Browsing by Author "Jeyakumar P"

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    A low-cost simple lysimeter soil retriever design for retrieving soil from small lysimeters
    (IOP Publishing, 2024-06-06) Gunaratnam A; McCurdy M; Grafton M; Jeyakumar P; Davies CE; Bishop P
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    Assessing Controlled Traffic Farming as a Precision Agriculture Strategy for Minimising N2O Losses
    (MDPI AG, 2025-08-04) Raveendrakumaran B; Grafton M; Jeyakumar P; Bishop P; Davies C; Li D
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    ASSESSMENT OF NITROGEN FERTILIZERS UNDER CONTROLLED ENVIRONMENT – A LYSIMETER DESIGN
    (12/04/2019) Gnaratnam A; McCurdy M; Grafton M; Jeyakumar P; Bishop P; Davies C; Currie, L; Christensen, C
    This paper introduces a closed system lysimeter design to measure fertilizer performance on ryegrass. The lysimeter will measure plant mass growth, gas emissions and leachate in a controlled climate environment based on a long term 90 day spring climate from the Taranaki. A range of commercial fertilizers will be compared to bespoke fertilizers manufactured under this project. This work, although undertaken in laboratory conditions will help quantify the impacts of nitrogenous fertilizers on the environment by mimicking actual conditions in a controlled setting. The study should provide data on the effectiveness of novel fertilizers manufactured within the programme; and other slow and controlled fertilizers, in reducing nitrogen leaching and greenhouse gas (GHG) emissions on pasture. Nitrogenous fertilizers readily leach as nitrates are highly soluble and GHG are emitted through volatilisation of ammonia and nitrous oxide. Reduced leaching and volatilisation increases fertilizer efficiency as less is wasted and more is attenuated in the plant. The aims of the research are to increase the effectiveness and efficiency of nitrogen fertilizer use in New Zealand. This should benefit farmers by reducing the amount of fertilizer applied, ideally reducing fertilizer cost, or at no extra cost by improved plant attenuation. This would also have an environmental benefit through reduced leaching and GHG emissions.
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    Biochar and soil properties limit the phytoavailability of lead and cadmium by Brassica chinensis L. in contaminated soils
    (Springer Nature on behalf of the Shenyang Agricultural University, 2022-12) Houssou AA; Jeyakumar P; Niazi NK; Van Zwieten L; Li X; Huang L; Wei L; Zheng X; Huang Q; Huang Y; Huang X; Wang H; Liu Z; Huang Z
    The current study investigated the effect of biochars derived from cinnamomum woodchip, garden waste and mulberry woodchip on soil phytoavailable lead (Pb), cadmium (Cd) pools, and their uptake by Chinese cabbage (Brassica chinensis L.). The biochars were produced at 450 °C of pyrolysis temperature. The contaminated soils were collected from Yunfu (classified as Udept), Jiyuan (Ustalf) and Shaoguan (Udult) cities in China at the depth of 0–20 cm and amended with biochars at the rate of 3% w/w. After mixing the soil with biochar for 14 days, the Chinese cabbage was planted in the amended soils. Then, it was harvested on the 48th day after sowing period. In Udult soil, Chinese cabbage died 18 days after sowing period in control and soils amended with cinnamomum and mulberry biochars. Although only plants grown with the garden waste biochar treatment survived in Udult soil, amendment of garden waste or mulberry biochars at 3% w/w (450 °C) to Udult soil significantly increased (4.95–6.25) soil pH compared to other biochar treatments. In Udept and Ustalf soils, the application of garden waste and mulberry biochars significantly improved plant biomass compared to control, albeit it was dependent on both biochar and soil properties. Garden waste biochar significantly decreased soil Cd phytoavailable concentration by 26% in the Udult soil, while a decrease of soil Cd phytoavailable concentration by 16% and 9% was observed in Ustalf and Udept soils, respectively. The available phosphorus in biochar and soil pH were important factors controlling toxic metal phytouptake by the plant. Thus, the amendment of soil with biochar at 3% can effectively reduce the mobility of Cd and Pb in soil and plant uptake. However, biochar and soil properties should be well-known before being used for soil toxic metal immobilization.
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    Biochar can Increase Chinese Cabbage (Brassica oleracea L.) Yield, Decrease Nitrogen and Phosphorus Leaching Losses in Intensive Vegetable Soil
    (Tech Science Press, 16/08/2021) Sun H; Jeyakumar P; Xiao H; Li X; Liu J; Yu M; Rana P; Shi W
    There are few evidences on the effect of biochar on vegetable yield, nitrogen (N) and phosphorus (P) leaching losses under intensive vegetable production soil. The current field plot scale study evaluated responses of Chinese cabbage (Brassica oleracea L.) yield, N and P leaching losses using five N treatments of common N application rate according to local farmers’ practice (N100%), reducing 20% or 40% N fertilizer (N80% and N60%), and reducing 40% N fertilizer but incorporating 10 or 20 t/ha biochar (N60% + BC10 and N60% + BC20). Results showed that N80% and N60% decreased both the cabbage economic and leaf yields by 6.8%–36.3% and 27.4%–37.7%, respectively. Incorporation of biochar with reduced N fertilizer rates improved the cabbage yield, in particular the N60% + BC20 matched the yield that observed in N100% treatment. Enhanced N and P uptake capacities of cabbage shoot probably contributed the higher vegetable production under both biochar amendment schemes. Biochar application mitigated the NH+4-N and total P leaching losses by 20%–30% and 29%–32%, respectively, compared with their counterpart treatment N60%. Nevertheless, biochar exerted no influence on the NO–3-N leaching. In addition, soil organic matter content was recorded with 7.4%–28.7% higher following 10–20 t/ha bio-char application. In conclusion, biochar application can increase economic yield of cabbage via increasing N and P use efficiency, decrease N and P leaching losses, and improve soil quality in an intensive vegetable production system.
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    Characterization traffic induced compaction in controlled traffic farming (CTF) and random traffic farming (RTF) - A multivariate approach
    Raveendrakumaran B; Grafton MC; Jeyakumar P; Bishop P; Davies CE; Horne, D; Singh, R
    A field scale experiment was carried out in Pukekohe in 2020 under an annual grass crop season to characterize the subsoil compaction in controlled traffic farming (CTF) and random traffic farming systems (RTF). Soil penetration resistance (PR) measurements were taken in each field using a cone penetrometer fitted with a 100 mm2 60° top angle cone. Multivariate analysis was performed to identify penetration resistance by depth through cluster analysis and principal component analysis (PCA). Repeated measures ANOVA was performed on the penetration data using the mixed model procedure to determine the treatment effects. In RTF, the penetrometer values increased more rapidly with depth resulting in higher values being recorded from 20cm compared to CTF. In contrast, it was greater in CTF than in RTF at the subsurface (55-60cm). The differences in PR declined beyond 55cm depth at both sites. All depths showed that differences in soil PR were most apparent in the 5-40cm depth, with significant differences between CTF and RTF (P<0.0001). This shows that traffic management at both CTF and RTF sites caused significant changes in the 5-40cm depth. However, there were no differences in PR between CTF and RTF below 40cm and at 0-5cm depth (P >0.05) showing that the soil layers were homogeneous in both systems beyond 40cm depth. The propagation of subsurface compaction was identified at the deeper layer (40-60cm) in CTF systems whereas it was identified from shallower depths (25-55cm) in RTF system.
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    COMPARATIVE EVALUATION OF CONTROLLED RELEASE FERTILISERS FOR NITRATE LEACHING
    Raveendrakumaran B; Grafton M; Jeyakumar P; Bishop P; Davies C; Christensen, C; Horne, D; Singh, R
    A lysimetric study was carried out with an objective of evaluating the leaching behaviour of different fertilisers on spinach growth on Manawatu sandy soil. The fertiliser treatments applied were urea, two controlled release fertilisers called ‘g’and ‘SmartN’ at the rates of 50 kg N/ha (50N), 100 kg N/ha (100N) and 200 kg N/ha (200N). The 200 kg N/ha urea application was made in 10 split doses at a rate of 20 kg N/ha in 7-day intervals, whereas 200N application of ‘g’ and ‘SmartN’ were made twice at a rate of 100 kg N/ha at the time of planting and six weeks after planting. The control treatment did not receive any fertiliser application (0N). The application of Urea and ‘g’ at all rates except ‘g’-50N produced significantly higher nitrate leaching losses (19.8 to 27.7 kgN/ha) compared to the control (9.1 kgN/ha), while SmartN at all rates produced no significant increase in nitrate leaching. The total nitrate leached per ton of dry matter production was significantly reduced by the application of N fertilisers compared to the control (135.1 kgNO3 - -N/MgDM). On an average, 16.4 kg NO3 - -N/MgDM was leached from the fertilised treatments. Dry matter production increased at 200N application rates with all three fertilisers, but urea-200N produced the highest dry matter yield of 2377 kg/ha. In conclusion, frequent split applications of urea (urea - 200N) increased dry matter yield thereby significantly reduced nitrate leaching.
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    Copper induces nitrification by ammonia-oxidizing bacteria and archaea in pastoral soils
    (Wiley, 12/12/2022) Matse D; Jeyakumar P; Bishop P; Anderson C
    Copper (Cu) is the main co-factor in the functioning of the ammonia monooxygenase (AMO) enzyme, which is responsible for the first step of ammonia oxidation. We report a greenhouse-based pot experiment that examines the response of ammonia-oxidizing bacteria and archaea (AOB and AOA) to different bioavailable Cu concentrations in three pastoral soils (Recent, Pallic, and Pumice soils) planted with ryegrass (Lolium perenne L.). Five treatments were used: control (no urine and Cu), urine only at 300 mg N kg-1 soil (Cu0), urine + 1 mg Cu kg-1 soil (Cu1), urine + 10 mg Cu kg-1 soil (Cu10), and urine + 100 mg Cu kg-1 soil (Cu100). Pots were destructively sampled at Day 0, 1, 7, 15, and 25 after urine application. The AOB/AOA amoA gene abundance was analyzed by real-time quantitative polymerase chain reaction at Days 1 and 15. The AOB amoA gene abundance increased 10.0- and 22.6-fold in the Recent soil and 2.1- and 2.5-fold in the Pallic soil for the Cu10 compared with Cu0 on Days 1 and 15, respectively. In contrast, the Cu100 was associated with a reduction in AOB amoA gene abundance in the Recent and Pallic soils but not in the Pumice soil. This may be due to the influence of soil cation exchange capacity differences on the bioavailable Cu. Bioavailable Cu in the Recent and Pallic soils influenced nitrification and AOB amoA gene abundance, as evidenced by the strong positive correlation between bioavailable Cu, nitrification, and AOB amoA. However, bioavailable Cu did not influence the nitrification and AOA amoA gene abundance increase.
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    Crawfish shell- and Chinese banyan branch-derived biochars reduced phytoavailability of As and Pb and altered community composition of bacteria in a contaminated arable soil.
    (20/03/2023) Gu S; Yang X; Chen H; Jeyakumar P; Chen J; Wang H
    Globally, soil contamination with arsenic (As) and lead (Pb) has become a severe environmental issue. Herein, a pot experiment was conducted using pak choi (Brassica chinensis L.) to investigate the effects of biochars derived from crawfish (Procambarus clarkia) shells (CSB) and Chinese banyan (Ficus microcarpa) branches (CBB) on the phytoavailability of As and Pb, and bacterial community composition in soils. Our results showed that the application of CSB and CBB decreased the concentrations of DTPA-extractable Pb in soils ranging from 26.8 % to 28.8 %, whereas CSB increased the concentration of NH4H2PO4-extractable As in soils, compared to the control. Application of both biochars reduced the uptake of As and Pb in the edible part of pak choi. In addition, application of CBB significantly (P < 0.05) increased the activities of α-glucosidase, β-glucosidase, cellobiohydrolase, and acid phosphomonoesterase by 55.0 %, 54.4 %, 195.1 %, and 76.7 %, respectively, compared to the control. High-throughput sequencing analysis revealed that the predominant bacteria at the phyla level in both biochar-treated soils were Firmicutes, Proteobacteria, and Actinobacteriota. Redundancy and correlation analyses showed that the changes in bacterial community composition could be related to soil organic carbon content, As availability, and nutrient availability in soils. Overall, the Chinese banyan branch biochar was more suitable than the crawfish shell biochar as a potential amendment for the remediation of soils co-contaminated with As and Pb.
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    Effect of Reaction-Finished Solution of Hydrochar (HRFS) Application on Rice Grain Yield and Nitrogen Use Efficiency in Saline Soil
    (Tech Science Press, 2022) Yi Z; Jeyakumar P; Jiang J; Zhang X; Yue C; Sun H
    We conducted a pot experiment to examine the feasibility of applying a reaction-finished solution of hydrochar (HRFS) to enhance rice production in a saline soil. With this purpose, HRFS was applied (0, 10, 20, 40, 60, 80 and 100 mL/pot) and rice yield and nitrogen (N) use efficiency (NUE) were determined. HRFS application significantly (P < 0.05) increased rice grain yield by 19.6%–30.0% compared to the control treatment (CKU, with N but without HRFS addition). Moreover, HRFS application promoted plant height and straw biomass of rice. Increases of rice yield were mainly achieved by increases in the number of panicles and grains per panicle. Compared with the CKU treatment, the NUE of HRFS amendments significantly (P < 0.05) increased by 56.3%–71.7%. This indicated that the improvement of NUE was one of the mechanisms to improve rice grain yield with HRFS amendment. The results of regression analysis showed that there was a positive relationship (R2 = 0.8332) between rice yield and HRFS application rate within an appropriate range. The highest rice yield was recorded with the HRFS application of 40 mL/pot, but a further increase in HRFS application rate appeared to reduce rice yield. Based on the results of this pot study, HRFS application can increase rice yield in a saline soil by regulating its yield components and enhancing NUE. However, impact of HRFS on these variables showed a “dose effect”.
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    Effects of biochar in combination with varied N inputs on grain yield, N uptake, NH3 volatilization, and N2O emission in paddy soil
    (Frontiers Media, 12/05/2023) Yi Z; Jeyakumar P; Yin C; Sun H
    Biochar application can improve crop yield, reduce ammonia (NH3) volatilization and nitrous oxide (N2O) emission from farmland. We here conducted a pot experiment to compare the effects of biochar application on rice yield, nitrogen (N) uptake, NH3 and N2O losses in paddy soil with low, medium, and high N inputs at 160 kg/ha, 200 kg/ha and 240 kg/ha, respectively. The results showed that: (1) Biochar significantly increased the rice grain yield at medium (200 kg/ha) and high (240 kg/ha) N inputs by 56.4 and 70.5%, respectively. The way to increase yield was to increase the rice N uptake, rice panicle number per pot and 1,000 grain weight by 78.5–96.5%, 6–16% and 4.4–6.1%, respectively; (2) Under low (160 kg/ha) N input, adding biochar effectively reduced the NH3 volatilization by 31.6% in rice season. The decreases of pH value and NH4+-N content in surface water, and the increases of the abundance of NH4+-N oxidizing archaea and bacteria (AOA and AOB) communities contributed to the reduction of NH3 volatilization following the biochar application; (3) Under same N input levels, the total N2O emission in rice season decreased by 43.3–73.9% after biochar addition. The decreases of nirK and nirS gene abundances but the increases of nosZ gene abundance are the main mechanisms for biochar application to reduce N2O emissions. Based on the results of the current study, adding biochar at medium (200 kg/ha) N level (N200 + BC) is the best treatment to synchronically reduce NH3 and N2O losses, improve grain yield, and reduce fertilizer application in rice production system.
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    Effects of full inversion tillage during pasture renewal on soil and plant cadmium concentrations: a case study in New Zealand
    (CSIRO Publishing, 5/12/2022) Peng Y; Hanly JA; Jeyakumar P; Calvelo-Pereira R
    Context: Cadmium (Cd) accumulation is a concern in permanent pasture soils, as it can lead to increased Cd uptake by plants. Aims: This study aimed to quantify the effect of full inversion tillage (FIT or ploughing deeper than 30 cm), used during pasture renewal, on the redistribution of Cd within the soil profile and on plant Cd concentration. Methods: Two field trials (Trial 1, Alfisol; Trial 2, Andisol) were established in New Zealand using contrasting tillage practices (FIT; SIT, shallow tillage; and NT, no tillage) to sow turnips as summer forage crops, followed by autumn re-sowing of perennial ryegrass/white clover pasture. Key results: In the Alfisol, no measurable differences (P > 0.05) in soil and plant Cd were detected among the tillage treatments. In the Andisol, FIT decreased (P < 0.05) total (0.25 mg/kg) and extractable soil Cd (0.013 mg/kg) in the 0–5 cm depth, compared to pre-tillage (0.42 and 0.031 mg/kg, respectively). Moreover, at this soil depth, FIT achieved a 52% lower (P = 0.034) extractable soil Cd concentration than the ST treatment. In addition, the subsequent new pasture had lower (P = 0.007) average Cd concentration following FIT compared to ST (0.03 vs 0.05 mg/kg). Conclusions: We demonstrated that the use of FIT during pasture renewal is a potential solution to reduce topsoil Cd concentration. Implications: The FIT is more effective in soil where total soil Cd concentration or its degree of vertical stratification with depth is relatively high.
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    Enhanced denitrification driven by a novel iron-carbon coupled primary cell: chemical and mixotrophic denitrification
    (Springer, 2024-01-10) Wu R; Jeyakumar P; Nanthi B; Zhai X; Wang H; Pan M; Lian J; Cheng L; Li J; Hou M; Cui Y; Yang X; Dai K
    Iron-carbon micro-electrolysis system is a promising method for promoting electron transfer in nitrate removal. However, many traditional approaches involving simple physical mixing inevitably suffered from the confined iron-carbon contact area and short validity period, leading to the overuse of iron. Here, a ceramsite-loaded microscale zero-valent iron (mZVI) and acidified carbon (AC) coupled-galvanic cell (CMC) was designed to support chemical, autotrophic and heterotrophic denitrification. Long-term experiments were conducted to monitor the nitrogen removal performance of denitrification reactors filled with CMC and thus optimized the denitrification performance by improving fabrication parameters and various operating conditions. The denitrification contributions test showed that the chemical denitrification pathway contributed most to nitrate removal (57.3%), followed by autotrophic (24.6%) and heterotrophic denitrification pathways (18.1%). The microbial analysis confirmed the significant aggregation of related denitrifying bacteria in the reactors, while AC promoted the expression of relevant nitrogen metabolism genes because of accelerated uptake and utilization of iron complexes. Meanwhile, the electrochemical analysis revealed a significantly improved electron transfer capacity of AC compared to pristine carbon. Overall, our study demonstrated the application of a novel mZVI-AC coupled material for effective nitrate removal and revealed the potential impact of CMC in the multipathway denitrification process. Graphical Abstract: [Figure not available: see fulltext.]
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    Enhanced removal of arsenic and cadmium from contaminated soils using a soluble humic substance coupled with chemical reductant.
    (1/03/2023) Wei J; Tu C; Xia F; Yang L; Chen Q; Chen Y; Deng S; Yuan G; Wang H; Jeyakumar P; Bhatnagar A
    Soil washing is an efficient, economical, and green remediation technology for removing several heavy metal (loid)s from contaminated industrial sites. The extraction of green and efficient washing agents from low-cost feedback is crucially important. In this study, a soluble humic substance (HS) extracted from leonardite was first tested to wash soils (red soil, fluvo-aquic soil, and black soil) heavily contaminated with arsenic (As) and cadmium (Cd). A D-optimal mixture design was investigated to optimize the washing parameters. The optimum removal efficiencies of As and Cd by single HS washing were found to be 52.58%-60.20% and 58.52%-86.69%, respectively. Furthermore, a two-step sequential washing with chemical reductant NH2OH•HCl coupled with HS (NH2OH•HCl + HS) was performed to improve the removal efficiency of As and Cd. The two-step sequential washing significantly enhanced the removal of As and Cd to 75.25%-81.53% and 64.53%-97.64%, which makes the residual As and Cd in soil below the risk control standards for construction land. The two-step sequential washing also effectively controlled the mobility and bioavailability of residual As and Cd. However, the activities of soil catalase and urease significantly decreased after the NH2OH•HCl + HS washing. Follow-up measures such as soil neutralization could be applied to relieve and restore the soil enzyme activity. In general, the two-step sequential soil washing with NH2OH•HCl + HS is a fast and efficient method for simultaneously removing high content of As and Cd from contaminated soils.
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    Enhancing Biological Nitrogen Fixation Through Diverse Pasture Swards
    (MDPI (Basel, Switzerland), 2025-09) Sutharsan R; Jeyakumar P; Burkitt L; Matse DT; Dhanuskodi R; Hanly J; Donaghy DJ; Cai H
    Regenerative agricultural practices emphasize the use of diverse pasture species within sustainable agriculture production systems. The inclusion of a range of legume species in diverse pasture swards is likely to increase biological N fixation (BNF) across seasons, reducing the system’s reliance on synthetic N inputs. The present field study aims to quantify BNF in selected legume species within diverse pasture (combining 9 species) and standard pastures (ryegrass and clover combination) and assess their performance to identify the potential for improving N supply while maintaining year-round pasture quality. A year-round seasonal BNF was assessed by evaluating soil N status, nodulation patterns, plant composition, and conducting 15N natural abundance studies. The results revealed that the diverse pasture sward produced 5.4% more dry matter compared to the standard pasture, while soil mineral N (NO3−, NH4+) remained statistically similar between the two treatments. Nitrogen yield was 9.3% higher in the diverse pasture than in the standard pasture. 15N natural abundance analysis assessment revealed no substantial variation in BNF rates across treatments throughout the study. However, in contrast to standard pasture, the BNF rate in diverse pasture experienced a 3-fold increase from winter to summer, while the standard pasture exhibited a 1.5-fold increase. In both pasture systems, BNF increased with clover proportion up to 30%, indicating optimal fixation at moderate clover levels. The findings underscore the potential of diverse pastures when strategically managed to enhance seasonal BNF while sustaining pasture productivity.
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    Exploring Phosphorus Dynamics in Submerged Soils and Its Implications on the Inconsistent Rice Yield Response to Added Inorganic Phosphorus Fertilisers in Paddy Soils in Sri Lanka
    (2024-03-01) Palihakkara J; Burkitt L; Jeyakumar P; Attanayake CP
    Rice is the primary energy source of more than half of the global population. Challenges persist in managing phosphorus (P) in paddy soils of tropical rice-growing countries. In Sri Lanka, one specific challenge is the inconsistent yield response observed when inorganic P fertilisers are applied to paddy soils. Previous research conducted in Sri Lanka has shown that the rice yield response to added P fertilisers cannot be adequately explained by factors such as soil available P, irrigation schemes, soil texture, pH, electrical conductivity, total carbon content and available Fe and Mg concentrations. Due to the submerged conditions in which rice is grown for a significant portion of its lifespan, a unique environment controlled by redox-driven processes is developed in paddy soils. Therefore, releasing P from submerged soils is an outcome influenced by complex hydrological and biogeochemical processes, strongly influenced by inherent soil characteristics. The present review paper aimed to critically examine existing literature on soil P behaviour in submerged paddy soils of Sri Lanka, to clarify the behaviour of P under submergence, identify the factors affecting such behaviour and highlight the research gaps that need to be addressed, in order to effectively manage P in the paddy soils of Sri Lanka.
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    Formulation and characterization of polyester-lignite composite coated slow-release fertilizers
    (Springer Nature Switzerland AG, 26/09/2022) Gunaratnam A; Bishop P; Jeyakumar P; Grafton M; Davies CE; McCurdy M
    Two polyester-lignite composite coated urea slow-release fertilizers (SRFs; Poly3 and Poly5) were developed and their physicochemical properties were studied. Both these SRFs significantly (p < 0.05) extended the urea release compared to uncoated urea; Poly3 and Poly5 by 117 and 172 h, respectively. The urea release characteristics of Poly5 were further enhanced by linseed oil application (Poly5-linseed). The SEM images demonstrated the coatings were in contact with the urea and encase urea particles completely with the average coating thickness of 167.2 ± 15 µm. The new interactions between polyester and lignite in the composite coating were confirmed by the FTIR analysis. Polyester-calcium carbonate (Polyester-CaCO3) coated SRFs (Calc3 and Calc5) were developed using CaCO3 as a filler in place of lignite and the urea dissolution rate was compared with Poly3 and Poly5. The urea release times for the polyester-CaCO3 formulations, 48 and 72 h, were significantly (P < 0.05) lower than the polyester-lignite formulation, showing that lignite imparted greater control over release time than CaCO3. Findings from this work showed that polyester-lignite composites can be used as a coating material for SRFs.
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    Influence of Soil Moisture Status on Soil Cadmium Phytoavailability and Accumulation in Plantain (Plantar lanceolata)
    (MDPI (Basel, Switzerland), 2018-03) Stafford A; Jeyakumar P; Hedley M; Anderson C
    The effect of fluctuating soil moisture cycles on soil cadmium (Cd) phytoavailability was investigated in a pot trial with two contrasting soils (Kereone (Allophanic), total Cd 0.79 mg kg−1; and Topehaehae (Gley), total Cd 0.61 mg kg−1) that were either sown with plantain (Plantago lanceolata) or left unseeded. Varying soil moisture contents were established using contrasting irrigation regimes: “flooded” (3 days flooded and then 11 days drained); or “non-flooded” (irrigation to 70% of potted field capacity every 7 days). Overall, there was no significant difference in mean 0.05 M CaCl2 soil extractable Cd concentrations or plant tissue Cd concentrations between flooded and non-flooded irrigation. However, there was a consistent trend for an increase in soil extractable Cd concentrations following irrigation, regardless of the irrigation regime. Mean soil extractable Cd and plant tissue Cd concentrations were significantly greater (approximately 325% and 183%, respectively) for the Topehaehae soil than the Kereone soil, despite the lower soil total Cd concentration of the Topehaehae soil. These results indicate that Cd solubility is sensitive to increases in soil moisture following periods of soil drainage, but insensitive to short-term periods of soil saturation. Plant tissue Cd concentrations in Cd-sensitive forage crops such as plantain are likely to be greater following large rainfall events over summer and autumn. This has the potential to increase animal dietary Cd exposure and rate of liver/kidney Cd accumulation.
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    Iron-rich sand promoted nitrate reduction in a study for testing of lignite based new slow-release fertilisers
    (Elsevier, 20/12/2022) Abhiram G; Grafton M; Jeyakumar P; Bishop P; Davies C; McCurdy MM
    The N losses and agronomic performances of newly developed slow-releasing fertilisers (SRFs; Epox5 and Poly5) were tested against conventional N fertilisers, urea and diammonium phosphate (DAP), in a climate-controlled lysimeter system. The dry matter (DM) yield and N losses of SRFs were not significantly different from urea and DAP. However, nitrate leaching and nitrous oxide (N2O) losses were unexpectedly low and therefore, it was inferred that nitrate underwent a chemical transformation. It was observed that a thick fibreglass wick interrupted drainage and created an anaerobic condition in the soil. The subsoil was found to have a high extractable total iron and it was postulated that iron played a role in the observed low level of N losses. An investigation was carried out with a factorial design using sand types and rates of N application as the main factors. Two types of sand; with high and low iron concentration and four levels of N applications; 0 (control), 50, 100 and 200 kg N ha-1 were employed in a leaching column and nitrate and N2O losses were measured. The nitrate leaching was significantly (P < 0.05) affected by sand types wherein a lower nitrate level was recorded for high‑iron concentration sand than for low-iron concentration sand at all N application levels. The N2O emission was significantly (P < 0.05) lower for high-iron sand than for low-iron sand for the 200 N treatment, but not significantly different between sand types for other treatments. These observations provide evidence for the involvement of iron in nitrate transformation under anaerobic conditions and it was hypothesised path was dissimilar nitrate reduction (DNR). Further studies are recommended, to identify the underlying mechanism responsible for nitrate reduction with iron-rich sand.
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    Nitrate leaching mitigation options in two dairy pastoral soils and climatic conditions in New Zealand
    (MDPI (Basel, Switzerland), 17/09/2022) Matse DT; Jeyakumar P; Bishop P; Anderson CWN
    This lysimeter study investigated the effect of late-autumn application of dicyandiamide (DCD), co-poly acrylic-maleic acid (PA-MA), calcium lignosulphonate (LS), a split-application of calcium lignosulphonate (2LS), and a combination of gibberellic acid (GA) and LS (GA + LS) to reduce N leaching losses during May 2020 to December 2020 in lysimeter field sites in Manawatu (Orthic Pumice soil) and Canterbury (Pallic Orthic Brown soil), New Zealand. In a second application, urine-only, GA only and GA + LS treatments were applied during July 2020 in mid-winter on both sites. Results showed that late-autumn application of DCD, 2LS and GA + LS reduced mineral N leaching by 8%, 16%, and 35% in the Manawatu site and by 34%, 11%, and 35% in the Canterbury site, respectively when compared to urine-only. There was no significant increase in cumulative herbage N uptake and yield between urine-treated lysimeters in both sites. Mid-winter application of GA and GA + LS reduced mineral N leaching by 23% and 20%, respectively in the Manawatu site relative to urine-only treated lysimeters, but no significant reduction was observed in the Canterbury site. Our results demonstrated the potential application of these treatments in different soils under different climate and management conditions.