differences in C and N storage between CT and NT soils in the 0–30 cm layer were not significant. Silt and clay fractions contained the largest amount of organic carbon (60–95% of total organic carbon), and free light fraction was the most sensitive pool of organic carbon to detect changes in SOM due to soil tillage and crop rotations.

Soil carbohydrates in aggrading and degrading agroecosystems: influences of fungi and aggregates

Differences in soil organic carbon, nitrogen and carbohydrates as a result of different tillage practices under continuous cropping were studied in a 12 year old sorghum/rye rotation experiment in the Georgia piedmont. Soil organic C and N concentrations in an aggrading agroecosystem (no-tillage, NT) were significantly higher than in a degrading agroecosystem (conventional tillage, CT) at all dates. Soil carbohydrates followed a pattern similar to total organic C. Carbohydrate concentrations in macroaggregates (>250 μm) from NT surface soils were significantly higher than in microaggregates (<250 μm), although >2000 μm aggregates contained the lowest total organic C concentration. A significantly higher mannose to xylose ratio in microaggregates than in macroaggregates suggested that organic matter (OM) in microaggregates was strongly metabolized by soil microorganisms, but OM in macroaggregates was much less processed. The inhibition of fungi by the fungicide captan significantly reduced the concentrations of soil C and acid-hydrolyzable carbohydrates in NT soils but not in CT soils, indicating that fungi play a more significant role in organic C retention in the NT system than in the CT system.

SOIL MICROARTHROPODS IN LONG-TERM NO-TILLAGE AND CONVENTIONAL TILLAGE CORN PRODUCTION

Cultivation is known to reduce the number and diversity of microarthropod (Acarina and Collembola) populations from levels observed under natural forest or grassland vegetation. Under no-tillage crop production, the soil remains relatively undisturbed and plant litter decomposes at the soil surface, much like in natural soil ecosystems. The objective of this study was to investigate whether microarthropod populations under long-term (19 yr) continuous corn (Zea mays L.) production were increased by no-tillage (NT) vs. conventional tillage (CT; moldboard plow and harrowing) management. Numbers of microarthropods were also obtained from a soil managed as the CT treatment for 15 yr until seeding to bromegrass (Bromus inermus L.) hay for the last 4 yr. During the growing seasons over 2 yr, soil cores were taken every 2–3 wk and extracted for microarthropods using a high gradient extractor. The surface 5 cm of soil was sampled during the first year. All three treatments were different (P &lt; 0.05), with bromegrass, NT and CT soils containing respectively, 15.9, 12.4, and 5.8 microarthropods × 1000 m−2 of which 84, 69, and 70% were Acarina. In the second year, the surface 15 cm was sampled and the number of microarthropods in the corn soils was similar (P &lt; 0.05), containing 33.6 microarthropods × 1000 m−2, 92–98% of which were Acarina. However, microarthropods and soil organic-C were more concentrated in the surface 5 cm of soil in NT than CT. The soil under bromegrass contained 1.3 times more microarthropods (99% were Acarina) than under continuous NT and CT corn. Thus, when examined to a depth of 15 cm, 19 yr of NT corn did not increase the size of the microarthropod populations compared to CT, whereas production of bromegrass hay for 3–4 yr following long-term continuous CT corn did increased microarthropod numbers. Key words: Microarthropods, Collembola, Acarina, Zea mays, Bromus inermus, no-tillage, conservation tillage, soil carbon