Factors and mechanisms controlling soil organic carbon turnover in subsoils of agricultural sites

Two-third of the terrestrial C is stored in soils, and more than 50% of soil organic C (SOC) is stored in subsoils from 30 – 100 cm. Hence, subsoil is important as a source or sink for CO2 in the global carbon cycle. Especially the stable organic carbon (OC) is stored in subsoil, as several studies have shown that subsoil OC is of a higher average age than topsoil OC. However, there is still a lack of knowledge regarding the mechanisms of C sequestration and C turnover in subsoil. Three main factors are discussed, which possibly reduce carbon turnover rates in subsoil: Resource limitation, changes in the microbial community, and changes in gas conditions. The experiments conducted in this study, which aimed to elucidate the importance of the mentioned factors, focused on two neighbouring arable sites, with depth profiles differing in SOC stocks: One Colluvic Cambisol (Cam) with high SOC contents (8-12 g kg-1) throughout the profile and one Haplic Luvisol (Luv) with low SOC contents (3-4 g kg-1) below 30 cm depth. The first experiment was designed to gain more knowledge regarding the microbial community and its influence on carbon sequestration in subsoil. Soil samples were taken at four different depths on the two sites. Microbial biomass C (MBC) was determined to identify depth gradients in relation to the natural C availability. Bacterial and fungal residues as well as ergosterol were determined to quantify changes in the in the microbial community composition. Multi-substrate-induced-respiration (MSIR) was used to identify shifts in functional diversity of the microbial community. The MSIR revealed that substrate use in subsoil differed significantly from that in topsoil and also differed highly between the two subsoils, indicating a strong influence of resource limitations on microbial substrate use. Amino sugar analysis and the ratio of ergosterol to microbial biomass C showed that fungal dominance decreased with depth. The results clearly demonstrated that microbial parameters changed with depth according to substrate availability. The second experiment was an incubation experiment using subsoil gas conditions with and without the addition of C4 plant residues. Soil samples were taken from topsoil and subsoil of the two sites. SOC losses during the incubation, were not influenced by the subsoil gas conditions. Plant-derived C losses were generally stronger in the Cam (7.5 mg g-1), especially at subsoil gas conditions, than in the Luv (7.0 mg g-1). Subsoil gas conditions had no general effects on microbial measures with and without plant residue addition. However, the contribution of plant-derived MBC to total MBC was significantly reduced at subsoil gas conditions. This lead to the conclusion that subsoil gas conditions alter the metabolism of microorganisms but not the degradation of added plant residues is general. The third experiment was a field experiment carried out for two years. Mesh bags containing original soil material and maize root residues (C4 plant) were buried at three different depths at the two sites. The recovery of the soilbags took place 12, 18, and 24 months after burial. We determined the effects of these treatments on SOC, density fractions, and MBC. The mean residence time for maize-derived C was similar at all depths and both sites (403 d). MBC increased to a similar extent (2.5 fold) from the initial value to maximum value. This increase relied largely on the added maize root residues. However, there were clear differences visible in terms of the substrate use efficiency, which decreased with depth and was lower in the Luv than in the Cam. Hence freshly added plant material is highly accessible to microorganisms in subsoil and therefore equally degraded at both sites and depths, but its metabolic use was determined by the legacy of soil properties. These findings provide strong evidence that resource availability from autochthonous SOM as well as from added plant residues have a strong influence on the microbial community and its use of different substrates. However, under all of the applied conditions there was no evidence that complex substrates, i.e. plant residues, were less degraded in subsoil than in topsoil.

Soil Stabilization with Lime, Iowa Highway Research Board Bulletin No. 25, 1961

This is the fifth publication in a series of compilations of the reports on research completed for the Iowa State Highway Commission. This research was done for the Iowa State Highway Research Board Project HR-1, "The Loess and Glacial Till Materials of Iowa; an Investigation of Their Physical and Chemical Properties and Techniques for Processing Them to Increase Their All-Weather Stability for Road Construction." The research, started in 1950, was done by the Iowa Engineering Experiment Station under its project 283-S. The project was supported by funds from the Iowa State Highway Commission. The principal objectives of the project may be summed up as follows: 1. To determine by means of both field and laboratory studies the areal and stratigraphic variation in the physical and chemical properties of the loess and glacial till materials of Iowa. 2. To develop new equipment and methods for evaluating physical and chemical properties of soil where needed. 3. To correlate fundamental soil properties with the performance of soils in the highway structure. 4. To develop a scientific approach to the problem of soil stabilization based on the relationships between the properties of the soils and those of the admixtures. 5. To determine the manner in which the loess and glacial till materials of Iowa can be processed for optimum performance as highway embankments, sub-grades, base courses, and surface courses.

Rainfall infiltration and soil hydrological characteristics below ancient forest, planted forest and grassland in a temperate northern climate

How rainfall infiltration rate and soil hydrological characteristics develop over time under forests of different ages in temperate regions is poorly understood. In this study, infiltration rate and soil hydrological characteristics were investigated under forests of different ages and under grassland. Soil hydraulic characteristics were measured at different scales under a 250-year-old grazed grassland (GL), 6-year-old (6yr) and 48-year-old (48yr) Scots pine (Pinus sylvestris) plantations, remnant 300-year-old individual Scots pine (OT) and a 4000-year-old Caledonian Forest (AF). In situ field-saturated hydraulic conductivity (Kfs) was measured, and visible root:soil area was estimated from soil pits. Macroporosity, pore structure and macropore connectivity were estimated from X-ray tomography of soil cores, and from water-release characteristics. At all scales, the median values for Kfs, root fraction, macroporosity and connectivity values tended to AF>OT>48yr>GL>6yr, indicating that infiltration rates and water storage increased with forest age. The remnant Caledonian Forest had a huge range of Kfs (12 to >4922mmh-1), with maximum Kfs values 7 to 15 times larger than those of 48-year-old Scots pine plantation, suggesting that undisturbed old forests, with high rainfall and minimal evapotranspiration in winter, may act as important areas for water storage and sinks for storm rainfall to infiltrate and transport to deeper soil layers via preferential flow. The importance of the development of soil hydrological characteristics under different aged forests is discussed.

A field agronomic evaluation of Typha grass in Tomas dam Kano State Nigeria

The study was carried out by measuring plant height, length of leaves, width of the leaves, length of inflorescent, length of inflorescent tip were also measured with a measuring tape. Number of tillers per plants was counted. Soil auger was used to take soil samples randomly from ten different locations in Tomas Dam Kano states Nigeria. At the depths of 0-5cm, 5cm 13 10cm, 10cm 13 15cm. The soil samples were put into polyethylene bags and labelled according to their depth for mineral analyses. In the two season calcium, nitrogen and phosphorus constitute the highest concentration of the minerals at 0 155 cm depth. There is no significant differences in terms of mineral composition between wet season and dry season. (P<0.005).There is significance differences between plant Length of inflorescent and length of inflorescent tip when the two season are compared. KEYWORDS: Typha grass, field, agronomic evaluation,

Influence of mucuna fallow crop on selected soil properties, weed suppression and taro yields in Taveuni, Fiji

Two field experiments were carried out in Taveuni, Fiji to study the effects of mucuna (Mucuna pruriens) and grass fallow systems at 6 and 12 month durations on changes in soil properties (Experiment 1) and taro yields (Experiment 2). Biomass accumulation of mucuna fallow crop was significantly higher (P<0.05) than grass fallow crop at both 6 and 12 month durations. The longer fallow duration resulted in higher (P<0.05) total soil organic carbon, total soil nitrogen and earthworm numbers regardless of fallow type. Weed suppression in taro grown under mucuna was significantly greater (P<0.05) than under natural grass fallow. Taro grown under mucuna fallow significantly outyielded taro grown under grass fallow (11.8 vs. 8.8 t ha-1). Also, the gross margin of taro grown under mucuna fallow was 52% higher than that of taro grown under grass fallow. © ISHS.

Wheats developed for high yield on stored soil moisture have deep vigorous root systems

Many rainfed wheat production systems are reliant on stored soil water for some or all of their water inputs. Selection and breeding for root traits could result in a yield benefit; however, breeding for root traits has traditionally been avoided due to the difficulty of phenotyping mature root systems, limited understanding of root system development and function, and the strong influence of environmental conditions on the phenotype of the mature root system. This paper outlines an international field selection program for beneficial root traits at maturity using soil coring in India and Australia. In the rainfed areas of India, wheat is sown at the end of the monsoon into hot soils with a quickly receding soil water profile; in season water inputs are minimal. We hypothesised that wheat selected and bred for high yield under these conditions would have deep, vigorous root systems, allowing them to access and utilise the stored soil water at depth around anthesis and grain-filling when surface layers were dry. The Indian trials resulted in 49 lines being sent to Australia for phenotyping. These lines were ranked against 41 high yielding Australian lines. Variation was observed for deep root traits e.g. in eastern Australia in 2012, maximum depth ranged from 118.8 to 146.3 cm. There was significant variation for root traits between sites and years, however, several Indian genotypes were identified that consistently ranked highly across sites and years for deep rooting traits.

Soil survey.

Vols. after Series 1963, no. 1 lack series year and numbering.

Bacterial communities of the specialty crop phyllosphere: response to biological soil amendment use, rainfall, and insect visitation

Microorganisms in the plant rhizosphere, the zone under the influence of roots, and phyllosphere, the aboveground plant habitat, exert a strong influence on plant growth, health, and protection. Tomatoes and cucumbers are important players in produce safety, and the microbial life on their surfaces may contribute to their fitness as hosts for foodborne pathogens such as Salmonella enterica and Listeria monocytogenes. External factors such as agricultural inputs and environmental conditions likely also play a major role. However, the relative contributions of the various factors at play concerning the plant surface microbiome remain obscure, although this knowledge could be applied to crop protection from plant and human pathogens. Recent advances in genomic technology have made investigations into the diversity and structure of microbial communities possible in many systems and at multiple scales. Using Illumina sequencing to profile particular regions of the 16S rRNA gene, this study investigates the influences of climate and crop management practices on the field-grown tomato and cucumber microbiome. The first research chapter (Chapter 3) involved application of 4 different soil amendments to a tomato field and profiling of harvest-time phyllosphere and rhizosphere microbial communities. Factors such as water activity, soil texture, and field location influenced microbial community structure more than soil amendment use, indicating that field conditions may exert more influence on the tomato microbiome than certain agricultural inputs. In Chapter 4, the impact of rain on tomato and cucumber-associated microbial community structures was evaluated. Shifts in bacterial community composition and structure were recorded immediately following rain events, an effect which was partially reversed after 4 days and was strongest on cucumber fruit surfaces. Chapter 5 focused on the contribution of insect visitors to the tomato microbiota, finding that insects introduced diverse bacterial taxa to the blossom and green tomato fruit microbiome. This study advances our understanding of the factors that influence the microbiomes of tomato and cucumber. Farms are complex environments, and untangling the interactions between farming practices, the environment, and microbial diversity will help us develop a comprehensive understanding of how microbial life, including foodborne pathogens, may be influenced by agricultural conditions.

Influence of Soil Biogeochemical Properties on the Invasiveness of Old World Climbing Fern (Lygodium microphyllum)

The state of Florida has one of the most severe exotic species invasion problems in the United States, but little is known about their influence on soil biogeochemistry. My dissertation research includes a cross-continental field study in Australia, Florida, and greenhouse and growth chamber experiments, focused on the soil-plant interactions of one of the most problematic weeds introduced in south Florida, Lygodium microphyllum (Old World climbing fern). Analysis of field samples from the ferns introduced and their native range indicate that L microphyllum is highly dependent on arbuscular mycorrhizal fungi (AMF) for phosphorus uptake and biomass accumulation. Relationship with AMF is stronger in relatively dry conditions, which are commonly found in some Florida sites, compared to more common wet sites where the fern is found in its native Australia. In the field, L. microphyllum is found to thrive in a wide range of soil pH, texture, and nutrient conditions, with strongly acidic soils in Australia and slightly acidic soils in Florida. Soils with pH 5.5 - 6.5 provide the most optimal growth conditions for L. microphyllum, and the growth declines significantly at soil pH 8.0, indicating that further reduction could happen in more alkaline soils. Comparison of invaded and uninvaded soil characteristics demonstrates that L. microphyllum can change the belowground soil environment, with more conspicuous impact on nutrient-poor sandy soils, to its own benefit by enhancing the soil nutrient status. Additionally, the nitrogen concentration in the leaves, which has a significant influence in the relative growth rate and photosynthesis, was significantly higher in Florida plants compared to Australian plants. Given that L. microphyllum allocates up to 40% of the total biomass to rhizomes, which aid in rapid regeneration after burning, cutting or chemical spray, hence management techniques targeting the rhizomes look promising. Over all, my results reveal for the first time that soil pH, texture, and AMF are major factors facilitating the invasive success of L. mcirophyllum. Finally, herbicide treatments targeting rhizomes will most likely become the widely used technique to control invasiveness of L. microphyllum in the future. However, a complete understanding of the soil ecosystem is necessary before adding any chemicals to the soil to achieve a successful long-term invasive species management strategy.

Singularity and multifractal characterization of signals with wavelets. Application to clay soil images

In the field of multiscale analysis of signals, including images, the wavelet transform is one of the most attractive and powerful tool due to its ability to focus on signals structures at different scales. Wavelet Transform at different scales is successfully applied to image characterization (which can be applied to a watermarking scheme) and multiscale singularity detection and processing. In this work we show further research of computation of multifractals properties such as the multifractal spectrum (D(alpha)) applied to dye stained images of natural terrain. This can be useful for statically describing preferential flow path geometry.

Potential mitigation of midwest grass-finished beef production emissions with soil carbon sequestration in the United States of America

Beef production can be environmentally detrimental due in large part to associated enteric methane (CH4) production, which contributes to climate change. However, beef production in well-managed grazing systems can aid in soil carbon sequestration (SCS), which is often ignored when assessing beef production impacts on climate change. To estimate the carbon footprint and climate change mitigation potential of upper Midwest grass-finished beef production systems, we conducted a partial life cycle assessment (LCA) comparing two grazing management strategies: 1) a non-irrigated, lightly-stocked (1.0 AU/ha), high-density (100,000 kg LW/ha) system (MOB) and 2) an irrigated, heavily-stocked (2.5 AU/ha), low-density (30,000 kg LW/ha) system (IRG). In each system, April-born steers were weaned in November, winter-backgrounded for 6 months and grazed until their endpoint the following November, with average slaughter age of 19 months and a 295 kg hot carcass weight. As the basis for the LCA, we used two years of data from Lake City Research Center, Lake City, MI. We included greenhouse gas (GHG) emissions associated with enteric CH4, soil N2O and CH4 fluxes, alfalfa and mineral supplementation, and farm energy use. We also generated results from the LCA using the enteric emissions equations of the Intergovernmental Panel on Climate Change (IPCC). We evaluated a range of potential rates of soil carbon (C) loss or gain of up to 3 Mg C ha-1 yr-1. Enteric CH4 had the largest impact on total emissions, but this varied by grazing system. Enteric CH4 composed 62 and 66% of emissions for IRG and MOB, respectively, on a land basis. Both MOB and IRG were net GHG sources when SCS was not considered. Our partial LCA indicated that when SCS potential was included, each grazing strategy could be an overall sink. Sensitivity analyses indicated that soil in the MOB and IRG systems would need to sequester 1 and 2 Mg C ha-1 yr-1 for a net zero GHG footprint, respectively. IPCC model estimates for enteric CH4 were similar to field estimates for the MOB system, but were higher for the IRG system, suggesting that 0.62 Mg C ha-1 yr-1 greater SCS would be needed to offset the animal emissions in this case.

Organic and nitrogen fertilization of soil under Syrah grapevine: effects on soil chemical properties and nitrate concentration.

Viticulture is an activity of great social and economic importance in the lower-middle region of the São Francisco River valley in northeastern Brazil. In this region, the fertility of soils under vineyards is generally poor. To assess the effects of organic and nitrogen fertilization on chemical properties and nitrate concentrations in an Argissolo Vermelho-Amarelo (Typic Plinthustalf), a field experiment was carried out in Petrolina, Pernambuco, on Syrah grapevines. Treatments consisted of two rates of organic fertilizer (0 and 30 m3 ha-1) and five N rates (0, 10, 20, 40, and 80 kg ha-1), in a randomized block design arranged in split plots, with five replications. The organic fertilizer levels represented the main plots and the N levels, the subplots. The source of N was urea and the source of organic fertilizer was goat manure. Irrigation was applied through a drip system and N by fertigation. At the end of the third growing season, soil chemical properties were determined and nitrate concentration in the soil solution (extracted by porous cups) was determined. Organic fertilization increased organic matter, pH, EC, P, K, Ca, Mg, Mn, sum of bases, base saturation, and CEC, but decreased exchangeable Cu concentration in the soil by complexation of Cu in the organic matter. Organic fertilization raised the nitrate concentration in the 0.20-0.40 m soil layer, making it leachable. Nitrate concentration in the soil increased as N rates increased, up to more than 300 mg kg-1 in soil and nearly 800 mg L-1 in the soil solution, becoming prone to leaching losses.

Nitrate and potassium concentration in fertigated soil cultivated with wine vines.

In the semiarid region of Brazil the use of irrigation systems for applying fertilizers in horticulture is the primary means for incorporating nutrients in the soil. However, this technique still requires its use in wine vines to be assessed. In view of this, this study aimed to assess nitrate and potassium concentrations in soil fertigated with nitrogen and potassium fertilizers in 3 wine grape growing cycles. A field experiment was conducted with ?Syrah? wine grapes, in Petrolina, Pernambuco, Brazil; it assessed five nitrogen doses (0, 15, 30, 60 and 120 kg ha-1) and five K2O doses (0, 15, 30, 60 and 120 kg ha-1) applied by drip irrigation system with two emitters per plant, with a flow rate of 4 L h-1. The experimental design used was the factorial split-plot, making up 13 combinations arranged in 4 randomized blocks. Soil solution samples were collected weekly with the aid of porous cup extractors for all treatments and at depths of 0.4 and 0.6 m by determining nitrate and potassium concentrations and electrical conductivity. Increased levels of both nutrients in the irrigation water increased the availability of nitrate and potassium in the soil solution. The highest nitrate and potassium concentrations were found in the second growing cycle at both depths studied.

An algebraic pedotransfer function to calculate standardized in situ determined field capacity.

Despite the large applicability of the field capacity (FC) concept in hydrology and engineering, it presents various ambiguities and inconsistencies due to a lack of methodological procedure standardization. Experimental field and laboratory protocols taken from the literature were used in this study to determine the value of FC for different depths in 29 soil profiles, totaling 209 soil samples. The volumetric water content (θ) values were also determined at three suction values (6 kPa, 10 kPa, 33 kPa), along with bulk density (BD), texture (T) and organic matter content (OM). The protocols were devised based on the water processes involved in the FC concept aiming at minimizing hydraulic inconsistencies and procedural difficulty while maintaining the practical meaning of the concept. A high correlation between FC and θ(6 kPa) allowed the development of a pedotransfer function (Equation 3) quadratic for θ(6 kPa), resulting in an accurate and nearly bias-free calculation of FC for the four database geographic areas, with a global root mean squared residue (RMSR) of 0.026 m3·m-3. At the individual soil profile scale, the maximum RMSR was only 0.040 m3·m-3. The BD, T and OM data were generally of a low predicting quality regarding FC when not accompanied by the moisture variables. As all the FC values were obtained by the same experimental protocol and as the predicting quality of Equation 3 was clearly better than that of the classical method, which considers FC equal to θ(6), θ(10) or θ(33), we recommend using Equation 3 rather than the classical method, as well as the protocol presented here, to determine in-situ FC.

Soil management, seed treatment and soil compaction on the sowing furrows affect grain yields of upland rice genotypes.

The water availability for flood irrigated rice (Oryza sativa L.) is decreasing worldwide. Therefore, developing technologies to allow growing rice in aerobic condition, such as a no-tillage system (NTS) can contribute to produce upland rice grains without yield losses and also in saving more water. The objective of this study was to determine the effect of soil management, seed treatment and compaction on the sowing furrow on grain yield of upland rice genotypes. We made two trials, one in an NTS and another using conventional tillage, CT (one plowing and two diskings). The field experiments were performed in the Central Region of Brazil in Cerrado soils. For each trial, the experimental design was a randomized block design in a factorial scheme, with three replications. The treatments consisted of a combination of 10 genotypes with 2 compaction pressures on the sowing furrow (25 kPa and 126kPa) and 2 types of seed treatment (with and without pesticide). Under CT, the seed treatment did not contribute to increase upland rice grain yields. However, under NTS the grain yield of some genotypes [BRS Esmeralda (from 723 to 1,766 kg ha-1), BRS Pepita (from 930 to 1,874 kg ha-1), AB072044 (from 523 to 1,579 kg ha-1), and AB072085 (from 632 to 1,636 kg ha-1) at 25 kPA soil compaction pressure, and Sertaneja (from 994 to 2,167 kg ha-1), BRS Pepita (from 1,161 to 2,100 kg ha-1), and AB072085 (from 958 to 2,213 kg ha-1), at 126 kPA soil compaction pressure] increased with the use of this practice. At CT the higher soil compaction pressure on the sowing furrow (from 25 kPa to 126 kPa) increased rice grain yield only when it was used seed treatment and the genotypes Serra Dourada (from 1,239 to 2,178 kg ha-1), Sertaneja (from 1,510 to 2,379 kg ha-1), and Cambará (from 1,877 to 2,831 kg ha-1). On the other hand, under NTS, increasing soil compaction pressure on the sowing furrow allowed for an increased rice grain yield of Serra Dourada (from 1,553 to 2,347 kg ha-1), Esmeralda (from 723 to 1,643 kg ha-1), AB072044 (from 523 to 2,040 kg ha-1), and Cambará (from 1,243 to 2,032 kg ha-1) without seed treatment and Sertaneja (from 1,385 to 2,167 kg ha-1) and AB072044 (from 1,579 to 2,356 kg ha-1) with seed treatment. In CT the most productive genotypes were AB062008 (2,714 kg ha-1) and BRSMG Caravera (2,479 kg ha-1), while at NTS were the genotypes: BRSGO Serra Dourada (2,118 kg ha-1), AB072047 (1,888 kg ha-1), AB062008 (1,823 kg ha-1), BRSMG Caravera (1,737 kg ha-1), Cambará (1,716 kg ha-1), AB072044 (1,625 kg ha-1), BRS Esmeralda (1,604 kg ha-1), and BRS Pepita (1,516 kg ha-1).