Unlimed Soil Research Articles

The Jyndevad Experiment: Revealing long-term interactions between liming and phosphorus fertilization in a coarse sand soil

The Jyndevad field experiment, initiated in 1942 on a coarse sand soil in South of Denmark, explores the effect of four liming levels (0, 4, 8 and 12 Mg lime ha−1). These were in 1944 combined with two levels of mineral phosphorus (P) fertilizer (0 and 15.6 kg P ha−1 year−1), with or without a high initial dose of 156 kg mineral P ha−1. This study assesses interactions between liming and P fertilization on soil pH, Olsen-P contents and barley yields covering the last three decades. Annual P application improved barley yield regardless of liming, but the optimal liming level differed from year to year. This emphasizes the need for long-term field experiments to detect the complex interactions between liming and P availability on crop performance. The initial high P dose in 1944 and annual P fertilization increased Olsen-P contents in soil. The unlimed soil with pH(CaCl2) values below 4 had the highest Olsen-P content. The Jyndevad Experiment now harbors wide gradients in soil P (Olsen-P contents: 9–82 mg P kg−1 soil) and pH (3.6–6.9), providing a unique research platform for future studies on interactions between liming and P fertilization on coarse sand soils. We present a selection of studies that have used the Jyndevad Experiment to illustrate the research potential of the experiment.

Arsenic, cadmium, and chromium concentrations in contrasting phosphate fertilizers and their bioaccumulation by crops: Towards a green label?

Potentially toxic elements such as arsenic (As), cadmium (Cd), and chromium (Cr) are severely regulated in fertilizers and deserve continuous investigation. Phosphate-derived Cd has been a stepping-stone toward achieving sustainable and safe worldwide food production, especially after a new regulation aiming for reduced limits of Cd in P fertilizers (EU, 2019/1009). Three pot experiments were conducted to assess the variability of As, Cd, and Cr concentrations - with a particular focus on Cd - from monoammonium phosphates (MAP 1, MAP 2, and MAP 3 from different geographic origins) and their accumulation in limed and unlimed soils, and contrasting crops, representing staple food and significant sources of these elements for humans (i.e., potato, tobacco, and rice). A diverse array of sensitive techniques for trace elements determination were used to reveal the highest level of Cd of MAP 3 (20.71 mg kg−1 MAP), which loaded the highest amounts of this element to the soil matrix and solution, plant shoots, and xylem sap, contrasting with results for MAP 1 (0.87 mg kg−1 MAP), which has almost ten times less Cd than that required for low-Cd labeling of P fertilizers (≤20 mg Cd kg−1 P2O5). MAP 3 also had the highest Cr concentration (139.3 mg kg−1 MAP). Among crops, rice accumulated 16-fold less Cd than potato plants. Liming decreased Cd in tobacco and potato shoots up to 35%. Moreover, reductions of about 20% were also observed for Cd accumulation in tubers and sap. Conversely, Cd from MAP 3 was always much more accumulated in soil solution, achieving up to 20 μg L−1, while values < 5 μg L−1 (i.e., a groundwater limit) were obtained from MAP 1. Our findings may be used as a reference in developing green labels for fertilizers in scenarios where Cd accumulation represents a potential risk for soil and human health.

Manganese and phosphorus maize shoot concentrations are differently affected by nitrification inhibitor‐driven rhizosphere acidification

AbstractHigh soil pH can lead to Mn2+ and P deficiency and yield losses. In addition, it is unclear which process, nitrification‐induced acidification of bulk soil or nitrification inhibitor‐driven rhizosphere acidification, is more effective in increasing Mn2+ availability and shoot concentration. Thus, this topic was investigated in this study. Moreover, we also evaluated if applying NIs can avoid P deficiency in soil with high pH and high buffering capacity. Two greenhouse experiments were carried out to investigate the impact of applying 3,4‐Dimethylpyrazole phosphate (DMPP) in sandy soil subjected to the application of different lime rates, simulating several soil pH and buffering capacity conditions. The utilized lime rates were 0, 0.5, 1, 2 and 4 g CaCO3 kg−1. The measured variables were bulk and rhizosphere soil pH, Mn2+ and P availability, maize biomass production, as well as Mn and P shoot concentrations. DMPP significantly reduced shoot biomass by 10% in unlimed soil; however, it promoted the overall shoot biomass by 30% in limed soil in both experiments. In addition, DMPP decreased the overall Mn shoot concentration by 24 and 21% in experiments I and II, respectively. In contrast, DMPP increased the overall P shoot concentration due to rhizosphere acidification by 24 and 17% in experiments I and II, respectively. The DMPP application did not avoid P deficiency under the highest lime rate (4 g CaCO3 kg−1) despite alleviating it. In conclusion, the application of NIs is not beneficial for increasing Mn2+ shoot concentration and, when performed to increase P availability in high pH soils, should consider the likelihood of causing Mn deficiency.

Do soil enzyme activities explain stimulated carbon mineralization following liming?

Losses of soil organic carbon (C) following liming have been proposed to result from stimulated C mineralization, which could occur through a variety of mechanisms including soil enzymes. Given the pH-sensitivity of enzyme activities, liming could impact catalysis of C mineralization by extracellular enzymes independently of microbial response. To this end, we evaluated the responses of C mineralization as CO2 flux, permanganate-oxidizable C (POXC), and the activities of C-hydrolytic enzymes to liming of a Haplic Ferralsol (Typic Kandiudox) in western Kenya under three differing 11-year soil fertility managements: unfertilized (UNF), mineral fertilized (MIN), and organic fertilized (ORG). Five rates of Ca(OH)2 (1.5, 3.0, 4.5, 6.0, and 7.5 t ha−1) and an unlimed control were used to establish a pH gradient of 4.6–6.4. Soil C mineralization rates assessed as CO2 production peaked within 5 d for high liming rates, and converged to a similar rate as unlimed soils after 21 d. At 28 d, activities of β-glucosidase and cellobiohydrolase decreased with increasing pH, increased for β-glucosaminidase, and were unaffected for β-galactosidase. POXC generally increased with liming rate for fertilized soils, more so in ORG and less in MIN soils, with relative increases of 18%, 5%, and 1% for ORG, MIN and UNF soils, respectively, at 7.5 relative to 0 t ha−1 liming. This study identifies potentially rapid albeit short-lived stimulation of C mineralization following addition of a highly soluble liming agent. Notably, decreases in activities of soil enzymes that catalyze the first and last step of the cellulosic C depolymerization suggests that short-term losses of soil C were not driven by enzyme activities, and may occur in spite of lowered C-hydrolytic enzyme activity. The enhanced C mineralization observed could reflect augmentation of labile C pools via non-enzymatic processes (e.g., desorption) in the short-term.

Long-term liming mitigates the positive responses of soil carbon mineralization to warming and labile carbon input

Liming, as a common amelioration practice worldwide, has the potential to alleviate soil acidification and ensure crop production. However, the impacts of long-term liming on the temperature sensitivity (Q10) of soil organic carbon (SOC) mineralization and its response to labile C input remain unclear. To fill the knowledge gap, soil samples were collected from a long-term (∼10 years) field trial with unlimed and limed (CaO) plots. These soil samples were incubated at 15 °C and 25 °C for 42 days, amended without and with 13C-labeled glucose. Results showed that compared to the unlimed soil (3.6–8.6 mg C g−1 SOC), liming increased SOC mineralization (6.1–11.2 mg C g−1 SOC). However, liming significantly mitigated the positive response of SOC mineralization to warming, resulting in a lower Q10. Long-term liming increased bacterial richness and Shannon diversity as well as their response to warming which were associated with the decreased Q10. Furthermore, the decreased Q10 due to liming was attributed to the decreased response of bacterial oligotrophs/copiotrophs ratio, β-glucosidase and xylosidase activities to warming. Labile C addition had a strong impact on Q10 in the unlimed soil, but only a marginal influence in the limed soil. Overall, our research highlights that acidification amelioration by long-term liming has the potential to alleviate the positive response of SOC mineralization to warming and labile C input, thereby facilitating SOC stability in agroecosystems, especially for acidic soils in subtropical regions.

Synergistic benefits of lime and 3,4-dimethylpyrazole phosphate application to mitigate the nitrous oxide emissions from acidic soils

Acidic soils cover approximately 50 % of the arable land with high N2O emission potential. 3,4-dimethylpyrazole phosphate (DMPP) inhibits N2O emission from soils; however, its efficiency is affected by acidity. Liming is used for soil conditioning to ameliorate the effects of acidity. In the present study, we investigated the effects of liming on the efficiency of DMPP in inhibiting N2O emission in acidic soils and the mechanisms involved. We evaluated the impact of liming, DMPP, and combined application and its microbial responses in two acidic soils from Zengcheng (ZC) and Shaoguan (SG) City, Guangdong Province, China. Soils were subjected to four treatments: un-limed soil (low soil pH) + urea (LU), un-limed soil + urea + DMPP (LD), limed soil (high soil pH) + urea (HU), and limed soil + urea + DMPP (HD) for analyses of the mineral N, N2O emissions, and full-length 16S and metagenome sequencing. The results revealed that, HU significantly decreased and increased the N2O emission by 17.8 % and 235.0 % in ZC and SG, respectively, compared with LU. This was caused by a trade-off between N2O production and consumption after liming, where microbial communities and N-cycling functional genes show various compositions in different acidic soils. LD reduced N2O emission by 23.5 % in ZC, whereas decreased 1.5 % was observed in SG. Interestingly, DMPP efficiency considerably improved after liming in two acidic soils. Compared with LU, HD significantly reduced N2O emissions by 61.2 % and 48.5 % in ZC and SG, respectively. Synergy of mitigation efficiency was observed by lime and DMPP application, which was attributed to the changes in the dominant nitrifiers and the increase in N2O consumption by denitrifiers. The combined application of lime and DMPP is a high-efficiency strategy for N2O mitigation can ensure agricultural sustainability in acidic arable soils with minimal environmental damage.

Variation in microbial biomass and enzymatic activities in metal contaminated soils during storage at low temperature (4°C)

ABSTRACT Microbial response to soil storage at low temperature in limed and unlimed samples has not been investigated. For this study, soil samples were kept at 4°C for six weeks. Soil microbial biomass was determined using phospholipid fatty acid analysis (PLFA). Nine enzymes were targeted including β-glucosidase (BG), cellobiohydrolase (CBH), β-N-acetylglucosaminidase (NAGase), aryl sulfatase (AS), acid phosphatase (AP), alkaline phosphatase (AlP), glycine aminopeptidase (GAP), leucine aminopeptidase (LAP), and peroxidase (PER). PLFA results revealed a significant increase in total microbial biomass in limed area compared to unlimed soil samples. Microbial biomass decreased during the first two weeks of storage and remained unchanged thereafter for both limed and unlimed samples. Analysis of microbial activities revealed that most enzymes inconsistently decreased over time during storage at 4°C. Activities of BG, CBH, NAGase, AlP, AS, GAP, LAP were significantly higher in limed compared to the unlimed samples. Overall, the levels of activities of most enzymes in limed soils decreased significantly after the second week of storage and remained unchanged thereafter. The reduction of enzyme activity in the unlimed soil samples varied over time, with some enzymes such as LAP increasing on the sixth week. PER activity decreased after two weeks and increased thereafter.

The Response of Retisol’s Carbon Storage Potential to Various Organic Matter Inputs

Organic carbon sequestration and its quality in soil is a crucial aspect in maintaining the productivity of the soil and the whole ecosystem. The study examined the changes in soil organic carbon (SOC), its sequestration potential, and the mean effect size under various long-term organic matter inputs in acid soil (Dystric Retisol). Cattle manure (CM 60 t ha−1) and various plant residues were used for the fertilization of acid and limed soil. The following treatments were included in the experimental design: (1) natural Retisol; (2) natural Retisol + CM; (3) natural Retisol + various plant residues; (4) calcium carbonate (CaCO3) at a 1.0 rate every five years); (5) CaCO3 + CM; (6) CaCO3 + various plant residues. The data demonstrated that the treatments including the use of organic material (CM and various plant residues) showed a greater SOC content accumulation with a storage of up to 0.2–0.6% more carbon in the topsoil. Alternative organic fertilizers had a detrimental impact when applied to unlimed soil, with a loss of 0.59 g kg−1 C per year. All the fertilization treatments significantly increased the SOC level with the mean effect size of 0.02–0.28, and the increase varied from 1.89% to 32.89%. This result suggested that liming, together with organic fertilizers, proved to be a relatively efficient approach to improving the soil’s health and quality.

Ammonium Fertilization Enhances Nutrient Uptake, Specifically Manganese and Zinc, and Growth of Maize in Unlimed and Limed Acidic Sandy Soil

Although NH4+ fertilization is known to acidify rhizosphere and enhance nutrient uptake, the effects on a nutrient-sufficient acidic soil amended with lime are not demonstrated. Thus, the influence of NH4+ fertilization of an unlimed and limed (3 g calcium carbonate per kg soil) acidic soil on the nutrient uptake and growth of maize was studied in comparison to NH4NO3 fertilization. The pH of limed rhizosphere soil was about two units higher than that of the unlimed soil. The maize plants were grown in pots under greenhouse conditions for about two months. The results showed that the pH of the NH4+-fertilized unlimed and limed soil was 0.54 and 0.15 units lower than the NH4NO3-fertilized soil. Liming negatively affected shoot and root dry matter production, whereas the NH4+-fertilized plants produced higher dry matter than the NH4NO3-fertilized plants, with significant difference of 28% in the limed soil only. Liming decreased Fe concentration in rhizosphere soil from 99 to 69 mg kg−1 and decreased plant-available Mn the most (71%), whereas the NH4+-fertilized unlimed and limed soil had 48% and 21% higher Mn concentration than the respective NH4NO3-fertilized soils. Similarly limed rhizosphere soil had 50% lower plant-available Zn concentration than the unlimed soil, and the NH4+-fertilized soil had an 8% higher Zn concentration than the NH4NO3-fertilized unlimed soil. The liming negatively affected P, K, Mn, and Zn concentrations and contents in maize shoot to a lower degree in the NH4+-fertilized soil, whereas the positive effect of NH4+ on the nutrient concentration and contents was vigorous in the unlimed soil than the limed soil. It is concluded that NH4+ fertilization could be beneficial in enhancing nutrient uptake and growth of maize in both acidic and alkaline soils, despite the higher inherent plant-available concentrations of the nutrient in soil.

Tolerance to soil acidity of soybean (Glycine max L.) genotypes under field conditions Southwestern Ethiopia.

Soil acidity with associated low nutrient availability is one of the major constraints to soybean production in southwestern Ethiopia. Integrated use of lime and acid-tolerant crops is believed to reduce soil acidity and improve crop production. The experiment was conducted in the field condition of Mettu, southwestern Ethiopia during the 2017/18 main cropping season. The experiment comprised fifteen soybean genotypes and two soil amendment (lime and unlimed) treatments arranged in a split-plot design with three replications. For each treatment, four rows were planted per plot; data related to growth, root, nodule, and yield of the crop were collected at a necessary stage for each. Liming and genotype interaction had significantly (P = 0.01) affected all parameters considered except for hundred seed weight and root volume and were affected only by the main effects of genotypes and liming. A significant reduction for most parameters was found on lime-untreated soil than treated soil. Though some genotypes showed higher performance for root, growth parameters, and yield components under unlimed soils; however, gave higher yield and yield components, when grown on lime-untreated with an average yield reduction of 13.7%, due to soil acidity. The maximum grain yield of (1943.93 kg ha-1) was obtained under lime treated acid soil from PI567046A genotype; while the lowest (510.49 kg ha-1) were recorded from SCS-1genotype under the lime untreated acid soil. Genotype BRS268 showed higher yield (1319.83 kg ha-1) under lime untreated acid soil than lime treated acid soil (1143.47 kg ha-1) and showed less reduction percentage for a number of the nodules, root weight, and number of seeds per plant; while PI567046A showed high reduction percentage for yield, biomass, number of pod and seed per plant. A high difference was observed among the soybean genotypes for soil acidity tolerance, which might be further exploited by breeders for the genetic improvement of soybean. Genotype BRS268 had performed better than other tested genotypes under increased soil acidity. selection would be effective to improve soybean genotypes performance on acid soils and identify low Phosphorus tolerant genotype that helps smallholder farmers optimize soybean productivity on acid soils in the study area. HAWASSA-04 variety is the most tolerant among the tested materials. However, further study is required by considering additional genotypes to reach a conclusive recommendation.

Liming decreases the emission and temperature sensitivity of N2O following labile carbon addition

Lime has been widely applied for ameliorating soil acidification, potentially improving soil fertility and crop production. However, the long-term effects of liming and its interaction with carbon (C) availability on the emission and temperature sensitivity (Q10) of greenhouse gas nitrous oxide (N2O) from acidic arable soil are not well understood. Here, the limed and unlimed acidic soils collected from a long-term field trial, amended with and without glucose as labile C, were incubated at 15℃ and 25℃ to investigate the responses of the emission and Q10 of N2O and the underlying mechanisms. Results showed that liming had no effect on N2O emission without labile C addition. While after labile C addition, N2O emissions were 13–28% lower in the limed relative to unlimed soils, indicating that the mitigation effect of liming on N2O emission can mainly be seen when labile C (e.g., from rhizodeposition) is highly available in soils. High temperature did not affect N2O emissions from soil without labile C addition, but greatly increased N2O emissions after labile C addition with significantly lower Q10 of N2O in the limed (1.23) relative to unlimed soils (1.48). These results suggested that liming could decrease the Q10 of N2O emission in the presence of labile C. Elevated soil pH by liming caused increases in the abundances of N2O reductase genes (nosZI and nosZII) over nitrite reductase genes (nirK and nirS), thus significantly lowering (nirK + nirS)/(nosZI + nosZII) ratio compared to the unlimed soil, particularly after labile C addition. Soil N2O emissions were strongly positively related to the nirK abundance, (nirK + nirS)/(nosZI + nosZII) ratio, and NO3− consumption after labile C addition, indicating that denitrification was mostly responsible for N2O emission. Concluding, long-term liming could potentially reduce N2O emission and its Q10 via decreased (nirK + nirS)/(nosZI + nosZII) ratio in acidic soils in the presence of labile C.

Combined Application of Lime and a Nitrification Inhibitor (3,4-Dimethylpyrazole Phosphate) Markedly Decreased Nitrous Oxide Emissions from an Acid Soil

High nitrous oxide (N2O) emissions (2–10% of fertiliser N) were observed previously from acid soils cropped with sugarcane (Saccharum officinarum) in Australia. We assessed the impact of lime, a nitrification inhibitor (NI, as 3,4-dimethylpyrazole phosphate, DMPP), and copper (Cu) on N2O emissions from an acid sugarcane soil in a laboratory experiment using (1) urea (U), (2) U + DMPP, (3) U + CuSO4.5H2O (U + Cu), and (4) U + DMPP + Cu. The treatments were applied to both an un-limed soil (pH 5.1) and a limed soil (pH 6.9) and incubated at 25 °C and 55% water holding capacity (WHC) for 28 d, and then increased to 90% WHC for another 8 d to favour denitrification. At 55% WHC, both the addition of the NI (U + DMPP) and the liming of the acid soil significantly decreased cumulative N2O emissions, due to significantly lower net nitrifications. Liming and DMPP decreased N2O emissions by 79% and 90%, respectively. However, where lime and DMPP were applied together, N2O emissions decreased by 94% compared to those in the un-limed (acid) U-treated soil. In contrast, the addition of Cu and the increase in water content to 90% WHC had no significant effect on N2O emissions. Therefore, the combined use of lime and DMPP provides the best option to decrease N2O emissions from the acid soil.

Response of acid forest soils to helicopter liming in the Monongahela National Forest, West Virginia

AbstractTypical of soils in humid climates, soils in the Monongahela National Forest (MNF) in West Virginia are acidic because of leaching of base cations, uptake of Ca and Mg by vegetation, and release of organic acids by organic matter (OM) decomposition. Soil acidity has increased because of anthropogenic acid deposition causing declines in forest health. In anticipation of a large‐scale liming project in the MNF, soils at 10 sites were sampled and analyzed in 2009. In 2018, lime was applied by helicopter to a total of 323 ha at a rate of 10 Mg ha−1. One year after liming, soils were resampled and analyzed in 2019 representing five limed and five unlimed areas using the same procedures. The objectives were to determine whether unlimed soils had changed between 2009 and 2019 and to evaluate changes in soils resulting from liming in 2019 for pH, acidity, and Al and Ca concentrations. In O and A horizons, unlimed soils had changed only slightly in the 10‐yr interval. Liming increased soil pH in O horizons from 4.6 to 5.9. Liming reduced acidity values by 73% and Al concentrations by 80% in O horizons. Liming increased Ca concentrations by at least three times in O and A horizons. Based on first‐year results, liming had a significant effect on soil properties of O and A horizons. Future sampling at 3 and 5 yr after liming will help to evaluate further changes in soils as a result of liming and under reduced acid deposition rates.

Responses in growth, yield and cob protein content of baby corn (

Cropping of acid sulfate soils requires effective treatment of their inherently low pH. We evaluated the efficacy of applications of two levels of lime (0 or 2 Mg/ha), two levels of organic fertiliser (0 or 5 Mg/ha), and three levels of biochar (0, 10 or 30 Mg/ha) in a factorial design for ameliorating acidity in an acid sulfate soil, and measured the subsequent growth and yield of baby corn (Zea mays L.). Lime increased soil pH(H2O) from 3.75 to 4.12, salinity from 1.72 to 1.95 dS/m, and cob yield by 30%. None of the amendments significantly altered total organic carbon or total nitrogen concentrations in the soil. Biochar additions increased cob yields by an average of 28% on both unlimed and limed soil. Addition of organic fertiliser increased cob yield by 45% on unlimed soil but had no significant effect on yields on limed soil. The yields obtained with liming were similar to the highest yields achieved with biochar or organic fertiliser applied either separately or in combinations. Overall, cob yields were increased by 19% with addition of organic fertiliser. The yield increseas from additions of biochar or organic fertiliser were associated with improvements in nutrient supply. However, the increases in cob yield were associated with reduced cob protein, probably resulting from poor availability of nitrogen late in the season. We conclude that biochar and organic fertiliser applied in relatively large quantities can be viable treatments for cropping acid sulfate soils.

Effect of long-term application of organic fertilizers on improving organic matter quality in acid soil

ABSTRACT Soil organic carbon (SOC) content can greatly affect soil quality by determining and maintaining important soil functions. The study examined SOC, humic substances and molecular composition characteristics of acid soil (Dystric Retisol) with different long term (54 years) fertilization in Western Lithuania. Farmyard manure (FYM 60 t ha−1) and alternative organic fertilizers (wheat straw, green mass of lupine and oats, rape stubble and straw) applied on the two soil backgrounds – acid and limed. The experimental design included the following treatments: 1) unlimed soil; 2) unlimed soil + FYM; 3) unlimed soil + alternative organic fertilizers; 4) limed soil (1.0 rate every 5 years); 5) limed soil + FYM; 6) limed soil + alternative organic fertilizers. The result indicates that application of organic fertilizers exerted a significant positive effect on SOC accumulation (0.1–0.4% more carbon than the control). The combination of soil liming and FYM resulted in the accumulation of valuable humic acids. The higher amount of humic acids (0.67% of C) was maintained under FYM applied plots. The application of organic fertilizers and liming exerted the transformation of carbon compounds changes in the direction of polymerization of humic acids, which creates more favourable conditions for carbon sequestration.

Cadmium, silicon and nutrient accumulation by maize plants grown on a contaminated soil amended with a diatomaceous Earth fertilizer

ABSTRACT: Given that cadmium (Cd) poses high persistence in the environment and toxicity to humans, strategies to either decrease or avoid Cd entry in the trophic chain are fundamental to secure food safety. Here we assessed the effects of applying rates of Si as a diatomaceous Earth-based fertilizer on the amelioration of Cd toxicity towards maize plants grown on soil with or without pH correction. Besides determining Si and Cd concentrations, we also evaluated plant accumulation of nutrients (N, P, K, Ca, Mg, Fe, Mn, Cu, and Zn) as a function of Si doses applied to the soil. Results showed that both the Si application and the liming had a positive effect on biomass and nutrient uptake, but the Si effect on plants’ performance took place irrespectively to the soil pH. Silicon ameliorated Cd phytotoxicity in both limed and unlimed soils by decreasing Cd concentration in shoots and improving biomass yield and plant nutrition. Silicon alleviation of Cd-inhibitory effects on plants was more effective in the unlimed soil owing to the higher Cd availability in acidic soils. Also, taking into account the reduced transfer of Cd to shoots driven by Si, lower Cd accumulation in maize grains is likely, with implications to food safety. So, further studies on field conditions are warranted.

Low pH of a High Carbon Gleysol Contributes to Nitrification Inhibition Resulting in Low N2O Soil Emissions and Limited Effectiveness of Nitrification Inhibitors

Nitrous oxide (N2O) is a potent greenhouse gas, and drained tropical/subtropical wetland soils that are high in carbon (C) make a substantial contribution to global anthropogenic N2O emissions. However, we previously reported negligible N2O emissions from an acidic, C-rich Gleysol under aerobic rice (Oryza sativa L.) production in the subtropics despite ample moisture and fertiliser nitrogen (N). In a field experiment, seasonal cumulative N2O emissions in the field following the application of 90 kg ha−1 N as urea were low (0.15 kg N2O-N ha−1·season−1). An incubation study examining the effects of temperature (20 °C, 25 °C and 30 °C) and water-filled pore space (WFPS; 40% vs. 60%) on N transformations showed that incubation temperature had a larger influence on nitrification than WFPS (40% vs. 60%). There was limited nitrification at 20 °C at either WFPS over 30 days, but low concentrations of NO3− (&lt;100 mg kg−1) began to accumulate between 16–23 days at 30 °C and between 23–30 days at 25 °C. Liming soil resulted in nitrification after 10 days, while only minor nitrification was evident in the unlimed soil. The presence of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) with urea delayed nitrification for up to 4 days in the limed soil, suggesting such inhibitors may not provide substantial benefits in high C soils. Our results suggest that a low soil pH contributes to impaired nitrification in the C-rich Gleysol examined, which is associated with low fluxes of N2O in the field. We suggest that soil pH could potentially be manipulated to sustain low rates of nitrification and lower N losses, without compromising crop growth.

The distribution of soil nitrifiers and efficacy of 3,4-dimethylpyrazole phosphate changes with soil depth and calcium carbonate application

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is used to limit nitrogen (N) losses incurred following nitrification of applied N fertilisers. Inhibitor efficacy changes with soil conditions including pH and organic matter (OM) content, both of which can be stratified down the soil profile. An incubation study was conducted using acidic soil that exhibited pH stratification. Soil samples were collected from the field in 2 cm depth increments to a depth of 10 cm. Two liming treatments were applied to each depth where the pHCa was raised above 6 or left in its initial acidic state. Nitrogen treatments (urea ammonium nitrate (UAN) with and without DMPP) were applied to each liming treatment per depth and incubated for four weeks. Destructive sampling for mineral N, DMPP concentration and pH occurred every week. The abundance of nitrifiers was determined using semi-quantitative real-time polymerise chain reaction (PCR) targeting the amoA gene at weeks 0, 1 and 4. Liming significantly increased nitrification rates and bacterial amoA gene abundance. Results showed the top 0–2 cm recorded the largest population of bacterial nitrifiers. Changes in pH influenced the composition of nitrifiers present in the soil. Bacterial nitrifiers were absent from the 8–10 cm soil layer in unlimed soils (pHCa 4.25) but liming caused an increase in gene abundance. Archaeal amoA gene abundance was highest in unlimed plots at 4–8 cm depth although populations decreased over the incubation period and also with lime application. DMPP effectively inhibited nitrification in limed plots, however no significant difference existed between UAN and DMPP treatments for unlimed treatments. DMPP successfully decreased bacterial amoA gene abundance in all depths that were limed but not in unlimed soils. Decreases in inhibitor concentrations occurred within one week in the 0–2 cm layer possibly due to bacterial decomposition associated with greater OM concentration at the soil surface. This study highlighted that DMPP use is more effective in relatively neutral soils and liming will change the abundance and distribution of nitrifiers within the top 10 cm of soil.

Phosphorus Adsorption-Desorption Isotherm of Lime Treated and Untreated Acid Soils of Assosa and Bambasi Districts, West Ethiopia

ABSTRACT The objective of the study was to evaluate effects of liming on phosphorus (P) adsorption and desorption capacity of acid soils in Assosa and Bambasi Districts. The soil samples were collected from six rural Kebeles; three from each Kebele and totally 18 samples were collected. The study was conducted in accordance with batch equilibrium method and adsorption values were fitted to Langmuir, Freundlich, and Temkin models to evaluate the goodness of curve fit. Differences between the models’ indices and soil property parameters were analyzed by analysis of variance (ANOVA). The study revealed that unlimed soils of Amba-7, Sonka, and Amba-1 sites had higher range of P-sorption maxima (416.7–500.0 mg/kg) than the limed ones. In addition, the limed soils had shown lower adsorption maxima than the unlimed soils based on the Langmuir model. According to Freundlich model, limed soils had a lower Kf value than the unlimed soils. Similarly, Temkin model also verified that unlimed soils had higher b value (sorption energy) than limed soils. Total P desorbed (TPD) value of limed soils had shown a significant difference (p = .022) between the soils of different sites; then soils of Amba-16, Amba-7 and Sonka had relatively higher TPD value than the soils of the left sites. On lime treated soils the total P desorbed had shown increment relative to the untreated soils. The P-sorption isotherm was fitted best to Temkin model than the Langmuir and Freundlich models. Soils of the study area require liming to improve the P-adsorption problem; especially soils of Amba-7, Sonka, and Amba-1.

Surface soil liming reduces cadmium uptake in cacao seedlings but subsurface uptake is enhanced.

Cadmium concentrations in cacao (Theobroma cacao L.) beans from South America often exceed trade limits. Liming soil is advocated as a remediation option, but amendments cannot be incorporated into the entire root zone without harming the trees. An experiment was set up to identify how Cd uptake varies within the root zone when surface and subsurface soil layers are either limed or not. The experiment used 22-cm-height pots with top and bottom layers using surface and subsurface soil samples from a cacao field. The potted soils were either surface limed or not or fully limed and layers spiked with stable 108 Cd isotope in various combinations to trace the plant Cd provenance. The root distribution was neither affected by liming nor by soil source; 70% of the root biomass was present in the top layer. Plants grown on the fully limed surface soil had 1.7 times lower Cd concentrations in leaves than the unlimed treatments, whereas this concentration was 1.2 times lower when only the top layer was limed (surface soil used in both layers). The isotope dilution data showed that surface soil liming enhanced Cd uptake from the unlimed bottom layer compared with the unlimed soil, suggesting compensating mechanisms. The pots containing surface soil over subsurface soil also showed that compensating effect but, due to lower phytoavailable Cd in the subsurface soil, surface liming still effectively reduced foliar Cd. We conclude that liming might be a feasible mitigation strategy, but its effectiveness is limited when Cd phytoavailability remains untreated in the subsurface layer.