Leaching Losses Research Articles

Long-Term Simulated Direct N2O Emissions from German Oilseed Rape Cultivation below the IPCC Emission Factor

The low nitrogen (N)-use efficiency of intensive winter oilseed rape (WOSR) cropping systems may cause negative environmental impacts, especially due to N leaching and gaseous losses. The aim of this study was to use data from field experiments (five sites across Germany representing typical WOSR regions) for parametrization of a nitrous oxide (N2O) emission component for implementation into a process-based dynamic plant-soil-atmosphere model (PSAM). After calibration and evaluation with three years of field data from five different N fertilizer treatments, a long-term simulation with 25-year historical weather data was conducted to derive functional relations and emission factors (EFs). The model performed best at higher aggregation levels (cumulative emissions over the entire cropping period, R2 of 0.48/0.77 for calibration/evaluation), but also reasonably simulated short-term dynamics (e.g., fertilizer applications, extreme weather events). Site-specific and year-specific N2O emissions varied within the range of medians from 0.56–4.93 kg N2O-N ha−1. Mineral fertilizer-induced EFs at economic optimal N inputs ranged from 0.16–0.65%, which was markedly below the aggregated IPCC standard value of 1% for direct N2O emissions. Generally, the simulated emissions were consistently higher with finer soil textures and increasing N inputs. The process-based approach, moreover, allowed the identification of the major source of N2O, which mainly originated from nitrification processes.

Electric field-induced deterioration of cement mortars owing to calcium leaching

This paper investigated the calcium leaching from plain and fly ash/limestone blended cement mortars under an electric field. The Ca2+ leaching degree and reduced CaO content were measured to assess the extent of calcium leaching, and the compressive strength loss was used as an indicator to evaluate the degradation of the mortars due to leaching. Additionally, the changes in mineralogical composition, micrograph, Ca/Si ratio of C–S–H gel, and pore structure of leached samples were analyzed through X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS), and mercury intrusion porosimetry (MIP). The findings indicated a notable acceleration in the leaching of Ca2+ due to the application of an electric field. Consequently, the calcium leaching degree of mortars continuously increased with time. The accelerated calcium leaching resulted in the loose microstructure and increased porosity mainly for the cathode part as well as the reduction in compressive strength of mortars. The addition of fly ash was beneficial in reducing the calcium leaching and strength loss of mortars after 90 days of exposure to the electric field, contrary to the effects observed with the incorporation of limestone powders. Attention should be paid to the durability issues of cement-based materials induced by the electric field.

A comprehensive assessment of superabsorbent resin produced using modified quinoa husk and coal fly ash - Preparation, characterization and application

About 200 million tons of coal fly ash (CFA) is not effectively used in China every year. To enhance the utilization of biomass waste quinoa husk (QH) and solid waste CFA and reduce the preparation cost of superabsorbent resin (SAR), a low-cost, biodegradable modified quinoa husk-g-poly (acrylic acid)/coal fly ash superabsorbent resin (MQH-g-PAA/CFA SAR) was synthesized using modified quinoa husk (MQH), acrylic acid and CFA and used to improve the drought resistance and fertilizer conservation ability of soil. The surface morphology and performance of SAR were characterized by Fourier transform infrared (FTIR) spectrometry, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), which provided evidence for improving the properties of SAR by grafting MQH and adding CFA. In addition, the synthesis conditions were studied and optimized, together with the contents of initiator, crosslinker, MQH, and CFA to acrylic acid as well as the neutralization degree of acrylic acid. After optimization, the optimum water absorbency of SAR in deionized water, tap water, and physiological saline was 1302, 356, and 91 g/g respectively. The swelling and water-retention mechanisms of SARs were analyzed by a dynamic model and the results were in good agreement with the experimental data. In the soil experiment, the addition of SAR improved the drought resistance ability of soil, and reduced the leaching loss of fertilizer in the soil (from 49.5 % to 36.7 %). Therefore, this material exhibits significant potential in the field of agriculture and offers a novel approach with economic benefit for the utilization of MQH and CFA.

Effectiveness of a 10-year continuous reduction of controlled-release nitrogen fertilizer on production, nitrogen loss and utilization of double-cropping rice

Considerable literature has demonstrated the advantage of controlled-release nitrogen (CRN) fertilizer in improving crop productivity. However, few researches have explored the long-term impacts of using CRN fertilizers as alternative to common urea on production and N utilization in double-cropping paddy. To address this gap, our study utilized a database derived from a 10-year field experiment from 2013 to 2022. During early and late rice seasons, compared to common urea (early rice, 150 kg hm−2; late rice, 180 kg hm−2), CRN fertilizer (150 kg hm−2; 180 kg hm−2) input significantly increased yield by 7.4 %, and 11.7 %, as well as N use efficiency (NUE) from 23.0 % and 24.6 % to 33.0 % and 37.5 %, respectively. CRN application significantly reduced N losses, evidenced by decrease in runoff (23.1 % and 19.4 %), leaching (12.7 % and 12.1 %), ammonia volatilization (28.9 % and 30.2 %), and N2O emissions (10.4 % and 16.1 %). A reduction of 10 % in CRN fertilizer input maintained yield. Compared with normal amount, reducing 10, 20, and 30 % CRN input increased NUE by 7.0–7.6 %, 7.3–7.4 %, and 11.6–12.6 %; reduced runoff loss by 16.1–17.9 %, 27.9–30.7 %, and 35.0–37.2 %; decreased leaching loss by 7.6–12.8 %, 18.1–22.6 %, and 26.5–31.4 %; decreased ammonia volatilization by 9.9–12.3 %, 16.3–22.7 %, and 23.2–29.3 %, and decreased N2O loss by 7.8–13.3 %, 12.8–32.8 %, and 20.3–36.9 %, respectively. Soils with CRN input showed higher total and inorganic N contents than the soils with common urea, and the content increased in parallel with CRN fertilizer input. Soil N content and N runoff loss were significantly related to yield and N uptake, and N runoff and leaching losses were significantly related to NUE. These results support the sustainable use of CRN fertilizers as a viable alternative to common urea, indicating that application rate of 135 and 162 kg N hm−2 of early and late rice, respectively, maintain yield and enhance N utilization in double-season paddy of southern China.

Meta-analysis unveils differential effects of agroforestry on soil properties in different zonobiomes

AimsCurrent comprehensive meta-analysis study aims to explore how agroforestry practices influence soil quality across different climate zones. Since numerous studies proposed agroforestry as the promising agroecological farming systems over conventional monoculture systems to maintain soil quality and to regenerate disturbed soil to counteract the negative consequences of global extensive agricultural approaches.MethodsBy employing the comprehensive meta-analysis technique on data from 125 studies conducted in tropical, temperate, and Mediterranean environments, we quantitatively assessed the effects of agroforestry on physical, chemical, and biological soil quality indicators.ResultsRates of soil erosion, the most important indication of land degradation, were improved in agroforestry systems compared to monocultures, especially in temperate (-138%) and Mediterranean soils (-40%), due to agroforestry-induced improved soil texture, aggregate stability, and soil water regulation. Soil acidification was decreased in tropical (-128%) and Mediterranean soils (-96%), but increased in temperate soils (+ 104%) due to agroforestry practices. Low temperate soil pH suggests high Ca2+ leaching losses as evidenced by decreased Ca2+ (-68%) and increased Fe2+ (+ 129%) and Al3+ (+ 235%) contents. Agroforestry systems increased organic matter accumulation in temperate (+ 86%) and Mediterranean soils (+ 65%), carbon sequestration in all climatic zones (+ 48%: 33–73%), and respiration rates in temperate (+ 119%) and tropical soils (+ 105%). Soil microbial communities, enzyme activities as well as nutrient cycling and availability were generally enhanced in agroforestry systems compared to monocultures.ConclusionsOur results provide compelling evidence that agroforestry practices can contribute substantially to sustainable improvement of global soil quality.

Impact of Simulated Acid Rain on Soil Base Cations Dissolution between Eucalyptus Pure Plantations and Eucalyptus–Castanopsis fissa Mixed Plantations

The soils of Eucalyptus pure plantations and Eucalyptus–Castanopsis fissa mixed plantations were studied using soil column leaching experiments with acid solutions to mimic the effects of acid rain on the soils. This helped researchers learn more about how soil base ions react to acid deposition and their ability to protect the soil from excessive acidity under pure and mixed-species plantations. The results showed that acid rain leaching increased the leaching loss, desorption, and desorption rate of soil base ions while decreasing the soil pH value, adsorption, and adsorption rate of soil base ions. The soil pH value and the leaching loss ranges of K+, Na+, and Mg2+ were all greater in the pure plantations than in the mixed plantations, while the leaching range of Ca2+ was greater in the mixed plantation than in the pure plantations. In the two types of plantations, the adsorption rates of Ca2+ and Na+ in the mixed plantations were higher than in the pure plantations, while K+ and Mg2+ showed higher adsorption rates in the pure plantations than in the mixed plantations. Therefore, soil pH and base ions were greatly affected by the pH value of acid rain. Compared with the pure plantations, the establishment of Eucalyptus–Castanopsis fissa mixed plantations can slow soil acidification and leaching of K+, Na+, and Mg2+ and contribute to the adsorption of Ca2+ and Na+, which is beneficial for the soil nutrient fixation of Eucalyptus plantations. The mixed plantations were found to increase the exchange reaction between H+ and base ions, thereby improving the acid buffer performance of the soil. This, in turn, helped to mitigate the decline in soil fertility. Therefore, establishment of Eucalyptus–Castanopsis fissa mixed-species plantations can slow down the impact of acid rain on soil acidification in artificial plantation land to a certain extent and play an important role in optimizing the plantation structure of Eucalyptus stands and maintaining their productivity.

Design of innovative agrochemical delivery system for sustainable agriculture and to alleviate environmental and health hazards

This article deals with formation of hydrogels encapsulated with agrochemicals for minimizing agrochemical-environmental pollution and health hazards. These copolymers as controlled release formulations (CRF) were designed by grafting reaction onto natural polymers starch-agar-gelatin and poly(2-acrylamido-2-methylpropanesulphonic acid) (AMPS). Copolymers were characterized by SEM, AFM, and XRD along with FTIR and 13C NMR techniques. SEM and AFM confirmed the un-even morphology with surface roughness and XRD indicated the amorphous nature of the polymers after grafting. Controlled diffusion of thiophante methyl fungicide for 72 h occurred with diffusion non-Fickian type. It is useful observation for preventing leaching and evaporation loss of fungicide and to alleviate environmental and health hazards. After degradation CRF may improve micronutrients and soil quality.

Converting natural forests to tea plantations reduced soil phosphorus sorption capacity in subtropical China

AbstractConverting natural forests to agricultural lands has been widespread globally due to increasing population and the demand for food. Phosphorus (P) is often applied to agricultural lands in excessive amounts which can saturate the natural P sorption capacity of the soil, leading to P leaching and subsequent off‐site water eutrophication. We studied the effect of land‐use conversion from natural forests to tea plantations on total soil P, P fractions, and P sorption capacity in subtropical China. Compared to natural forests, total soil P concentrations increased significantly in both 0–20 and 20–40 cm depths in tea plantations, indicative of the accumulation of P fertilizer. The increases in total soil P were primarily found in NaOH‐extractable inorganic P and residual P fractions in both depths, suggesting that P fertilizer was sorbed and occluded into more stable forms due to the high abundance of sorbents (i.e., iron [Fe], aluminum [Al] minerals, and clay). Across all soil samples, oxalate‐extractable Fe was the best predictor of soil maximum P sorption capacity (r = 0.94, p < 0.001). Surprisingly, the conversion from natural forests to tea plantations decreased both oxalate‐extractable Fe concentration and soil maximum P sorption capacity, hereby increasing the degree of P saturation in soils. Depletion of P sorbents (i.e., soil amorphous Fe) is likely a consequence of Fe removal through tea production and soil erosion, indicating soil degradation. Plantation soils have also shown other signs of degradation including the loss of nutrients (e.g., total soil nitrogen and oxalate‐extractable calcium) and soil organic matter. Our results demonstrate that the conversion of natural forests to tea plantations reduced the ability of the soil to sorb P by both saturating the natural P sorption capacity and depleting P sorbents. Soil degradation resulting from land‐use conversion has increased the environmental risk of P leaching loss, emphasizing the need for improved P fertilization management.

Nitrogen Dynamics in Soil Treated with Plant-Growth Promoting Bacteria and Urea Fertilizer

The mineralization of urea fertilizer significantly impacts nitrogen movement in the soil. An incubation study was done on a lab scale basis to examine nitrogen dynamics in soil inoculated with plant growth-promoting bacteria (PGPB) supplemented with varying levels of nitrogen fertilizer in the form of urea (0% N, 25% N, 50% N, 75% N, and 100% N). In the present experiment, sandy clay loam soil was used and incubated for four weeks, and the concentrations of NH4+‒N and NO3–‒N were monitored using the destructive method (Kjeldahl) to determine the mineralization rate of urea. Results showed higher NH4+‒N (11.880 mg/kg mineralized with UPMRB9N50 treatment) and NO3–‒N (20.060 mg/kg mineralized with UPMRB9N50 treatment) concentrations in the bacteria-treated soil compared to the uninoculated control. Urea-N remains higher (0.0353% and 0.0253% from UPMRB9N50 treatment in the first and second weeks, respectively) in bacteria-treated soil during the first two weeks, then gradually becomes zero towards the end of the observing period. Nitrogen (N) leaching loss was lower in bacterial inoculated soil compared to the control, and the leaching loss of N was greater with the increased N fertilizer rates. Cumulative N leaching loss is higher (29.797 mg/kg) in 100% N-treated soil than in other treatments. The findings observed that the beneficial bacteria could enhance the N mineralization to make the nutrient available for the crop while, at the same time, reducing leaching losses of fertilizer when supplied with a minimum amount of chemical fertilizer, thereby saving the input cost and protecting the environment.

Leaching of soil legacy nitrogen in intact soil columns and significance of soil macropore structure

Excessive application of chemical fertilizers accumulates nitrogen in soil (soil legacy nitrogen), and its release has a long-term impact on environmental quality. The information regarding leaching of soil legacy nitrogen and role of soil pore structure is scarce. Fifteen undisturbed soil cores with a depth of ~200 mm were collected from five paddy fields in a subtropical area of China, and soil pore structure was characterized with X-ray computed tomography. The batch leaching column experiments were conducted to investigate the nitrogen leaching from the soil cores. In the leachate, inorganic nitrogen (NO3−–N and NH4+–N) accounted for 73–85 % of total dissolved nitrogen (TDN), which showed small variations among the five sampling sites. The NO3−–N, NH4+–N and TDN concentrations in the leachate over the number of leaching times could be well fitted with the Gaussian, exponential or linear models, suggesting that different nitrogen forms showed variable leaching dynamics. NO3−–N and TDN leaching losses continued to increase with the number of leaching times, whereas NH4+–N leaching from the soil had a threshold value. Combination of changes in soil nitrogen content after leaching, the lagging effect of soil legacy nitrogen may be partly attributed to the continuous transformation of NH4+–N and organic nitrogen into NO3−–N in the soils. Besides the nitrogen content in the soil, the most important factor of soil pore structure controlling NO3−–N and TDN leaching loss was the fractal dimension; NH4+–N was mainly controlled by connectivity. The present study highlighted the importance of soil pore structure and nitrogen format transformation in the leaching of soil legacy nitrogen.

Agronomic Comparison of Mechanochemically Synthesized Zinc Borate and Other Boron Sources Granulated with Macronutrient Fertilizers

PurposeBoron (B) is an essential micronutrient required throughout the growth cycle of plants so effectively supplying crops with B using fertilizers is challenging. The purpose of this study was to assess the agronomic effectiveness of mechanochemically synthesized zinc borate as a slow release B source and compare it to commonly used B sources after incorporation with different macronutrient carriers.MethodsZinc borate synthesized using a green mechanochemical method as well as commercial B sources (borax, colemanite, and commercial zinc borate) were incorporated with various macronutrient fertilizers (monoammonium phosphate – MAP, muriate of potash – MOP and urea). The fertilizers were evaluated by a) assessing the solubility behaviour of these products; and b) comparing potential leaching losses, plant growth, and plant uptake through a greenhouse study.ResultsThe mechanochemically synthesized zinc borate, commercial zinc borate, and colemanite had similar dissolution rates when MAP was the carrier, but both zinc borates dissolved more B than colemanite when MOP and urea were the carriers. In the pot trial, high losses of B in leachates resulted in low B uptake by plants fertilized with soluble sodium tetraborate. All the slow-release B sources showed less B leaching and greater B uptake compared to the soluble B treatment, but more B was leached for the mechanochemically synthesized than for the commercial zinc borate.ConclusionsOur study indicates that mechanochemically synthesized zinc borate could be effective in matching plant demand for B and reducing leaching losses in high rainfall environments, particularly with urea as the carrier, while providing the benefit of lower waste stream production compared to commercial zinc borate sources.

Hydrus-1D Model for Simulating Phosphorus Transport in Paddy Crop Irrigated with Alternate Wetting and Drying Practice

ABSTRACT The alternate wetting and drying (AWD) irrigation practice involves soil moisture stress-based irrigation scheduling which possibly affects the rice field’s phosphorus (P) transport and balance components. The focus of this study was to understand P-transport under AWD irrigation and estimate the associated balance components in rice using a solute transport model, Hydrus-1D. In this study, rice was cultivated in 30 lysimeter plots with three irrigation treatments (no soil water stress/NS, mild soil water stress/400 cm/MS, and severe soil water stress/750 cm/SS) and each treatment was replicated 10 times. The field experimental data were used to simulate P transport with the help of the Hydrus-1D model. The Hydrus-1D model was calibrated and validated for P transport within the soil matrix under AWD irrigation practice. The P distribution was mostly concentrated within the top puddled soil layer (0–20 cm) and did not move to the deeper soil layers. The simulated results indicate that the recommended dose of P with 3–5 cm ponding water depth will increase the P availability for rice and reduce the P leaching loss in AWD irrigation practice. The Hydrus-1D model can be used as a management tool to determine the appropriate P application rate and ponding water depth irrigated with AWD for which the required P nutrients are sufficiently available to rice and the P loss to the environment can be controlled for sustainable rice production.

Agro-Waste Biochar to Reduce the Leaching of Heavy Metals from Coal Fly Ash Amended Soil

The soils added with coal fly ash may contain heavy metals potentially up to the levels of toxicity. Biochars have been successfully used in the past to reduce the bioavailability and leaching of heavy metals in contaminated soils. Therefore, the co-application of biochar together with coal fly ash could positively change the bioavailability and leaching characteristics of heavy metals in sandy soils through various fixing mechanisms. In the present study, the authors investigated the effect of agro-waste biochar in modifying the leaching loss of heavy metals from coal fly ash contaminated soils. Column leaching tests with simulated rainfall conditions were conducted for sandy Ultisol soils mixed with coal fly ash and avocado branch cut biomass biochar at 5 tons/ha rate. The results showed the presence of heavy metals in the leachate of fly ash added soil. Application of biochar significantly reduced the leachability of all the tested heavy metals in the study. The reduction rates were up to 55% compared to non-amended samples. Therefore, the agro-waste biochar can effective be used in stabilizing the heavy metals in coal fly ash contaminated soils, to minimize the risk of environmental contamination.

Urea-Straw-Starch Fertilizer with Tunable Water- and Nutrient-Retaining Properties Assisted by High-Energy Electron-Beam Irradiation.

A novel type of water- and nutrient-retaining fertilizer (WNRF) was prepared by mixing, melting, and extruding high-energy electron-beam (HEEB)-irradiated corn straw, urea, and starch. HEEB irradiation technique effectively killed pathogenic microorganisms in straw and further improved the adsorption and binding capacity of straw to urea and water. Compared to nonirradiated HEEB samples, the optimal WNRF improved the water retention rate by 25.63%, the migrate-to-surface loss control rate by 60.2%, and the leaching loss control rate by 34.71%, respectively. Thus, it effectively facilitated the growth of pak choi with a 24% increase in the dry matter weight of the shoot. This work provides a promising approach to improve water and nutrient availability in arid and semi-arid regions and to promote the efficient utilization of straw resources.

Synthesis of biochar‐embedded slow‐release nitrogen fertilizers: Mesocosm and field scale evaluation for nitrogen use efficiency, growth and rice yield

AbstractIncreasing consideration is being paid to sustainable slow‐release fertilizers (SRFs). Biochar is a novel carbon material, and gaining momentum as a natural carrier for sustainable nutrient application and release and improved soil health. Accordingly, a recent biochar‐embedded slow‐release nitrogen (N) fertilizer has been prepared using acacia biochar, urea, ammonium chloride, starch and organic acid. This and other biochar‐embedded slow‐release N fertilizers (BSRNFs) were characterized using Fourier transform‐infrared spectroscopy (FT‐IR) and scanning electron microscope (SEM). BSRNFs were tested in the laboratory and field experiments for their N release pattern, nitrate (NO3‐N) leaching loss, N use efficiency (NUE) and growth and yield of rice crops. Among the BSRNFs tested, the one with 75% urea‐N (BSRNF‐U75) released 109 mg kg−1 of N in an incubation study and the least NO3‐N leaching losses of 8.8, 14.6 and 26.4 mg kg−1 at 10, 20 and 30 cm depth in a column study, respectively, compared with conventional urea. Application of biochar‐embedded slow‐release N fertilizer 100% urea‐N (BSRNF‐U100) augmented plant growth to increase grain yield (6610 kg ha−1), straw yield (9612 kg ha−1) and NUE (12%) in rice.

Connecting the dots: Path model to identify key phenotypic traits for screening plants with tolerance to nitrogen deficiency.

Varieties that tolerate low nitrogen (N) application rates can reduce fertilizer costs, minimize nitrate leaching and runoff losses, and lower overall CO2 emissions associated with fertilizer manufacturing. The goal of our research is to show the usefulness of path models to identify key phenotypic traits for screening plants with a tolerance to low N application rates. We grew tolerant and sensitive cultivars of poinsettia (Euphorbia pulcherrima) using a water-soluble fertilizer (15-5-15 Cal Mag) in both optimal (electrical conductivity of 2.5 dS·m-1) and N-deficient (electrical conductivity of 0.75 dS·m-1) treatments and measured 24 different traits at the cellular, leaf, and whole-plant scales in both cultivars and treatments. The experiment was laid out as a split-plot design with N treatments as main plots and cultivars as sub-plots, with five replications. Path analysis was conducted to develop sequential relationships among these traits. Statistical comparisons between tolerant and sensitive cultivars in the N-deficient treatment indicated an increase in shoot biomass (19.9 vs 14.4 g), leaf area (2775 vs 1824 cm2), leaf dry weight (14.7 vs 10.0 g), lateral root dry weight (3.7 vs 2.4 g), light-saturated photosynthesis (14.5 vs 10.1 μmol∙m-2∙s-1), maximum electron transport rate (119 vs 89 μmol∙m-2∙s-1), chlorophyll content (28.1 vs 12.9 g∙100g-1), leaf N content (27.5 vs 19.9 mg∙g-1), and fine root N content (26.1 vs 20.9 mg∙g-1), and a decrease in anthocyanin content (0.07 vs 0.16 ΔOD∙g-1). The path model indicated that an increase in the lateral root growth and fine root N content can lead to an increase in the leaf N content, in the N-deficient treatment. There were three separate paths that connected higher leaf N content to increased shoot biomass. These paths were mediated by the levels of anthocyanin, chlorophylls, and light-saturated photosynthesis rate (or rubisco capacity). The light-saturated photosynthesis model suggested that the increased uptake of N by fine roots in the tolerant cultivar was likely supported by the photosynthates translocated from the shoot to the root. Leaf N content was associated with multiple plant responses in the N-deficient treatment, and can be a useful screening trait for developing new cultivars, especially in marker-assisted molecular breeding.

Characteristics of agricultural phosphorus migration in different soil layers on purple soil sloping cropland under natural rainfall conditions

Limited by the current monitoring and collection methods of subsurface flow data, the characteristics of phosphorus (P) migration loss in different soil layers on sloping cropland under natural rainfall conditions need to be clarified. In this study, a reliable U-trough collection method was used to explore P migration losses in different purple soil layers (L0: surface, L1: 0–20 cm, L2: 20–40 cm, and L3: 40–60 cm) for purple soil sloping cropland during a field monitoring campaign spanning two calendar years under natural rainfall conditions. The results suggested that the annual surface P loss load was 1.08 kg*ha−1*yr−1, where 92.1% was particulate P. The annual leaching loss load of total P from the L1 layer was 3.55 kg*ha−1*yr−1, where 74.2% and 10.5% were intercepted by the L2 and L3 layers, respectively, to increase the in situ soil P stocks. Only 15.3% of L1’s annually leached P, and only half the surface P loss load (L0), was lost to underground water. Heavy-rain events on the purple soils in the studied sloping cropland induced 43.9% of the annual surface P loss load. In contrast, 36.1%, 30.5%, and 30.3% of P’s eventual annual leached loss loads resulted from heavy, moderate, and torrential rain events, respectively. The maize season was the main period of surface and subsurface P migration loss. Due to the limitation of experimental conditions, the results of this experiment could not represent the soil phosphorus migration process in the natural purple slope farmland in nature, but it could partially represent the soil phosphorus migration in the newly cultivated purple sloping cropland in Chongqing.

Effect of nitrogen application on nitrogen leaching pattern and leaching loss from drip irrigated cotton fields in Southern Xinjiang

Farmers provided excessive nitrogen fertilizer to obtain high cotton yield in Xinjiang, Northwest China. Although drip irrigation could save water resources and improve nitrogen use efficiency, it is not known if leaching is occurring or not and whether leaching will harm the water environment under different nitrogen application. The purpose of our study was to estimate the effect of different nitrogen (N) application on the N leaching loss in drip irrigated cotton fields in South Xinjiang. A field experiment was conducted with N application rates of 317(N317), 395(N395) and 476(N476) kg hm−2 from 2021 to 2022. The characteristics of N pattern and leaching amount were analyzed. The concentration of NO3- and total nitrogen in the leaching water significantly decreased with the decrease of N application. The proportion of NO3–to total nitrogen reached the highest values of 51.52%–58.16%, 49.53%–56.91%, and 57.52%–62.87% at bud, flower, and boll stages of cotton, respectively. Moreover, the proportion of NO3– to total nitrogen remained at a stable level, which indicated that NO3–was the main pattern of N leaching. The N loss in the treatment N395 and N317 was 79.67% and 67.48% of that in the N476 treatment (1.23 kg hm−2), while the yield was 120.56% and 112.46% of that in the N476 treatment. Compared with conventional fertilizer application (476 kg hm−2), the reasonable N fertilizer application would not only reduce the amount of N leaching, but also increase the cotton yield.

Effects of Irrigation and Nitrogen Fertilizer on Soil Carbon Leaching in Cotton Fields in Arid Areas

In order to formulate a reasonable water input model for cotton fields in southern Xinjiang for scientific and rational fertilization, to reduce soil carbon leaching, and to improve soil carbon sequestration capacity, an undisturbed soil column leaching test was used to simulate the current field management method in the study area. Two methods, drip irrigation and flood irrigation, were set up, and three irrigation and three nitrogen fertilizer levels were used to carry out the undisturbed soil column leaching test. The results showed that the amount and mode of water and nitrogen input affected the distribution and leaching loss of organic carbon and inorganic carbon in the soil. When the nitrogen application rate increased from 270 kg·hm−2 to 450 kg·hm−2, the leaching loss of soluble organic carbon and soluble inorganic carbon increased significantly. When the water input increased from 6000 m3·hm−2 to 9000 m3·hm−2, the leaching loss of DOC and DIC increased significantly. The carbon leaching loss under drip irrigation was higher than that under flood irrigation. The leaching rates of DOC and DIC were fastest under the conditions of high water (9000 m3·hm−2) and high fertilizer (450 kg·hm−2). This shows that water and nitrogen input and irrigation methods are important factors affecting soil carbon leaching. In the case of excessive water input, long-term high-frequency irrigation is the main factor affecting carbon leaching.

Does phytoextraction with Sedum plumbizincicola increase cadmium leaching from polluted agricultural soil?

Sedum plumbizincicola is a cadmium (Cd) and zinc hyperaccumulator that can activate Cd by rhizosphere acidification. However, there is little understanding of the Cd leaching risk from polluted soil during phytoextraction process. Here, pot and column experiments were conducted to monitor soil Cd leaching characteristics under different rainfall simulation conditions during S. plumbizincicola phytoextraction. Soil Cd leaching increased significantly with increasing simulated rainfall intensity. Compared with normal rainfall (NR), weak rainfall (WR) resulted in a 34.3% decrease in Cd uptake by S. plumbizincicola and also led to a 68.7% decline in Cd leaching. In contrast, Cd leaching under heavy rainfall (HR) was 2.12 times that of NR in the presence of S. plumbizincicola. After two successive growing periods, phytoextraction resulted in a 53.5–66.4% decline in the amount of soil Cd leached compared with controls in which S. plumbizincicola was absent. Even compared with maize cropping as a control, S. plumbizincicola did not instigate a significant increase in Cd leaching. The contribution of Cd leaching loss to the decline in soil total Cd concentration was negligible after phytoextraction in the pot experiment. Overall, the results contribute to our understanding of soil Cd leaching risk by phytoextraction with S. plumbizincicola.