Soil Column Experiments Research Articles

Buried layers change soil water flow and solute transport from the Yellow River Delta, China

For the limitation of techniques on the saline soil improvement, the effect of a new method with some effective materials on saline soil improvement was studied by soil column experiment. Biochar and wood fibre were used as a buried layer to identify their effects on the saline soil reclamation. Soil samples were packed in each column (height, 130 cm; diameter, 20 cm). A tape measure (length, 100 cm) was fixed vertically to the outer wall of each soil column; it was used to record the location of the wetting front during infiltration. Biochar and wood fibre were inserted at depths of either 30 cm or 50 cm (thickness in each treatment, 2 cm). Soil columns were irrigated once with 15 L of brackish water (2 g/L). Soil water content and salt content were measured with a TRIME-PICO sensor at the 25, 60 and 100 cm layers, and Mariotte’s bottle was used at the 100-cm layer to measure the underground water level. Wood fibre and biochar used as the buried layer was found that they caused a breakdown in the continuity of capillary movement and salt reduction. Wood fibre and biochar were able to retard the rate of water infiltration at 0–30-cm depth, for high water potential created when the buried layer contained sufficient water; it improved the more water infiltration than evaporation. Thus, it could serve to increase the salt leaching efficiency during the longer time scales of soil water infiltration; results showed that the buried layer was at 30-cm depth; the desalting rates were 3.69% (biochar) and 29.38% (wood fibre); the desalting rates were 4.76% (biochar) and 17.07% (wood fibre) when buried layer at 50 cm. And, the better performance in soil water infiltration and salt reduction was caused by a higher pore width, abundant fibrous tissue and saturation moisture content (Ɵs). The buried layer can improve the soil water infiltration process, especially when the wood fibre layer was at 30 cm. Both biochar and wood fibre layers could limit salt accumulation in surface soil, indicating that the continuity of capillary movement was broken after embedding the interlayer; wood fibre was superior to biochar in this regard. This study provides a new method on the saline soil improvement that could improve the mulching development, and the effect of the evaporation could be further considered by the buried layer.

Soil Texture, Sampling Depth and Root Hairs Shape the Structure of ACC Deaminase Bacterial Community Composition in Maize Rhizosphere.

Preservation of the phytostimulatory functions of plant growth-promoting bacteria relies on the adaptation of their community to the rhizosphere environment. Here, an amplicon sequencing approach was implemented to specifically target microorganisms with 1-aminocyclopropane-1-carboxylate deaminase activity, carrying the acdS gene. We stated the hypothesis that the relative phylogenetic distribution of acdS carrying microorganisms is affected by the presence or absence of root hairs, soil type, and depth. To this end, a standardized soil column experiment was conducted with maize wild type and root hair defective rth3 mutant in the substrates loam and sand, and harvest was implemented from three depths. Most acdS sequences (99%) were affiliated to Actinobacteria and Proteobacteria, and the strongest influence on the relative abundances of sequences were exerted by the substrate. Variovorax, Acidovorax, and Ralstonia sequences dominated in loam, whereas Streptomyces and Agromyces were more abundant in sand. Soil depth caused strong variations in acdS sequence distribution, with differential levels in the relative abundances of acdS sequences affiliated to Tetrasphaera, Amycolatopsis, and Streptomyces in loam, but Burkholderia, Paraburkholderia, and Variovorax in sand. Maize genotype influenced the distribution of acdS sequences mainly in loam and only in the uppermost depth. Variovorax acdS sequences were more abundant in WT, but Streptomyces, Microbacterium, and Modestobacter in rth3 rhizosphere. Substrate and soil depth were strong and plant genotype a further significant single and interacting drivers of acdS carrying microbial community composition in the rhizosphere of maize. This suggests that maize rhizosphere acdS carrying bacterial community establishes according to the environmental constraints, and that root hairs possess a minor but significant impact on acdS carrying bacterial populations.

Effect of biofertilizer and wheat straw biochar application on nitrous oxide emission and ammonia volatilization from paddy soil.

Biofertilizer can improve soil quality, especially the microbiome composition, which potentially affect soil nitrogen (N) cycling. However, little is known about the responses of nitrous oxide (N2O) emission and ammonia (NH3) volatilization from biochar-amended paddy soil to the biofertilizer application. Therefore, we conducted a soil column experiment using four 240kgN ha-1 (equivalent to 1.7gN pot-1) treatments consisting of biofertilizer (3tha-1, equivalent to 21.2g pot-1), biochar (7.5tha-1, equivalent to 63.6g pot-1), and a mixture of biofertilizer and biochar at the same rate and a control (CK). The results showed that the N2O emissions and NH3 volatilizations were equivalent to 0.15-0.28% and 18.0-31.5% of rice seasonal N applied to the four treatments, respectively. Two treatments with biofertilizer and biochar individual amendment significantly increased (P<0.05) the N2O emissions to same degree by 30.2%, while co-application of biochar and biofertilizer further increased the N2O emission by 74.4% compared to the control. The higher N2O emission was likely attributed to the increased gene copies of AOA, nirK, and nirS. Applying biofertilizer significantly increased (P<0.05) NH3 volatilization by 24.7% relative to the control, while applying biochar had no influence on NH3 volatilization. Co-application of biofertilizer and biochar significantly decreased (P<0.05) NH3 volatilization by 12.3% compared to the control. Overall, the net global warming potential based on NH3 and N2O in current study increased by 13.0-26.0% in both the individual- and co-application of biofertilizer and biochar. Interestingly, both individual- and co-applications of biofertilizer and biochar increased the rice grain yield by 16.5-38.3%. Therefore, applications of biofertilizer and biochar did not increase the GHGI. Particularly, the co-applying of them significantly lowered (P<0.05) the GHGI by 15.2%. In conclusion, biofertilizer and biochar should be co-applied to achieve the goals of environment protection and food security.

Effects of influent concentration and different valence cations on solute preferential transport in inter-tidal zone of Yellow River Estuary

The migration of land-based pollutants in tidal flat sediments has an important impact on the marine ecological environment. The effects of three influent concentrations and two cation valence states on the preferential transport of NO3-N in the sediments of the Yellow River Estuary were studied by soil column experiments. Results showed that the preferential flow and solute transport were more obvious with the increase of influent concentration; The solute potential was increased in the process of solute transport, which led to the rapid flow, shortened the total time, and facilitated the solute transport speed in the soil; The cation in the sediment of the Yellow River Estuary has little effect on the transport of nitrate nitrogen, and the initial penetration time of the penetration curve using Ca (NO3)2 as tracer was a little later than that using KNO3 as tracer, but it is not obvious.

Investigating the remediation potential of iron oxide nanoparticles in Cu-polluted soil-plant systems: coupled geochemical, geophysical and biological approaches.

Although the use of iron oxide nanoparticles (IONPs) has high potential in remediation and agriculture, a major hindrance to their use includes the risk of contamination of soil and water resources with underexplored effects of IONPs on biota. The fate, phytotoxicity and remediation potential of IONPs are investigated with soil column experiments using 7 nm-sized magnetite (Fe3O4) nanoparticles (magnNPs) and sunflower (Helianthus annuus). Control soil, magnNP-containing soil (10 g magnNPs per kg soil), copper-polluted soil (500 mg Cu per kg soil) and copper-polluted soil containing magnNPs (10 g magnNPs per kg soil and 500 mg Cu per kg soil) support sunflower growth for 57 and 95 days. In magnNP-exposed plants, the occurrence of magnNPs does not affect the growth of the vegetative aerial parts and photosynthetic efficiency. Decreased lipid peroxidation indicates an enhanced antioxidant enzymatic response of magnNP-exposed plants. In plants grown in Cu- and magnNP–Cu-soils, the physiological and biochemical impacts of excess copper are clearly identified, resulting in growth retardation, decreased pigment contents and photosynthetic efficiency, and increased lipid peroxidation and peroxidase (POD) activities. Based on magnetic susceptibility, a higher amount of magnNPs is detected after 57 days in the roots of magnNP-exposed plants (1400 mg kg−1) than in the roots of magnNP–Cu-exposed plants (920 mg kg−1). In the latter, magnNP internalization is likely hampered because of the plants' physiological responses to Cu toxicity. At the working Cu and magnNP concentrations, magnNPs neither decrease Cu accumulation in the plant tissues nor alleviate the overall growth retardation of sunflowers and certain phytotoxic effects induced by excess Cu. However, this study highlights several positive environmental aspects relative to magnNP use, including the harmless effects of magnNPs on sunflowers (1% magnNPs in soil) and the ability of magnNPs to influence Cu mobility in the soil (which could be even more pronounced at lower Cu concentration).

Effects of bio-subsoilers on subsoil pore-system functionality: Case study with intact soil columns

Field traffic-induced subsoil compaction poses an escalating problem in relation to key soil functions because of the use of increasingly heavier machinery. Natural recovery from subsoil compaction is slow and therefore there is a need for measures such as bio-subsoilers to stimulate the recovery. This study thus investigated the influence of potential bio-subsoilers on pore functionality and morphology of a sandy loam soil, with an emphasis on the transition between the topsoil and compacted subsoil and on the compacted subsoil per se, in an intact soil column experiment. The control crop was spring barley, and potential bio-subsoilers included chicory, lucerne, fodder radish, tall fescue and kernza. The intact soil columns (Ø = 0.20 m, h = 0.50 m) were X-ray CT-scanned prior to and two years after crop establishment. Undisturbed subsamples (246 cm3) were collected one and two years after crop establishment in five replicates at 0.10, 0.25 and 0.35-m depth from the soil columns. The laboratory measurements and derived indices showed that after one-year non-restrictive air-filled porosity (εa = 0.13 m3 m−3) and relative gas diffusivity (Ds/Do = 0.0059) was reached by lucerne in the Transition layer (0.25 m). In the second year, lucerne also showed a significantly higher εa (0.09 m3 m−3), and a non-significantly higher Ds/Do (0.0029) compared to barley in the Compacted layer (0.30 m). Pore geometry indices derived from the relationship between εa, Ds/Do and air permeability indicated the formation of less tortuous and more connected small pores (at −100 hPa matric potential) throughout the Transition and Compacted layers by chicory, lucerne and tall fescue. A significantly higher CT-number of pores < 1 mm3 was found for lucerne and a higher CT-volume of pores < 1.5 mm in diameter for lucerne and chicory in the Compacted layer. Root number density was significantly higher for chicory, lucerne and tall fescue compared to barley from the first year, and also for kernza from the second year. Lucerne had the greatest subsoil compaction mitigation potential in our experiment in intact columns. Further studies in real field situations are needed.

Preparing and characterizing repacked columns for experiments in biochar-amended soils

Laboratory soil column experiments have been frequently performed for investigating various soil-related processes. In recent years, the demand for using biochar as a soil amendment for environmental and agricultural purposes has increased significantly. To assess the beneficial impacts of biochar, laboratory column experiments may be conducted using repacked biochar-amended soil before large-scale biochar application. Biochar is a porous material that might have transient hydrophobicity, and particle density, size, and shape that often differ from native soil. These factors might cause several experimental problems in repacked laboratory columns, including unrealistic hydraulic and solute transport and transformation measurements, spatial variation of biochar content, and error in estimating the repacked biochar-amended soil properties. Therefore, it is necessary to modify standard repacked column packing procedures for biochar-amended soil. In this work, several modifications are described for preparing repacked biochar-amended soils. The modifications are rinsing and oven-drying biochar, determining the optimum moisture content to achieve a homogenous mixture, determining the desired bulk density before column packing, and mixing and packing under wet conditions. In addition, repacked columns should be characterized by their inter, intra, and total porosities and pore volume after column packing.•Steps are recommended prior to packing the repacked biochar-amended soil columns: rinsing biochar and pre-determining optimum moisture content and bulk density.•Columns are wet-packed in subsections at the optimum moisture content to the desired bulk density. Following packing, the inter, intra, and total porosities and pore volume should be determined.•These steps will reduce unrealistic transient results, inhibit nonuniform packing and heterogeneity of biochar content, and provide important information for interpreting the performance of biochar-amended media.

Mobility of contaminants of emerging concern in soil column experiments

In this study, laboratory column experiments under water saturated conditions were conducted for over 35 days to investigate the transport of nine pharmaceuticals (nadolol, sulfamethizole, sulfamethoxazole, sulfamethoxypyridazine, carbamazepine, ibuprofen, diclofenac, hydrochlorothiazide, and gemfibrozil) and four artificial sweeteners (acesulfame, saccharin, cyclamate, and sucralose) in two soils (S and C) with similar organic carbon content (between 0.8 and 1.1%) and pH (7.90 and 7.25) but different texture (58.3 and 85.5% of silt+clay, respectively). Ibuprofen and artificial sweeteners reached maximum concentrations at the outlet of the columns and showed a homogenous vertical profile in the aqueous phase, with the same concentration in all sampling ports under flow percolation conditions. Regarding carbamazepine and hydrochlorothiazide, apparent retardation was observed for both and was attributed to sorption. Nadolol, a positively charged beta-blocker, did not show any apparent breakthrough. After 35 days, the columns were washed using tap water for over one week. Soils were then analyzed at different depths and vertical concentration profiles were plotted. Overall, highest concentrations were measured in the top most layers for contaminants in the soil column with higher clay content (C), whereas vertical profiles were more uniform in that with lower clay content (S).

Effects of Modified Biowaste-based Hydrochar on Rice Yield and Nitrogen Uptake

Biochar application on farmlands is an efficient way to realize agricultural/forestry biowaste recycling in parallel with carbon sequestration. Recently, hydrochar produced by hydrothermal carbonization processes has attracted attention due to the advantages over conventional pyrolytic production (i.e., easier production process, higher carbon yield, reduced energy consumption, and lower flue gas emissions). To clarify the effects of hydrochar applied in farmlands on crop production, as well as to realize the recycling of agricultural/forestry biowaste resources, this study evaluated the effects of four types of modified-hydrochar addition on rice yield and nitrogen uptake in two typical soils and the possible influencing factors through soil-column experiments and material characterization. The results showed that sawdust hydrochar and/or straw hydrochar could increase rice yield and nitrogen uptake, as well as reduce N loss, in both treated soils after physical or biological modification, an effect that was independent of the application rate (5‰, 15‰; mass fraction). In comparison to the control, the rice yield and nitrogen uptake of hydrochar-addition treatments increased by 9.2%-20.7% and 7.7%-17.0% respectively. Sawdust hydrochar, with a wider C/N material, was conducive to improving nitrogen uptake in high fertility soils; meanwhile, the nitrogen utilization in low fertility soils was less affected by the type of hydrochar due to the limitations imposed by multiple factors. The results of material characterization showed that the surface of the hydrochar was rich in nutrients; the pore structure of hydrochar after washing or biological modification was greatly improved, the relative content of C was remarkably reduced, and the relative contents of N and O notably increased, which could affect nutrient fixation and supply. Thus, the improved pore structure and increased contents of N and O of modified hydrochars may be the key drivers for the increase in rice yield and nitrogen uptake with hydrochar addition. These results suggest that modified hydrochar is beneficial to realizing agricultural/forestry biowaste recycling and improving crop yield and nitrogen utilization, as well as reducing N loss from farmlands.

Behaviour of Capillary Barrier Covers Subjected to Rainfall with Different Patterns

The behaviour of capillary barrier covers (CBCs) subjected to rainfall has been extensively studied by many researchers. However, the patterns of rainfall are seldom considered in previous studies, and therefore, the behaviour of CBCs subjected to rainfall with different patterns is still unknown. To this end, this study aims to investigate the effect of rainfall patterns on the behaviour and performance of CBCs, and identify the rainfall pattern, under which the performance of the CBC is the worst. Using a newly developed soil column test apparatus, a series of laboratory soil column experiments were conducted. The results indicated that when rainfall duration is short, the patterns of rainfall only affect the volume water content (VWC) and pore water pressure (PWP) significantly at the upper part of the column; when rainfall duration is long, the patterns of rainfall can significantly affect the VWC and PWP throughout the whole column. The percolation and breakthrough time of the CBC were also influenced by rainfall patterns; the advanced rainfall pattern produced the largest percolation, and resulted in the shortest time for CBCs to break through, whereas the delayed rainfall pattern generated the least percolation and resulted in the longest time for CBCs to break through. Based on the percolation and breakthrough time, it seems that the advanced pattern is the worst-case scenario for the CBCs subjected to rainfall. The obtained results not only imply the necessity of rainfall patterns to be involved in the study of the CBCs subjected to rainfall but they also can be helpful for the practical design of the CBCs.

Hydrochar did not reduce rice paddy NH3 volatilization compared to pyrochar in a soil column experiment

Pyrochar (PC) is always with high pH value, and improper application might increase rice paddy ammonia volatilization (PAV), which is the main nitrogen loss through air during rice production. Differently, hydrochar (HC) takes the advantages of high productive rate and always with lower pH value compared with PC. However, effect pattern and mechanism of HC on PAV are still unclear. In the present study, soil column experiments were conducted to investigate the effect of PC and HC application on PAV. In total, treatments with four types of biochar (WPC, SPC, WHC and SHC, i.e., PC and HC prepared with wheat straw and sawdust, respectively) and two application rates (0.5% and 1.5%, w/w) were set up and non-biochar application was used as control. Results showed that, application of HC with low pH value could not reduce PAV compared with PC. Total PAV increased significantly as the increase of HC application rate (especially for WHC). The increment of PAV under high rate HC application might be due to the strong buffer capacity of soil, the aging of biochar, the high nitrogen from HC. The results indicated that HC should be pretreatment before utilization in agricultural environment considering PAV reduction.

Application of earthworm cast improves soil aggregation and aggregate-associated carbon stability in typical soils from Loess Plateau

Earthworm casts exhibit remarkable fertility and have been widely used as an organic fertilizer. This study focused on the effects of earthworm cast application on soil aggregates and aggregate-associated carbon in typical soils from the Loess Plateau (China). Soil column experiments were conducted in the laboratory using cultivated loessial soil (CS), dark loessial soil (DS), and aeolian soil (AS). Application of earthworm casts significantly reduced the content of aggregates sized <0.5 mm but increased the content of water-stable aggregates. Compared to without-cast treatment, earthworm cast application increased the organic carbon content by 13.4–58.3%, 14.4–51.1%, 17.9–45.3%, 16.7–62.4%, 18.4–43.3%, and 19.8–62.9% in soil aggregate fractions of sizes <0.25, 0.25–0.5, 0.5–1, 1–2, 2–5, and >5 mm, respectively. The application of earthworm casts significantly increased heavy fraction organic carbon (HFOC), CaCO3, and exchangeable Ca contents in soil by 14.5–69.4%, 12.8–51.9%, and 33.3–63.2%, respectively. Compared with macroaggregates, microaggregates had higher CaCO3 contents but smaller light-fraction organic carbon (LFOC) to HFOC ratios, indicating that earthworm cast application improved the organic carbon stability more in microaggregates than macroaggregates. Comparison analysis of the three soils showed AS performed better in aggregation and aggregate-associated carbon stability than CS and DS after applying earthworm casts. The findings improve our understanding of the effects of earthworm cast application on soil aggregate distribution and aggregate-associated carbon stability, which will help improve the application efficiency of earthworm casts as an organic fertilizer in the Loess Plateau area.

Leaching characteristic of potentially toxic metals of artificial soil made from municipal sludge compost

Landscaping of municipal sludge is a good choice to solve the sludge disposal problem, and EDTA treatment can effectively promote the uptake of heavy metals (HMs) by plants, but the heavy metal leaching process and its main control factors are still poorly understood during the sludge landscaping disposal. In this study, the migration behavior of HMs in artificial soil made from municipal sludge compost (MSC) were investigated using soil column experiments. After six leaching events for a total of one year’s rainfall, the average reduction percentage of total phosphorus, total nitrogen, organic matter in the MSC artificial soil were 13.4%, 10.1%, and 7.8%, respectively, while those of copper, lead, zinc, cadmium, nickel were 12.9%, 8.37%, 11.5%, 5.94%, and 10.7%, respectively. Treating ethylenediaminetetraacetic acid (EDTA) to the MSC artificial soil further enhanced the leach index of HMs to different degrees. HM concentration in leachate were increased with peak times postponed. Though EDTA treatment increased HM concentrations in subsoil, it did not change their water washing efficiency. The retention of HMs in subsoil was related to properties of local soil and its interaction with leachate. The potential ecological risk was of quite strong risk category in the MSC artificial soil and rapidly decreased from moderate to slight risk in subsoil. Cadmium was the main contribution accounting for 46%–93% of ecological risk. For landscaping applications, the composition of MSC artificial soil and local soil, as well as the capacity of the surrounding water, needs to be considered.

Dynamics of localised nitrogen supply and relevance for root growth of Vicia faba (\u2018Fuego\u2019) and Hordeum vulgare (\u2018Marthe\u2019) in soil

Root growth responds to local differences in N-form and concentration. This is known for artificial systems and assumed to be valid in soil. The purpose of this study is to challenge this assumption for soil mesocosms locally supplied with urea with and without nitrification inhibitor. Soil column experiments with Vicia faba (‘Fuego’) and Hordeum vulgare (‘Marthe’) were performed to investigate soil solution chemistry and root growth response of these two species with contrasting root architectures to the different N-supply simultaneously. Root growth was analysed over time and separately for the fertiliser layer and the areas above and below with X-ray CT (via region growing) and WinRHIZO. Additionally, NO3− and NH4+ in soil and soil solution were analysed. In Vicia faba, no pronounced differences were observed, although CT analysis indicated different root soil exploration for high NH4+. In Hordeum vulgare, high NO3− inhibited lateral root growth while high NH4+ stimulated the formation of first order laterals. The growth response to locally distributed N-forms in soil is species specific and less pronounced than in artificial systems. The combination of soil solution studies and non-invasive imaging of root growth can substantially improve the mechanistic understanding of root responses to different N-forms in soil.

Win-win: Application of sawdust-derived hydrochar in low fertility soil improves rice yield and reduces greenhouse gas emissions from agricultural ecosystems

As a good soil synergist, biochar has a wide prospect in improving soil fertility and crop production. Although hydrochar, produced by hydrothermal carbonization process has attracted attention due to production advantages, hydrochar application in low fertility soils as well as its impact to the associated greenhouse gas (GHG) emissions in farmlands is rarely reported. To advance our understanding on the effect of hydrochar addition on grain yield from low fertility soils and the corresponding CH4 and N2O emissions, a soil-column experiment, with two hydrochar types (sawdust-derived hydrochar (SDH), microbial-aged hydrochar (A-SDH)) at two application rates (5‰, 15‰; (w/w)), was conducted. The results showed that hydrochar addition evidently increased rice yield. The N2O emissions were mainly related to the substrate supply of the hydrochar itself and less affected by the denitrifiers (functional genes) present. Hydrochar amendment at low application rate (5‰; SDH05, A-SDH05) significantly decreased the cumulative N2O emissions by 26.32% ~ 36.84%. Additionally, hydrochar amendment could not increase the CH4 emissions due to the substrate limitation; the cumulative emissions were similar with those from the control, ranging between 11.1–12.8 g m−2. Regarding grain yield and global warming potential, greenhouse gas intensity from the soils subjected to hydrochar (SDH05, A-SDH05, A-SDH15) were significantly lower than that of the control, observation attributed to the high yield and low N2O emissions. Overall, hydrochar addition is an effective strategy to ensure grain yield in low fertility soils with relatively low/controlled GHG emissions, especially when the amendment is applied at low application rate.

Wood vinegar and biochar co-application mitigates nitrous oxide and methane emissions from rice paddy soil: A two-year experiment

Both biochar (BC) and wood vinegar (WV) influence the nitrous oxide (N2O) and methane (CH4) emissions from agricultural systems. However, the impacts of BC and WV co-application on rice production, N2O and CH4 emissions are not well documented. We here conducted a two-year soil columns experiment with four treatments: WV (5 t WV ha−1), BC (7.5 t BC ha−1), WV + BC (5 t WV ha−1 +7.5 t BC ha−1) and a control (no treatment). The results showed that BC and WV + BC produced higher rice grain yield than the control by 14.1–15.9% in 2016 and by 4.1–5.2% in 2017, respectively. While WV increased rice grain yield by 11.2% in 2016, it had no significant influence on yield in 2017. Both WV and BC significantly mitigated N2O emissions by 22.4–41.8% in 2016 and 22.4–36.9% in 2017, respectively. Interestingly, WV + BC treatment showed the highest N2O mitigation efficiency, with a 52.9–62.8% mitigations in 2016 and 2017. Furthermore, the co-application of WV and BC significantly mitigated CH4 emissions by 42.6% in 2016 and 35.3% in 2017, respectively, while applying WV or BC alone had no annually-consistent mitigation effect on CH4 emissions. Overall, GWPt of rice growth cycle was most significantly suppressed by WV + BC with a 48.7–56.1% reduction, followed by WV and BC with 20.4–28.0% and 19.7–35.7% reductions, respectively. Consequently, the WV + BC treatment had the highest GHGI mitigation effect, averaging with 56.7% over two consecutive rice growth cycles. In conclusion, co-application of WV and BC is recommended for rice cultivation, which can both improve rice yield and minimize GHG emissions.

Responses of Amygdalus pedunculata Pall. in the sandy and loamy soils to water stress

Amygdalus pedunculata Pall. is a major species that is widely planted in afforested soils with different textures in the transitional zone between Mu Us Desert and Loess Plateau, China. However, the responses of A. pedunculata to increasing intensity of water stress in different textural soils are not clear. Here, we conducted a soil column experiment to evaluate the effects of different textures (sandy and loamy) on water consumption, water use efficiency (WUE), biomass accumulation and ecological adaptability of A. pedunculata under increasing water stress, i.e., 90% (±5%) FC (field capacity), 75% (±5%) FC, 60% (±5%) FC, 45% (±5%) FC and 30% (±5%) FC in 2018. A. pedunculata grown in the sandy soil with the lowest (30% FC) and highest (90% FC) water contents had respectively 21.3%–37.0% and 4.4%–20.4% less transpiration than those with other water treatments (45%–75% FC). In contrast, A. pedunculata transpiration in the loamy soil decreased with decreasing water content. The magnitude of decrease in transpiration increased with increasing level of water deficit (45% and 30% FC). Mean daily and cumulative transpirations of the plant were significantly lower in the sandy soil than in the loamy soil under good water condition (90% FC), but the reverse was noted under water deficit treatments (45% and 30% FC). Plant height, stem diameter and total biomass initially increased with decreasing water content from 90% to 75% FC and then declined under severe water deficit conditions (45% and 30% FC) in the sandy soil. However, these plant parameters decreased with decreasing water content in the loamy soil. WUE in the sandy soil was 7.8%–12.3% higher than that in the loamy soil, which initially increased with decreasing water content from 90% to 75% FC and then declined under water deficit conditions (45% and 30% FC). The study showed that plant transpiration, biomass production and WUE responded differentially to increasing intensity of water stress in the sandy and loamy soils. The contrasting responses of A. pedunculata to water stress in different textural soils can guide future revegetation programs in the northern region of Chinese Loess Plateau by considering plant adaptability to varying soil and water conditions.

Zinc Speciation in Organic Waste Drives Its Fate in Amended Soils.

Recycling of organic waste (OW) as fertilizer on farmland is a widespread practice that fosters sustainable development via resource reuse. However, the advantages of OW fertilization should be weighed against the potentially negative environmental impacts due to the presence of contaminants such as zinc (Zn). Current knowledge on the parameters controlling the environmental fate of Zn following OW application on cultivated soils is scant. We addressed this shortcoming by combining soil column experiments and Zn speciation characterization in OWs and amended soils. Soil column experiments were first carried out using two contrasted soils (sandy soil and sandy clay loam) that were amended with sewage sludge or poultry manure and cropped with lettuce. The soil columns were irrigated with identical amounts of water twice a week, and the leachates collected at the column outlet were monitored and analyzed. This scheme (OW application and lettuce crop cycle) was repeated for each treatment. Lettuce yields and Zn uptake were assessed at the end of each cycle. The soil columns were dismantled and seven soil layers were sampled and analyzed at the end of the second cycle (total experiment time: 12 weeks). X-ray absorption spectroscopy analyses were then conducted to assess Zn speciation in OW and OW-amended soils. The results of this study highlighted that (i) the fate of Zn in water-soil-plant compartments was similar, regardless of the type of soil and OW, (ii) >97.6% of the Zn input from OW accumulated in the soil surface layer, (iii) Zn uptake by lettuce increased with repeated OW applications, and (iv) no radical change in Zn speciation was observed at the end of the 12-week experiment, and phosphate was found to drive Zn speciation in both OW and amended soils (i.e., amorphous Zn-phosphate and Zn sorbed on hydoxylapatite). These results suggest that Zn speciation in OW is a key determinant controlling the environmental fate of this element in OW-amended soils.

High yield and mitigation of N-loss from paddy fields obtained by irrigation using optimized application of sewage tail water

Reuse of treated wastewater effluent for crop irrigation can be a promising strategy to substitute/reduce chemical fertilizers and mitigate contamination of water environment. The effect of the effluent irrigation strategies on crop yield and nitrogen (N) loss to the environment have not been yet well explored. In the present study, a soil column monitoring experiment was conducted for over two years (2016–2017) to assess the effect of domestic sewage tail water (DSTW) irrigation on rice growth and N-loss. DSTW irrigation was established substituting N fertilizer at percentages of 15 %, 30 % and 45 % (namely N3S1, N2S2 and N1S3) with a total nitrogen (TN) input of 210 kg·hm−2; controls with conventional fertilizer (N210) and no fertilizer (N0) but tap water irrigation were also set up. A field plot experiment was also conducted using the same treatments in 2017. The results of the soil column experiment showed that the grain yield from treatments with different proportions of DSTW and N fertilizer were no lower than those subjected to conventional fertilizer in both years. The NH3 volatilization from the treatments using reclaimed DSTW accounted for 20.9 %–34.4 % TN in 2016, but this fell to 6.9 %–16.1 % in 2017. Compared with N210, the DSTW irrigation treatment (N1S3) significantly reduced NH3 emissions by 32.8 %–61.3 % over the two years (p < 0.05). The field plot experiment also indicated that DSTW reclamation could not significantly affect the rice growth and yield, and treatments with a higher proportion of N substituting by DSTW tended to have lower NH3 volatilization. With respect to the rice yield and N-loss, the recommended ratio of N fertilizer substitution is 30 %–45 %; however, long-term trials would be required to further evaluate of any adverse environmental impacts.

Water and pesticide transfers in undisturbed soil columns sampled from a Stagnic Luvisol and a Vermic Umbrisol both cultivated under conventional and conservation agriculture

The main goals of conservation agriculture are to enhance soil fertility and to reduce soil degradation especially through erosion. However, conservation agriculture practices can exhibit a higher risk of contamination through vertical flows. The objectives of this study were to (i) characterise water and pesticide transfers in two different soils both managed under conventional and conservation agriculture and (ii) assess the effects of pesticide properties, soil type and agricultural system on pesticide fate. We studied the behaviour of two herbicides (nicosulfuron and mesotrione) and a molluscicide (metaldehyde) in percolation experiments in undisturbed soil columns. A series of two rain events (one with a high, the other with a low intensity) separated by a two-day flow interruption was applied three days after the pesticides and bromide application. Batch sorption coefficients, Kd, were also measured. While the Pesticides Properties Data Base (2020) indicated a decrease of sorption in the order mesotrione > metaldehyde > nicosulfuron, the measured Kd, decreased in the order mesotrione (2.3 ± 1.4 L.kg−1) > nicosulfuron (0.7 ± 0.4 L.kg−1) > metaldehyde (0.1 ± 0.1 L.kg−1). We highlighted distinct behaviour of pesticide leaching depending mainly on soil type, agricultural practices and pesticide properties. For low degree of preferential flow, pesticide leaching can be related to the sorption properties of pesticides. Nicosulfuron and mesotrione delays are more pronounced under conservation management while metaldehyde always arrived with no delay. During the high intensity rain event, on one soil type, high degree of preferential flow masked sorption effect on leaching since every pesticide arrived at the same time as the tracer and amounted to up to 21% of pesticide recovery compared to 4% on the other soil type. Conservation agriculture was found to improve the vertical transfers of water and pesticides while, on one of the studied soil type, the presence of a low conductive plough pan significantly limits water drainage.