Wetting properties of fungi mycelium alter soil infiltration and soil water repellency in a γ-sterilized wettable and repellent soil

Soil water repellency (SWR) has a drastic impact on soil quality resulting in reduced infiltration, increased runoff, increased leaching, reduced plant growth, and increased soil erosion. One of the causes of SWR is hydrophobic fungal structures and exudates that change the soil–water relationship. The objective of this study was to determine whether SWR and infiltration could be manipulated through inoculation with fungi. The effect of fungi on SWR was investigated through inoculation of three fungal strains (hydrophilic – Fusarium proliferatum, chrono-amphiphilic – Trichoderma harzianum, and hydrophobic – Alternaria sp.) on a water repellent soil (WR-soil) and a wettable soil (W-soil). The change in SWR and infiltration was assessed by the water repellency index and cumulative infiltration respectively. F. proliferatum decreased the SWR on WR-soil and slightly increased SWR in W-soil, while Alternaria sp. increased SWR in both the W-soil and the WR-soil. Conversely T. harzianum increased the SWR in the W-soil and decreased the SWR in the WR-soil. All strains showed a decrease in infiltration in W-soil, while only the F. proliferatum and T. harzianum strain showed improvement in infiltration in the WR-soil. The ability of fungi to alter the SWR and enmesh soil particles results in changes to the infiltration dynamics in soil.     

Gradients in soil solution composition between bulk soil and rhizosphere – In situ measurement with changing soil water content

Soil solution composition changes with time and distance from the root surface as a result of mass flow, diffusion, plant nutrient uptake and root exudation. A model system was designed, consisting of a root compartment separated from the bulk soil compartment by a nylon net (30 m mesh size), which enabled independent measurements of the change of soil solution composition and soil water content with increasing distance from the root surface (nylon net). K⁺ concentration in the rhizosphere soil solution decreased during the initial growth stage (12 days after planting, DAP). Thereafter K⁺ accumulated with time, due to mass flow as the dominating process. The extend of K⁺ accumulation depended on the initial fertiliser application. As K⁺ concentrations in soil solution increase, not only as a result of transport exceeding uptake, but also as a result of decreasing soil water content, it is hypothesised that K concentration in soil solution is not the only trigger for the activity of K transporters in membranes, but ABA accumulation in roots induced by decreasing soil matric potentials may add to the regulation. A strong decrease of rhizosphere pH with time is observed as a result of H⁺ efflux from the roots in order to maintain cation-anion balance. In addition the K⁺ to Ca²⁺ ratio was altered continuously during the growing period, which has an impact on Ca²⁺ uptake and thus firmness of cell walls, apoplast pH, membrane integrity and activity of membrane transporters. The value of osmotic potential in the rhizosphere soil solution increased with time indicating decreasing soil water availability. Modelling approaches based on the data obtained with the system might help to fill in the time gaps caused by the low temporal resolution of soil solution sampling method.     

Protozoan grazing of bacteria in soil—impact and importance

Interactions between bacteria and protozoa in soil were studied over 2-week periods in the field and in a pot experiment. Under natural conditions the total biological activity was temporarily synchronized by a large rainfall, and in the laboratory by the addition of water to dried-out soil, with or without plants. In the field, peaks in numbers and biomass of bacteria appeared after the rain, and a peak of naked amoebae quickly followed. Of the three investigated groups—flagellates, ciliates, and amoebae—only populations of the latter were large enough and fluctuated in a way that indicated a role as bacterial regulators. The bacterial increase was transient, and the amoebae alone were calculated to be able to cause 60% of the bacterial decrease. The same development of bacteria and protozoa was observed in the pot experiment: in the presence of roots, amoebic numbers increased 20 times and became 5 times higher than in the unplanted soil. In the planted pots, the amoebic increase was large enough to cause the whole bacterial decrease observed; but in the unplanted soil, consumption by the amoebae caused only one-third of the bacterial decrease.     

Mycorrhizal responses to biochar in soil – concepts and mechanisms

Experiments suggest that biomass-derived black carbon (biochar) affects microbial populations and soil biogeochemistry. Both biochar and mycorrhizal associations, ubiquitous symbioses in terrestrial ecosystems, are potentially important in various ecosystem services provided by soils, contributing to sustainable plant production, ecosystem restoration, and soil carbon sequestration and hence mitigation of global climate change. As both biochar and mycorrhizal associations are subject to management, understanding and exploiting interactions between them could be advantageous. Here we focus on biochar effects on mycorrhizal associations. After reviewing the experimental evidence for such effects, we critically examine hypotheses pertaining to four mechanisms by which biochar could influence mycorrhizal abundance and/or functioning. These mechanisms are (in decreasing order of currently available evidence supporting them): (a) alteration of soil physico-chemical properties; (b) indirect effects on mycorrhizae through effects on other soil microbes; (c) plant–fungus signaling interference and detoxification of allelochemicals on biochar; and (d) provision of refugia from fungal grazers. We provide a roadmap for research aimed at testing these mechanistic hypotheses.     

Does an earthworm species acclimatize and/or adapt to soil calcium conditions? The consequences of soil nitrogen mineralization in forest soil

Calcium (Ca)-rich food can increase feeding of Lumbricidae. Earthworms can be genetically differentiated at a small spatial scale and acclimatize to the local environment during growth. Soil feeding and subsequent cast production by earthworms affects soil N mineralization. Here, we hypothesized that soil feeding and subsequent cast production by Lumbricidae species increases with high soil Ca content and that this increase is stronger in worms from high-Ca soil. We also hypothesized that changes in the soil feeding of Lumbricidae species along with the Ca content affects the soil N mineralization via changes in the cast production. Using a geophageous earthworm species (Eisenia japonica) originated from two different Ca environments (calcareous soil and sedimentary soil), we investigated cast production and soil N mineralization in three soils (sedimentary soil, sedimentary soil with Ca addition, and calcareous soil). The soil feeding of E. japonica from both origins did not always increase despite the high soil Ca content. We suggest that both the Ca content and other soil conditions (e.g., soil C:N) might be major factors in increasing soil feeding by E. japonica. Furthermore, the influence of Ca addition on cast production varied according to the earthworm origin. As expected, these differences in cast production are linked to soil N mineralization (especially nitrification). In summary, our study suggests that the acclimatization and/or adaptation of Lumbricidae species to local environmental factors not only soil Ca content explains spatially heterogeneous soil N mineralization in forest soil.     

EDTA and Pb—EDTA accumulation in Brassica juncea grown in Pb—amended soil

Previous studies have shown that EDTA is necessary to solubilize soil Pb and facilitate its transport from the soil to the above ground plant tissues. These studies have also suggested that Pb is accumulated in the plant tissue with transpiration as the driving force. We conducted further studies to evaluate the relationship between EDTA soil treatment, plant transpiration, and plant accumulation of Pb and EDTA. Indian mustard (Brassica juncea) plants were grown in soils containing Pb at three different concentrations (1.5, 3.0 and 4.8 mmol/kg) for 5 weeks before being treated with EDTA concentrations ranging from 0 to 10 mmol/kg. Plant shoots and xylem sap were collected and analyzed for Pb and EDTA content using ICP and HPLC, respectively. Water loss was measured for 7 days following EDTA application. Transpiration was not affected at <5 mmol/kg EDTA but, at 10 mmol/kg EDTA transpiration decreased by 80%, whereas accumulation of Pb and EDTA increased. In the Sassafras soil, Pb and EDTA accumulation in the plant shoots continued to increase as the applied EDTA concentration increased, except at the highest level (10 mmol/kg). In soil amended with 4.8 mmol/kg Pb and 10 mmol/kg EDTA, the concentrations of EDTA and Pb in shoots decreased and visible signs of phytotoxicity were observed. The results presented herein support recent studies in hydroponic systems showing that EDTA and Pb are taken up by the plant and suggest that Pb is translocated in the plant as the Pb-EDTA complex. The results also show that the maximum Pb accumulation by plants occurs by maximizing the concentration of the Pb-EDTA complex based on the EDTA extractable soil Pb. This revised version was published online in July 2006 with corrections to the Cover Date.     

Does biochar influence soil physical properties and soil water availability?

Aims

This study aims to (i) determine the effects of incorporating 47 Mg ha^?1 acacia green waste biochar on soil physical properties and water relations, and (ii) to explore the different mechanisms by which biochar influences soil porosity.

Methods

The pore size distribution of the biochar was determined by scanning electron microscope and mercury porosimetry. Soil physical properties and water relations were determined by in situ tension infiltrometers, desorption and evaporative flux on intact cores, pressure chamber analysis at ?1,500 kPa, and wet aggregate sieving.

Results

Thirty months after incorporation, biochar application had no significant effect on soil moisture content, drainable porosity between –1.0 and ?10 kPa, field capacity, plant available water capacity, the van Genuchten soil water retention parameters, aggregate stability, nor the permanent wilting point. However, the biochar-amended soil had significantly higher near-saturated hydraulic conductivity, soil water content at ?0.1 kPa, and significantly lower bulk density than the unamended control. Differences were attributed to the formation of large macropores (>1,200 μm) resulting from greater earthworm burrowing in the biochar-amended soil.

Conclusion

We found no evidence to suggest application of biochar influenced soil porosity by either direct pore contribution, creation of accommodation pores, or improved aggregate stability.     

DenNit – Experimental analysis and modelling of soil N2O efflux in response on changes of soil water content, soil temperature, soil pH, nutrient availability and the time after rain event

To quantify the effects of soil temperature (T_soil), and relative soil water content (RSWC) on soil N₂O emission we measured N₂O soil efflux with a closed dynamic chamber in situ in the field and from soil cores in a controlled climate chamber experiment. Additionally we analysed the effect of soil acidity, ammonium, and nitrate concentration in the field. The analysis was performed on three meadows, two bare soils and in one forest. We identified soil water content, soil temperature, soil nitrogen content, and pH as the main parameters influencing soil N₂O emission. The response of N₂O emission to soil temperature and relative soil water content was analysed for the field and climate chamber measurements. A non-linear regression model (DenNit) was developed for the field data to describe soil N₂O efflux as a function of soil temperature, soil moisture, pH value, and ammonium and nitrate concentration. The model could explain 81% of the variability in soil N₂O emission of all individual field measurements, except for data with short-term soil water changes, namely during and up to 2 h after rain stopped. We validated the model with an independent dataset. For this additional meadow site 73% of the flux variation could be explained with the model.     

Spatial and temporal dynamics of hotspots of enzyme activity in soil as affected by living and dead roots—a soil zymography analysis

Aims

Hotspots of enzyme activity in soil strongly depend on carbon inputs such as rhizodeposits and root detritus. In this study, we compare the effect of living and dead Lupinus polyphyllus L. roots on the small-scale distribution of cellulase, chitinase and phosphatase activity in soil.

Methods

Soil zymography, a novel in situ method, was used to analyze extracellular cellulase, chitinase and phosphatase activity in the presence of i. living L. polyphyllus roots prior to shoot cutting and ii. dead/dying roots 10, 20 and 30 days after shoot cutting.

Results

After shoot cutting, cellulase and chitinase activities increased and were highest at the root tips. The areas of high cellulase and phosphatase activity extend up to 55 mm away from the root. Moreover, we observed microhotspots of cellulose, chitinase, and phosphatase activity up to 60 mm away from the next living root. The number and activity of microhotspots of chitinase activity was maximal 10 days after shoot cutting.

Conclusions

The study showed that young root detritus stimulates enzyme activities stronger than living roots. Soil zymography allowed identification of microhotspots of enzyme activity up to several cm away from living and dying roots, which most likely were caused by arbuscular mycorrhizal fungi.     

Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with 203Hg‐radiolabeled compounds

Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with ²⁰³Hg‐labeled HgCl₂ and CH₃HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl ²⁰³Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of ²⁰³Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.     

Can ground-penetrating radar detect adjacent roots and rock fragments in forest soil?

Plant and Soil - Root hemiparasite infection is considered a potential biotic stress that affects the growth of cool-season grasses, and the damage caused by a hemiparasitic plant to host grasses...     

Tree species and wood ash affect soil in Michigan’s Upper Peninsula

Tree species and wood ash application in plantations of short-rotation woody crops (SRWC) may have important effects on the soil productive capacity through their influence on soil organic matter (SOM) and exchangeable cations. An experiment was conducted to assess changes in soil C and N contents and pH within the 0–50 cm depth, and exchangeable cation (Ca²⁺, Mg²⁺, K⁺, and Na⁺) and extractable acidity concentrations within the 0–10 cm depth. The effects of different species (European larch [Larix decidua P. Mill.], aspen [Populus tremula L. × Populus tremuloides Michx.], and four poplar [Populus spp.] clones) and wood ash applications (0, 9, and 18 Mg ha⁻¹) on soil properties were evaluated, using a common garden experiment (N = 70 stands) over 7 years of management in Michigan’s Upper Peninsula. Soils were of the Onaway series (fine-loamy, mixed, active, frigid Inceptic Hapludalfs). The NM-6 poplar clone had the greatest soil C and N contents in almost all ash treatment levels. Soil C contents were 7.5, 19.4, and 10.7 Mg C ha⁻¹ greater under the NM-6 poplar than under larch in the ash-free, medium-, and high-level plots, respectively. Within the surface layer, ash application increased soil C and N contents (P < 0.05) through the addition of about 0.7 Mg C ha⁻¹ and 3 kg N ha⁻¹ with the 9 Mg ha⁻¹ ash application (twofold greater C and N amounts were added with the 18 Mg ha⁻¹ application). During a decadal time scale, tree species had no effects—except for K⁺—on the concentrations of the exchangeable cations, pH, and extractable acidity. In contrast, ash application increased soil pH and the concentration of Ca²⁺ (P < 0.05), from 5.2 ± 0.4 cmol_c kg⁻¹ (ash-free plots) to 8.6 ± 0.4 cmol_c kg⁻¹ (high-level ash plots), and tended to increase the concentration of Mg²⁺ (P < 0.1), while extractable acidity was reduced (P < 0.05) from 5.6 ± 0.2 cmol_c kg⁻¹ (ash-free plots) to 3.7 ± 0.2 cmol_c kg⁻¹ (high-level plots). Wood ash application, within certain limits, not only had a beneficial effect on soil properties important to the long-term productivity of fast-growing plantations but also enhanced long-term soil C sequestration.     

Partitioning of soil respiration components and evaluating the mycorrhizal contribution to soil respiration in a semiarid grassland北大核心CSCD

Aims Soil respiration component partitioning is pivotal to understand the belowground carbon (C) cycle. Mycorrhizal fungi have been proven to play an important role in the soil C turnover, but only a few studies have been conducted to quantify the contribution of mycorrhizal respiration to total soil respiration in grassland ecosystems. Methods The mini-trenching mesh method was applied to partition soil respiration components of a semi-arid grassland in Inner Mongolia. A shallow collar (measuring soil total respiration), a deep collar (excluding roots and mycorrhizal hypahe) and a deep collar with 40 μm pore mesh window (excluding roots but not mycorrhizal hyphae) were installed in each plot. Soil respiration rate of each collar was measured every two weeks during the growing season from 2014 to 2016. The differences in the rate of soil respiration among different type of collars were used to partition the components of soil respiration. Important findings The results showed that the contribution of heterotrophic, root and mycorrhizal respiration to total soil respiration was 49%, 28%, and 23%, respectively. Across the three years, the proportion of mycorrhizal respiration varied from 21%-26%, which is comparable with the results reported by other studies recently. Our results demonstrated that the mini-trenching mesh method is a suitable method for separating mycorrhizal respiration component in grassland ecosystems. Evaluating the contribution of mycorrhizal respiration to total soil respiration is very important for predicting the responses of soil carbon release to future climate change. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Heterogeneity in soil water and light environments and dispersal limitation: what facilitates tree species coexistence in a temperate forest?

In the present study, we analysed the habitat association of tree species in an old‐growth temperate forest across all life stages to test theories on the coexistence of tree species in forest communities. An inventory for trees was implemented at a 6‐ha plot in Ogawa Forest Reserve for adults, juveniles, saplings and seedlings. Volumetric soil water content (SMC) and light levels were measured in 10‐m grids. Relationships between the actual number of stems and environmental variables were determined for 35 major tree species, and the spatial correlations within and among species were analysed. The light level had no statistically significant effect on distribution of saplings and seedlings of any species. In contrast, most species had specific optimal values along the SMC gradient. The optimal values were almost identical in earlier life stages, but were more variable in later life stages among species. However, no effective niche partitioning among the species was apparent even at the adult stage. Furthermore, results of spatial analyses suggest that dispersal limitation was not sufficient to mitigate competition between species. This might result from well‐scattered seed distribution via wind and bird dispersal, as well as conspecific density‐dependent mortality of seeds and seedlings. Thus, both niche partitioning and dispersal limitation appeared less important for facilitating coexistence of species within this forest than expected in tropical forests. The tree species assembly in this temperate forest might be controlled through a neutral process at the spatial scale tested in this study.     

Bioavailability of Cd in a soil–rice system in China: soil type versus genotype effects

Human exposure to toxic heavy metals via dietary intake is of increasing concern. In this regard, the bioavailability of heavy metals in the soil–crop system is considered to be a key factor controlling plant uptake and, therefore, public health risk through food chain transfer [J. Environ. Sci. Health B 34(4) (1999) 681]. In 2002, a pot experiment was conducted to elucidate the relative significance of soil types and rice genotype on the bioavailability, uptake and partitioning of Cd by two rice cultivars with distinct affinity for Cd. The results indicated that the total uptake of Cd and accumulation in grain was dependent on both soil type and genotype effects. Cd spiking enhanced high Cd uptake and partitioning in grain. Inherent differences in soil type effecting Cd bioavailability were less significant under the Cd spiking regime as compared to non-Cd spiking. In the case of Soil-P, with low Cd bioavailability as indicated by the comparatively lower MgCl₂ extractableCd, differences in metal affinity between genotypes dominated uptake. Conversely, inherent differences in soil type affecting Cd bioavailability dominated uptake in the low metal affinity cultivar treatments. Under the experimental conditions evaluated, the positive interaction between soil type and genotype results in elevated levels of Cd in rice grain with the Cd values exceeding the Chinese food guideline limit of 0.2 mg kg^–1. The results indicated that Cd bioavailability and plant uptake is dependent on soil chemical and physical properties affecting Cd mobility, rice genotype and soil pollution status. The results further suggested that caution should be paid to rice production with the new high metal affinity genotypes on soils with inherent Cd bioavailability as with acidic Red Soils of Jiangxi Provinces, China.     

Spatial–temporal variation in soil respiration in an oak–grass savanna ecosystem in California and its partitioning into autotrophic and heterotrophic components

The spatial upscaling of soil respiration from field measurements to ecosystem levels will be biased without studying its spatial variation. We took advantage of the unique spatial gradients of an oak–grass savanna ecosystem in California, with widely spaced oak trees overlying a grass layer, to study the spatial variation in soil respiration and to use these natural gradients to partition soil respiration according to its autotrophic and heterotrophic components. We measured soil respiration along a 42.5 m transect between two oak trees in 2001 and 2002, and found that soil respiration under tree canopies decreased with distance from its base. In the open area, tree roots have no influence on soil respiration. Seasonally, soil respiration increased in spring until late April, and decreased in summer following the decrease in soil moisture content, despite the further increase in soil temperature. Soil respiration significantly increased following the rain events in autumn. During the grass growing season between November and mid-May, the average of CO₂ efflux under trees was 2.29 μmol m⁻² s⁻¹, while CO₂ efflux from the open area was 1.40 μmol m⁻² s⁻¹. We deduced that oak root respiration averaged as 0.89 μmol m⁻² s⁻¹, accounting for 39% of total soil respiration (oak root + grass root + microbes). During the dry season between mid-May and October, the average of CO₂ efflux under trees was 0.87 μmol m⁻² s⁻¹, while CO₂ efflux from the open areas was 0.51 μmol m⁻² s⁻¹. Oak root respiration was 0.36 μmol m⁻² s⁻¹, accounting for 41% of total soil respiration (oak root + microbes). The seasonal pattern of soil CO₂ efflux under trees and in open areas was simulated by a bi-variable model driven by soil temperature and moisture. The diurnal pattern was influenced by tree physiology as well. Based on the spatial gradient of soil respiration, spatial analysis of crown closure and the simulation model, we spatially and temporally upscaled chamber measurements to the ecosystem scale. We estimated that the cumulative soil respiration in 2002 was 394 gC m⁻² year⁻¹ in the open area and 616 gC m⁻² year⁻¹ under trees with a site-average of 488 gC m⁻² year⁻¹.     

The relationship between ‘labile soil phosphorus’ and the aluminium and iron-bound phosphorus in tropical soils

Summary When millet was grown in short-term pot experiments in the greenhouse, in the red-clay and sand-veld soils of Southern Rhodesia and the red clay loams of Uganda, a very close correlation was obtained between labile soil phosphorus and the aluminium- and iron-bound phosphate in these soils. A large increase in labile soil phosphorus was obtained when millet was grown in Uganda soils that had been stored in the air-dry condition for 15 weeks, and a greater increase after 24 weeks. The increase is attributed to the mineralisation of soil organic phosphorus. The maximum temperature used to dry the soils had no effect on the labile soil phosphorus values obtained.     

Do climate and soil influence phenotypic variability in leaf litter,microbial decomposition and shredder consumption?

We tested the hypothesis that water stress and soil nutrient availability drive leaf-litter quality for decomposers and detritivores by relating chemical and physical leaf-litter properties and decomposability of Alnus glutinosa and Quercus robur, sampled together with edaphic parameters, across wide European climatic gradients. By regressing principal components analysis of leaf traits [N, P, condensed tannins, lignin, specific leaf area (SLA)] against environmental and soil parameters, we found that: (1) In Q. robur the condensed tannin and lignin contents increased and SLA decreased with precipitation, annual range of temperature, and soil N content, whereas leaf P increased with soil P and temperature; (2) In A. glutinosa leaves N, P, and SLA decreased and condensed tannins increased with temperature, annual range of temperature, and decreasing soil P. On the other hand, leaf P and condensed tannins increased and SLA decreased with minimum annual precipitation and towards sites with low temperature. We selected contrasting leaves in terms of quality to test decomposition and invertebrate consumption. There were intraspecific differences in microbial decomposition rates (field, Q. robur) and consumption by shredders (laboratory, A. glutinosa). We conclude that decomposition rates across ecosystems could be partially governed by climate and soil properties, affecting litter quality and therefore decomposers and detritivores. Under scenarios of global warming and increased nutrients, these results suggest we can expect species-specific changes in leaf-litter properties most likely resulting in slow decomposition with increased variance in temperatures and accelerated decomposition with P increase.     

Application of nitrogen in NO 3 − form increases rhizosphere alkalisation in the subsurface soil layers in an acid soil

Leaching of NO ₃ ^? derived from ammoniacal fertilizers in the topsoil and subsequent uptake of NO ₃ ^? by plants from deeper layers may be used as a method of biological amelioration of subsurface soil acidity. This paper reports a glasshouse column experiment testing the above concept. Nitrogen with labelled ¹⁵N was supplied with and without lime to the surface soil (0–10 cm) as urea, (NH₄)₂SO₄ or Ca(NO₃)₂ at a rate equivalent to 120 kg N ha^?1. Soil columns were regularly watered from the top to facilitate NO ₃ ^? leaching. An aluminium-tolerant wheat genotype was grown for 38 days. The application of lime with nitrogen fertilizers increased growth of shoot and roots in all soil layers. The application of Ca(NO₃)₂ resulted in about 66% of recovery efficiency irrespective of whether lime was applied in the surface. This in turn resulted in about 0.2 units increase in rhizosphere pH in the subsurface (10–15 cm) soil layer compared to the same layer of the unlimed control. The supply of urea and (NH₄)₂SO₄ alone or with lime did not increase rhizosphere pH in the subsurface soil layers. Importantly, this study indicates that it is possible to exploit the process of nitrate uptake by wheat to increase pH in acidic subsurface soil.