Sulphur mineralisation in some New Zealand soils

Summary An open incubation technique was used to measure S mineralisation in a range of New Zealand soils. For most of the soils studied, the release of S as sulphate was curvilinear with time, and during a 10-week incubation, the amounts of S mineralised ranged from less than 3 g S g^-1 soil to more than 26 g S g^-1 soil. The best predictor of mineralised S appeared to be the amount of C-bonded S in the soil (explaining 59% of the variation in mineralised S between soils). Examination of the soils after incubation also revealed that the bulk of the mineralised S was derived from the C-bonded S pool. Hydriodic acid-reducible forms of organic S appeared to make little contribution to mineralised S.Attempts were made to predict total potentially mineralisable S (S _o) from incubation data using an exponential equation and a reciprocal-plot technique. However, the dependence of estimated values of S _o on the length and temperature of incubation cast doubts on the validity of this approach.     

Cadmium leaching from some New Zealand pasture soils

Cadmium (Cd) inputs and losses from agricultural soils are of great importance because of the potential adverse effects Cd can pose to food quality, soil health and the environment in general. One important pathway for Cd losses from soil systems is by leaching. We investigated loss of Cd from a range of contrasting New Zealand pasture soils that had received Cd predominantly from repeated applications of phosphate fertilizer. Annual leaching losses of Cd ranged between 0.27 and 0.86 g ha^–l, which are less than most losses recorded elsewhere. These losses equate to between 5 and 15% of the Cd added to soil through a typical annual application of single superphosphate, which in New Zealand contains on average 280 mg Cd kg^?1 P. It appears that Cd added to soil from phosphate fertilizer is fairly immobile and Cd tends to accumulate in the topsoil. The pH of the leachate and the total volume of drainage to some extent control the amount of Cd leached. Additional factors, such as the soil sorption capacity, are also important in controlling Cd movement in these pasture soils. The prediction of the amount of Cd leached using the measured concentrations of Cd in the soil solution and rainfall data resulted in an overestimation of Cd losses. Cadmium concentrations in drainage water are substantially less than the current maximum acceptable value of 3 µg l^?1 for drinking water in New Zealand set by the Ministry of Health.     

Composition of iron-manganese concretions from some New Zealand soils

A selection of iron-manganese concretions from five reference soil profiles and a buried loess deposit in New Zealand have been studied. Concretions appear to have developed by the precipitation of amorphous iron and manganese oxides among soil particles. X-ray fluorescence analysis shows that the concentrations of Fe, Mn, Co and Ba in the concretions are generally higher, and those of K, Ca, Si, and Al are generally lower, than in the soil materials surrounding the concretions, whereas Ti, Zn, S, and P show little variation. Other approximate analyses indicate that Cu, Ni, Mo, V, and Pb tend to be concentrated in concretions but for Ga, Zr, Sr, Li, and Rb there was no discernible trend. Electron probe microanalyses of some concretions show that Co and Ba are concentrated in Mn-rich phases rather than Fe-rich phases.Comparison with published results for concretions (Mn nodules) from the ocean floor and the floor of Lake Ontario indicates that, on average, marine concretions have higher Mn, and lower Si and Al concentrations than soil concretions, and that marine concretions have lower Fe concentrations than either Ontario or soil concretions.     

Dissolved organic matter leaching in some contrasting New Zealand pasture soils

Leaching of dissolved organic matter (DOM) from pastoral soils is increasingly seen as an important but poorly understood process. This paper examined the relationship between soil chemical properties, microbial activity and the losses of dissolved organic carbon (DOC) and nitrogen (DON) through leaching from six pasture soils. These soils differed in carbon (C) (4.6–14.9%) and nitrogen (N) (0.4–1.4%) contents and in the amount of organic C and N that had accumulated or been lost in the preceding 20+ years (i.e. −5131 to +1624 kg C ha⁻¹ year⁻¹ and −263 to +220 kg N ha⁻¹ year⁻¹, respectively). The paper also examined whether between‐soil‐type differences in DOC and DON leaching was a major explanatory factor in the observed range of soil organic matter (SOM) changes in these soils. Between 280 and 1690 kg C ha⁻¹ year⁻¹ and 28–117 kg N ha⁻¹ year⁻¹ leached as DOC and DON, respectively, from the six soils in a lysimeter study, with losses being greater from two poorly drained gley soils. Losses of C and N of this magnitude, while at the upper end relative to published data, could not fully explain the losses at Rawerawe, Bruntwood and Lepperton sites reported by Schipper et al. (2007) . The study highlights the leaching of DOM as a significant pathway of loss of C and N in pasture soils that is often ignored or given little attention in predictive models and nutrient budgeting. Leaching losses of DOC and DON alone, or in combination with slightly increased respiration losses of SOM given a 0.2°C increase in the mean annual soil temperature, do not fully explain long‐term changes in the SOM observed at these sites. When soils examined in the present study were separated on the basis of drainage class, the losses of DOC by leaching were correlated with both total and hot‐water extractable C (HWC), the latter being a measure of the labile SOM fraction. Basal microbial CO₂ respiration rates, which varied between 1 and 3.5 µg CO₂‐C g⁻¹ soil hour⁻¹ in surface soils (0–75‐mm depth), was also linked to HWC and the quantities of C lost as DOC. Adoption of the HWC method as an approach that could be used as a proxy for the direct measurement of the soil organic C lost by leaching as DOC or respired needs to be examined further with a greater number of soils. In comparison, a poor relationship was found between the hot‐water extractable N (HWN) and loss of DON by leaching, despite HWN previously being shown to be a measure of the mineralizable pool of N in soils, possibly reflecting the greater competition for N than C in these soils.     

Effects of liming on soil magnesium on some soils in New Zealand

Abstract

Results from 2 pastoral field lime trials showed that liming reduced exchangeable Mg. This effect increased with increasing rate of lime and with time following lime application, and was greatest in the top 0–50 mm depth. Soil solutions, sampled 2 years after liming, showed that solution Mg increased in increasing rate of lime. This effect was greatest in the top 20 mm of soil.

Lime incubation studies indicated that Mg fixation did occur on some of the soil studied, at pH >6.2. However, this did not account for the size of the observed effects of liming on exchangeable Mg in the field or explain the observed effects of liming at pH <6.2.

It is suggested therefore, that the major mechanism by which liming reduces exchangeable Mg, on these soils, is through displacement of exchangeable Mg into solution by the added Ca in lime, and subsequent leaching.

Results from other field trials suggest that liming will decrease exchangeable Mg if the change in pH‐dependent CEC (?ECEC) per unit change in soil pH is <15 me 100 g‐¹.     

Distribution of elements in some Fe-Mn nodules and an iron-pan in some gley soils of New Zealand

Three soil nodules and an iron-pan have been analysed for the elements Al, Si, Ti, V, Mn, Fe, Co, Ni, Cu and Zn using an electron microprobe. From the surface analysis it appears that the nodules consist of two major concentration zones of enrichment, viz. Mn-rich, Fe-rich zones and a third zone low in Mn and Fe. The elements Co, Ni, Cu and Zn are enriched in the first zone, whereas vanadium is enriched in the second zone. Four concentration zones are distinguishable in the iron-pan, Ti-rich, Fe-rich, Ti and Fe-rich and a zone low in Ti and Fe. The metals Mn, Co, Ni, Cu and Zn are mainly enriched in the Ti/Fe-rich zone. The associations of the trace elements with the major components of the nodules and iron pan are discussed in terms of physico-chemical factors.     

Fractionation of soil cadmium from some new zealand soils

Abstract

The concentrations and forms of soil cadmium (Cd) in 12 different New Zealand topsoils were investigated using a sequential fractionation procedure. Total soil Cd concentrations were low and ranged between 0.03 μg g^‐1 to 1.34 μg g^‐1 and were highly correlated with total soil phosphorus (r²=0.85, P<0.01). Results indicated that there was a wide range in the concentrations of Cd associated with individual soil fractions and large variations between soils. On average for all soils, the smallest proportion of Cd was in exchangeable forms, i.e., 3%, with 12% in the crystalline oxide fraction, 13% in the amorphous oxide fraction and the greatest proportion of Cd associated with the organic 34% and residual 38% fractions. There was evidence to show that a soil extractant which is commonly used to predict plant uptake of Cd from soils, i.e., 0.04 M ethylene diamine terra acetic acid (EDTA), extracts Cd from both exchangeable and organic forms of soil Cd.     

A comparison of three methods of organic carbon determination in some New Zealand soils

A dry combustion (Dumas) reference method for measuring total organic C (T), is compared with two other methods: the wet acidified dichromate oxidation, Walkley-Black procedure (an estimator of organic C) and loss on ignition (L) (an estimator of organic matter) for 40 samples from various depths from five New Zealand mineral soils, spanning a range of textures and cultivation treatments. Regression analyses reveal the following: (1) an excellent linear relation exists for all samples between Walkley-Black procedure and reference method results, with a mean conversion factor 1.25, which compares with the original value 1.32 recommended by Walkley & Black (1934). (2) L and T are less well-related by an equation of the form L=a+bT. In contrast to the traditional assumption that b? 1.72 and a? 0, a strong ‘intercept effect’ (a > 0) is revealed, reflecting removal on ignition of non-organic soil constituents. An improved regression of the form L=a+bT+cC, where C= percentage of clay, obtained by inclusion of the clay as an independent variable, points to the role of clay in releasing these constituents, chiefly adsorbed water.     

Movement of aluminium as an inorganic complex in some podzolised soils,New Zealand

Chemical and mineralogical data are presented for three Spodosols (podzols) and a related Inceptisol (yellow-brown loam). Allophane with an Al/Si atomic ratio close to two is identified in the B horizons of all four soils, and minor amounts of imogolite are present in association with allophane in all but one soil where small-particle gibbsite occurs. Parent materials for these soils are essentially non-vitric. Allophane (Al/Si = 2) has been estimated quantitatively in all soils using oxalate-extractable Si (Si₀) and is selected clay fractions using both Si₀ and infrared spectroscopy. Maximum concentrations of allophane (Al/Si = 2) range from 5% to 18% of fine earth (< 2 mm) fractions and all occur in B horizons. Fe₀ values are low relative to Al₀ values except for the upper horizons of the Inceptisol. Al₀ values peak in B horizons and the ratio pyrophosphate-extractable Al to Al₀ decreases from about 1 in A and upper B horizons to 0.1–0.4 in lower B horizons.An interpretation of the data is consistent with recent proposals that the movement of Al in podzolisation is due primarily to the formation of inorganic complexes with Si. Chemical criteria for spodic horizons should be consistent with the total illuviation of Al and Fe (and perhaps Si), rather than just the organic-bound fraction of Al and Fe in these horizons as indicated by amounts in extractants such as pyrophosphate.     

Mercury intrusion porosimetry of some New Zealand soils in relation to clay mineralogy and texture

Pore size distributions in the 10/10⁴ nm e.c.d. range in aggregates from three New Zealand soils with largely monomineralic clay fractions, were determined by mercury porosimetry after oven drying and also after critical point drying following methanol and then CO² exchange from a range of water contents. A soil containing halloysite showed considerable porosity in the fine pores (10–30 nm) regardless of the method of drying. A smectitic soil showed virtually no porosity in the 10²–10⁴ nm range when oven dry. A soil containing allophane was dominated by large pores (> 10³ nm). The change from a fine (clayey) to a coarser (clay loam) texture within the profile of one soil was reflected in an increase in large pores.     

伊朗一些石灰性土壤中锌解吸动态研究

Desorption of zinc (Zn) from soil is an important factor governing Zn concentration in the soil solution and Zn availability to plants. Batch experiments were performed to study the kinetics of Zn desorption by diethylenetriaminepentaacetic acid (DTPA) from 15 calcareous soil samples taken from Golestan Province in northern Iran. Soils were equilibrated with 0.005 mol L-1 DTPA solutions for 0.25 to 192 h. The results showed that the extraction process consisted of rapid extraction in the first 2 h followed by much slower extraction for the remainder of the experiment. Desorption kinetic data was fitted to pseudo-first-order kinetic model. The experimental data were found to deviate from the straight line of the pseudo-first-order plots after 2 h. The model of two first-order reactions was fitted to the kinetic data and allowed to distinguish two pools for Zn: a labile fraction (Q1 ), quickly extracted with a rate constant k1 , and a slowly labile fraction (Q2 ), more slowly extracted with a rate constant k2 . The applicability of pseudo-second-order model in describing the kinetic data of Zn desorption was also evaluated.     

The mineralogy and potassium supplying power of some loessial and related soils of New Zealand

Sixteen Pallic (Aqualfs, Ustalfs, Aquepts, Ochrepts) and related soils collected from the North and South Islands of New Zealand were studied to determine if variations in nonexchangeable K supply could be explained by mineralogical composition. A strong relationship was found which indicates that mica is weathering to vermiculite. Proportions of vermiculite and kandite are generally higher in the North Island than in the South Island. Dominance of either micas or vermiculite or kandite is determined by the stage of weathering and/or the nature of parent materials. Soils that supplied more nonexchangeable K (K_nex) to ryegrass plants contained more mica in the clay fraction than soils that supplied less K_nex. The results confirmed that use of a soil test that includes a measure of K_nex (i.e. acid-extractable K) may be a vital part of identifying variations in plant available K status of the soils. It is concluded that the K supplying power of the Pallic and related soils is related directly to the amounts of mica present in clay fraction and that good K supplying soils will be transformed to K depleted soils as a result of increased weathering and leaching (pedogenic factors) and K exploitation in intensive farming systems.     

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.     

Aluminium release in relation to the determination of cation exchange capacity of some podzolized New Zealand soils

In upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba²⁺ as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined with m NH₄OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg²⁺ and Ba²⁺ chlorides than K⁺ and NH₄⁺ chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH₄⁺ and K⁺, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al-chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K⁺ and NH₄⁺, than with Mg²⁺ and Ba²⁺, chlorides. The implication of the results for CEC measurements is discussed.     

Ionic strength of soil solution and its effect on charge properties of some New Zealand soils

Selected horizons from six New Zealand soils under permanent natural vegetation, four of which form a development sequence, were chosen to provide variations in organic matter, phyllosilicate clay mineral and short-range ordered aluminosilicate (allophane) contents. The ionic strength of the soil solution (μ) extracted from the soils of the development sequence was low, being always less than 0.005. For all horizons of the six soils, the negative charge changes linearly with μ^1/2 within the ionic strength range of 0.001 to 1. The change was negligible for the least weathered and leached soil, indicating that it contained mainly permanently charged colloids. As soil development increased and/or the components carrying variable charge increased in amount, the change in charge with ionic strength increased. A regression equation showed a strong relationship between change in negative charge with ionic strength and organic carbon and oxalate-extractable A1 (R²=0.976). This equation was tested by predicting observed changes in charge with ionic strength for a second selection of soils. The change in positive charge with ionic strength was correlated with oxalate-extractable A1 (r²=0.914). The results are discussed in relation to measurement of soil charge and iron movement in soils.     

Effects of drying on the ion exchange capacity and cation adsorption properties of some New Zealand soils

Abstract

The effect of drying on the cation (CEC) and anion (AEC) exchange capacity, and on potassium (K) and magnesium (Mg) adsorption by three New Zealand soils was investigated. Air‐drying resulted in no significant changes in these properties compared with the field‐moist samples. Oven‐drying at 105°C significantly decreased the CEC and increased the AEC of most soils compared with air‐dried samples. The decrease in CEC was related to increased solubility of organic matter and a decrease in surface area on which charge could be developed. The increase in AEC was attributed to a decrease in soil pH.

Potassium and Mg adsorption by two soils decreased following oven‐drying. This was consistent with the effect of drying on CEC. For the remaining soil, K adsorption increased following oven‐drying. This was attributed to K fixation.     

The zinc status of some Nova Scotia soils and crops

Abstract

Ranges for total, 0.1N HCl and EDTA‐(NH₄)₂CO₃ extractable Zn in 69 samples of surface soil (0–15 cm), representing nine soil series, were 14–108, 0.9–10.5 and 0.5–8.0 ppm respectively. Total Zn in barley (Hordeum vulgare), carrot (Daucus carata sativa), corn (Zea mays L), grape (Vitis spp.), onion (Allium cepa), pea (Pisum sativum, strawberry (Fragaria spp.), and wheat (Triticum spp.) leaves and in barley and wheat grain ranged from 13.5 to 80.6 ppm.

The results suggest that, with the possible exception of corn leaf samples from one location, Zn levels in plant tissue were adequate. However, the results also indicate that liming strongly acid sandy soils reduces Zn availability and may induce a deficiency in Zn sensitive crops.     

Evaluation of availability and quantity-intensity relationship of zinc in some tropical soils

Zinc was extracted from seven soils collected from Haryana state (India), representing the tropical region of the country, to predict the availability of Zn to crops. Weakly adsorbed Zn extracted by 0.05 M CaCl₂ was almost negligible. Similarly 1 M MgCl₂, designated to extract the lattice Zn, extracted small quantities of Zn indicating that no Zn was substituted for any other cation in clay lattice. Maximum zinc was extracted by chelating agents like DTPA and EDTA and were correlated significantly among themselves. None of the methods tested was significantly correlated to plant Zn indicating that in addition to crop requirement, other soil factors play a major role in determining the Zn availability. Equilibrium Zn values in all except a sandy soil, were less than 1 μg Zn/ml indicating the possibility of moderate to severe Zn deficiency in these soils.     

Fractionation and distribution of selenium in soils

Abstract

A modified selenium (Se) fractionation procedure was used to study Se distribution in three soils (two silt loams and one silty clay). This sequential procedure consisted of: i) 0.2 M potassium sulfate (K₂SO₄)‐soluble fraction, ii) 0.1 M potassium dihydrogen phosphate (KH₂PO₄)‐exchangeable fraction, iii) 0.5 M ammonium hydroxide (NH₃H₂O)‐soluble fraction, iv) 6 M hydrochloric acid (HCl)‐extractable fraction, and v) residual fraction digested with perchloric (HClO₄) and sulfuric (H₂SO₄) acids. The fractionation procedure had high recovery rates (92.5 to 106%). The Se distribution in soil was controlled by soil properties, such as pH, oxide, clay, and calcium carbonate (CaCO₃) contents. In the untreated soil samples, residual Se fraction was dominant. In the Se‐enriched soils, the silty clay had significantly more Se in the NH₃H₂O and residual fractions while in the two silt loams the largest were KH₂PO₄ and residual fractions. The Se availability in the two silt loams was higher than in the silty clay. The Se availability pattern in the untreated soils was: unavailable (HCl + residual fractions) >> potentially available (KH₂PO₄ + NH₃H₂O fractions) > available (K₂SO₄ fraction), while in the Se‐enriched soils it was potentially available > unavailable > available.     

Copper and zinc sorption on some B horizons of Quebec soils

Abstract

The sorption of Cu and Zn on soils, as a function of pH, is important to an understanding of their mobility in the soil solution and their availability for plant nutrition. Copper and Zn sorption as a function of the pH were measured for six B horizons of two Orthic Humic Gleysols, two Orthic Humo‐Ferric Podzols, one Orthic Dystric Brunisol and one Orthic Sombric Brunisol. The results show that: 1) for the same amount of metal in solution and the same pH, more Cu is sorbed than Zn and 2) there is a maximum of sorption at or just above pH 5.00 and a large decrease as pH decreases.

During the pH‐dependent sorption of Cu and Zn on six B horizons of Quebec soils, it was found that ions were released into solution thus altering the charge generated by the soil at low pH and the sorption behavior of Cu and Zn. The solid phase most likely to control the level of ions in solution is believed to be the amorphous and oxide forms of Al and Fe. The dissolution of these metal oxide or hydrous oxide materials also releases cations adsorbed on, or occluded in, the amorphous material.