Soil‐Test Methods for Florida Sands Treated with an Aluminum–Water Treatment Residual and Various Phosphorus Sources

Use of aluminum (Al)–rich water treatment residuals (Al‐WTR) has been suggested as a practice to immobilize excessive phosphorus (P) in Florida soils that could represent an environmental hazard. Fertilizer P requirements can differ in WTR‐amended and unamended soil, so careful selection of soil‐testing methodology is necessary. Acidic extractants can dissolve WTR sorbed P and overestimate plant‐available P. We evaluated the suitability of the Mehlich 1 P (M‐1P) and other agronomic soil‐test procedures in an Al‐WTR‐treated Florida soil. Bahiagrass (paspalum notatum Fluggae), ryegrass (Lolium perenne L.), and a second bahiagrass crop were grown in succession in a Florida topsoil amended with four sources of P at 44 kg P ha^?1 (P‐based rates) and 179 kg PAN ha^?1 [nitrogen (N)–based rates] and three WTR rates (0, 10, and 25 g kg^?1 oven‐dry basis). Both water‐extractable P (WEP) and iron (Fe) strip P (ISP), but not M‐1P, values of soil sampled at planting of each grass were greater in the absence than in the presence of WTR. Total plant P uptake correlated with WEP (r² = 0.82^***) and ISP (r² = 0.75^***), but not M‐1P (r² = 0.34^***). Correlations of the dry‐matter yield, P concentration, and P uptake of the first bahiagrass were also better with WEP and ISP than with M‐1P values. However, regression of plant responses with M‐1P improved after the first crop of bahiagrass. Both WEP and ISP values were better predictors of available soil P than M‐1P in a field study with same four P sources surface applied to established bahiagrass at the same two P rates, with and without WTR. Both WEP and ISP are recommended as predictors of P adequacy in soils treated with WTR, especially for soils recently (< 5 months) treated with Al‐WTR.     

Phosphorus Extraction Methods for Water Treatment Residual–Amended Soils

Abstract

Water treatment residuals (WTR) can adsorb tremendous amounts of phosphorus (P). A soil that had biosolids applied eight times over 16 years at a rate of 6.7 Mg ha^?1 y^?1 contained 28 mg kg^?1 ammonium–bicarbonate diethylenetriaminepentaacetic acid (AB‐DTPA), 57 mg kg^?1 Olsen, 95 mg kg^?1 Bray‐1, and 53 mg kg^?1 Mehlich‐III extractable P. To 10 g of soil, WTRs were added at rates of 0, 0.1, 1, 2, 4, 6, 8, and 10 g, then 20 mL of distilled deionized H₂0 (DI) were added and the mixtures were shaken for 1 week, filtered, and analyzed for soluble (ortho‐P) and total soluble P. The soil–WTR mixtures were dried and P extracted using DI, AB‐DTPA, Olsen, Bray‐1, and Mehlich‐III. Results indicated that all methods except AB‐DTPA showed reduced extractable‐P concentrations with increasing WTR. The AB‐DTPA extractable P increased with increasing WTR rate. The water‐extractable method predicted P reduction best, followed by Bray‐1 and Mehlich‐III, and finally Olsen.     

Mehlich 3 or modified olsen for soil testing in Malawi

Abstract

Soil nutrient extraction methods, which are currently being used in Malawi, are time consuming and require too many resources. The use of a universal soil extractant would greatly reduce resource requirements. The objectives of the study were to (i) compare the universal soil extractants, Mehlich 3 (M3) and Modified Olsen (MO) with ammonium acetate (AA), Bray P1 (BPl), and diethylene triamine penta acetic acid (DTPA) in the amount of nutrients extracted, (ii) determine the relationship among the extractants for the nutrients they extract, and (iii) determine the critical soil‐test levels of phosphorus (P), potassium (K), and zinc (Zn) for a maize crop. Missing nutrient trials involving P, K, and Zn were conducted on thirty sites across Malawi using maize (Zea mays L.). Phosphorus application rates ranged from 40 to 207 kg P₂O₅ ha^‐1. Potassium and Zn were applied at 75 kg K₂O and 10 kg Zn ha^‐1, respectively. Procedures of Cate and Nelson were used to identify soil nutrient critical levels. Results showed that the correlations between M3 and BP1, and MO and BPl were highly significant (r=0.93, 0.94, respectively). Mehlich 3 extractable K and AA extractable K (r=0.90), MO and AA extractable K (r=0.94) were highly significant (P<0.01) and the correlations between M3 and AA and MO and AA extractable calcium (Ca) (r=0.92, 0.90, and 0.94, respectively) were also highly significant (P<0.01). The correlations between M3, MO, and AA extractable magnesium (Mg) (r=0.99) were highly significant (P<0.01). Zinc, copper (Cu), and manganese (Mn) extracted with M3 and DTPA were significantly correlated (r=0.89, 0.87, and 0.95, respectively). Correlations between MO and DTPA extractable Zn, Cu, and Mn were also highly correlated (r=0.89,0.85, and 0.95, respectively). Maize grain yields ranged from 730 to 9,400 kg ha^‐1. Mehlich 3‐P and MO‐P critical levels were 31.5 and 28.0 μg g^‐1, respectively. Mehlich 3 and MO gave a similar critical level of 0.2 cmol kg^‐1 for K while Zn critical levels were 2.5, and 0.8 μg g^‐1 for M3 and MO, respectively. Mehlich 3 and MO were equally effective in separating responsive to none responsive soils for maize in Malawi.     

Crop production impacts on soil phosphorus removal and soil test levels

An 8-year field study documented the impact of tillage, crop rotations, and crop residue management on agronomic and soil parameters at Brookings, South Dakota. The greatest annual proportion of above-ground biomass phosphorus (P) removed was from the grain (78–87% of total) although crop residue removed some P as well. Greater above-ground total biomass P (grain P + crop residue P) was removed from corn than from soybean and spring wheat crops mainly due to the greater corn grain biomass harvested. Cumulative above-ground biomass P removal was greatest for the corn-soybean rotation (214 kg P ha^?1), while it was lowest for the soybean-wheat rotation (157 kg P ha^?1). Tillage treatments within crop rotation or residue management treatments did not influence annual or cumulative P removal rates. Olsen extractable soil orthophosphate-P levels declined consistently through time from a mean of 40 µg g^?1 (2004) to 26 µg g^?1 (2011). Biomass P removal was calculated to be 15.7 ha^?1 yr^?1 to decrease Olsen extractable soil orthophosphate-P levels by 1 µg g^?1 yr^?1 over 8 years of the study.     

Predicting Maize Yield,Nutrient Concentration,and Uptake in Phosphorus- and Potassium-Fertilized Soils: Pressurized Hot Water and Other Alternatives to Mehlich I Extraction in Guatemala Soils

Abstract

Poor accessibility and cost of soil testing reduce effectiveness of fertilizer use on small‐scale subsistence farms, and inadequate funding promotes adoption of soil tests in developing countries with minimal validation. For example, Mehlich I extraction of phosphorus (P) currently used extensively in Guatemala may not be suitable for Guatemala's broad range of soils. At least four alternatives are available but relatively untested [Bray 1, Mehlich III, Olsen, and pressurized hot water (PHW)]. Pressurized hot water is relatively simple and inexpensive but is not yet tested against other extraction methods under variable P or potassium (K) fertilization levels. To determine whether PHW‐extracted nutrients could be used to predict maize yield and nutrient concentration and uptake, soil, plant tissue and grain samples were obtained from a multiple‐site field study, and calibration studies were conducted using five rates of P and three rates of K on soils incubated without plants or cropped with maize in greenhouse and field conditions. In the multiple‐site field study, maize yield related significantly to PHW‐extractable P (r²=0.36) and to leaf P concentration (r²=0.23), but Mehlich I–extractable P did not. In the two soils used in the greenhouse study, maize yield, vegetative P concentration, and total P uptake by maize were predicted by PHW‐extractable P (R²=0.72, 0.75, and 0.90, respectively). In the field experiment, grain yield was not improved by P or K application, but P concentration of maize leaf tissue did relate significantly with PHW‐extracted P (R²=0.40). Mehlich I did not. There were no yield responses to K application in any experiment, but relationships defined between extractable K for all five K‐extraction procedures and soil‐applied K were similarly significant. In comparison, PHW was as good as or better than Olsen whereas Bray 1 and Mehlich III were less consistent. Mehlich I was overall the poorest P extractant. Mehlich I extraction of P should be replaced by one of the four alternatives tested. PHW is the least expensive and, therefore, most viable for use in Guatemala soils.     

Plant-Available Phosphorus after Application of Synthetic Chelating Agents

Fertilizer phosphorus (P) can become immobilized in acidic soils through bonds with iron (Fe) and aluminum (Al). Two chelating agents, ethylenediamine tetraacetic acid disodium salt (EDTA) and hydroxyethyl ethylenediamine triacetic acid (HEEDTA), were tested in a greenhouse study for efficiency at increasing plant-available P to corn (Zea mays L.). Fertilizer P was added with or without chelate to the center of pots, simulating a starter band of P. Without the presence of chelates, biomass above and below ground increased linearly as P fertilizer rates increased at 0, 9.6, 19.3, 28.9, and 38.5 kg P ha^?1. Applications of EDTA and HEEDTA did not significantly increase water-soluble P (WSP), Mehlich 1 P, and Mehlich 3 P compared to soils without chelates. Applications of EDTA increased P uptake in the belowground biomass. Despite previous research showing that chelates increased WSP in soils, a decrease in P sorption was not observed with the additions of chelating agents to soils.     

Influence of Elemental Sulfur on Sugarcane Yield on Histosols with Near-Neutral pH

Soil subsidence of Florida Histosols caused by microbial oxidation following drainage of these soils has resulted in decreased depth. Soil pH has increased from tillage operations and vertical movement of carbonates from underlying limestone bedrock through evapotranspiration and seepage irrigation. This study was conducted to determine sugarcane (Saccharum spp.) yield response to banded elemental sulfur (S) (granular 90% S and granular 80% S with 5% manganese (Mn)) in soils with unamended pH ranging from 6.5 to 7.2. Four field experiments were established as small-plots on Histosols in the Everglades Agricultural Area (EAA). Each experiment was a randomized complete block design with six replications and elemental S rates of 0, 90, 224, and 448 kg S ha^?1. Less than optimum leaf Mn at two locations were associated with Mehlich 3-extractable Mn<5 g m^?3. There were no sugarcane yield responses to elemental S with unamended pH<7.2, although S significantly reduced in-row pH.

Abbreviations: EAA, Everglades Agricultural Area; ICP, inductively coupled argon plasma; KSM, kg sucrose Mg^?1 cane; MAP, monoammonium phosphate; M3-Mn, Mehlich 3-extractable Mn; RCB, randomized complete block; STM5, granular 80% S with 5% Mn; MCH, Mg cane ha^?1; MSH, Mg sucrose ha^?1     

Correlation of Mehlich 3, bray 1, and ammonium acetate extractable P,K, Ca,and Mg for Alaska agricultural soils

Abstract

Soil test recommendations currently used in Alaska are based on a limited amount of in‐state data along with consideration of data from other states. Recently, Mehlich 3 extractable P has been found to be highly correlated to yield on representative agricultural soils in Alaska. To fully use its multi‐element capability, a study was conducted to correlate Mehlich 3 extractable P and cations (K, Ca, and Mg) with the P and cations extracted by the Bray 1 and ammonium acetate methods respectively.

When Mehlich 3 extractable K and Mg were regressed with ammonium acetate extractable K and Mg respectively, the relationship was essentially one‐to‐one and the relationship held across all soils tested. Significant variation was observed among soils in the extraction of Mehlich 3‐P and Ca relative to Bray 1‐P and ammonium acetate‐Ca. Individual soil character appeared to affect the regressions for extractable P and Ca, even though the R² values were generally high. The regression slopes for Mehlich 3‐P versus Bray 1‐P ranged from 1.01 to 1.88 with Mehlich 3 extracting an average of 66% more P than Bray 1 in the volcanic ash soils, and 12% more in the loess soils. The regression slopes for Mehlich 3‐Ca versus ammonium acetate‐Ca ranged from 0.95 to 1.33, and the former extracted an average of 17% more Ca than the latter. It is suggested that the regression data of P and Ca can be extrapolated to other soils based on soil classification; to extend the soil test data over a geographic base.     

Comparison of Multi-element to Single‐Element Extractants for Macro‐ and Micronutrients in Acid Soils from Spain

Abstract

Different chemical reagents are used to assess plant‐available nutrients from soils with similar properties. The use of different extractants is a serious limitation when comparing results between different soil‐testing laboratories, often leading to large differences in fertilizer recommendations for similar crops.

In this study, 80 samples from acid soils from Galicia (Spain) were used to compare several soil nutrient extractants. Traditional and tested extractants for acid soil such as Bray 2 and ammonium acetate were used to evaluate multielement extractants such as ethylenediaminetetraacetic acid–ammonium acetate (EDTA‐aa), ammonium bicarbonate–diethylenetriaminepentaacetic acid (AB‐DTPA), and Mehlich 3.

Linear regression analyses were performed to relate the amount of each nutrient obtained by traditional soil extractants to the amount obtained by multielement extractants. Strong correlation was found between extractable Bray 2 P and Mehlich 3 P (r²=0.97, slope=0.87, and intercept=?0.48). The slope of the regression line between EDTA‐aa‐extractable calcium (Ca) and that from ammonium acetate (Aa) approached 1∶1 (r²=0.86). Similar results were obtained for magnesium (Mg) (r²=0.99). Soil zinc (Zn) concentrations extracted by Mehlich 3 and EDTA‐aa were similar; slope of the regression line was 0.95 (r²=0.88). With regard to copper (Cu), Mehlich 3 extracted approximately 20% more Cu than EDTA‐aa.

The results showed that Mehlich 3 and EDTA‐aa are suitable for assessment of plant available phosphorus (P), potassium (K), Ca, Mg, Cu, Zn, and iron (Fe) in acid soils.     

Evaluation of Mehlich 3 extractant for estimating phosphorus deficiency and phosphorus sorption of Zimbabwean soils

Abstract

The Mehlich 3 extractant was compared with the resin method for its ability to predict the phosphorus (P) status of Zimbabwean soils. Correlation of P extraction between the two methods and with plant growth was found to vary with soil texture. Because the Mehlich 3 extractant was less influenced by texture, it was better able to predict the P status over a wide range of soil types. The Mehlich 3 extractant correctly predicted P deficiency for all Zimbabwean soils, except for those that contained visible calcium carbonate. Mehlich 3‐extractable aluminum (Al) was very highly correlated with the maximum P‐sorption capacity of a wide range of soils, excluding those with calcium carbonate. Adoption of the Mehlich 3 extractant for multiple elemental analysis of soils in Zimbabwe is recommended, particularly if routine Al measurement is included as an indicator of soil P requirements.     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.     

Comparison of Soil P Test Procedures for St. Augustinegrass

St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze] is a home lawn grass widely used in the southern United States. At present, phosphorus (P) fertilization of St. Augustinegrass is based primarily on Mehlich 1 P test. One criticism of Mehlich 1 extractant is that it extracts some fraction of soil P pool that is not available to plants, whereas, iron (Fe) oxide P and water‐extractable P methods are reported to be better related to plant growth in some cases. Literature relative to the soil test procedure comparison for St. Augustinegrass was not found. The objective of this study was to evaluate Mehlich 1 P, Fe oxide P, and water‐extractable P to identify the most suitable soil test method for St. Augustinegrass growth. Established pots of ‘Floratam’ were subjected to P application of 0, 0.14, 0.27, 0.54, and 1.07 g m^?2 every 4 wk for 12 wk. Measurements included tissue growth rates, tissue P concentration, soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations. Phosphorus application increased soil test P concentrations. Soil Mehlich 1 P, Fe oxide P, and water‐extractable P concentrations were closely correlated to each other. Three soil test P levels and tissue P concentrations were highly correlated with Mehlich 1 P, which best predicted tissue P levels. Three soil test P levels were also closely correlated to the St. Augustinegrass top growth rate. Critical minimum Fe oxide P and water‐extractable P concentration was 3 mg kg^?1. Overall, Mehlich 1 P was the best soil P test for St. Augustinegrass among the three extractants tested.     

Exchangeable cations and CEC determinations of some highly weathered soils

Abstract

Eight methods to determine exchangeable cations and cation exchange capacity (CEC) were compared for some highly weathered benchmark soils of Alabama. The methods were: (1) 1N NH₄OAc at pH 7.0 by replacement (for CEC only), (2) 1N NH₄OAc at pH 7.0 (summation of basic cations plus 1N KCl extractable Al), (3) 1N NH₄OAc at pH 7.0 (summation of basic cations plus exchangeable H⁺), (4) 0.1M BaCl₂ (summation of basic cations plus exchangeable Mn, Fe and Al), (5) Mehlich 1 (summation of basic cations plus 1N KCl extractable Al), (6) Mehlich 1 (summation of basic cations plus exchangeable H⁺), (7) Mehlich 3 (summation of basic cations plus 1N KCl extractable Al), and (8) Mehlich 3 (summation of basic cations plus exchangeable H⁺). The 0.1M BaCl₂ was chosen as the standard method for the highly weathered soils and the other methods compared to it. The results indicated that the 1N NH₄OAc replacement method gave significantly higher CEC values compared to the summation methods. This was probably due to the overestimation of the field CEC caused by measurement of pH dependent cation exchange sites in these soils. There was, however, close agreement between the BaCl₂ method and the summation methods that included extractable Al. The generally good agreement between these summation methods suggests that the Mehlich 1 and Mehlich 3 extractants, commonly used to determine available nutrients in the southeastem USA, may also be used to measure effective CEC of some acid‐rich sesquioxide benchmark soils of Alabama. However, 1N KCl extractable Al as opposed to exchangeable H⁺ should be included in the computation.     

不同磷水平对红壤溶液中锰、铝、镁和钙浓度变化以及小麦生长的影响

为了探明不同磷水平对红壤中土壤溶液主要金属离子变化的影响以及小麦对磷的响应,确定红壤中小麦适宜的施磷水平,采用原位提取土壤溶液和比较生物量的方法,监测了短期内红壤溶液中主要金属离子浓度变化及小麦生物量的变化。结果表明:碳酸钙的加入可以显著升高酸性红壤的p H,土壤溶液中铝、锰和镁浓度显著低于未加碳酸钙处理;800 mg/kg磷处理后铝、锰、镁和钙的浓度要比未加磷处理分别至少降低47%、44%、37%和33%。随着施磷量的增加,小麦在200 mg/kg磷处理时积累的生物量最大,随后磷增加,小麦生物量反而降低。而加碳酸钙处理小麦地下部生物量随着施磷量增加则降低。结果表明碳酸钙不仅可以有效升高土壤p H,降低土壤溶液铝浓度,还降低土壤溶液中锰的浓度。磷的加入同样可以降低锰和铝的浓度,缓解铝和锰毒害。红壤中生长小麦的适宜施磷量为200 mg/kg。     

On-Site Assessment of Extractable Soil Nutrients after Long-Term Biosolid Applications to Perennial Forage

The objective of this study was to evaluate soil nutrient loading and depth distributions of extractable nitrogen (N), phosphorus (P), and potassium (K) after long-term, continuous annual surface applications of anaerobically digested class B biosolids at a municipal recycling facility in central Texas. Commercial forage production fields of coastal bermudagrass (Cynodon dactylon L.) were surface applied at 0, 20, 40, or 60 Mg dry biosolids ha^?1 y^?1 for 8 years. Application duration was evaluated in fields treated with 20 Mg dry biosolids ha^?1 y^?1 for 0, 8, or 20 years. Total soil loads of extractable inorganic N and P increased linearly with application rate, but only extractable P increased with duration. Neither total load nor soil distribution of extractable K was affected by biosolid applications. Mineralization of biosolid-derived organic N and P likely contributed to elevated concentrations of nitrate throughout the soil profile (0–110 cm) and orthophosphate in surface soils (0–40 cm).     

Incubation of Dried and Sieved Soils Can Induce Calcium Phosphate Precipitation/Adsorption

Abstract

Soil incubations are a common practice typically employed in assessing the effect of some treatment on the availability and solubility of phosphorus (P). However, standard sample preparation (drying and sieving) can alter soil chemical and physical properties, resulting in possible changes in P behavior upon soil incubation. Sixty surface soil samples were collected, air dried, and sieved before being incubated at field capacity for 7days. After incubation, soils were allowed to air dry and were analyzed along with nonincubated samples for pH and water‐ and Mehlich‐3‐extractable elements. Incubation increased pH and decreased water‐soluble P, calcium (Ca), and magnesium (Mg) relative to nonincubated soils. Increases in pH may have been due to increased solubility of residual calcium carbonates by drying and sieving. This increase in pH among soils with sufficient levels of P, Ca, and Mg resulted in the formation of Ca and Mg phosphates as confirmed by chemical speciation modeling.     

SEASONAL CHANGES IN NUTRIENT AVAILABILITY FOR SULFUR-AMENDED EVERGLADES SOILS UNDER SUGARCANE

The objective of this study was to evaluate effects of elemental sulfur (S) addition on soil pH and availability of macro- and micronutrients during the sugarcane growing season. Sulfur application did not significantly reduce soil pH when applied at 0 to 448 kg S ha^?1 due to the high soil buffering capacity. Water extractable phosphorus (P) and potassium (K) for soils receiving the highest S rate were 188% and 71% higher than for unamended soils only at two months after application, indicating a short-term enhancement of macronutrient availability. Soil amended with 448 kg S ha^?1 contained 134% more acetic acid-extractable zinc (Zn) than unamended soil, although stimulatory effects did not extend beyond two months. Sugar yield was not affected by S addition, averaging 17 Mg sugar ha^?1. The failure of S to enhance nutrient availability throughout the growing season indicates the limited benefit of applying elemental S to reduce pH and increase nutrient availability to sugarcane.     

Economics of phosphorus fertilization of barley as influenced by concentration of extractable phosphorus in soil

Abstract

Field experiments were conducted at 60 sites in central and north‐central Alberta to determine the yield response of barley (Hordeum vulgare L.) to phosphorus (P) fertilizer and economics of P application on soils with different concentrations of extractable P in the 0–15 cm soil layer. On the unfertilized plots, barley yield increased with increasing concentration of extractable P in the soil up to 22 mg P kg^‐1, but the yield response to applied P decreased. The net present value (NPV) of returns from P fertilization increased with increasing rate of P up to approximately 51 kg P₂O₅ ha^‐1. The NPV of applied P decreased with increasing concentration of extractable P in soil. On soils with extractable P more than 22 mg P kg^‐1, P application did not result in positive NPV.     

Aluminum and iron estimated by Mehlich‐3 extractant in mine soils in Galicia,northwest Spain

Abstract

The efficiency of Mehlich‐3 reagent as an extractant for aluminum (Al) and iron (Fe) was studied in Galician coal mine soils, in the process of reclamation. Mehlich‐3 Al and Fe values were compared to those from other Al and Fe tests and with phosphorus (P) sorption. The soils are very heterogeneous, consisting mainly of carbonaceous and non‐carbonaceous clays and shales, which are often rich in pyrite. Some of them have been amended with topsoil or fly ash. One hundred forty samples, from 0 to 15 or 15 to 30 cm, were analyzed. The pH values ranged from 2.7 to 8.4; oxalate and pyrophosphate Al from 0 to 1.17%, and 0.02 to 0.58%, respectively; and oxalate and pyrophosphate Fe from 0.02 to 2.25% and 0 to 1.28%, respectively; PSI (P sorption index) values varied between 0 and 55.1. The Mehlich‐3 Al values ranged from 24 to 2600 mg kg^‐1. A close relationship was observed between Mehlich‐3 and oxalate Al values (r=0.77), although the regression line tended to be curvilinear. Mehlich‐3 Al was better correlated than oxalate Al to pyrophosphate Al (r=0.66 vs. r=0.59) and also to pH‐NaF (r=0.89 vs. r=0.74). The Mehlich‐3 Al is almost as good as oxalate Al in estimating non‐crystalline Al, the correlation coefficients between log PSI and log (Mehlich‐3 Al) or log (oxalate Al) being 0.51 and 0.57, respectively. The Mehlich‐3 Fe correlated to available (r=0.63), exchangeable (r=0.65) and soluble Fe (r=0.66), but not to non‐crystalline Fe.     

Correlation of Soil pH and Mehlich‐3 Phosphorus with Postflood Rice Phosphorus Concentrations in Arkansas

Abstract

Plant‐available phosphorus (P) measured by routine soil‐test methods is poorly correlated with rice grain yield in Arkansas. Our objective was to determine whether soil water pH (pH_w) and Mehlich‐3 P were correlated with growth and yield of rice grown on silt loam soils. Data from 35 field studies were used to correlate Mehlich‐3 P and pH_w with relative yield, dry matter accumulation, and P concentration at the midtillering stage. Significant linear or nonlinear relationships between pH_w or Mehlich‐3 P with rice growth parameters were delineated but explained less than 27% of the variability in dry matter and P concentrations at the midtillering stage and grain yield at maturity. Mehlich‐3 P and pH_w together explained 61% of the variability in midtillering P concentrations. Midtillering whole‐plant P concentrations were positively related to relative grain yield and dry matter production and will be used to identify soils with limited P availability for rice in Arkansas.