Changes in δ15N in a soil–plant system under different biochar feedstocks and application rates

The application of biochar in soils has been hypothesised to improve soil quality whilst enhancing carbon (C) sequestration. However, its effect on nitrogen (N) dynamics in the soil–plant system is still not fully understood. In the present work, N isotope composition (δ¹⁵N) was used to facilitate the understanding of the processes involved in the N cycling when biochar is applied. We evaluated, through a wheat pot trial, the effect of different application rates of two types of biochar produced from jarrah and pine woodchips on the wheat biomass at harvest and on the soil and plant C and N contents and δ¹⁵N. In addition, the potential benefit of using nutrient-saturated biochar for the soil–plant system was also investigated. Whilst biochar produced from different feedstocks had similar effects on soil and plant nutrient contents, they induced differences in wheat grain biomass and plant δ¹⁵N. The effect of the biochar application rate was more pronounced, and at rates higher than 29 t ha^?1, the application of biochar decreased grain biomass by up to 39 % and potentially increased N losses. Isotopic analyses indicated that this acceleration of N dynamics had probably occurred before the stage of wheat grain formation. The application of nutrient-enriched biochar resulted in an improved wheat grain production, most likely due to the enhanced nutrient availability, and in reduced N cycling rates in the plant–soil system, which could offset the competition between biochar and plants for nutrients and could decrease adverse environmental impacts due to N losses.     

Tomato yield and water use efficiency – coupling effects between growth stage specific soil water deficits

To investigate the sensitivity of tomato yield and water use efficiency (WUE) to soil water content at different growth stages, the central composite rotatable design (CCRD) was employed in a five-factor-five-level pot experiment under regulated deficit irrigation. Two regression models concerning the effects of stage-specific soil water content on tomato yield and WUE were established. The results showed that the lowest available soil water (ASW) content (around 28%) during vegetative growth stage (here denoted θ₁) resulted in high yield and WUE. Moderate (around 69% ASW) during blooming and fruit setting stage (θ₂), and the highest ASW (around 92%) during early fruit growth stage (θ₃), fruit development (θ₄) and fruit maturity (θ₅) contributed positively to tomato yield, whereas high WUE was achieved at lower θ₂ and θ₃ ( around 44% ASW) and higher θ₄ and θ₅ (around 76% ASW). The strongest coupling effects of ASW in two growth stages were between θ₂ and θ₅, θ₃. In both cases a moderate θ₂ was a precondition for maximum yield response to increasing θ₅ and θ₃. Sensitivity analysis revealed that yield was most sensitive to soil water content at fruit maturity (θ₅). Numerical inspection of the regression model showed that the maximum yield, 1166 g per plant, was obtained by the combination of θ₁ (c. 28% ASW), θ₂ (c. 82% ASW), θ₃ (c. 92% ASW), θ₄ (c. 92% ASW), and θ₅ (c. 92% ASW). This result may guide irrigation scheduling to achieve higher tomato yield and WUE based on specific soil water contents at different growth stages.     

Carbon,nitrogen, and gaseous profiles in a humid,temperate region,maize field soil under no‐tillage

Abstract

The effect of four consecutive years of tillage method [conventional tillage (CT) or no‐tillage (NT)] and fertilizer N rate (84, 168, 336 kg N·ha^‐1·yr) on soil carbon, nitrogen and and gaseous profiles was examined in a Wharton‐Cookport (Aquic Hapludults‐Aquic Fragiudults) silt loam soil in West Virginia cropped to continuous maize (Zea mays L.). At midseason (July) of the last cropping year, soil mineral N profile differences were generally discernible only at the high N (336 kg·ha^‐1) rate in the topsoil (0‐ to 30‐cm layer). Ammonium (NH₄ ⁺‐N) levels at this time were significantly (p ≤ 0.05) higher under CT, while NO₃ ^‐‐N levels were the same under both tillage methods. However, after silage harvest in September NH₄ ⁺‐N levels were the same under both tillage systems, while NO₃ ^‐‐N levels were significantly higher under CT. Although no significant (p ≥ 0.05) tillage effects were found for TC, the level was increased by ～16% under NT in the surface soil (0 to 15‐cm) layer at the low N (84 kg·ha^‐1) rate treatment. Total N (TN) was significantly (p ≤ 0.05) increased under NT compared to CT only in the soil surface layer at the high N rate treatment. Soils under both tillage methods after cropping appeared to be equally well aerated to the deepest layer (60 cm) as O₂ levels were near atmospheric concentrations, and no gases commonly associated with more anaerobic environments (CH₄, C₂H₄) were detected. Carbon dioxide (CO₂) levels increased 30‐ to 40‐times atmospheric levels in the deepest layers, and were generally higher under NT. The incidence of detectable N₂O (‐0.36 × 10 ^‐2μg·ml^‐1) was two‐ to seven‐times more numerous at the high N rate, and twice as numerous under NT compared to CT. These results generally corroborate previous results for soil mineral N changes as related to tillage method, but not for organic C, N and microbial activity, as has usually been reported, especially for more arid region soils.     

Application rate and composting method affect the immediate and residual manure fertilizer value in a maize–rice–rice–maize cropping sequence on a degraded soil in northern Vietnam

A field experiment was carried out in northern Vietnam to investigate the effects of adding different additives [rice (Oriza sativa L.) straw only, or rice straw with added lime, superphosphate (SSP), urea or a mixture of selected microorganism species] on nitrogen (N) losses and nutrient concentrations in manure composts. The composts and fresh manure were applied to a three-crop per year sequence (maize–rice–rice) on a degraded soil (Plinthic Acrisol/Plinthaquult) to investigate the effects of manure type on crop yield, N uptake and fertilizer value. Total N losses during composting with SSP were 20% of initial total N, while with other additives they were 30–35%. With SSP as a compost additive, 65–85% of the initial ammonium-N (NH₄-N) in the manure remained in the compost compared with 25% for microorganisms and 30% for lime. Nitrogen uptake efficiency (NUE) of fresh manure was lower than that of composted manure when applied to maize (Zea mays L.), but higher when applied to rice (Oriza sativa L.). The NUE of compost with SSP was generally higher than that of compost with straw only and lime. The mineral fertilizer equivalent (MFE) of manure types for maize decreased in the order: manure composted with SSP?>?manure composted with straw only and fresh manure?>?manure composted with lime. For rice, the corresponding order was: fresh manure?>?manure composted with SSP/microorganisms/urea?>?manure composted with lime/with straw alone. The MFE was higher when 5 tons manure ha^?1 were applied than when 10 tons manure ha^?1 were applied throughout the crop sequence. The residual effect of composted manures (determined in a fourth crop, with no manure applied) was generally 50% higher than that of fresh manure after one year of manure and compost application. Thus, addition of SSP during composting improved the field fertilizer value of composted pig manure the most.     

Coupled effects of biochar use and farming practice on physical properties of a salt-affected soil with wheat–maize rotation

Purpose

Being carbon-rich and porous, biochar has the potential to improve soil physical properties, so does conventional farming practice. Here, a field trial was conducted to investigate the combined effects of biochar use and farming practice on the physical properties of a salt-affected compact soil for wheat–maize rotation in the Yellow River Delta region.

Materials and methods

Salix fragilis L. was used as feedstock to produce biochar in the field via aerobic carbonization at an average temperature of 502 °C, terminated by a water mist spray, for use as a soil amendment at 0, 1, 2, and 4 g kg^?1 doses (CK, T1, T2, and T3, respectively). Farming practices included rotary tillage/straw returning for wheat sowing, spring irrigation, no-tillage seeding of maize, and autumn irrigation. Both cutting ring and composite samples of the soil were collected at four stages of wheat–maize rotation (22, 238, 321, and 382 d after the benchmark date of land preparation for wheat sowing) for the determination of soil properties by established methods.

Results and discussion

Rotary tillage/straw returning reduced soil bulk density (BD) from 1.48 to 1.27 g cm^?3 (CK) and 1.14 g cm^?3 (T3) and increased saturated hydraulic conductivity (Ks) from 0.05?×?10^?5 to 0.75?× 10^?5 cm s^?1 (CK) and 1.25?× 10^?5 cm s^?1 (T3). This tillage effect on BD and Ks gradually disappeared due to the disturbance from the subsequent farming practice. Biochar use lessened the disturbance. At maize harvest, BD was 1.47 (CK) vs. 1.34 g cm^?3 (T3), and Ks was 0.06?×?10^?5 (CK) vs. 0.28?×?10^?5 cm s^?1(T3); in comparison with CK, T3 increased Na⁺ leaching by 65%, Cl^? leaching by 98%, organic carbon content by 40.3%, and water-stable aggregates (0.25–2 mm) by 38%, indicating an improvement in soil properties.

Conclusions

Biochar use and rotary tillage improved soil physical properties (BD, Ks) and favored soil aeration, water filtration, and salt leaching, which further helped the accumulation of soil organic carbon, the formation of water-stable aggregates, and the amelioration of salt-affected compact soil.

     

Amelioration of saline–sodic soil with gypsum can increase yield and nitrogen use efficiency in rice–wheat cropping system

A 2-year field experiment was conducted to determine crop yield and N use efficiency (NUE) from a saline–sodic soil (clay loam) with and without application of gypsum. Treatments included two N application rates (15% and 30%) higher than the recommended one to the normal soil, and gypsum added at 50% and 100% of soil gypsum requirement (SGR) to the saline–sodic soil, both cultivated with rice and wheat during 2011–2013. Results revealed a decrease in pH of saturated soil paste (pH_s), electrical conductivity of saturation extract (EC_e), sodium adsorption ratio (SAR) and exchangeable sodium percentage with N fertilizer along with gypsum application in saline–sodic soil. However, the effect was most prominent when gypsum was added at 50% of SGR. Crop yield and NUE remained significantly lower (p < 0.05) in saline–sodic-soils as compared to normal soil. However, gypsum application reduced this difference from 47% to 17% since both yield and NUE increased considerably. Crop yield and NUE remained higher for wheat than for rice. During first year, higher doses of N with gypsum application at 50% SGR proved most effective, whereas, in subsequent year, recommended N along with gypsum at 50% SGR became more profitable. All these results lead us to conclude that gypsum application can ameliorate saline–sodic soil thereby increasing crop yield and NUE.     

Is sewage sludge a valuable fertilizer? A soil microbiome and resistome study under field conditions

Journal of Soils and Sediments - Sewage sludge land application is strongly recommended to improve soil quality and fertility despite the presence of pollutants, pathogens and antibiotic resistance...     

Nitrogen accumulation efficiency: Relationship between excess fertilizer and soil‐plant biological activity in winter wheat

The point at which nitrogen (N) applied approaches 100% recovery in the soil once plant and microbial sinks have been saturated has not been determined in winter wheat (Triticum aestivum L.) production systems. In dryland winter wheat, subsoil accumulation has not been found to occur until N rates exceed that required for maximum yield. Many conventional N rate experiments have not properly evaluated subsoil N accumulation due to the lack of equally spaced N rates at the high end of the spectrum over which accumulation is expected to occur. Therefore, the objectives of this study were to (i) determine when soil profile accumulation efficiencies reach 100% in continuous winter wheat production and (ii) to evaluate the potential for nitrate‐nitrogen (NO₃ ^‐N) leaching in continuous winter wheat when extremely high rates of fertilizer N are used. Two field experiments (T505 and T222) were conducted for two years using ten N rates (preplant‐incorporated) ranging from 0 to 5376 kg N ha¹. No additional preplant fertilizer was applied in the second year. Following the first and second year wheat harvest, soil cores were taken to 2.4 m and bulk density, ammonium‐nitrogen (NH₄‐N) and NO₃‐N were determined. Crop N‐use efficiency (NUE) (N uptake treated ‐ N uptake check/rate applied) and soil profile inorganic N accumulation efficiencies (NAE) [net inorganic N accumulation in the soil profile/(fertilizer applied ‐ net N removed in the crop)] changed with fertilizer rate and were inversely related. Priming (increased net mineralization of organic N pools when low rates of fertilizer N are applied) may have occurred since increased NUE was observed at low N rates. The highest N‐accumulation efficiencies were at N rates of 168 and 448 kg ha^‐1 in experiments T505 and T222, respectively. At both T222 and T505, no subsoil accumulation of NH₄‐N or NO₃‐N beyond 100 cm was observed for any of the N treatments when compared to the 0‐N check, even when N rates exceeded 448 kg ha^‐1.     

Soil microbial communities and enzyme activities in a reclaimed coastal soil chronosequence under rice–barley cropping

Purpose

A field experiment with a reclamation chronosequence under rice?Cbarley cropping was conducted to investigate soil enzyme activities and microbiology in a coastal saline soil. The aim of this study was to test whether changes in enzyme activity and microbial community structure are directly impacted by changes in soil pH, electrical conductivity (EC), and organic carbon (SOC) due to reclamation.

Materials and methods

The research area is located in south-eastern China. Four experimental sites were reclaimed in 1976, 1984, 1996, and 2006, respectively, and each site was divided into three plots, each of which was 22?m?×?10?m. Each year, the plots were planted with rice (cv Xiushui) in summer and barley (cv Yanmai) in winter. Soil pH and EC were determined in an aqueous suspension with a 1:5 ratio of soil and water. Soil organic carbon content was measured by dichromate oxidation with heating. Measured soil enzyme activities included catalase, urease, and protease. Soil microbial community structures were assessed using denaturing gradient gel electrophoresis.

Results and discussion

Reclamation under rice?Cbarley cropping reduced EC and pH, but increased SOC, the activities of catalase, urease and protease, and the cell numbers of bacteria, actinomycetes, and fungi, resulting in an increase in the bacterial community diversity. The enzyme activities and bacterial community diversity were significantly positively correlated with SOC, and negatively correlated with pH and EC. Five bacterial groups related to Gaetbulibacter, Sporosarcina, Flavobacterium, Aequorivita, and Gillisia, which have been associated with saline waters, did not appear in the soils that had been reclaimed prior to 1996.

Conclusions

Results of this field study suggest that soil properties which affect microbial activity such as EC, pH, and SOC significantly influence the activities of catalase, urease, and protease, and microbial community composition. More than 10?years after reclamation under rice?Cbarley cropping, EC had decreased and bacteria typically found in marine and saline environments had disappeared from the soil.     

Biochar use in a legume–rice rotation system: effects on soil fertility and crop performance

The aim of this study was to determine whether by applying biochar, it is possible to augment the beneficial effects of legume–crop rotation systems on soil fertility and crop performance. Repeated experiments were established in 2012 and 2013 in South-western Benin using a split-split plot design. Two legumes, Mucuna pruriens (mucuna) and Vigna unguiculata (cowpea), were planted for 42 days on biochar-amended and unamended plots and subsequently cut and applied as mulch 5 days before planting rice. Rice plants were either fertilized or not using a fertilizer rate of 60, 30, and 30 kg ha^?1 of N, P₂O₅, and K₂O, respectively. The results showed that the application of legume green manures and fertilizer, either singly or in combination, improved soil nutrient availability, CEC, shoot yield, and grain yield of rice on both biochar-amended and unamended plots. However, the effect was significantly (p < 0.05) greater on biochar-amended plots. The mean grain yield for all cropping seasons was 1.8 t ha^?1 for biochar-amended plots and 1.3 t ha^?1 for unamended plots. The greater grain yield of rice on biochar-amended plots was associated with improved soil fertility and increased N uptake.     

Interelemental relationships in the soil and plant tissue and photosynthesis of field‐cultivated wheat growing in naturally enriched copper soils

Several interelemental relationships have been examined in field‐cultivated wheat (Triticum aestivum L. cv Vergina) growing on naturally enriched copper (Cu) soils. Mean soil Cu concentration per site ranged from 103–394 μg.g^‐1 dry weight (DW). Interrelationships between Cu, iron (Fe), calcium (Ca), potassium (K), zinc (Zn), lead (Pb), and magnesium (Mg) concentrations in the soil and plant tissue (roots, stems, and leaves) were examined using Principle Components Analysis. Soil samples were clustered according to collection site and were primarily differentiated according to their Cu concentrations. Soil Cu concentrations were positively correlated with Zn, Ca, Fe, and K in the soil, with Cu, K, and Ca in the roots, and Cu and Fe in the leaves and negatively correlated with Fe in the roots. The increase in Cu in the roots and leaves was positively correlated with increases in K and Ca in the roots and Fe and Ca in the leaves, but negatively with Fe in the roots. Increases in leaf Ca concentrations were correlated with increases in Mg and decreases in Zn concentrations in the leaf. Plants growing in soil with high Cu concentration exhibited toxicity symptoms with reduced height, decreased total leaf area and lower chlorophyll concentrations. Photosynthesis expressed per unit leaf area was not affected by increasing Cu concentrations in the soil or plant tissue.     

Freeze–thaw cycle amplitude and freezing rate effects on extractable nitrogen in a temperate old field soil

Freeze–thaw cycles can promote soil N losses as a result of microbial and root cell lysis; however, minimal freeze–thaw effects have typically been observed in studies that have imposed moderate temperature cycles. We conducted laboratory incubations on surface soil (top 3 cm) collected in a temperate old field from late fall through mid-winter to examine how variation in freeze–thaw amplitude, number, timing of collection, and freezing rate altered soil extractable N. We varied freeze–thaw amplitude by imposing minimum cycle temperatures of 0, −1, −2, −5, and −10°C for a series of either one or two cycles and held control samples constant at 3°C. We also examined the effects of freezing rates of 1, 3, and 30°C h⁻¹. We hypothesized that extractable N would be highest for both the maximum freezing amplitudes and rates. While multiple freeze–thaw cycles at −10°C and freeze–thaw cycles associated with artificially high freezing rates increased extractable N, freeze–thaw cycles representative of field conditions at our site had no effect on extractable N in late fall and early winter. By mid-winter there was a significant freeze–thaw cycle effect but, contrary to our prediction, less N was extracted from freeze–thaw treated samples than from the control samples, which remained thawed over the treatment period. Increased extractable N in control samples was driven by increased organic N rather than increased inorganic N. Our results suggest that freeze–thaw damage to soil organisms does not contribute substantially to N release in our system. Instead, soil extractable N may increase during mid-winter thaws as a result of increased soil proteolytic activity above freezing temperatures.     

Mobile Si-rich compounds in the soil–plant system and methods for their determination

Different aspects of Si biogeochemistry in the soil have been reviewed. Interaction mechanisms of monosilicic acid with aluminum, phosphorus, and heavy metal compounds have been generalized. Polysilicic acids are chemically inert substances, but they participate in the formation of soil structure. Organosilicon compounds in the soil are very little investigated. From literature and our own data, the cycle of mobile Si forms in the soil–microorganism–plant system has been suggested, which shows the main fluxes of soluble Si migration and transformation. A new classification of the Si compounds based on their physicochemical and biological activities in the soil has been suggested as well as a method for the determination of mono- and polysilicic acids in the soil matrix.     

Impact of organic and inorganic nutrition on soil–plant nutrient balance in arecanut (Areca catechu L.) on a laterite soil

The study assessed the impact of continuous application of vermicompost and chemical fertilizers nitrogen, phosphorus and potassium (NPK) on arecanut in India. Key parameters examined were biomass production, nutrient uptake, yield, soil fertility and net benefit. Pooled analysis of 8-year data revealed that nutrient application registered significantly higher yield (2585–3331 kg ha^?1) than no nutrition (1827 kg ha^?1). Yields in organic nutrition were around 85% of the yields obtained in inorganic NPK. The concentrations of leaf N and K were significantly higher with NPK than with vermicompost. Vermicompost significantly increased soil organic carbon and the availability of calcium (Ca), magnesium (Mg), manganese (Mn) and copper (Cu), but reduced exchangeable K in soil. The total uptake of K and Ca together contributed positively to 75% variability in total biomass production. Nutrient removal of iron (Fe), P, K and Cu positively influenced the yield with about 81% variability. Biomass partitioning and nutrient uptake pattern are important for fertilization program of arecanut.     

The effects of biochar and hoggery biogas slurry on fluvo-aquic soil physical and hydraulic properties: a field study of four consecutive wheat–maize rotations

Purpose

The degeneration of fluvo-aquic soils due to long-term excessive fertilization is increasing in the Huang-Huai-Hai Plain, China. Products from crop straw and livestock breeding wastewater, biochar, and biogas slurry provide safe and efficient biomass resources for soil quality improvement. We assumed that biochar and biogas slurry could improve soil structure and soil water retention capacity for their special characteristics. The present study aimed to compare the effects of biochar and hoggery biogas slurry treatments on improvements to soil physical properties and water-holding capacity, and their different driving mechanisms.

Materials and methods

This study was based on a field experiment of four consecutive winter wheat–summer maize rotations on the Huang-Huai-Hai Plain, China. Using the principle of equal nitrogen inputs, three treatments were conducted: conventional farming fertilizers, biochar, and hoggery biogas slurry. The differences in indicators such as soil bulk density, total porosity, aggregate structure, saturated hydraulic conductivity, and hydraulic property parameters between different treatments were compared and analyzed. The driving factors generating these differences were also discussed.

Results and discussion

Compared to conventional fertilization, soil bulk density decreased under biochar and hoggery biogas slurry treatments, whereas soil total porosity increased after hoggery biogas slurry treatment. In the 0–20-cm soil layer, biochar treatment increased the content of >2-mm macrosoil aggregates and hoggery biogas slurry treatment increased the content of 0.25–0.5 or 1–2-mm soil aggregates. The soil saturated hydraulic conductivity in the 0–20-cm soil layer did not change significantly with biochar application, but increased with hoggery biogas slurry treatment. The application of biochar and hoggery biogas slurry improved the water-holding capacity, increasing the field capacity by 15.34 and 13.83 %, and the available water content by 16.20 and 25.87 %, respectively, in the 0–20-cm soil layer.

Conclusions

Both biochar and hoggery biogas slurry treatments significantly improved soil structure and water-holding capacity. Biogas slurry treatment significantly increased soil saturated hydraulic conductivity, soil aggregate content, while biochar treatment significantly decreased bulk density and increased total porosity of the soil.

     

Transformation of soil and plant cover contaminated with oil and salt water in the middle Ob’ river basin

Changes in the soil and plant cover caused by contamination with oil and salt water in the middle Ob’ river region were estimated using geoinformatic and geostatistic approaches. The largest technogenically salinized areas include oligotrophic peat soils due to the extensive spill of highly saline waters on the flat bog surface and eutrophic soils located in lower topographic positions. The natural self-purification of salinized mineral forest soils proceeds within 1–2 years after the spill. The dominant species of secondary plant communities were detected. Correlations were revealed between the residual oil and chloride contents and the total projective plant cover.     

Evaluation of wheat and maize evapotranspiration determination by direct use of the Penman–Monteith equation in a semi-arid region

The Penman–Monteith (PM) equation was introduced as one of the most reliable equations to determine crop ET_c, without using crop coefficient or ET_o values. In this study, the PM equation was evaluated using lysimeters in a semi-arid region for wheat and maize. Different equations for aerodynamic resistance (r _a) and canopy resistance (r _c) were tested in the PM equation and they were ranked using statistical analysis. It was shown that the combined method of r _a and r _c in FAO-56 does not lead to a good prediction of ET_c for wheat and maize in comparison with the lysimeter-measured data. The results indicated that a modified equation for r _c was the most accurate method for both wheat and maize. Using this equation, the suggested model of FAO-56 and another investigation for r _a led to the best results for wheat and maize, respectively. Furthermore, it was shown that the previously modified equation for r _c was newly modified as a function of vapor pressure deficit (VPD) and the results were as accurate as before. Therefore, an equation as a function of VPD can be used when solar radiation (R _n) is not available easily.     

Seasonal levels of water‐extractable cations and anions in soil under blight‐affected and healthy citrus trees

Abstract

Soil samples were collected under blight‐affected and healthy citrus trees at 30‐day intervals for 24 months, at 20‐to 50‐cm depth. Analyses of water extracts (1:1 soil: water) for K, Ca, Mg, Na, SO₄, and Cl showed few differences in cations, but lower anion levels under blighted trees. The cation/anion ratio was significantly higher under blight‐affected trees. Samples collected once at different locations in the same time period showed the same differences. In one location, K was lower and Na higher under healthy trees than under blight‐affected trees, in others K was higher too.     

Bioremediation of a polycyclic aromatic hydrocarbon–contaminated urban soil: degradation dynamics and phytotransformation pathways

Journal of Soils and Sediments - Bioremediation experiments of polycyclic aromatic hydrocarbon (PAHs) using ryegrass (Lolium perenne), a turfgrass in urban landscapes, were carried out aiming to...