Sites and processes of nutrient accumulation in the subsoil through water percolation from the plow layer in a submerged paddy soil microcosm

The leaching of nutrients from the plow layer by water percolation and their accumulation in the subsoil observed in a Japanese paddy field (Katoh et al. 2004: Soil Sci. Plant Nutr., 50, 721-729) were determined semi-quantitatively in a soil column experiment. Ca²⁺, Mg²⁺, K⁺, Mn²⁺, Fe²⁺, and phosphate in percolating water from the plow layer soil column were retained in the subsoil columns that were connected to the plow layer soil column. Fe²⁺, K⁺, and phosphate accumulated in the uppermost part of the subsoil. Accumulation of Fe²⁺ in the uppermost part of the subsoil was presmnably due to the cation exchange process with concomitant desorption of Ca²⁺. In contrast, Ca²⁺ and Mg²⁺ in percolating water from the plow layer soil colmnn accumulated once in the subsoil, and translocated downwards slowly with successive water percolation. Considerable amounts of inorganic carbon (IC) and dissolved organic carbon (DOC) in percolating water from the plow layer soil column were also retained in the subsoil columns. IC did not accumulate a gaseous form.     

Vertical Changes in Bacterial Communities in Percolating Water of a Japanese Paddy Field as Revealed by PCR-DGGE

Percolating water was sampled from the plow layer and subsoil layer in a Japanese paddy field, and the bacterial communities were compared together with floodwater by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) targeting a partial 16S rRNA gene and subsequent sequencing. The number of DGGE bands ranged from 16 to 28 with no significant differences among the sampling sites and times. Only 2 bands were common for the three sources of water samples. DGGE bands specific for the floodwater samples and percolating water samples from the plow layer were identified, while percolating water samples from the subsoil layer did not show specific bands but displayed common bands to those of the floodwater samples (7 bands) and percolating water samples from the plow layer (1 band). Cluster analysis of the DGGE banding patterns showed a distinct clustering in the samples of percolating water from the plow layer and a closer relationship between the others. These results suggest that the bacterial communities in percolating water changed during downward movement through the plow layer and subsoil layer. Sequences of the DGGE bands specific for the samples of percolating water from the plow layer showed a close relationship with anaerobic bacteria such as iron-reducers or uncultured bacterial DNA isolated from environments that are considered to be less oxic. On the other hand, the sequences of the bands specific for the samples of floodwater and percolating water from the subsoil layer showed a close relationship with uncultured bacterial DNA isolated from freshwater environments.     

Methane production and its fate in paddy fields

Abstract

Oxidation of methane and total water soluble organic carbon (TOC) in the subsoil, which percolated from the plow layer, was investigated in a column experiment. The amounts of both methane and TOC in the leachate decreased by percolation in the subsoil.

Fe²⁺ percolated from the plow layer was nearly completely retained in the subsoil. The decomposition of methane and TOC in the subsoil was considered to result in the coupling with the formation of Fe²⁺. Methane was estimated to contribute ca. 19–21% to the total amount of Fe²⁺ formed in the subsoil by the organic materials in the leachate.     

Impact of water percolation on nutrient leaching from an irrigated paddy field in Japan

Abstract. We examined the effect on soil nutrient status and sustainability of water percolation through an irrigated paddy field in Japan, to the depth of drainage (40 cm). The difference between amounts of nutrients leached by percolation and those supplied by irrigation indicated that 25–130 kg ha⁻¹ Ca, 8–24 kg ha⁻¹ Mg, from −1 to 9 kg ha⁻¹ K, and 8–17 kg ha⁻¹ Fe, respectively, were lost each year from the 0–40 cm soil layer during rice cultivation, when the supply from fertilization and rainfall and the loss in grain harvest were not accounted for. When the supply of K from rainfall and the loss in grain harvest were taken into account, a total K loss of about 10 kg ha⁻¹ was estimated. The electrical neutrality of inorganic ions in the percolating water was always maintained. From these results we estimate that the amounts of exchangeable Ca and Mg in the soil to a depth of 40 cm would decrease by 50% within 50–260 and 30–100 years, respectively, if similar management were continued without fertilization. The total amount of carbon dioxide (ΣCO₂) leached in percolating water during the period of rice cultivation was 120–325 kg C ha⁻¹, which corresponded to 0.47–0.94% of the soil organic carbon to 40 cm depth.     

Bacterial numbers and biomass in leachate and in subsoil of a submerged paddy field

By a leaching experiment with glass columns packed with submerged paddy soils, the relationships among numbers of total bacteria, total Gram-positive bacteria, culturare aerobic bacteria and a amount of bacterial biomass both in the leachate, and in the subsoil after leaching incubation were studied. The leachate from soil columns was collected every 3 d during the 30-d incubation period. The soil columns were packed with plow layer soil samples with and without rice straw (RS) amendment, and the subsoil column was connected to the plow layer soil column without RS. Numbers of total bacteria, culturable aerobic bacteria, and a amount of bacterial biomass in the leachate decreased with the incubation time. There was no correlation between the number of total bacteria in the leachate and the concentration of total organic carbon in the leachate. Bacteria less than 0.1 µsm³ in size predominated in the leachate, especially in that from the plow layer soil column with RS. Percentages of the number of Gram-positive bacteria in the leachate were very low (less than 7% of the total bacterial number), while the percentage in the subsoil after the leaching experiment was in the range of 21–82%. The sum of the number of bacteria percolated from the plow layer soil column with RS during the 30-d period of incubation and the sum of the amount of biomass C were 39 and 77% less than the corresponding values for the bacteria percolated from the plow layer soil column without RS. Percentages of culturable aerobic bacteria among the total bacteria ranged between 2.8 and 37% in the leachate, while less than 0.6% in the subsoil after the leaching experiment.     

The Transfer of Chemical Elements within a Heath-Ecosystem (Calluna vulgaris) in Northwest Germany

The purpose of this investigation was to describe the element budget of a heathland area in Northwest Germany by measuring the fluxes of elements within the ecosystem. The following fluxes were considered: input by precipitation, canopy-drip, mineralisation, ion uptake, litterfall, output with seepage water. The elements H, Na, K, Ca, Mg, Mn, Fe, Al, S, P, CI, NO, NH, N_org were analysed, the period of investigation was one year. The results demonstrate the high importance of deposited nutrients like N (especially No3), Ca and Mg for the element budget and the stability of a heath-ecosystem. The internal turnover of K, Ca, Mg and Mn within the ecosystem mainly took place by leaching. No leaching was found for N, P, AI, Fe, S, CI, Na. For these elements litterfall was the dominant internal way of cycling. The humus layer was a sink for total-N, NO, Ca, Mg, Mn, Fe and S. NO, Ca, Mg, Mn and S were removed from the percolating solution, while for Fe and especially N and Mn an inhibition of mineralisation was found. The element balance for the mineral soil showed that this part is a sink for Hand a source mainly for Al, Ca and Mg, less for K and Na. From the cation/anion balance of the storage changes in mineral soil the ecosystem-internal H ion production was calculated as 0.4 keq per ha and year. It may be traced back to an uptake of NH, and dissociation of fulvic acids in the mineral soil. The results are discussed with respect to the development, stability and management of heath-ecosystems.     

Origin and properties of humus in the subsoil of irrigated rice paddies

A pot experiment was conducted to estimate the amount of dissolved organic carbon (DOC) leached from the submerged plow layer of rice paddies during the cultivation period and its accumulation in the subsoil. Organic matter in the leachate was fractionated using insoluble polyvinylpyrrolidone (PVP) which can adsorb aromatic components having hydroxyl and/or carboxyl groups. Total amount of DOC leached throughout the growth period of rice plant corresponded to ca. 0.5% of total-C in the plow layer soil sample (total C, 17.8 g kg^-1) irrespective of the presence of rice plant, and the PVP-adsorbed fraction accounted for 34–43% of it. The amount of DOC in the leachate decreased by more than 50%, and that of the PVP-adsorbed and non-adsorbed fractions decreased by 79–82 and 45–47% by passing through the subsoil packed in the glass columns, respectively. The decreases were considered to be due to the adsorption to the subsoil, since a corresponding increase was observed in the total carbon content in the subsoil. Successive extraction of organic matter from the subsoil before and after the rice growth period with water, 0.25 M NaNSON and 0.1 m Na₄P₂O₇ (pH 7.0) solutions showed that the amount of organic carbon adsorbed on PVP mainly increased in the Na₄P₂O₇ (pH 7.0)-extractable fractions during the rice growth period, while the amount of organic carbon non-adsorbed on PVP increased in all the fractions extracted. These results suggested that the PVP-adsorbed fractions in the leachate were adsorbed to the subsoil mainly by coordinate bonding while the PVP-non-adsorbed fractions were adsorbed by physical adsorption, weak hydrogen bonding, ion bonding, and coordinate bonding.     

Nutrient changes in decomposing beech leaf litter assessed using a solution flux approach

The decomposition of beech (Fagus sylvatiea L.) leaf litter was examined in lysimeters. The experiment allowed comparison of data from mass changes of bioelements in leaf litter and the solution flux balance of through fall input and lysimeter output over a two-year period (1983 and 1984). The annual C loss from the leaf litter was 19%. Na and K concentrations in this leaf litter decreased in the first year and remained constant in the second, while those of Ca and Mg showed no significant changes. N and S amounts per ha increased during the first year by about 7 kg N ha^?1 and 0.5 kg S ha^?1. Ash, Fe, Mn and Al amounts per ha increased to 470, 130 and 240% of their initial levels. These net increases in the first year of decomposition are discussed. The mean annual water and element input by through fall during the experiment corresponded approximately to the long-term average. Thirty to 40 mm more water was evaporated from the litter layer in the drier year (1983) than in 1984. Total N, NO, Na and C1 flux rates of through fall inputs and lysimeter outputs were equal. NH, input rates were greater and organic N smaller than the output rates of the lysimeters. Water balance data indicated that the lysimeter output of K, Mg, Ca and SO, exceeded through fall input. Probable reasons for these differences are discussed.     

Carbon cycling in rice field ecosystems in the context of input, decomposition and translocation of organic materials and the fates of their end products (CO2 and CH4)

Rice fields are intensively managed, unique agroecosystems, where soil flooding is general performance for rice cultivation. Flooding the field results in reductive soil conditions, under which decomposition of organic materials proceeds during the period of rice cultivation. A large variety of organic materials are incorporated into rice soils according to field management. In this review, the kind and abundance of organic materials entering carbon cycling in the rice field ecosystem are evaluated first. Then, decomposition of plant residues and soil organic matter in rice fields is reviewed quantitatively. Decomposition of plant residues is shown to be the active process in carbon cycling in rice fields. Rice releases photosynthates into the rhizosphere (rhizodeposition), and they follow a different avenue of decomposition in soil from that of plant residues. Incorporation of rhizodeposition into microbial biomass and soil organic matter during the period of rice cultivation, and their fates after harvesting are evaluated quantitatively from ¹³C pulse labeled experiments. Percolating water transports inorganic and organic carbon from the plow layer to the subsoil layer. The amounts of their transport and accumulation in the subsoil layer are evaluated in relation to the amounts of soil organic C in the plow layer. Not only CO₂ but also CH₄ are produced in the decomposition process of organic materials in flooded rice fields. CH₄ evolution from rice fields is of global concern from the viewpoint of global warming. Origins of CH₄ evolved from rice fields are estimated first, followed by the fates of CH₄ in rice field ecosystems. Rhizodeposition is shown to be the main origin of CH₄ evolved from rice fields. Evolution to the atmosphere is not the sole pathway of CH₄ produced in rice fields. The amounts of CH₄ retained in soil, percolated to the subsoil layer and decomposed in soil are evaluated in the context of the amounts of CH₄ efflux. Thus, this review focuses on carbon cycling in the rice field ecosystem from the viewpoints of input, decomposition, and translocation of organic materials and the fates of their end products (CO₂ and CH₄).     

Phospholipid fatty acid composition of microbiota in the percolating water from a rice paddy microcosm

The microbiota in the percolating water from the plow layer soil in paddy fields was studied based on the composition of phospholipid fatty acids (PLFAs) in a pot experiment. The mean concentrations of PLFAs in the percolating water were 17±5 and 11±4 µg L^-1 in the planted and non-planted pots, respectively. The dominant PLFAs in the percolating water were 16: 0, 16: 1ω7c, 18: 1ω7, 18: 1ω9, il5: 0, and ail5: 0 PLFAs in both the planted and non-planted pots. The dominance percentage of 18: 3ω6c and 17: 1ω8 PLFAs increased at the late stage of rice growth in the planted pots. The percolating water from the planted pots contained in a higher percentage of straight mono-unsaturated PLFAs and a lower percentage of branched-chain PLFAs than that from the non-planted pots. Considerable differences in the PLFA composition in the percolating water were observed between the planted and non-planted treatments and with the duration of the growth period. Principal component analysis indicated that the microbiota in the percolating water was derived from the microbiota in the floodwater and in the plow layer soil. Cluster analysis showed that the similarity of the PLFA composition in the percolating water to the PLFA composition in the plow layer soil was higher than that in the floodwater. The stress factor that was estimated from the trans/cis ratio of 16: 1ω7 PLFA was 0.08±0.04 and 0.14±0.05 in the percolating water from the planted and non-planted pots, respectively, which indicated that the degree of stress on the microbiota in the percolating water from the planted pots was low in a similar way to the degree of stress on the microbiota in the floodwater, while the degree in the percolating water from the non-planted pots was similar to that in the plow layer soil, respectively.     

Batch‐Determined Elements Release from Wood Ash Mixed with an Acidic Forest Soil Sample

Abstract

A serial batch leaching experiment was carried out to evaluate the release of elements from wood ash mixed with a strongly acidic forest soil sample. Wood ash application resulted in increased leachate pH, dissolved organic carbon (DOC), and electrical conductivity (EC). Increasing application of wood ash increased cumulative release of inorganic carbon (IC), chloride (Cl), nitrate (NO₃), sulfate (SO₄), potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), manganese (Mn), phosphorus (P), and copper (Cu). Release of NO₃, P, iron (Fe), aluminum (Al), Cu, and lead (Pb) continued. Large amounts of DOC, K, Ca, and SO₄ were mobilized. Inorganic C, Fe, and Mg were released in moderate quantities. Manganese, Na, Al, Cl, and NO₃ were released in limited amounts. Amounts of leached P, Pb, and Cu were lower. The mixed order equation adequately described the release of elements in the soil‐ash mixture. Accumulation of elevated amounts of trace elements does not appear to be a problem when higher wood ash rates are avoided. Wood ash should be applied in split application to avoid short‐term concentrated alkaline and salty conditions that could interfere with plant growth.     

Leaching of metals from a spruce forest soil as influenced by experimental acidification

Acidified (H₂SO₄+HNO₃, 3:1) throughfall waters (pH 3.16 and 3.40 as volume weighted means or control (untreated throughfall water, pH 3.72) were applied for 3.5 yr by an automatic irrigation device to lysimeters containing podzolized spruce forest soils of 0–5, 0–15 and 0–35 cm soil depth. The total volume of the leachates was measured together with their pH and total content of DOC, Na, K, Ca, Mg, Fe, Mn, Al, Cu, Zn, Cd and Pb and the initial amounts of metals and H in the soil. The main part of H⁺ added with the throughfall waters was retained within the soil. Concentrations and fluxes of Mg, Ca, Mn, Zn and Cd in the soil were significantly increased by addition of acidified throughfall waters; K was less affected. As a consequence of lowered flux of DOC in the A horizon as acid input increased, Fe, Al, Cu, and Pb fluxes also decreased. The mobility of these metals in the A horizon was shown to be regulated mainly by the formation of watersoluble organic compounds rather than directly by pH variations. Compared to the control, the additional annual loss of Mg from the soil profile in the most acid treatment was c. 10% of the currently exchangeable amount.     

Peatland Interstitial Water Chemistry in Relation to that of Surface Pools along a Peatland Mineral Gradient

The elemental (including silica (Si), calcium (Ca), magnesium (Mg), manganese (Mn) and iron (Fe)) and nutrient composition of peatland surface pools and concentrations of Ca, Mg, Mn, and Fein peat interstitial waters and surface peat concentrations of oxides of Mn and Fe were determined for 15 peatlands sampled along a mineral gradient. Surface pool concentrations of Si wereca. ten fold less in surface pools of mineral-poor peatlands thanin the mineral rich, supporting the use of this element as an indicator of minerotrophic influence in peatlands. Principle component analysis of surface pool water chemistry parametersdifferentiated mineral-poor and moderately-poor peatlands frommineral-rich peatlands based on the concentrations of Ca, Mgand alkalinity of pools. Several lines of evidence indicated that peatland interstitial waters were important contributors to peatland alkalinity and included; (1) maximum interstitial water concentrations of Ca and Mg correlating with overlying surface pool alkalinity, (2) a negative correlation between interstitial water Ca:Mg ratios and surface pool concentrationsof Si and (3) Ca:Mg ratios of moderately-poor to mineral-poorpeatland interstitial waters approaching the Ca:Mg ratio of rainwater rather than those of bedrock. Interstitial water concentrations of dissolved Mn and Fe correlated with amountsof reducible Fe and Mn (oxides of Fe and Mn) recovered from thepeat/water interface indicating that groundwater inputs areimportant sources of these two elements to fens. As a consequence, for peatlands that are not truly ombrotrophic,groundwater inputs of Mn and Fe may interfere with interpretingpeat metal profiles thought to be due to anthropogenic inputs alone.     

Mineral element concentration of two barley cultivars in relation to water deficit and aluminum toxicity

The separate and combined effects of water and Al stress on concentrations of P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Al, Sr, and Ba were determined in tops of ‘Dayton’ (Al‐tolerant) and ‘Kearney’ (Al‐sensitive) barley (Hordeum vulgäre L.) grown in an acid, Al‐toxic, Tatum subsoil (clayey, mixed, thermic, Typic Hapludult). Plants were grown 4 weeks in a plant growth chamber at high (pH 4.7) or low (pH 6.6) Al stress. During the last 2 weeks they were also subjected to low (‐20 to ‐40 kPa), moderate (‐40 to ‐60 kPa), or high (‐60 to ‐80 kPa) water stress. In general, Al stress had a greater overall effect on mineral element concentration of tops than water stress. Aluminum stress significantly decreased concentrations of P, Ca, and Mg and increased concentrations of Zn, Sr, and Ba, irrespective of the cultivar or water stress treatment. Cultivar differences in Mn concentration were observed with Al stress under all water stress conditions. In each case, Mn concentration was lower in ‘Kearney’ than in ‘Dayton’. Potassium, Ca, and Mg were lower in ‘Kearney’ than in ‘Dayton’ only at low and moderate water stress, under low Al stress, ‘Kearney’ had significantly higher concentrations of K and Ca than did ‘Dayton’ under all water stress conditions. The effects of water stress on mineral element concentration varied greatly with cultivar, Al stress treatment, and severity of water stress. Under high Al stress, increasing drought conditions from low water stress (‐20 to ‐40 kPa) to high water stress (‐60 to ‐80 kPa) significantly increased the concentrations of Ca, K, Zn, Sr, and Ba in Al‐sensitive ‘Kearney’ and reduced the concentrations of Zn, Sr, and Ba in Al‐tolerant ‘Dayton'; P and Mg concentration were unaffected by water stress. In contrast, under low Al stress, a corresponding increase in water stress significantly increased the concentrations of Ca and reduced that of P in ‘Kearney’ and increased Ca and B concentration in ‘Dayton'; Mg concentrations were unaffected in either cultivar. Thus, it appears that Al stress and water stress had opposite effects on Ca accumulation in barley tissue.     

Distribution of mineral elements in the outer layer of rice and wheat grains,using electron microprobe X-Ray analysis

Electron microprobe X-ray analysis was used to determine the transversal microdistribution of P, K, Mg, Ca, Fe, and Mn, with special attention to the outer layers of rice and wheat grains. P, K, Mg, Fe, and Mn were concentrated in the aleurone layer in each case. In particular, P, Mg, and K were highly concentrated in the subcellular particles of the aleurone layer, and had very similar distribution patterns in the outer layers of the matured grain of rice and wheat. By contrast, Ca was abundant in the pericarp.     

Throughfall of plant nutrients in relation to crown thinning in a swedish coniferous forest

Throughfall has been sampled in SW Sweden from 60 to 80 yr old Norway spruce (Picea abies) of two stands with different crown thinning classes, representing healthy reference trees and injured trees. the condition of the canopy had a significant influence on quantity and quality of deposition to the forest floor. Annual throughfall deposition from injured spruce showed an increase in glucose 270%, total sugar 80%, organic carbon (DOC) 40%, organic N 50%, Mg 100%, Ca 30%, and Fe 40% while Mn and K deposition decreased 30% and 20%, respectively, compared to annual throughfall deposition from healthy spruce.     

Amelioration of subsoil acidity in an Oxisol of the humid tropics

Summary This work investigated the effectsof amendments of fertilizer N and lime on subsoil acidity and maize rooting depth in an acid soil of the central Amazon basin. A split-plot designed field experiment was conducted on a clayey Oxisol (Typic Acrudox) during a 16-month period. Main plots received 0 or 4 Mt ha^-1 of lime. Subplots were four crop sequences: (1) Maize-green manure (Canavalia ensiformes); (2) maize-green manure (Mucuna aterrima); (3) maize-bare fallow, with the maize receiving 300 kg ha^-1 of urea-N; and (4) bare fallow, with an application of 300 kg ha^-1 of urea-N at the same time as sequence 3. Plots were periodically sampled to 1.2 m. The experimental site received 4265 mm of precipitation during 16 months; approximately 60%–90% of this rain percolated through the profile. Substantial amounts of Ca were leached from the 0–30 cm horizon during the experimental period, but only limited amounts accumulated in the subsoil. Base saturation below 45 cm was less than 50% at the end of the experiment regardless of lime treatment. Roots of maize were concentrated in the 0–30 cm layers in limed plots and the 0–20 cm layers in unlimed plots. In all treatments less than 5% of the roots was found below 50 cm. An acidity balance indicated that considerable acidity was leached below the plow layer and out of the profile.     

Correlations Between Soil Exchangeable Ca2+, Mg2+, K+ and Foliar Nutrient Concentrations in Mature Biological Olive Groves (Olea europaea L., cv. ‘Chondrolia Chalkidikis’)

Leaf and soil samples were taken and analyzed from two mature biological olive groves (Olea europaea L., cv. ‘Chondrolia Chalkidikis’), in Thessaloniki, Macedonia, Northern Greece, in order to determine the correlations between soil exchangeable cations and foliar calcium (Ca), magnesium (Mg) and potassium (K) concentrations, and the interrelations among leaf nutrients. Τhe nutritional requirements of trees for both biological groves were exclusively based on patent kali supply and nutrient recycling (via pruning material and weed cut recycling). Foliar K, Ca and Mg were positively correlated with soil exchangeable K, Ca and Mg, in the 40–60 cm layer, then in the 20–40 cm layer. Synergistic uptake mechanisms among Ca²⁺, Mg²⁺ and K⁺ probably exist. Leaf N was negatively correlated with foliar K, and positively with leaf Ca, Mg and manganese (Mn). Foliar P was negatively correlated with leaf Ca, Mg and Mn, while foliar Ca was positively correlated with leaf Mg and Mn. Foliar Mg was positively related with leaf Mn. High phosphorus (P) may decrease leaf Ca, Mg and Mn. Enhanced Ca may increase leaf Mg and Mn, while high Mg may also enhance foliar Mn. Finally, based on the determination of foliar nutrient concentrations, the nutritional requirements of olive trees in Ca, Mg, K, P, Fe, Zn were sufficiently (or over-sufficiently) satisfied. However, additional organic fertilization is needed, in order to achieve optimum levels of N, B and Mn (since their foliar concentrations were slightly insufficient). The correlations between leaf and soil exchangeable Ca, Mg and K, as well as among foliar nutrients should be taken into consideration, in order to achieve successful organic fertilization for mature biological olive groves, and to avoid nutritional imbalances and disorders.     

冀北山地油松蒙古栎混交林水化学特征

对冀北山地油松蒙古栎混交林穿透雨、树干茎流和枯透水中的Ca、Fe、K、Mg、Mn、Zn共6种养分元素进行测定。结果表明:(1)大气降水经过林冠层后化学元素含量均有不同程度增加,化学元素含量排序为Ca>K>Mg>Fe>Mn>Zn,树干茎流各项指标均增长较多,化学元素含量排序为Ca>K>Mg>Fe>Zn>Mn,枯落物水中K和Ca元素浓度增加最大。(2)大气降雨中Zn的变异系数最大,达2.853;K和Ca元素的变异系数最小,分别为0.158,0.163。穿透雨中变异系数最大的为Fe元素,其值为0.692;树干茎流中变异系数最大的为Zn元素,其值为0.594;枯透水中变异系数最大的为Fe元素,其值为1.164。(3)经过淋洗后水样中各元素的浓度均有所增加,穿透水、树干茎流和枯透水中Ca、K增加较多,Fe、Mn、Zn的淋溶量较少。     

Downward Movement of Soil Cations in Highly Weathered Soils Caused by Addition of Gypsum

Abstract

Besides supplying calcium (Ca) and sulfur (S) to plants, gypsum has recently been used in agriculture to ameliorate some soil physical and chemical properties, especially to alleviate aluminum phytotoxicity in subsoils. When applied in large quantities, however, gypsum may leach significant amounts of nutrients from the plow layer. This study was conducted to assess the effect of gypsum addition to the soil on the magnitude of cation leaching as well as the relationship of leaching with some soil properties in a group of seven Brazilian soils. Rates of gypsum equivalents to 0, 5.0, 10, and 20 t ha^?1 (0, 2.5, 5.0, and 10 g kg^?1) were mixed with triplicate soil samples consisting of 3.0 kg of dry base soil. After 60 days of incubation at room temperature (15–25°C), the experimental units were packed into polyvinyl chloride leaching columns (32‐cm‐high×10 -cm-diameter) at a density of 0.9 g cm^?3. Thereafter, they were percolated once a week with a volume of distilled water equivalent to 1.5 times the total soil porosity over 11 weeks. Soil samples were collected before the first and after the last percolation, for chemical analysis. Averaged across soils, 11 percolation events leached about 26% of each Ca, magnesium (Mg), and potassium (K) from the treatment without gypsum. Averaged across soils and rates, addition of gypsum leached 41–94% of added Ca, 13–90% of exchangeable Mg, and 13–58% of exchangeable K, and the highest losses occurred on the sandiest soils. The relationship between soil parameters and Ca leaching varied with gypsum rate: in the treatments that received gypsum, leaching was negatively related to cation exchange capacity (CEC), clay, and organic matter, and positively correlated with sand; in the treatment with no gypsum, leaching correlated with the same parameters above, nevertheless, all coefficients presented opposite signs. Leaching of K caused by gypsum was negatively associated with clay and positively with sand, whereas leaching of Mg was poorly correlated with any soil parameter. Gypsum is a good source to promote high and fast downward movement of Ca in the soil profile, but rates must be cautiously chosen because of excessive leaching of Mg especially on soils with low CEC.