Subsoil pH Research Articles

Spatial relationship between peach tree productivity and soil properties in a newly reclaimed orchard

ABSTRACT The construction of banks and surface soil cutting involved in newly reclaiming orchards may cause spatial variability in soil properties, which could cause poor fruit tree productivity. This study examined spatial relationships between variations in peach tree properties and soil properties around each tree and assessed the possibility of site-specific field management for individual trees in a newly reclaimed orchard. Three and four years after reclamation in 2016, the 0.1-ha field located in Kyoto, Japan was divided into 32 grid cells at 5-m intervals for all individual peach trees and 128 grid cells at 2.5-m intervals for measuring soil properties around each tree (field scale). The 128 grid cells were each further divided into five positions at 0.71-m intervals for assessing selected soil properties (grid-cell scale). The soil data were geostatistically analyzed by calculating the nugget/sill ratios and anisotropy ratios (degree of variation in relation to direction) and drawing kriged maps. Coefficients of variation of soil properties at the grid-cell scale were much higher than those at the field scale. Pearson’s correlation analysis at the field scale indicated that the tree productivity was most strongly correlated with relative altitude, followed by the degree of soil reduction, time-domain reflectometry electrical conductivity (TDR-EC), subsoil pH (H2O), and TDR-volumetric water content. Tree productivity tended to be lower at lower elevations, where the degree of soil reduction, TDR-EC, subsoil pH (H2O), and soil water content tended to be high. Poor productivity appeared to be related to wet injury. Semivariograms of the soil properties related to soil water showed strong spatial dependence and had nugget/sill ratios of ≤24.0%. Kriged maps and anisotropy ratios further indicated that most tree property values decreased from southeast to northwest and showed variations similar to those of the soil properties related to soil water. Fine-scale mapping of soil properties in the orchard could reveal spatial soil-property variations around individual peach trees, and the result would imply the importance of soil management practices on a per-tree basis. Our findings could help to improve tree productivity in the northwestern area by increasing soil drainage for individual trees.

Inducing Inorganic Carbon Accrual in Subsoil through Biochar Application on Calcareous Topsoil

Biochar amendments add persistent organic carbon to soil and can stabilize rhizodeposits and existing soil organic carbon (SOC), but effects of biochar on subsoil carbon stocks have been overlooked. We quantified changes in soil inorganic carbon (SIC) and SOC to 2 m depth 10 years after biochar application to calcareous soil. The total soil carbon (i.e., existing SOC, SIC, and biochar-C) increased by 71, 182, and 210% for B30, B60, and B90, respectively. Biochar application at 30, 60, and 90 t ha-1 rates significantly increased SIC by 10, 38, and 68 t ha-1, respectively, with accumulation mainly occurring in the subsoil (below 1 m). This huge increase of SIC (mainly CaCO3) is ∼100 times larger than the inorganic carbon present in the added biochar (0.3, 0.6, or 0.9 t ha-1). The benzene polycarboxylic acid method showed that the biochar-amended soil contained more black carbon particles (6.8 times higher than control soil) in the depth of 1.4-1.6 m, which provided the direct quantitative evidence for biochar migration into subsoil after a decade. Spectral and energy spectrum analysis also showed an obvious biochar structure in the biochar-amended subsoil, accompanied by a Ca/Mg carbonate cluster, which provided further evidence for downward migration of biochar after a decade. To explain SIC accumulation in subsoil with biochar amendment, the interacting mechanisms are proposed: (1) biochar amendment significantly increases subsoil pH (0.3-0.5 units) 10 years after biochar application, thus forming a favorable pH environment in the subsoil to precipitate HCO3-; and (2) the transported biochar in subsoil can act as nuclei to precipitate SIC. Biochar amendment enhanced SIC by up to 80%; thus, the effects on carbon stocks in subsoil must be understood to inform strategies for carbon dioxide removal through biochar application. Our study provided critical knowledge on the impact of biochar application to topsoil on carbon stocks in subsoil in the long term.

Dissection of the Contributing Factors to the Variable Response of Crop Yield to Surface Applied Lime in Australia

Modern agricultural farming systems acidify the soil profile due to application of fertilisers with acidifying properties. In most parts of Australia, lime has been used to improve agricultural soil conditions and restore its productive potential. The observed response of crop yield to applied lime often varies with soil type, acidity profile and seasonal conditions, so it is difficult to specify the expected yield response in a given situation. We conducted a meta-analysis of 86 agricultural field trials from Western Australia (WA), New South Wales (NSW) and Victoria (VIC) where various rates of lime had been applied to the soil surface and crop yield (wheat, barley, canola, lupin or field pea) measured for a number of years after the initial application. Information from the meta-analysis was then paired with output from a crop simulation model, where the water-limited yield potential was estimated for both a neutral and acidified soil profile. The average increase in yield to applied lime across all locations and crops was 12%, but the response ranged from 0 to 185%. A trend was observed, where sites with topsoil pH (CaCl2) < 5 and subsoil pH < 4.5 had the greater benefit to liming. Soil type had little effect on the percentage yield increase. Overall, responses to applied lime were most likely when the yield of the trial site was at 50% of water-limited yield potential (or less), the quantity of lime applied was greater than 2.5 t ha−1 and the time since lime had been applied was greater than three years (with the maximum response occurring from four and sometimes up to eight years after liming). Therefore, soil pH measurements, combined with an assessment of actual yield relative to potential yield, provide the best guide to the response to surface applied lime and this response is likely to take more than four years to be realised.

Conventional flooding irrigation and over fertilization drives soil pH decrease not only in the top- but also in subsoil layers in solar greenhouse vegetable production systems

Conventional flooding irrigation combined with over-fertilization in intensively used solar greenhouse vegetable production systems are jeopardizing soil productivity and groundwater quality due to soil acidification and nitrogen (N) leaching. While it has been shown that excessive application of N fertilizer in greenhouse production systems significantly reduces topsoil pH values, it remains unknown if also subsoil pH values do change too and if surplus N fertilization and hydrological N losses lead to nutrient imbalances. In this study, soil samples from six soil layers from 0 to 300 cm were taken from 45 greenhouse fields with three representative cultivation years (2, 5, and 10 years). Soil samples from 5 adjacent corn fields served as comparison. Results show that (1) compared to soils from adjacent corn fields, the pH in the 0–30 cm soil layer was slightly elevated two years and five years after greenhouse establishment, but was lowered by 0.52 ± 0.06 units after ten years. Moreover, also the pH in deeper soil layers (30–300 cm) significantly decreased with cultivation years. (2) A significant imbalance of N:P:K ratios in greenhouse top soils was found, as P and K accumulates while N is leached to subsoils. (3) Structural equation modeling indicated that changes in the mineral N concentration in the 0–30 cm soil layer was driving soil pH changes. Our results demonstrate that N accumulation in top soils and N leaching to deep soil caused by excessive irrigation explains observed declines in surface and deep soil pH values of conventional greenhouse vegetable production systems. Consequently, for avoiding groundwater contamination with N and for ensuring sustainable soil productivity, current schemes of irrigation and fertilization management need to be adapted to avoid N leaching, soil acidification, nutrient accumulation and imbalances.

The Form of N Supply Determines Plant Growth Promotion by P-Solubilizing Microorganisms in Maize.

Phosphate-(P)-solubilizing microorganisms (PSM) are important drivers of P cycling in natural and agro-ecosystems. Their use as plant inoculants to improve P acquisition of crops has been investigated for decades. However, limited reproducibility of the expected effects, particularly under field conditions, remains a major challenge. This study demonstrates that the form of nitrogen fertilization has a significant impact on the performance of various fungal and bacterial PSM inoculants in maize grown on neutral to alkaline soils with limited P availability. Under these conditions, a high soil pH-buffering capacity frequently limits the efficiency of nutrient mobilization, mediated by plant roots and microorganisms via rhizosphere acidification. In a soil pH range between 7.0 and 8.0, nitrate fertilization promoting rhizosphere alkalinisation further aggravates this problem. Accordingly, in greenhouse experiments, six strains of Pseudomonas, Bacillus, Paenibacillus, Streptomyces, and Penicillium with proven P-solubilizing potential, completely failed to promote P acquisition in maize grown on a calcareous Loess sub-soil pH 7.6 with nitrate fertilization and rock phosphate (Rock-P) as a sparingly soluble P source. However, after replacement of nitrate fertilization by ammonium, stabilized with the nitrification inhibitor 3,4-dimethylpyrazole-phosphate (DMPP), five out of seven investigated PSM inoculants (comprising 12 fungal and bacterial PSM strains) exerted beneficial effects on plant growth and reached up to 88% of the shoot biomass production of a control supplied with soluble triple-superphosphate (TSP). Stabilized ammonium combined with PSM-inoculants improved P acquisition (Trichoderma harzianum T22, Pseudomonas sp. DMSZ 13134), while other strains particularly stimulated root growth (T. harzianum OMG16, Bacillus amyloliquefaciens FZB42), which promoted the acquisition also of other mineral nutrients, such as N, K, and Mn. A similar effect was recorded under field conditions on an alkaline clay-loam soil pH 8.6. The combination of stabilized ammonium with a range of consortium products based on T. harzianum OMG16, B. amyloliquefaciens, micronutrients, and humic acids completely compensated the effect of a TSP fertilization on field establishment, nutrient acquisition, and yield formation in maize, while non-stabilized urea-di-ammonium phosphate fertilization was largely ineffective. These findings suggest that the efficiency of PSM-plant interactions can be influenced by the form of N fertilization, offering promising perspectives for synergistic effects with stabilized ammonium fertilizers.

Changes in subsoil acidity with a new deep vertical lime placement practice for conservation tillage systems

Poorly drained claypan soils in the midwestern United States that are managed for corn (<i>Zea mays</i> L.) and soybean (<i>Glycine max</i> [L.] Merr.) production often have optimum surface pH for crop growth, but are characterized by acidic subsoils. Stratification of soil acidity may inhibit root growth leading to decreased drought tolerance and grain yields. Agricultural lime application can increase soil pH and provide calcium (Ca) to the soil, but these amendments rarely affect the subsoil, especially when a conservation tillage system that results in minimal lime incorporation is utilized. The objectives of this study were to determine the effects of surface lime placement compared to a novel deep vertical lime placement practice at various rates on subsoil characteristics under corn and soybean production. Field trials were conducted from 2012 to 2016 in northeast Missouri with treatments of aglime broadcast to the surface soil or incorporated as a vertical band using a custom built shank to a depth of 51 cm (20 in) into the subsoil at 0, 3.4, and 6.7 Mg lime ha⁻¹ (0, 1.5, and 3.0 tn lime ac⁻¹). Soil pH results indicated that the top 13 cm (5 in) of soil was not affected by deep lime placement, but at depths of 13 to 25 cm (5 to 10 in) soil pH increased up to 0.6 and 0.7 units for deep vertical placed lime at 3.4 and 6.7 Mg ha⁻¹, respectively. When compared with control treatments, vertical placement of lime at 3.4 and 6.7 Mg ha⁻¹ increased subsoil pH at depths of 13 to 25 and 25 to 38 cm (10 to 15 in), respectively, one year after application. A similar comparison with the control treatment indicated that deep vertical placement at 6.7 Mg ha⁻¹ increased subsoil pH at 13 to 25 cm depths by 6.5% and 5.7% two and three years after application, respectively. Analysis of the spatial distribution of soil pH and neutralizable acidity in the soil profile indicate penetration of liming effects up to 38 cm (15 in) into the subsoil, but there was minimal evidence of movement away from the initial vertical placement band during a seven-month period.

Digital soil monitoring of top- and sub-soil pH with bivariate linear mixed models

Intensive agricultural management practices and fluctuating rainfall patterns have the potential to significantly impact the status and change of important soil properties. This study looks at the change in soil pH during a 13-year period in a semi-arid, irrigated cotton-growing region in the lower Lachlan River valley in southern NSW, Australia under various land uses. Two soil surveys – one from 2002 and the other from 2015 – that had many of the same sites revisited and resampled, were used in conjunction with bivariate linear mixed models (BLMMs) to map soil pH status and change, at five depth increments to 1.2 m depth. The BLMM approach resulted in models with high predictive power and low prediction variance, likely due to the utilisation of the correlation of pH values at co-located sites through time. Results revealed an overall acidification trend throughout the soil profile, particularly in the subsoil. Test statistics were performed on this predicted acidification, showing that not all of this was statistically significant. This trend of decreasing pH over time is presumed to be at least partly due to management practices associated with irrigated cotton production, but also appears to be affected by increased water flow through the profile due to periods of very high rainfall. While acidification in the highly alkaline soils that cover much of the study area is of no great concern at this time, further acidification should be monitored. Further investigation into utilising the correlation from other co-located soil information should also be considered, such as different soil depths and soil properties in combination with the different time points used in this study.

Comparing traditional and digital soil mapping at a district scale using residual maximum likelihood analysis

Conventional soil mapping uses field morphological observations to classify soil profiles into predefined classification systems and extrapolates the classified soils to make a map based on aerial photographs and the experience of the surveyor. A criticism of this approach is that the subjectivity of the surveyor leads to non-reproducible maps. Advances in computing and statistical analysis, and an increased availability of ancillary data have cumulatively led to an alternative, referred to as digital soil mapping (DSM). In this research, two agriculturally productive areas (i.e. Warren and Trangie) located in central New South Wales, Australia, were considered to evaluate whether pedoderms and soil profile classes defined according to the traditional approach can also be recognised and mapped using a DSM approach. First, we performed a fuzzy k-means analysis to look for clusters in the ancillary data, which include data from remote-sensed gamma-ray (γ-ray) spectrometry and proximal-sensed electromagnetic (EM) induction. We used the residual maximum likelihood method to evaluate the maps for various numbers of classes (k = 2–10) to minimise the mean square prediction error (σ2p,C) of soil physical (i.e. clay content, field capacity (FC), permanent wilting point (PWP) and available water content (AWC)) and chemical (pH, EC of 1 : 5 soil water extract (EC1:5) and cation exchange capacity (CEC)) properties of topsoil (0–0.3 m) and subsoil (0.6–0.9 m). In terms of prediction, the calculated σ2p,C was locally minimised for k = 8 when accounting for topsoil clay, FC, PWP, pH and CEC, and subsoil FC, EC1:5 and CEC. A comparison of σ2p,C of the traditional (seven pedoderm components) and DSM approach (k = 8) indicated that only topsoil EC1:5 and subsoil pH was better accounted for by the traditional approach, whereas topsoil clay content, and CEC and subsoil clay, EC1:5 and CEC were better resolved using the DSM approach. The produced DSM maps (e.g. k = 3, 6 and 8) also reflected the pedoderm components identified using the traditional approach. We concluded that the DSM maps with k = 8 classes reflected the soil profile classes identified within the pedoderms and that soil maps of similar accuracy could be developed from the EM data independently.

Evaluation of Spatial Variability of Soil Physico-Chemical Characteristics on Rhodic Ferralsol at the Syferkuil Experimental Farm of University of Limpopo, South Africa

&lt;p&gt;Spatial variability among selected soil physical and chemical properties in twelve profiles dug across the research block of the University of Limpopo experimental farm was investigated. The soils were moderately shallow to deep, contain variable textural classes and classified as Rhodic ferralsol. Over 90% of the samples were considered as slightly alkaline based on the water-measured pHvalues but decreased to marginally over 27% when measured in KCl. The electrical conductivity of the soils revealed a generally non-saline field. Bray P1, EC, exchangeable cations, extractable Zn and effective cation exchange capacity contents differed significantly (p &amp;lt; 0.05) with depth while K, Mg, Ca, Mn, organic carbon and ECEC differed significantly (p &amp;lt; 0.05) across profiles. Semi-variograms for the measured variables had low values indicating the existence of considerable level of spatial variability. Spatial dependence among top and subsoil pH, EC, organic carbon, sand, silt clay and bulk density ranged between weak and strong. Results revealed a significant spatial variability of the characterized parameters across the research block because to differences in tillage, cropping pattern and nutrient specific application over the years.&lt;/p&gt;

Surface Amendments Can Ameliorate Subsoil Acidity in Tea Garden Soils of High-Rainfall Environments

Strongly acidic soils (pH < 5.0) are detrimental to tea (Camellia sinensis) production and quality. Little information exists on the ability of surface amendments to ameliorate subsoil acidity in the tea garden soils. A 120-d glasshouse column leaching experiment was conducted using commonly available soil ameliorants. Alkaline slag (AS) and organic residues, pig manure (PM) and rapeseed cake (RC) differing in ash alkalinity and C/N ratio were incorporated alone and in combination into the surface (0–15 cm) of soil columns (10 cm internal diameter × 50 cm long) packed with soil from the acidic soil layer (15–30 cm) of an Ultisol (initial pH = 4.4). During the 120-d experiment, the soil columns were watered (about 127 mm over 9 applications) according to the long-term mean annual rainfall (1 143 mm) and the leachates were collected and analyzed. At the end of the experiment, soil columns were partitioned into various depths and the chemical properties of soil were measured. The PM with a higher C/N ratio increased subsoil pH, whereas the RC with a lower C/N ratio decreased subsoil pH. However, combined amendments had a greater ability to reduce subsoil acidity than either of the amendments alone. The increases in pH of the subsoil were mainly ascribed to decreased base cation concentrations and the decomposition of organic anions present in dissolved organic carbon (DOC) and immobilization of nitrate that had been leached down from the amended layer. A significant (P < 0.05) correlation between alkalinity production (reduced exchangeable acidity – N-cycle alkalinity) and alkalinity balance (net alkalinity production – N-cycle alkalinity) was observed at the end of the experiment. Additionally, combined amendments significantly increased (P < 0.05) subsoil cation concentrations and decreased subsoil Al saturation (P < 0.05). Combined applications of AS with organic amendments to surface soils are effective in reducing subsoil acidity in high-rainfall areas. Further investigations under field conditions and over longer timeframes are needed to fully understand their practical effectiveness in ameliorating acidity of deeper soil layers under naturally occurring leaching regimes.

On‐Farm Evaluation of Corn and Soybean Grain Yield and Soil pH Responses to Liming

It is known that soil acidity can limit crop yield, but additional research is needed to identify more precisely optimum soil pH for corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] and the within‐field variation in yield response to liming. The objective of this study was to identify optimum soil pH for these crops by studying the variation of soil pH and grain yield response to liming within several Iowa fields. Fourteen 4‐yr strip‐trials were established in acidic Molisols from 2007 to 2009. The methodology used global positioning systems (GPS), dense soil sampling (0.12–0.18‐ha cells), yield monitors, and geographical information systems (GIS). One‐time treatments replicated two to five times were an unlimed control and limestone at 6.72 Mg ha−1 effective calcium carbonate equivalent (ECCE), incorporated into the soil in fields managed with tillage. Soil samples (15‐cm depth) were collected before liming and annually after crop harvest. The lowest initial soil pH at each site ranged from 4.75 to 5.70. Maximum pH increase was reached 1 to 3 yr after liming. Grain yield response to lime varied greatly. Corn yield responded more frequently than soybean yield but the magnitude of the response did not differ consistently. Liming seldom increased yield with pH &gt; 6.0 in soils having a high subsoil pH (≥ 7.4) and CaCO3 within a 1‐m depth but often increased yield up to pH 6.5 with lower pH subsoil. The results provided improved criteria for site‐specific soil pH and lime management.

Long-term changes in the chemical properties of Japanese cedar (Cryptomeria japonica) forest soils under high precipitation in southwest Japan

There is insufficient direct evidence of long-term changes in the chemical properties of forest soils to provide information for forestry management plans for sustainable site productivity. To understand changes in the chemical properties of forest soils in a specific high-precipitation climate in Japan, we re-investigated, in 1997, soil pits within a Japanese cedar (Cryptomeria japonica) forest in the Yanase region of Kochi Prefecture which had previously been surveyed in 1976. Comparison of the 1976 and 1997 results revealed significantly lower pH of surface and subsurface soils, and fewer exchangeable cations over time. In contrast, subsoil pH, concentrations of total carbon and nitrogen, and cation-exchange capacity (CEC) had not changed over the 21-year period. Estimation of proton and cation budgets in the forest ecosystem over 21 years, using data for the amounts in soil, biomass accumulation, and input through precipitation, revealed that biomass accumulation did not explain the cation depletion in soils. This suggests that cations were leached from the ecosystem. In contrast with previous reports, which showed Ca accumulation in Japanese cedar forest soils, our results indicated that high precipitation of more than 4,000 mm combined with acid deposition resulted in soil acidification and leaching of cations from soils, following the decrease in base saturation.

What controls the spatial patterns of the riverine carbonate system? — A case study for North America

In this study we analyzed the large scale spatial patterns of river pH, alkalinity, and CO2 partial pressure (PCO2) in North America and their relation to river catchment properties. The goal was to set up empirical equations which can predict these hydrochemical properties for non-monitored river stretches from geodata of e.g. terrain attributes, lithology, soils, land cover and climate.For an extensive dataset of 1120 river water sampling locations average values of river water pH, alkalinity and PCO2 were calculated. The catchment boundaries and catchment properties were calculated using GIS and different sets of geodata. The correlations between the hydrochemical properties and the catchment properties were explored using simple and multiple linear regression analysis.For each of the considered hydrochemical parameters, a multiple regression equation was fitted: for pH with the predictor's mean annual precipitation and areal proportions of carbonate rocks (r2=0.60); for alkalinity, in addition to these two predictors, with subsoil pH and areal proportions agricultural lands (r2=0.66); and for pPCO2 (i.e. the negative logarithm of PCO2) with mean air temperature, mean catchment slope gradient, and mean annual precipitation (r2=0.43). Based on these results, we argue that spatial patterns in river water pH and alkalinity are governed by catchment processes related to chemical rock weathering. For the PCO2, on the other hand, the spatial patterns are governed by in-river processes on which catchment properties can have an indirect effect. We conclude that our approach can be used to predict averages of these parameters for non-monitored river stretches, which in-turn allows for a better spatially explicit representation of the rivers' carbonate system at the regional to global scale, which will be needed for a refined analysis of rivers in the global carbon cycle.

Soil pH and Crop Grain Yield as Affected by the Source and Rate of Lime

Uncertainty exists concerning soil pH change and crop yield after applying different lime sources and rates. The objective of this study was to evaluate effects of different lime sources on soil pH and crop responses. Four trials were established on Iowa soils with pH 5.39 to 5.71. Pure CaCO3 and calcitic (2.3 g kg−1 Mg) or dolomitic (80.7 g kg−1 Mg) limestones were incorporated into the soil in spring 2009 at 0, 4.5, 9, 13.5, or 22.4 Mg ha−1 calcium carbonate equivalent (CCE). Soybean [Glycine max (L.) Merr.] was planted in 2009 and corn (Zea mays L.) in 2010. After liming we measured soil pH (15-cm depth) seven times for 16 mo, subsoil pH (15–30 cm) after 1 yr, and grain yield. On average, maximum pH was reached 86, 136, and 129 d after liming for CaCO3 and calcitic or dolomitic limestones, respectively. Maximum pH was reached earlier than usually assumed for similar conditions. Maximum pH with CaCO3 always was higher than with dolomitic limestone and sometimes higher than with calcitic limestone. Maximum pH with calcitic limestone was higher than with dolomitic limestone for at least two rates at all sites, which was explained by the dolomitic limestone coarser particle size and higher Mg content. Only the highest rate of all sources increased subsoil pH at one site. Liming increased yield of both crops in two sites but the sources did not differ. Differences among lime sources effects on soil pH did not affect the crop yield response to lime.

Effect of sewage sludge and synthetic fertilizer on pH, available N and P in pasture soils in semi-arid area, Turkey

Activated sewage sludge from the aerobically-digested treatment and synthetic fertilizer were used to determine total N, available P and pH in different soil depth of pasture in semi arid ecological condition, in Van, Turkey. The study was carried out in a completely randomized block. Four treatment of sewage sludge, one treatment of synthetic fertilizer and no treatment as a control were used in two consecutive years. Soil samples were collected from surface soil (0 to 20 cm) and subsoil (20 to 40 cm) 11 months after SS (sewage sludge) and TSP (triple super phosphate) application and 7 months after AN application for both years. By using sewage sludge and synthetic fertilizers treatments, surface and subsoil pH decreased. The decreases of pH in SF and control plots in both soil depths in 2008 were attributed to root biomass. Although, sewage sludge contains less amount of nitrogen than synthetic fertilizer does, it enabled nitrogen detection in both soil depths for a longer time and in a higher amount. While an increase in the amount of nitrogen in surface soil and subsoil was determined in 2007, a decrease in these was determined in 2008 in both depths. Amount of subsoil available phosphorus increased more by sewage sludge applications. However, amount of surface soil available phosphorus increased more by sewage sludge applications in 2007, while it increased more by synthetic fertilizer application in 2008. The lowest pH value, highest amounts of total N and available P was obtained by higher doses of sewage sludge. However, when long time applications and mineralization process were considered, sewage sludge’s dose of 2.5 ton/ha -1 ya -1 can be said to provide more beneficial results than the synthetic fertilization’s highest dose which is suggested for

The pH of Australian soils: field results from a national survey

The pH is one of the fundamental soil properties governing nutrient availability, metal mobility, elemental toxicity, microbial activity, and plant growth. The field pH of topsoil (0–0.10 m depth) and subsoil (~0.60–0.80 m depth) was measured on floodplain soils collected near the outlet of 1186 catchments covering &gt;6 Mkm2 (6 × 1012 m2) or ~80% of Australia. Field pH duplicate data, obtained at 124 randomly selected sites, indicate a precision of 0.5 pH unit (or 7%), and mapped pH patterns are consistent and meaningful. The median topsoil pH is 6.5, while the subsoil pH has a median of 7 but is strongly bimodal (6–6.5 and 8–8.5). In most cases (64%) the topsoil and subsoil pH values are similar; among the sites exhibiting a pH contrast, those with more acidic topsoils are more common (28%) than those with more alkaline topsoils (7%). The distribution of soil pH at the national scale indicates the strong controls exerted by precipitation and ensuing leaching (e.g. low pH along the coastal fringe, high pH in the dry centre), aridity (e.g. high pH where calcrete is common in the regolith), vegetation (e.g. low pH reflecting abundant soil organic matter), and subsurface lithology (e.g. high pH over limestone bedrock). The new data, together with existing soil pH datasets, can support regional-scale decision-making relating to agricultural, environmental, infrastructural, and mineral exploration decisions.

Biological amelioration of subsoil acidity through managing nitrate uptake by wheat crops

Subsoil acidity occurs in many agricultural lands in the world, and is considered to be an irreversible constraint due to amelioration difficulties. This field study aimed to develop a biological method to ameliorate subsoil acidity through the root-induced alkalisation resulting from nitrate uptake. Aluminium (Al)-tolerant wheat variety Diamondbird and Al-sensitive variety Janz (Triticum aestivum L.) were grown at two contrasting field sites with mild and severe subsurface acidity, respectively, and were supplied with either Ca(NO3)2 at the soil surface, Ca(NO3)2 at 10 cm depth or urea at 10 cm depth. Application of nitrate increased rhizosphere pH up to 0.5 units and bulk soil pH to 0.3 units, and to a depth >30 cm in the Kandosol. The placement of nitrate at 10 cm increased subsoil pH more than the surface application. Nitrate application increased nitrate concentration in soil profiles as expected, whereas urea application increased NH 4 + concentration which in turn favored acidification processes. Diamondbird generally produced more tillers and shoot biomass at anthesis but the two varieties did not differ in grain yield or rhizosphere alkalisation. Similar grain yields were achieved under supply of nitrate and urea. The results suggest that biological amelioration through managing nitrate uptake is possible as part of an integrated approach to combat subsoil acidity in farming systems.

Predicting dissolved inorganic nitrogen leaching in European forests using two independent databases

Regional-scale databases can be particularly useful for identifying relationships between dissolved inorganic nitrogen (N) leaching in forests and environmental drivers, which in turn allow an assessment of the risk of ecosystem damage, such as forest acidification and eutrophication of downstream water bodies. However, detecting the ‘signal’ of a significant correlate to N leaching against a background of wide variability in other factors requires a large number of sites, and the validation of models developed requires a similarly large number of independent sites. Here we use two large and fully independent databases of forest ecosystems across Europe to develop and validate indicators of N saturation and leaching. One database was used for model development and the other for validating these models. Among 35 variables considered, the most significant indicators of N leaching in the model development database were: the flux of dissolved inorganic N in deposition, mean annual temperature, mean altitude, the site drainage (plot vs catchment), needle- and litter-N concentration, organic horizon C:N ratio, and subsoil pH. Altitude was not a consistent predictor (it was significant in the development database but not in the validation database), and needle and litter N concentration, plot vs catchment, and subsoil pH all showed high intercorrelation with N deposition and so were not significant in models already including N deposition. The most consistent and useful indicators of N leaching were throughfall N deposition, organic horizon C:N ratio and mean annual temperature. Sites receiving low levels of N deposition (< 8 kg N ha − 1 y − 1 ) showed very low output fluxes of N and were simulated separately from more polluted forests. In general, the models successfully predicted N leaching (mean of ± 5 kg N ha − 1 y − 1 between observed and predicted) from forests at early to intermediate stages of nitrogen saturation but not from nitrogen-saturated sites. Thus, simple relationships developed from combining (1) external drivers (deposition, temperature) and (2) site conditions (nitrogen status of soils) can successfully estimate nitrogen leaching from forests that have not yet been highly damaged by N deposition.

Leaf responsiveness of Populus tremula and Salix viminalis to soil contaminated with heavy metals and acidic rainwater

Fast-growing trees such as Salix viminalis L. and Populus tremula L. are well suited to phytoremediate heavy metal contaminated soils. However, information on tree performance, particularly leaf function, under conditions of heavy metal contamination is scarce. We used yearly coppiced saplings of S. viminalis and P. tremula growing in model ecosytems to test four hypotheses: (1) heavy metal contamination impairs photosynthesis by injuring leaf structure; (2) the effects of heavy metal contamination are enhanced by acidified rainwater and low soil pH; (3) heavy metal contamination increases dark respiration and, thus, repair processes; and (4) heavy metal contamination is tolerated and remediated better by S. viminalis than by P. tremula. We investigated heavy metal accumulation, tissue injury and gas exchange in leaves of plants subjected to controlled soil contamination with heavy metal dust. Additional treatments included acidic and calcareous natural forest subsoils in combination with irrigation with rainwater at pH 5.5 or 3.5. In both provenances of P. tremula that were studied, but not in S. viminalis, heavy metal treatment reduced photosynthesis and transpiration by varying amounts, except in the hot and dry summer of 2003, but had no effect on dark respiration. At light saturation, net CO(2) uptake and water-use efficiency were reduced by heavy metal contamination, whereas the CO(2) concentration in the leaf intercellular air space was increased. Rainwater pH and subsoil pH only slightly modified the effects of the heavy metal treatment on P. tremula. Gas exchange responses of P. tremula to heavy metals were attributed to leaf structural and ultrastructural changes resulting from hypersensitive-response-like processes and accelerated mesophyll cell senescence and necroses in the lower epidermis, especially along the transport pathways of heavy metals in the leaf lamina. Overall, the effects of heavy metals on P. tremula corroborated Hypothesis 1, but refuted Hypotheses 2 and 3, and were inconclusive for Hypothesis 4. Both P. tremula and S. viminalis showed appreciable potential for storing heavy metals in aging foliage.

Effects of soil properties on variation in growth, grain yield and nutrient concentration of wheat and barley

High spatial and temporal variability is an inherent feature of dryland cereal crops over much of the southern cereal zone. The potential limitations to crop growth and yield of the chemical properties of the subsoils in the region have been long recognised, but there is still an incomplete understanding of the relative importance of different traits and how they interact to affect grain yield. Measurements were taken in a paddock at the Minnipa Agriculture Centre, Upper Eyre Peninsula, South Australia, to describe the effects of properties in the topsoil and subsoil on plant dry matter production, grain yield and plant nutrient concentrations in two consecutive years. Wheat (Triticum aestivum L. cv. Worrakatta) was grown in the first year and barley (Hordeum vulgare L. cv. Barque) in the second. All soil properties except pH showed a high degree of spatial variability. Variability in plant nutrient concentration, plant growth and grain yield was also high, but less than that of most of the soil properties. Variation in grain yield was more closely related to variation in dry matter at maturity and in harvest index than to dry matter production at tillering and anthesis. Soil properties had a stronger relationship with dry matter production and grain yield in 1999, the drier of the two years. Colwell phosphorus concentration in the topsoil (0–0.15 m) was positively correlated with dry matter production at tillering but was not related to dry matter production at anthesis or with grain yield. Subsoil pH, extractable boron concentration and electrical conductivity (EC) were closely related. The importance of EC and soil extractable boron to grain yield variation increased with depth, but EC had a greater influence than the other soil properties. In a year with above-average rainfall, very little of the variation in yield could be described by any of the measured soil variables. The results suggest that variation in EC was more important to describing variation in yield than variation in pH, extractable boron or other chemical properties.