Behavior of iron‐inefficient plants when grown in combinations of calcareous and noncalcareous soils

Abstract

When Fe‐inefficient plants were grown in mixtures of calcareous Hacienda loam soil and noncalcareous Yolo loam soil compared with plants grown in unmixed soils, characteristics and composition of the plants including Fe deficiency were generally intermediate to those with either soil alone. Noncalcareous soil adjacent to calcareous soil allowed PI 54619–5–1 soybeans (Glycine max L.) to obtain sufficient Fe.     

Manganese‐iron relationship in soybean grown in calcareous soils 1

Although a positive response to iron (Fe) is, usually, expected in calcareous soils; this has not been always the case; and in some instances a depressing effect has been observed. An induced micronutrient imbalance is suspected. This experiment was designed to study the effect of Fe fertilizer on the plant micronutrients. Twenty three highly calcareous soils (18–46% calcium carbonate equivalent; pH 7.7–8.4; and a wide range of extractable Fe) from southern Iran were used in an eight‐week greenhouse experiment to study the effect of Fe fertilizers on soybean [Glycine max (L.) Merr.] growth and chemical composition. The statistical design was a 23 × 3 factorial arranged in a completely randomized block with three replications. Treatments consisted of 23 soils and three levels of applied Fe (0, 10, and 20 mg Fe/kg as FeEDDHA). Uniform doses of nitrogen (N), phosphorus (P), copper (Cu), manganese (Mn), and zinc (Zn) were applied to all pots. Dry matter (DM) and micronutrients concentrations and uptakes of plant tops were determined and used as the plant responses. Application of Fe either had no significant effect on DM or even decreased it. The plant concentration and uptake of Fe increased significantly in all soils. The concentrations and uptakes of Cu and Zn did not change but those of Mn decreased significantly. The negative effect of Fe application was, therefore, attributed to the interference of Fe with Mn nutrition. The mechanism involved appears to be the restriction in Mn translocation from soil to root and/or from root to the plant tops.     

Influence of air drying and soil gas‐phase carbon dioxide on DTPA‐extractable iron in calcareous soils

Abstract

The extraction of a field‐moist soil with DTPA will result in a level of extractable iron (Fe) lower than that of the air‐dried soil. Soil gas‐phase carbon dioxide (CO₂) levels may be considerably higher than ambient atmospheric levels, especially in wet soils in the field. This study was undertaken to determine whether gas‐phase CO₂ level influences the quantity of Fe extracted by DTPA. Three moist calcareous soils were incubated for 21 days, each at three different partial pressures of CO₂, after which the moist soils were extracted with DTPA. A sample of each soil was also air dried, and was subsequently extracted with DTPA. In each case, DTPA‐extractable Fe from the moist sample was lower than that from the air‐dried sample; however, DTPA‐extractable Fe increased with increasing CO₂ partial pressure of in the moist soils. DTPA‐extractable Fe concentration for a given soil following air drying was not significantly influenced by the CO₂ partial pressure during incubation of the originally field‐moist soil. DTPA‐extract pH of the moist soils followed the same trend as soil‐solution pH (i.e., as CO₂ concentration of the soil gas‐phase increased, soil solution pH and DTPA extract pH both decreased); however, the slope of the pH versus log P_CO2 curve was less pronounced in the DTPA extract due to the buffering capacity of the triethanolamine. From this study, it is concluded that elevated soil gas‐phase CO₂ partial pressure does not contribute to the lower level of DTPA‐extractable Fe observed when the extraction is performed on a field‐moist versus an air‐dried soil; increased CO₂ partial pressure actually resulted in a slight increase in concentration of DTPA‐extractable Fe obtained from a field‐moist soil.     

Calcium‐ and iron‐related phosphorus in calcareous and calcareous marsh soils: Sequential chemical fractionation and 31p nuclear magnetic resonance study

Abstract

Phosphorus (P) forms in soils determine the amount of P available for crops and the potential for this element to be released to water. Sequential chemical fractionation can provide some information about major P forms in soils, and allow one to distinguish iron (Fe)‐related phosphorus from calcium (Ca)‐bound P. The ³¹P nuclear magnetic resonance (NMR) spectroscopy has been used in the identification of organic P, precipitated Ca‐phosphates, and aluminum (Al)‐related P in acid soils. Three calcareous soils and four calcareous marsh soils were used in this study. These two types of soils differ in the nature of iron oxides, which are the main P sorbent surfaces. The ratio of low crystalline to high crystalline iron oxides is higher in marsh soils than in calcareous soils as a consequence of the special genesis and conditions of the soil (reduction‐oxidation cycles). Such a ratio is related to the proportion of occluded P in low crystalline oxides relative to that of high crystalline oxides. Citrate‐bicarbonate extractable P (CB‐P) in the fractionation schemes can be ascribed to adsorbed P and high soluble calcium phosphates. CB‐P is correlated with the sum of P fractions in all the soils, thus indicating that the amount of the P that can be easily released is related to the rate of P enrichment of the soil. The ³¹P NMR spectral data reveal that hydroxyapatite is the dominant P form in the soils studied. This is consistent with the fractionation data, where acid‐extractable P is the main P fraction. The spectra also provide some information about the amount of total inorganic P and Ca‐phosphates in calcareous soils.     

Extractability of previously‐applied zinc as influenced by properties of calcareous soils

Abstract

The recovery of applied zinc (Zn) by plants is relatively small. Coupled with lack of leaching, this leads to accumulation of Zn in topsoil which may result in unfavorable growth conditions for the subsequent plants. Different extractants may be used for assessing the Zn status of soils previously treated with Zn sources. The extractability of retained Zn is influenced by soil properties. This experiment was conducted to study the influence of selected properties of calcareous soils on extractability of Zn by three popular Zn soil tests. Twenty samples from surface horizons (0–20 cm) of highly calcareous soils of southern Iran (pH 7.9 to 8.5; calcium carbonate equivalent 16 to 58%) previously treated with three levels of Zn (0, 10, and 20 mg Zn kg^‐1 soil as ZnSO₄#lb7H₂O) in triplicate and under one crop of corn (Zea mays L.) were extracted with DTPA, EDTA‐(NH₄)₂CO₃ and Na₂‐EDTA. Extractability (EXT) in a particular extractant was defined as the slope of the regression line, relating extractable Zn of each soil to the rate of applied Zn, multiplied by 100. The EXT values of soils ranged from 24.9 to 73.0% for DTPA, 47.2 to 84.4% for EDTA‐(NH₄)₂CO₃, and 28.2 to 56.7% for Na₂‐EDTA. Stepwise regression equations showed that cation exchange capacity (CEC) and calcium carbonate equivalent (CCE) followed by clay content were the most influential soil properties in EXT of retained Zn of highly calcareous soils. The EXT values decreased with increase in CEC, and CCE but increased with increase in clay.     

Use of basic salts of iron and zinc as plant amend‐ments in soils

Abstract

In a greenhouse experiment, the effects of adding zinc (Zn) and iron (Fe) as either their basic salts or as commercial chelates were compared for the production of lettuce. The basic salts were found to be as effective as the chelates in providing Zn and Fe as well as being more environmentally safe.     

Soil test modifiers for coarse‐textured calcareous soils

Abstract

Calcareous soils vary considerably in their characteristics which need to be considered in soil test interpretation. Yield data from 22 corn and 13 wheat field experiments were used to relate yield response, expressed in relative terms (Y%), to phosphorus (P), potassium (K), and zinc (Zn) soil test results based on NaHCO₃, NH₄OAc, and DTPA extraction procedures, respectively. The experiments were conducted for three years on newly reclaimed desert soils in Egypt. Relative infuence of different soil components was evaluated as modifiers of the critical levels (CL) based on 95% of maximum yield. The CL values obtained for corn were close to those for wheat. Therefore, results presented here were based on the combined data of the 35 corn plus wheat experiments. With Olsen P, a backward elimination regression procedure indicated that the variance in Y% that was accounted for increased in significance from 21 to 52% by including the CaCO₃ content of the soil. The CL increased from 9 to 17 mg P/kg as CaCO₃ increased from 1 to 30%. Coarser textured soils had lower CLs for K than finer textured ones. The critical exchangeable K levels were 200 and 500 mg K/kg for soils having more than 85% and 85 to 45% sand, respectively. With an increase in organic matter content, the response to applied Zn was observed at higher levels of extracted Zn. The DTPA‐critical levels for Zn were found to be 0.5 and 0.8 mg Zn/kg for soils containing less than 1% and 1.7% organic matter, respectively.     

Fertilizer phosphorus placement studies on calcareous and non‐calcareous chernozemic soils: Growth,p‐uptake and yield of flax

Abstract

We examined soil potassium (K) supply capacity as related to wheat response to K fertilization, using a cation exchange membrane (CEM) burial technique to measure potential K supply rate. A growth chamber experiment was conducted to determine soil and plant response relationships. Canadian Prairie Spring wheat (Triticum aestivum ’Biggar') was grown on three soils of different initial K fertility with three rates of added K. Wheat response to K fertilization was well related to the amount of exchangeable K and K supply rate in the soil. Soils with high initial K supply rate demonstrated an adequate K release rate which was associated with low response to added K fertilizer. A soil K supply rate less than 5 μg cm² hr^‐1 represented soil K supply power that is less than optimal for wheat nutrition.     

Determination of total cadmium in calcareous soils by extraction using aliquat‐336 and 3‐heptan‐one after aqua regia digestion

Abstract

Measurement of total soil cadmium (Cd) is difficult due to calcium (Ca) and other chemicals which cause high background absorbance when trace levels of Cd are to be determined. When soil Cd is low, even use of deuterium background correction with flame atomic absorption spectroscopy (AAS) cannot provide accurate Cd results. Use of furnace atomic absorption with method of standard additions can circumvent these interferences, but the cost and time required are substantial. We desired a more rapid, convenient, and reliable alternative to extraction using dithizone and back‐extraction into acid, or to ammonium pyrollidinedithiocarbamate (APDC) which does not require close pH adjustment nor have many sources of potantial contamination. We evaluated analysis of these complex soil extracts with the method of Viets (1978) which extracts metals from 1N acid solutions using Aliquat‐336 in methylisobutyl‐ketone (MIBK). We tested the use of the less toxic and less water soluble 3‐heptanone as an organic solvent alternative to MIBK which can be directly analyzed by flame atomic absorption. A series of extraction experiments were conducted to determine if Cd was extracted from standard solutions and from total metal digests of calcareous soils into an Aliquat‐336/3‐heptanone solution, and under what conditions extraction was optimum. In the optimum method, Cd was extracted from aqua regia soil digests by 10% Aliquat‐336 in 3‐heptanone without addition of ascorbic acid or potassium iodide (KI) used by Viets. Excellent recovery of Cd was obtained for both standard reference soils and low Cd highly calcareous soils from North Dakota and Minnesota. Addition of ascorbic acid and KI did not increase the efficiency of extraction indicating that the extraction system used was free of ferric‐iron [Fe(III)] interference. The ion‐association complex of Cd remained stable for at least 24 hr after extraction, providing a very convenient method to analyze low levels of total Cd in soils and other geologic materials.     

Distribution pattern of root‐supplied 59iron in iron‐sufficient and iron‐deficient bean plants

In order to study the iron (Fe) distribution pattern in bean plants with different Fe nutritional status, french bean (Phaseolus vulgaris L.) seedlings were precultured in a complete nutrient solution with 8x10^‐5 M FeEDTA for five days. Thereafter, plants were further supplied with 8x10^‐5 M FeEDTA (Fe‐sufficient) or with only 2x10^‐6 M FeEDTA (Fe‐deficient) for another eight days. At this stage, the Fe‐deficient plants had much lower chlorophyll contents and lower dry weight of the leaves but higher reducing capacity of the roots compared with the Fe‐sufficient plants. For studies on short‐term distribution of Fe, the Fe‐sufficient plants were supplied 8x10^‐5 M ⁵⁹FeEDTA (specific activity 9.9 GBq/mol) and the Fe‐deficient plants 1x10⁶ M ⁵⁹FeEDTA (specific activity 98.8 GBq/mol). The plants were harvested after 4 and 24 hours. Despite a much lower supply of ⁵⁹FeEDTA/(factor 80), the Fe‐deficient plants took up significantly more ⁵⁹Fe but translocated less to the shoots (14.6% after 24 h) compared with the Fe‐sufficient plants (29.4% after 24 h). However, regardless of the Fe nutritional status of the plants, the majority of ⁵⁹Fe was translocated in the primary leaves. Our results demonstrate a similar distribution patterns of root‐derived ⁵⁹Fe in the shoots of Fe‐sufficient and Fe‐deficient plants, and thus, no preferential direct translocation of Fe to the shoot apex in the Fe‐deficient plants.     

Yield of iron‐sprayed and non‐sprayed strawberry cultivars grown on high ph calcareous soil

Abstract

Iron (Fe) deficiency chlorosis (FeDC) results in extensive reduction in yield of strawberry (Fragaria x ananassa Duch.) grown on high pH calcareous soils. Three cultivars differing in response to FeDC were grown on a high pH (8.2) calcareous soil (25.4% calcium carbonate equivalent in surface 20 cm) in the field (Choueifat, coastal area of Lebanon) to determine the effects of FeDC on fruit yield of cultivars sprayed with FeEDDHA [ferric ethylene‐diiminobis (2‐hydroxyphenyl) acetate]. The unsprayed plots were used as a control. No significant interaction (P<0.05) between cultivars x FeEDDHA spray treatment, and no significant differences (P<0.05) between one and two FeEDDHA spray(s)/week treatment was noted for visual FeDC, fruit number, and fruit yield. Sprayed cultivars once a week produced higher yields than unsprayed ones; overall increases were 33% (13% for ‘Motto’, 30% for ‘Chandler’, and 56% for ‘Douglas'). Even though only slight FeDC was noted on the ‘Motto’ cultivar receiving no Fe EDDHA spray, fruit yields were increased when sprayed with FeEDDHA. However, significant increases in yield for ‘Chandler’ and ‘Douglas’ cultivars with severe FeDC ratings were rioted when sprayed with FeEDDHA.     

Effect of seed zinc content on grain yield and zinc concentration of wheat grown in zinc‐deficient calcareous soils

Field experiments were carried out to study the effect of different seed‐zinc (Zn) content on grain yield and grain Zn concentration in a bread wheat cultivar Atay 85 grown in a severely Zn‐deficient soil under rainfed and irrigated conditions for two years. Three groups of seeds with Zn contents of 355, 800, and 1,465 ng Zn seed^‐1 were obtained through different number of foliar applications of ZnSO₄.7H₂O in the previous crop year. Experiments were carried out with 23 kg Zn ha^‐1 (as ZnSO₄.7H₂O) and without Zn fertilization to the soil. Grain yield from seeds with 800 and 1,465 ng Zn seed^‐1 content was significantly higher than that from low seed‐Zn, especially under rainfed conditions. In the first year, under rainfed and Zn‐deficient conditions, yield of plants grown from the highest seed‐Zn content was 116% higher than the yield of plants grown from the low seed‐Zn content. However, in the first year soil‐Zn application combined with low‐Zn seed resulted in a yield increase of 466% compared to nill Zn treatment with low‐Zn seed, indicating that higher seed‐Zn contents could not compensate for the effects of soil Zn application. Soil Zn application significantly increased Zn concentrations in shoot and grain. However, the effect of different seed Zn contents on Zn concentrations of plants was not significant, probably due to the dilution of Zn in tissues resulting from enhanced dry matter production. The results presented show that wheat plants grown from seed with high Zn content can achieve higher grain yields than those grown from the low‐Zn seed when Zn was not applied to the soil. Therefore, sowing seeds with higher Zn contents can be considered a practical solution to alleviate Zn deficiency problem, especially under rainfed conditions in spite of it being insufficient to completely overcome the problem.     

Fertilizer placement studies on calcareous and non‐calcareous chernozemic soils: Growth,P‐UP‐take,oil content and yield of Canadian rape

Abstract

Field experiments were conducted on calcareous and non‐calcareous Orthic Black Chemozemic soils over a five year period to study the effect of rates and placements of P‐fertilizer on Canadian rape (Brassica napus L. cv Tower) production. Six rates of P as mono‐ammonium phosphate (MAP) were applied at seeding using four placement methods: i) broadcast and cultivated 10 cm into the soil (BC); ii) banded in the seed row with the seed (PWS); iii) banded 2.5 below and 2.5 cm to the side of the seed (PSS); iv) banded 2.5 cm directly below the seed (PBS). Soil type had no significant effect on rape growth, seed yield and P‐uptake. Rape responded best to P‐fertilizer banded with (PWS) or near (PSS, PBS) the seed. But, placing 15 kg/ha P or greater with the seed reduced seedling emergence; with 25 kg P/ha insufficient plants emerged to justify harvesting. The reduced seedling emergence resulted in reduced seed yield and P‐uptake. Maximum yields were obtained when the fertilizer was banded 2.5 cm away from the seed (PSS, PBS). The BC method produced the least growth, yield and P‐uptake responses of the four methods. Only when broadcast rates of P were in excess of 10 kg/ha did rape dry matter, seed and P‐uptake increase. Banding 10 kg/ha with or near to the seed was equivalent to broadcasting 25 kg/ha in terms of seed yield and P‐uptake. Application of P fertilizer also increased seed protein and oil concentrations.     

Colorimetric determination of phosphorus in citrate‐bicarbonate‐dithionite extracts of soils

Abstract

Existing colorimetric methods for determining phosphorus (P) in citrate‐bicarbonate‐dithionite (CBD) extracts from soils and sediments require pretreatments of extracts prior to the determination of the element. A method is proposed for the determination of P in CBD extracts without any chemical treatments. Maintaining the citrate concentration below 2.4 mM, maximum and stable absorbance develops in P‐Mo‐Sb system within one hour and remains stable for 20 hours. An evaluation of potential interference was made by adding varying amounts of P to CBD extracts over a range of extractable iron (Fe) and aluminum (Al) levels. Near 100 percent recovery of the added P suggests the applicability of the method to soils and sediments. Major advantages of the method are speed, simplicity, reliability and stability of the colored complex.     

A method for estimating organic‐bound iron and aluminum contents in soils

Abstract

Estimation of organic‐bound iron (Fe) and aluminum (Al) is an important diagnostic technique in pedology. The commonly used sodium pyro‐phosphate method yields somewhat ambiguous results and is inconvenient if an ultracentrifuge is not available in the laboratory. This study showed that 0.1M sodium nitrilotriacetate (NTA) could be used instead of pyrophosphate. The Fe and Al extracted by 0.1 M NTA were highly correlated to that by sodium pyrophosphate with R² = 0.993 for Fe and R² = 0.992 for Al, while the dissolution effects on standard mineral samples in NTA was kept at a minimum. NTA has the advantage of not requiring ultrafiltration, ultracentrifugation, or the addition of a flocculating agent as is the case for the pyrophosphate method.     

Agrophysical assessment of alluvial calcareous soils of the Çumra region of Central Anatolia in Turkey

Some physical (density, coefficient of filtration, particle-size composition, etc.) and chemical (contents of carbonates, organic carbon, nitrogen, etc.) properties of an alluvial calcareous soil were studied in Central Anatolia (Konya province, Çumra region). These heavy-textured (medium clay) soils with a low content of organic carbon (less than 1%) have favorable agrophysical properties due to the stable structure of the pore space. The studies of the water regime of soils under drop irrigation confirm the favorable hydrological properties of these soils. The use of the known agrophysical estimates (after Medvedev, the index of the optimal water regime, etc.) has revealed the high dispersal of the data related to the low humus content in these heavy-textured soils. The favorable structure of the pore space is suggested to be stipulated by the active activity of the numerous and diverse representatives of soil biota. Four phyla predominate in the microbio-logical composition of the soils studied; among them, Actinobacteria is the dominant. The composition of this phylum is dominated by the elevated number of both higher (Streptomyces) and lower (three species of Rhodococcus) actinobacteria. The high biodiversity of bacteria against the background of their great total number and the developed trophic interactions in the microbial community promote the well-balanced production of specific metabolites, including gaseous ones (CO₂, H₂). This circumstance allows this clayey soil to function rather actively while protecting the pore space against compaction and maintaining the optimal density, porosity, and hydrological properties.     

Effects of zinc fertilization and irrigation on grain yield and zinc concentration of various cereals grown in zinc‐deficient calcareous soils

Effects of varied irrigation and zinc (Zn) fertilization (0, 7, 14, 21 kg Zn ha^‐1 as ZnSO₄7.H₂O) on grain yield and concentration and content of Zn were studied in two bread wheat (Triticum aestivum), two durum wheat (Triticum durum), two barley (Hordeum vulgare), two triticale (xTriticosecale Wittmark), one rye (Secale cereale), and one oat (Avena sativa) cultivars grown in a Zn‐deficient soil (DTPA‐extractable Zn: 0.09 mg kg^‐1) under rainfed and irrigated field conditions. Only minor or no yield reduction occurred in rye as a result of Zn deficiency. The highest reduction in plant growth and grain yield due to Zn deficiency was observed in durum wheats, followed by oat, barley, bread wheat and triticale. These decreases in yield due to Zn deficiency became more pronounced under rainfed conditions. Although highly significant differences in grain yield were found between treatments with and without Zn, no significant difference was obtained between the Zn doses applied (7–21 kg ha^‐1), indicating that 7 kg Zn ha^‐1 would be sufficient to overcome Zn deficiency. Increasing doses of Zn application resulted in significant increases in concentration and content of Zn in shoot and grain. The sensitivity of various cereals to Zn deficiency was different and closely related to Zn content in the shoot but not to Zn amount per unit dry weight. Irrigation was effective in increasing both shoot Zn content and Zn efficiency of cultivars. The results demonstrate the existence of a large genotypic variation in Zn efficiency among and within cereals and suggest that plants become more sensitive to Zn deficiency under rainfed than irrigated conditions.     

Effect of temperature on EDTA‐extractable copper in soils

Abstract

Two contrasting soils were extracted with 0.05 M EDTA in 1 M CH₃ COONH₄ at pH 6, before and after incubation for 4 weeks at constant (10, 20 or 30°C) or fluctuating (10/30, mean 20°C) temperatures. Less copper was extracted from soils which were incubated at fluctuating temperature than from those maintained at a constant 20 C. Where incubation temperature was constant, extractable copper increased or decreased with increasing temperature depending on the soil and how it was treated. Recovery of added copper was low initially but increased during the incubation. Maximum recovery was associated with low incubation temperature in one soil, but high temperature in the other. The amounts of copper extracted were slightly increased by γ‐irradiation of the soils. Extractable copper was also increased by increasing the temperature at which the extraction was performed.     

Sulfur status of volcanic ash‐derived soils in Hawaii

Abstract

Several rainwater samples and 14 profiles of Hawaii's volcanic ash‐derived soils were analyzed for sulfur (S). Atmospheric deposition was an important S source at the coast (24 kg S/ha), but its contribution decreased with increasing distance from the sea (1 kg S/ha at 24‐km inland). The S concentration of rainwaters also decreased linearly with increasing rainfall.

Several thousand mg SO₄‐S/kg can be extracted from many volcanic ash‐derived soils of Hawaii, and it was often required at least four extractions [0.04 M Ca(H₂PO₄)₂, 1:10 soil to solution ratio] to completely desorb this SO₄. There was a close association of high SO₄ retention with high rainfall. This might have resulted from (1) the development of a solid phase with high SO₄ retention under intense weathering conditions, (2) more total SO₄ received by the soils from atmospheric deposition, and (3) past fertilization of sugarcane grown in high rainfall areas.

Low concentrations of soil solution SO₄‐S in relation to large amounts of P‐extractable SO₄ suggest that a S bearing mineral, such as basaluminite, may be controlling soil‐solution SO₄. Furthermore, SO₄ adsorption isotherms of these volcanic soils generally show a bi‐phasic property, and suggest that 40 to 80 mg SO₄‐S/kg is required to maintain 3 ‐ 6 mg SO₄‐S/L in the soil solution, a concentration range considered adequate for the growth of most crops.     

Phosphorus‐sorption characteristics of intensely weathered soils in south‐central kentucky

Abstract

Studies were conducted to investigate phosphorus (P)‐sorption characteristics of some intensely weathered soils in south‐central Kentucky. Phosphorus adsorption characteristics reflected the chemical and mineralogical properties of the soils studied. All adsorption data were adequately described by first order kinetic reactions which implied that the soils have uniform surfaces for P sorption. In spite of the limitations of the Langmuir equation, its usefulness in summarizing data into one adsorption maximum value was demonstrated by nearly identical adsorption maxima estimated by three linear transformations of the equation and small deviations from the observed maxima. Variations in adsorption maxima between surface and subsoils and among soils were best correlated with extractable aluminum (Al) (r = 0.93, p<0.01) and crystalline iron (Fe) oxy‐hydroxides (r = 0.97, p<0.01). Clay content was also highly correlated with P sorption (r = 0.97, p <0.01) as well as with extractable Al (r = 0.83, p<0.05) and crystalline Fe oxides (r = 0.92, p<0.01) suggesting that its contribution may have been through its association with these soil components. In contrast, organic matter had a negative association with P sorption (r = ‐0.83, p<0.05). The results indicate higher P sorption in subsoil than in surface horizons, controlled mainly by extractable Al and crystalline Fe oxyhydroxides.