Suppression of chlorate degradation in longan plantation soil after multiple applications of chlorate and accelerated degradation by sugar amendment

Potassium chlorate is widely used as an active substance for flower induction in longan plantations for off-season production of fruits in northern Thailand. Contamination of groundwater with residual chlorate in soil is a cause for concern because of its toxicity to human health. Based on the assumption that potassium chlorate might adversely affect chlorate-reducing soil microorganisms due to its disinfecting nature, the effect of repeated applications of chlorate on chlorate decomposition in soil was examined in a laboratory study. In the longan plantation field soil which had received an annual application of potassium chlorate for three years, chlorate decomposition was slower than that in the soil without application. The suppression of chlorate decomposition was confirmed in the soil to which potassium chlorate was applied repeatedly in the laboratory. However, even in such soils that had received multiple applications of potassium chlorate, chlorate decomposition was remarkably enhanced by soil amendment with glucose or sucrose. Sugar amendment seemed to be an effective way of cleaning-up the residual chlorate in longan plantation field soils.     

Loss of availability of phosphate in New Zealand soils

Phosphate sorption was measured by the method of Barrow (1980) using a laboratory incubation procedure for up to 60 d on four soils which had different mineralogies but medium to high phosphate retention. All the soils had slow reactions where phosphate sorption continued, but at a decreasing rate, with time. The rate of decrease in the slow reactions was similar on all the soils. Phosphate became less available to plants during the slow reactions, and results of a pot trial with white clover showed that, on all the soils, phosphate incubated with the soils for 218 d was about 65% as effective as phosphate incubated for 10d.
When 700 mg P kg⁻¹ was added to allophanic soils (Andisols), about 100 mg kg⁻¹ was strongly adsorbed, about 200 mg kg⁻¹ became unavailable in about 200 days and the remainder was weakly adsorbed. A similar result was obtained on Waiarikiki soil (Inceptisol), which contained ferrihydrite and Al-humus as the predominant reactive species. On the Kerikeri soil (Oxisol) about 150 mg P kg⁻¹ became unavailable with time as a result of reactions with geothite, hematite and Al-humus.
The phosphate uptake by the microbial biomass was similar to the uptake by the clover, and immobilization of phosphate in the biomass can contribute to the loss of availability of phosphate in soils.     

Geologic Nitrogen as a Source of Soil Acidity

The origin of highly acidic (pH<4.5) barren soils in the Klamath Mountains of northern California was examined. Soil parent material was mica schist that contained an average of 2,700 mg N kg⁻¹, which corresponds to 7.1 Mg N ha⁻¹ contained in a 10-cm thickness of bedrock. In situ soil solutions were dominated by H⁺, labile-monomeric Al³⁺ and NO₃⁻, indicating that the barren area soils were nitrogen saturated—more mineral nitrogen available than required by biota. Leaching of excess NO₃⁻ has resulted in removal of nutrient cations and soil acidification. Nitrogen release rates from organic matter free soil ranged from 0.0163 to 0.0321 mg N kg⁻¹ d⁻¹. Nitrogen release rate from fresh ground rock was 0.0465 mg N kg⁻¹ d⁻¹. This study demonstrates that geologic nitrogen may represent a large and reactive nitrogen pool that can contribute significantly to soil acidification.     

Effect of liming and phosphate additions on sulphate leaching in soils

The effect of lime (CaCO₃) and phosphate additions on surface charge characteristics and their effect on the leaching of sulphate were examined for two soils (Patua loam and Tokomaru silt loam) which differed in their adsorption capacities for sulphate.
Incubation of soils with either CaCO₃ (0–600 mmol kg⁻¹) or phosphate (0-208 mmol kg⁻¹) resulted in a two- to five-fold increase in the net negative charge and a similar decrease in the adsorption of sulphate. The effect of either lime or phosphate addition on both the surface charge and sulphate adsorption was more pronounced for the allophanic Patua soil than for the Tokomaru soil containing mainly vermiculite.
In a column experiment, liming induced the leaching of sulphur either by the desorp-tion of adsorbed sulphate or by the mineralization of organic sulphur. During a miscible displacement study, addition of either CaCO₃ or phosphate resulted in an early breakthrough of sulphate in the leachate. In a pulse experiment, in which soils were incubated with sulphate (3.12 mmol kg⁻¹) for 1 week and subsequently leached with water, more added sulphate was lost in the leachate of the soils previously incubated with either CaCO₃ or phosphate.     

Sequential extraction methods for soil organic nitrogen

(pp. 825–831)
This study was carried out to clarify the effects of soil nitrate before cultivation and amounts of basal-dressed nitrogen on additional N application rate and yields of semi-forced tomato for three years from 1998 to 2000. The amounts and timing of additional N dressing were determined based on diagnosis of petiole sap nitrate. The top-dressing was carried out with a liquid fertilizer when the nitrate concentration of a leaflet's petiole sap of leaf beneath fruit which is 2–4 cm declined below 2000 mg L⁻¹.
For standard yield by the method of fertilizer application based on this condition, no basal-dressed nitrogen was required when soil nitrate before cultivation was 150 mg kg⁻¹ dry soil or higher in the 0–30 cm layer; 38 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 25% of the standard rate of fertilizer application of Chiba Prefecture, was optimum when soil nitrate before cultivation was 100150 mg kg⁻¹ dry soil; 75 kg ha⁻¹ of basal-dressed nitrogen, which corresponds to 50% of the standard, was optimum when soil nitrate before cultivation was under 100 mg kg⁻¹ dry soil. A standard yield was secured and the rate of nitrogen fertilizer application decreased by 49–76% of the standard by keeping the nitrate concentration of tomato petiole sap between 1000–2000 mg L⁻¹ from early harvest time to topping time under these conditions.     

Total selenium content of agricultural soils in Japan

To evaluate the selenium (Se) level in agricultural soils in Japan and to investigate its determining factors, 180 soil samples were collected from the surface layer of paddy or upland fields in Japan and their total Se contents were determined. Finely ground soil (50 mg) was wet-digested with HNO₃ and HClO₄ solution and the released Se was reduced to Se(IV). The concentration of Se(IV) was then determined by high-performance liquid chromatography with a fluorescence detector after treatment with 2,3-diaminonaphthalene and extraction with cyclohexane. The total Se content ranged from 0.05 to 2.80 mg kg⁻¹ with geometric and arithmetic means of 0.43 and 0.51 mg kg⁻¹, respectively. The overall data showed a log-normal distribution. In terms of soil type, volcanic soils and peat soils had relatively high Se content and regosols and gray lowland soils had relatively low Se content. In terms of land use, upland soils had significantly higher Se content than paddy soils. Among regions, soils in the Kanto, Tohoku, Hokkaido and Kyushu regions had relatively high content. The total Se content had a significant positive correlation with the organic carbon content ( P  < 0.01) and the equation for the estimation of total Se content with organic carbon suggested that on average approximately 48% (0.24 mg kg⁻¹) of the total Se was in inorganic forms and approximately 52% (0.25 mg kg⁻¹) was in organic forms. Soil pH, on the contrary, did not show a significant relationship with the total Se content. In conclusion, the organic matter content, in combination with volcanic materials, was the main determining factor of the total Se content of agricultural soils in Japan.     

Net nitrogen mineralization and nitrification rates in forest soil in northeastern Taiwan

We used a laboratory incubation approach to measure rates of net N mineralization and nitrification in forest soils from Fu-shan Experimental Forest WS1 in northern Taiwan. Net mineralization rates in the O horizon ranged from 4.0 to 13.8 mg N kg⁻¹ day⁻¹, and net nitrification rates ranged from 2.2 to 11.6 mg N kg⁻¹ day⁻¹. For mineral (10–20 cm depth) soil, net mineralization ranged from 0.06 to 2.8 mg N kg⁻¹ day⁻¹ and net nitrification rates ranged from 0.02 to 2.8 mg N kg⁻¹ day⁻¹. We did not find any consistent differences in N mineralization or nitrification rates in soils from the upper and lower part of the watershed. We compared the rates of these processes in three soil horizons (to a soil depth of 30 cm) on a single sampling date and found a large decrease in both net N mineralization and nitrification with depth. We estimated that the soil total N pool was 6,909 kg N ha⁻¹. The present study demonstrates the importance of the stock of mineral soil N in WS1, mostly organic N, which can be transformed to inorganic N and potentially exported to surface and ground water from this watershed. Additional studies quantifying the rates of soil N cycling, particularly multi-site comparisons within Taiwan and the East Asia–Pacific region, will greatly improve our understanding of regional patterns in nitrogen cycling.     

Indicator of potential residual carbon in soils after exogenous organic matter application

An indicator to evaluate the proportion of exogenous organic matter (EOM) remaining in soils over the long-term after application has been developed. A database was constructed with analytical data corresponding to 83 EOMs, including sludges, composts, animal wastes, mulches, plant materials and fertilizers. The data included results of proximal analysis (soluble, SOL, hemicellulose-, HEM, cellulose-, CEL, and lignin-like, LIC, fractions, in g kg⁻¹ total organic matter) and of carbon (C) mineralization during long-term incubations under laboratory conditions (in g kg⁻¹ exogenous organic C, EOC). The potential residual organic C after EOM application to soil was assessed from the extrapolation of the incubation results. Then, partial least square regression was used to relate EOM characteristics to the proportion of potentially residual organic C previously determined from the incubations. The biochemical fractions of EOM were not predictive enough to develop the indicator. The proportion of organic C mineralized during 3 days of incubation (C_3d) was cumulated and appeared to be the most predictive variable of residual organic C. The proposed indicator of residual organic carbon in soils (expressed as g EOC kg⁻¹) was I_ROC = 445 + 0.5 SOL – 0.2 CEL + 0.7 LIC – 2.3 C_3d. The indicator was calculated for the main types of EOM applied to soils. When compared with the few field data of residual C measured in long-term field experiments, the values provided by the indicator seemed to be over-estimated (i.e. EOC degradation could be faster under field conditions than during laboratory incubations).     

Effect of phosphogypsum application on the growth and Ca uptake of Komatsuna Brassica rapa L. cv. Natsurakuten

(pp. 1–7)
Application of phosphogypsum PG and limestone to Andisol were compared in terms of their effects on the growth and uptake of Ca in Komatsuna Brassica rapa L. cv. Natsurakuten. The studies were carried out in soil pot cultures, and both PG and limestone were applied to the Andisol at the rates of 0, 0.30, 0.75, 1.50 g kg⁻¹ in the form of CaO.

• 1) 

  Limestone application resulted in an increase in the soil pH. On the other hand, no change was observed in the case of PG application at pH 6.1 ± 0.1 regardless of the application rate. Both soil EC and water-soluble Ca increased in proportion to the PG application rate, and this increase was approximately 5 times greater than that observed when limestone was applied at 1.50 g kg⁻¹. The w-Ca/ex-Ca ratio (water-soluble Ca: 1 M acetic acid-extractable Ca) was clearly increased from 0.12 up to 0.26 in PG, while the value was slightly decreased from 0.12 to 0.05 in limestone.

       
  
  

Aluminum toxicity of synthetic aluminum–humus complexes derived from non-allophanic and allophanic Andosols and its amelioration with allophanic materials

Natural non-allophanic Andosols often show aluminum (Al) toxicity to Al-sensitive plant roots. The significance of Al–humus complexes to Al toxicity has been emphasized. Allophanic Andosols also possess Al–humus complexes, but they rarely show any toxicity. In the present study, using model substances, we tested the toxicity of Al–humus complexes and its amelioration with allophanic materials. We extracted humic substances from the A horizons of a non-allophanic Andosol and an allophanic Andosol using a NaOH solution, and reacted the humic substances and partially neutralized AlCl₃ solution at pH 4. Allophanic material was purified from commercial Kanuma pumice. Plant growth tests were conducted using a medium containing the Al–humus complexes (50 g kg⁻¹), the allophanic material (0, 90, 180 and 360 g kg⁻¹) and perlite. The root growth of barley ( Hordeum vulgare L.) and burdock ( Arctium lappa ) was reduced in the media containing the Al–humus complexes derived from both the non-allophanic and allophanic Andosols when the allophanic material was not added. With the addition of the allophanic materials, particularly in the 360 g kg⁻¹ treatment, the growth of the barley roots was improved markedly. Although the root growth of the burdock tended to improve with allophanic materials, the effect was weaker than that for barley. Monomeric Al in a solution of the medium was not detected (< 0.05 mg L⁻¹) following the addition of 360 g kg⁻¹ of allophanic materials, whereas 0.8–1.7 mg L⁻¹ Al was recorded without the allophanic material.     

Accumulation of Denitrifying Bacteria and Enhancement of Denitrification Activity in Deep Subsurface Soil in Relation to the Geological Profile

We investigated the denitrification activity and the distribution of the denitrifying bacteria of a boring survey site located on a volcanic plateau, where the geological profiles from surface to deep subsurface soil at the groundwater level had been examined. There were differences between the water quality in the Ito pyroclastic flow deposit (Shirasu) layer (44.2 to 54.5 m) and that in the Osumi pumice fall deposit (Pumice) layer (below 54.5 m) corresponding to the impermeable layer of unconfirmed groundwater: The nitrate concentration was less than 1 mg kg⁻¹ in the Shirasu layer and more than 10 mg kg⁻¹ in the Pumice layer (Kubota et al. 2005). Denitrification activity decreased from the surface to the loam layer and was enhanced in the Shirasu layer and the Haraigawa clay impermeable layer at a depth of 65 m. It was observed that the highest potential denitrification activity (10³ ng-N₂O d⁻¹ g⁻¹) in the impermeable layer was almost equal to that of a Kuroboku surface soil with slurry application. Viable counts of the sonic-samples, which indicated the presence of bacterial group with soil particles attached, increased in the impermeable layer. The ratios of viable or denitrifying bacterial counts in the sonic-samples to those in the wash-samples were significantly higher in the impermeable layer than those in the surface layer. These results suggest that the hydrogeological conditions enhanced the denitrification activity in the impermeable layer, the niches of which might be relatively anaerobic and have a sufficient supply of substrates to enable the denitrifying bacterial populations to multiply.     

Measurement of ammonia volatilization loss using a dynamic chamber technique: A case study of surface-incorporated manure and ammonium sulfate in an upland field of light-colored Andosol

The present study aimed to elucidate ammonia (NH₃) volatilization loss following surface incorporation (0–15 cm mixing depth) of nitrogen (N) fertilizer in an upland field of light-colored Andosol in central Japan. A dynamic chamber technique was used to measure the NH₃ effluxes. Poultry manure, pelleted poultry manure, cattle manure, pelleted cattle manure and ammonium sulfate were used as N fertilizers for basal fertilization to a bare soil with surface incorporation. All three experiments in summer and autumn 2007 and in summer 2008 showed negligible NH₃ volatilization losses following the application of all N fertilizers with the same application rate of 120 kg N ha⁻¹ as total N; these negligible losses were primarily ascribed to chemical properties of the soil, that is, its high cation exchange capacity (283 mmol_c kg⁻¹ dry soil) and relatively low pH(H₂O) (5.9). In addition, the surface incorporation, the very small ratio of ammoniacal N to total N for the manure, and the decrease in soil pH to ≤5.5 following applications of ammonium sulfate were also advantageous to the inhibition of NH₃ volatilization loss from the field-applied N fertilizers.     

Kinetic Parameters of Gross N Mineralization of Peat Soils as Related to the Composition of Soil Organic Matter

Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using ¹³C CPMAS NMR. Mineralization potential ( N ₀), apparent activation energy ( E _a), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg⁻¹, 281–8,181 J mol⁻¹, and 0.009–0.020 d⁻¹, respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by ¹³C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates.     

The impact of long-term cultivation and management history on the status and dynamics of cobalt in a savanna Alfisol in Nigeria

The status of cobalt (Co) in savanna soils of Nigeria is largely unknown, and a long-term experiment including inorganic fertilizer (NPK) and farmyard manure (FYM) and uncultivated land provided information on the way management affected the dynamics of Co in the soil. Total Co increased with increasing depth, whereas readily extractable Co decreased. The mean concentration of Co (5.6–7.9 mg kg⁻¹) was close to the mean value of 8 mg kg⁻¹ reported for soils worldwide, whereas the concentration of extractable Co was less than that reported in most soils. Regression analysis indicated that total Fe predicted up to 78% of the soil Co. The potentially available Co correlated strongly with pedogenic or reducible Mn oxides extracted with dithionite–citrate–bicarbonate. Mass balance calculations showed that fertilization with either NPK or FYM caused losses of between 0.8 and 1.1 g Co m⁻² after 50 years of cultivation against the uncultivated site as a reference. However, Co increased by 1.8 g m⁻² in the soil receiving FYM + NPK, suggesting that the Co of the soil was best maintained under this management probably because of incidental additions of Co in the manures. Furthermore, the positive Co balance in the FYM + NPK plot was partly enhanced by its larger contents of clay, Fe and pedogenic Mn oxides than in either the FYM or NPK plots. Clay, Fe and pedogenic oxides served as Co sinks in this particular savanna soil.     

Visualization of root growth in heterogeneously contaminated soil using neutron radiography

We used neutron radiography (NR), a non-invasive and in situ technique, to study living plant roots in soil. Plant roots have a larger water content than their unsaturated surrounding media. As water strongly attenuates a neutron-beam, NR can identify root structures in detail. We investigated the use of NR to visualize the root growth of lupin in quartz sand and in a loamy sand field soil. Further experiments elucidated the root growth of lupin in the loamy sand heterogeneously contaminated with 10 and 20 mg kg⁻¹ boron (B) and 100 mg kg⁻¹ zinc (Zn). We obtained high-quality images of root growth dynamics in both media with a resolution range of 110–270 μm. The images with quartz sand revealed fine structures such as proteoid roots that are difficult to locate in situ by other methods without destruction of the soil. Though quartz sand provided excellent visibility of roots, it proved to be a poor medium for growing plants, probably because of its bulk density (1.8 Mg m⁻³). The images with field soil showed normal root growth with slightly less contrast than the quartz sand. The poorer contrast was due to the greater neutron interaction with soil water and soil organic matter. In the heterogeneously contaminated soil, root growth was significantly reduced in the contaminated part of the soil in all B and Zn treatments. This study shows that NR has potential as a non-invasive method to investigate root growth over time as well as the response of roots to various abiotic stress factors.     

Vertical Distribution of Physico-Chemical Properties and Number of Sulfur-Oxidizing Bacteria in the Buried Layer of Soil Profiles with Marine-Reduced Sulfur Compounds

We observed the presence of reduced sulfur compounds in the buried soil layer of a paddy field on Sado Island, Niigata Prefecture. We sampled the paddy field soil from 0 to 300 cm depth and analyzed the physico-chemical properties of the soil and the numbers of sulfur-oxidizing bacteria and iron-oxidizing bacteria in order to elucidate both the sulfur-oxidizing mechanism and the function of sulfur-oxidizing bacteria in the subsoil. Based on the physico-chemical properties of the soil, layers 4 and 5, which were located below 1 m in depth, were found to be potential acid sulfate soils and to be under semi-anaerobic conditions. However, the concentrations of water-soluble sulfate ions in layers 4 and 5 (88.2 to 444 mg S kg⁻¹) were higher than those in layers 1 and 3 (16.1 and 8.29 mg S kg⁻¹, respectively) and a significant number of sulfur-oxidizing bacteria (10^2–6 MPN g⁻¹) was detected in layer 4. These results suggested that the oxidation of reduced sulfur compounds by sulfur-oxidizing bacteria had occurred in layer 4. Since no iron-oxidizing bacteria were detected in any layers, and it was reported that sulfur-oxidizing bacteria such as Acidithiobacillus thiooxidans could not oxidize pyrite directly, it was considered that the oxidation of the reduced sulfur compounds in layer 4 occurred through the following processes. At first, reduced sulfur compounds such as pyrite were oxidized chemically by ferric ions to intermediary sulfur compounds such as thiosulfate ions. Subsequently, sulfur-oxidizing bacteria in layer 4 oxidized these intermediary sulfur compounds to sulfate ions. However, it was considered that the oxidation rate of the reduced sulfur compounds in layer 4 was far slower than would occur under aerobic conditions.     

Amelioration of a highly alkaline soil by trees in northern India

Abstract. A study was carried out to compare the impact of 6-year-old plantations of Prosopis juliflora (Swartz) D.C., Dalbergia sissoo Roxb. Ex. D.C. and Eucalyptus tereticornis Sm. on the physical and chemical properties of sodic soil in the Indo-Gangetic alluvial plains of Uttar Pradesh, India. Soil properties under the three tree species showed significant improvement through a reduction in the pH, electrical conductivity, exchangeable sodium percentage, CaCO₃ and gypsum requirement, and by increase in organic C, total N, and available P and K. The six years of reclamation had achieved a marked reduction in exchangeable sodium (from 11.5 to 4.5 cmol_c kg⁻¹) to a depth of 1.5 m in the soil profile, whereas the levels of exchangeable calcium, magnesium and potassium had increased. There was also a significant reduction in soil bulk density (from 1.66 to 1.24 g cm⁻³) and increases in porosity, water holding capacity, field capacity, permeability and infiltration rate. The equilibrium infiltration rate after 455 min increased from 0.03 cm h⁻¹ in the control to 0.13 cm h⁻¹ under P juliflora and D. sissoo and 0.10 cm h⁻¹ under E. tereticornis . It is concluded that salt-tolerant tree species have a significant impact on soil properties, which could help to rehabilitate the sodic wastelands in the region.     

Boron Fixation and Its Release in Soils and Bark Compost

Batch studies were conducted to investigate the fixing and release behavior of boron (B) in the soils from Haruo-cho, Kochi, and a bark compost (BC). Boron fixation on river sand (RS) was extremely low. The amount of B fixed was 6.3 mg kg⁻¹ for the greenhouse soil (GS). However, BC showed a 10-fold higher fixation of B (64.1 mg kg⁻¹) compared to GS, indicating that BC here displayed a significant capacity for B trapping. In GS, only around 9% of the adsorbed B was released during a 1-month period of incubation. Bark compost showed the highest amount of release during the incubation period, accounting for 64% of the adsorbed B. Moreover, the ratio of B release increased to 77% in the case of the soil mixed with BC. These results, suggest that different kinds of fixation-releasing mechanisms operate in the soil and BC. The B fixation on soil is considered as specific adsorption on minerals. A possible mechanism for B fixation on BC is ligand exchange. B-diol complexes might be formed with BC, and then after decomposition by microorganisms, they may release B during the incubation period.     

Rice-soil interactions in Vietnamese acid sulphate soils: impacts of submergence depth on soil solution chemistry and yields

Abstract. The aim of this study was to investigate the effects of water submergence depth on radial oxygen loss (ROL), soil solution chemistry and rice growth performance in acid sulphate soils in southern Vietnam. ROL was measured in a solution culture. In a separate pot experiment the impact of water submergence depth on rice growth and soil solution chemistry was studied. Three submergence depths were used in the two experiments (5, 10 and 15 cm). ROL declined with submergence depth and was significantly greater in young roots (with no root hairs) than in older roots. In the pot experiment rice growth and soil solution chemistry were clearly affected by the submergence depth. During the first crop at 5 cm submergence, there was a significantly higher yield and a higher oxidation state (pe+pH) compared to 10 or 15 cm submergence. The Fe concentration was significantly greater at the 5 cm depth compared to the 10 or 15 cm depth. SO₄^2– reduction was delayed at the 5 cm depth. Rice yield was c. 25% less at the 15 cm than at the 5 cm depth. During a second crop, there was a substantial SO₄^2- reduction and H₂S formation and almost no significant effects of submergence depth on either soil solution chemistry or crop yield. In a field experiment with a dry-season rice crop, yield and Fe, Al and SO₄^2– concentrations were higher at a shallow submergence depth than at greater depths in the same field, showing similar depth trends to those found during the first crop in the pot experiment. Farmers should be advised to use a shallow submergence depth and, if possible, avoid deep-rooted rice varieties. A conceptual model is suggested, which summarizes the relationships between ROL and soil solution chemistry.     

Assessing Passive Capillary-Wick Samplers for monitoring resident nitrate concentration in real field

Abstract. We evaluated the effectiveness of capillary-wick samplers (PCAPS) for continuous monitoring of resident nitrate concentration in three 'soil-crop-climate' systems differing in soil type, land use and climate. These systems involved: (i) acid silty soils under a beech-oak forest affected by heavy N-NH₄⁺ deposition in Belgium; (ii) silty soils under wheat cropping and a short rotation willow coppice plantation (SRC) in Belgium; and (iii) volcanic ash soils under plantain cultivation with and without urea fertilization in Colombia. The PCAPS continuously applied a suction of 0 to 5.4 kPa to the soil water below the effective rooting zone without the need for an auxiliary vacuum source. The nitrate concentrations showed large variations over time and ranged between 6–192 mg l^–1 under forest, 19–143 mg l^–1 under wheat, 11–47 mg l^–1 under SRC and 3–138 mg l^–1 under fertilized plantain. The analysis of the soil leachates collected with PCAPS confirms previous results dealing with leaching of nitrate and alkaline and alkaline-earth cations in similar 'soil-crop-climate' systems. It was concluded that PCAPS was a suitable tool to collect soil solutions and that it could help to assess nitrate leaching losses in various ecological or cropping conditions.