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Published in Soil Sci. Soc. Am. J. 69:266-272 (2005).
© 2005 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA

Division S-8—Nutrient Management & Soil & Plant Analysis

Correlation of a Resin Membrane Soil Phosphorus Test with Corn Yield and Routine Soil Tests

Antonio P. Mallarino* and Atta M. Atia

Dep. of Agronomy, Iowa State Univ., Ames, IA 50011. A.M. Atia currently at Alberta Agriculture Food and Rural Development, 6903 116 St., Edmonton, Alberta, Canada, T6H 4P2

* Corresponding author (apmallar{at}iastate.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Most tests for plant-available soil P are based on extraction with a chemical solution. Extraction of P through ion exchange could provide better estimates of plant-available P. The objective of this study was to field calibrate a test based on a commercially available ion-exchange resin membrane (RMP) and compare it with Bray-P1 (BP), Mehlich-3 (M3P), and Olsen (OP) tests. Replicated P response trials with corn (Zea mays L.) were established at 59 Iowa locations (78 site-years). The soils represented 17 series of the suborders Argiudolls, Endoaqualfs, Endoaquolls, Hapludalfs, and Hapludolls. Initial BP, M3P, RMP, and OP values ranged from 2 to 63, 7 to 79, 6 to 63, and 3 to 31 mg P kg–1, respectively. The r2 values of relationships between soil P extracted across sites ranged from 0.84 to 0.91, and the lowest values were for BP relationships. The BP test measured less P in a CaCO3–affected soil with pH 8.1 but not when pH was ≤7.7. Excluding the calcareous site improved correlations only for BP. Critical concentration ranges defined by Cate-Nelson (CN) and linear-plateau (LP) models and relative yield responses for various soil-test ranges indicated that 13 to 20 mg kg–1 for BP, 16 to 21 mg kg–1 for M3P, 13 to 19 mg kg–1 for RMP, and 8 to 11 mg kg–1 for OP corresponded to a 94 to 96% mean relative yield response. The sink-based RMP test was as effective as routine P tests at predicting corn response to P fertilization and could be adopted for production agriculture.

Abbreviations: BP, Bray-P1 • CN, Cate-Nelson • ICP, inductively coupled plasma emission spectroscopy • LP, linear-plateau • M3P, Mehlich-3 P • OP, Olsen P • RMP, ion-exchange resin membrane extractable P • QP, quadratic-plateau


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
SOIL TESTING is a useful diagnostic tool to assess plant P availability. The BP (Bray and Kurtz, 1945), M3P (Mehlich, 1984), and OP (Olsen et al., 1954) tests are widely used. These tests, with little or no modification, currently are recommended for soils of the north-central region of the USA by the North-Central Regional Committee for Soil Testing and Plant Analysis (Frank et al., 1998). Chemical reactions between soil constituents and P extractants can explain differences in the suitability of soil P tests for different soils. Bray-P1 is reliable on neutral or acid soils, but underestimates plant-available P on some high pH, CaCO3–affected soils (Sen Tran et al., 1990; Mallarino, 1997). This result has been explained by partial neutralization of the acid extracting solution by CaCO3 and/or precipitation of the fluoride by dissolved Ca (Smith et al., 1957; Fixen and Grove, 1990). Recently, Mallarino (2003) compared M3P field calibrations for corn when extracted P was determined with colorimetric (Murphy and Riley, 1962) or inductively coupled plasma (ICP) methods for Iowa soils varying in soil pH. Although the ICP-based M3P test measured more P than the traditional colorimetric test, both were similarly effective at predicting crop response to P across soils with acid to alkaline pH (CaCO3–affected soils) and varying organic C levels. Others have also observed that ICP often measures more P in soil extracts or water than colorimetric determination methods (Hylander et al., 1995; Masson et al., 2001; Nathan et al., 2002). The OP test and both the colorimetric and ICP versions of the M3P test are recommended across all Iowa soils while BP only is recommended for soils with pH < 7.3 (Sawyer et al., 2002).

Chemical sink-based tests have been proposed that rely on P sorption–desorption reactions instead of dissolving soil P with chemicals. One test is based on P extracted by Fe-oxide impregnated filter paper strips or discs (Menon et al., 1989; Sharpley, 1991). Other tests are based on ion-exchange resins, and initially were based on resin beads (Amer et al., 1955; Olsen et al., 1983). More recent technology allows for impregnating a resin onto a plastic membrane (Abrams and Jarrell, 1992; Tiessen and Moir, 1993) that is durable and facilitates laboratory procedures. Research with resin-based P tests (Fernandes and Coutinho, 1997; Nuernberg et al., 1998; Fernandes et al., 1999) has shown, as expected, that relationships between tests or between extracted P and of plant P availability indices are affected by soil properties (such as soil pH, particle-size composition, and mineralogy) and few generalizations are possible across contrasting soils. Rubaek and Sibbesen (1995) reported similar rankings across various P treatments and trends over time for OP and a resin-based P extraction and OP, although differences tended to be greater for the resin extractant. In Iowa, Atia and Mallarino (2002) found high linear correlations between soil P measured by OP, M3P, FeP, and RMP tests across calcareous and noncalcareous soils with histories of fertilizer or manure application. Measurements of P uptake by young corn and soybean [Glycine max (L.) Merr.] plants (grain yield was not measured) showed that tests were approximately equally correlated with plant P uptake within sites but correlations across sites were higher for OP and M3P.

The RMP test has not been calibrated with crop yield response under midwestern field conditions. Yield-based calibrations of RMP are necessary to be able to use it to predict crop response to added P. Comparisons of field calibrations for RMP and routine soil tests are of interest because RMP could be used for environmental P testing. Researchers have suggested that sink-based tests could be better predictors of soil P moving of fields and subsequent promotion of algal growth in surface water resources (Sharpley, 1991; Sharpley et al., 1996; Sims et al., 2000). The RMP test could be a more versatile tool if it were reliable in diagnosing P sufficiency for crops while also serving as an environmental P test. The objectives of this study were to calibrate the RMP test with grain yield response of corn to P fertilizer and to compare it with the routine BP, M3P, and OP tests. Soils and crop responses used in this study are the same used in a recent study (Mallarino, 2003) that calibrated BP and both colorimetric and ICP versions of M3P. Data for the BP and M3P-colorimetric tests are shown in this paper for comparative purposes.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Grain yields and soil samples for this study were collected from P response trials conducted at 59 Iowa locations from 1989 to 1997, which resulted in 78 site-year observations. Detailed descriptions of sites and field methods including treatments and sample collection were previously published by Mallarino (2003). Soils represented 17 series of the subgroups Aquic Argiudolls, Aquic Hapludolls, Mollic Hapludalfs, Typic Argiudolls, Typic Endoaquolls, Calcareous Typic Endoaquolls, Typic Hapludalfs, Typic Hapludolls, and Udollic Endoaqualfs. Thirty-one trials evaluated P fertilization rates for corn managed with chisel-plow or disk tillage, 13 trials evaluated P fertilization rates applied broadcast or banded for no-till corn, and 15 trials evaluated P fertilization rates applied either broadcast or banded for ridge-till corn. The P treatments always included a nonfertilized control, two to three P treatments, and the largest P rate at each trial ranged from 35 to 75 kg P ha–1 (applied with granulated triple superphosphate). Treatments and three to four replications at each site were arranged as completely randomized or randomized complete-block designs. Crop and soil management practices were those normally used by the farm operators, although supplemental N and K fertilizers were applied to avoid deficiencies of these nutrients.

Composite soil samples were collected before applying the treatments. In sites managed with chisel-plow or no-tillage, 12 random cores were collected from a 15-cm depth. In fields managed with ridge-tillage, 45 random cores were collected from a 15-cm depth in equal proportions from the ridge top, shoulders, and valley positions. After sampling, samples were dried at 30 to 40°C, crushed to pass a 2-mm sieve, and stored at approximately 23°C and 65% relative humidity. All soil samples were dried again at 35°C and re-analyzed for pH and any of BP, M3P, or OP tests that may have been conducted before. All test results were averaged because no consistent storage effects were found. Soil P was analyzed in duplicates with the BP, M3P, and OP tests using procedures recommended for the North Central Region (Frank et al., 1998). For the BP test, 1 g of soil was extracted with 10 mL of 0.03 M NH4F and 0.025M HCl by shaking for 5 min. For the M3P test, 1 g of soil was extracted with 10 mL of 0.2 M CH3COOH, 0.25 M NH4NO3, 0.015 M NH4F, 0.013 M HNO3, and 0.001 M EDTA by shaking for 5 min. For the OP test, 1 g of soil was extracted with 20 mL of 0.5 M NaHCO3 (pH 8.5) by shaking for 30 min. All extracts were filtered through Whatman No. 42 filter paper and P was determined colorimetrically with the Murphy and Riley (1962) method. Procedures followed for the RMP test were those described by Tiessen and Moir (1993). Sheets of a commercially available resin-impregnated plastic material (BH15 1TD, BDH Laboratory Supplies, Poole, England) were cut into strips measuring 4.6 by 1.0 cm. The strips were treated by shaking them in 0.5 M NaHCO3 for 30 min and allowed to dry at room conditions. Phosphorus was extracted from the soil by shaking one strip with 1 g of soil and 20 mL of deionized water in 200-mL bottles for 16 h. The strips were removed from the bottles, rinsed with deionized water, and were shaken for 1 h in 0.5 M HCl to desorb P. Desorbed P was measured colorimetrically by the Murphy and Riley (1962) method. Soil pH (based on a 1:1 soil/water ratio) ranged from 5.3 to 8.1 across sites. The sum of soil CaCO3 and MgCO3 was measured with a pressure-calcimeter method (Sherrod et al., 2002) in soils with pH > 7.2, and ranged from 0 to 58 g kg–1. Soil organic C was estimated by measuring total C with an induction furnace combustion method (Wang and Anderson, 1998) and subtracting inorganic C for samples with pH > 7.2.

Relative yield was calculated for each mean soil-test P value of control plots (established through previous fertilization and differences in native P levels across sites) by dividing the corresponding yield by the maximum yield obtained through adequate fertilization for each site year and multiplying by 100. For 1-yr trials, one pair of data (relative yield and soil-test P) is represented in figures by one point because initial soil P was measured on one composite soil sample. For trials evaluated 2 or 3 yr, one pair of data for each year is represented by one point, and the soil-test data represent the mean value for the control plots. Soil test critical concentrations were calculated with the statistical CN method (Cate and Nelson, 1971), and with the LP and quadratic-plateau (QP) segmented models (Waugh et al., 1973). The critical concentration defined by the CN method was determined with the General Linear Models (GLM) procedure of SAS (SAS Inst., 2000) as the value that split the yield response data into the two groups that accounted for the largest proportion of the total variability (R2). Critical concentrations defined by the segmented models were determined with the Nonlinear Model (NLIN) procedure of SAS, and represent the soil-test values at which the two portions of each model joined.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Amounts of Phosphorus Extracted by the Soil Tests
The average soil P across all sites measured by the BP, M3P, RMP, and OP tests was 17, 19, 17, and 9 mg P kg–1, respectively. Coefficients of determination (r2) of linear relationships between amounts of extracted P across sites ranged from 0.84 to 0.91. The lower r2 values were for relationships involving BP, while other values were approximately similar at 0.88 to 0.91. Excluding a site with the highest soil pH (8.1) and carbonate (CaCO3 plus MgCO3) concentration (58 g kg–1) from the regression analyses improved the r2 of relationships to a range of 0.88 to 0.97 (Fig. 1) . Excluding six sites with pH 7.3 to 7.7 did not change the r2 of the relationships, probably because lower calcareous content (>37 g kg–1) did not affect BP as much. Previous Iowa research has shown that BP extracts less P in relation to P extracted by M3P or OP from calcareous soil (Mallarino and Blackmer, 1992; Mallarino, 1997). However, the results suggests that pH alone is not a good indicator of a potential failure of the BP test and that the carbonate concentration has to be high, at least >36 g kg–1 according to our study.



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  		Fig. 1. Correlations between amounts of soil P extracted by four soil tests. Model fits excluded a site with the highest pH (8.1), which is indicated by an arrow.

 
Data in Fig. 1 show that when the site with pH 8.1 was excluded, BP and M3P were the best correlated tests (r2 = 0.97) and that all other relationships were approximately similar (r2 = 0.88–0.91). The highly calcareous site blends with other sites into a common relationship for M3P, RMP, and OP. These results suggest that all tests extract P from approximately the same P pools and with relatively similar intensity, except for BP in highly calcareous soils. The amount of P extracted by each test was not correlated (P ≤ 0.05) with soil pH or organic C across sites (not shown). Data in Fig. 2 show that the BP/OP extraction ratio decreased with increasing pH with or without the site with a soil pH of 8.1 (r2 = 0.39 and 0.31, respectively) but RMP/BP and RMP/OP extraction ratios were not related (P ≤ 0.05) to soil pH. Data in Fig. 3 show that only the BP/OP extraction ratio decreased with increasing organic C with or without the site with pH 8.1 (r2 = 0.26 and 0.20, respectively), although the strength of the relationship was poorer than for pH. The RMP/BP ratio (and also the RMP/M3P ratio, which is not shown) increased with increasing organic C, which could indicate greater P extraction by RMP from organic P pools. Other research (Rubaek and Sibbesen, 1993; Rubaek et al., 1999) has shown high correlation between labile soil organic P forms and resin-extractable P. However, changes in extraction ratios in this study were small and the strength of the relationships was poor (r2 = 0.26 and 0.17 for RMP/BP and RMP/M3P, respectively). Moreover, interpretations of cause and effect are difficult and speculation is risky because the high pH soils tended to have a greater organic C concentration (r2 = 0.14, P ≤ 0.01). Overall, these results agree with a previous suggestion in that only the BP test reacts significantly different from the other tests as soil pH increase to alkaline values.



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  		Fig. 2. Relationships between soil pH and selected ratios of P extracted by Bray-P1, resin, or Olsen tests. Model fits excluded a site with the highest pH (8.1), which is indicated by an arrow.

 


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  		Fig. 3. Relationships between soil organic C and selected ratios of P extracted by Bray-P1, resin, or Olsen tests. Model fits excluded a site with the highest pH (8.1), which is indicated by an arrow.

 
Field Correlation of Yield Response to Phosphorus
Field response trials that encompass various crop production conditions and wide soil-test P ranges provide the most appropriate basis for soil-test interpretations. The growing conditions across sites and years in this study resulted in grain yields that ranged from 5.5 to 13.2 Mg ha–1 (means of the treatment that received the largest P rate at each site). Analysis of variance of P effects on yield indicated a yield response (P ≤ 0.05) in approximately 40% of the site-years (not shown). Relationships between relative corn yield response and soil-test P are shown in Fig. 4 . When the result for the soil with highest pH is excluded, the shapes of relationships for the four tests suggest no major differences in the efficacy of the tests to estimate plant-available P. The location of the data point for the soil with the highest pH indicates that BP grossly underestimated plant-available P at this site compared with the other tests. Previous Iowa field correlations showed that in CaCO3–affected soils BP often underestimates plant-available P compared with OP and the colorimetric version of M3P (Mallarino and Blackmer, 1992; Mallarino, 1997) or the ICP version of M3P (Mallarino, 2003). Data in Fig. 4 indicate that RMP also is better than BP across all soils and approximately similar to OP and M3P. However, the results indicated that this sink-based P test is not superior to commonly used tests based on chemical extraction at predicting crop response to P fertilization.



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  		Fig. 4. Relationships between relative yield response of corn and soil P extracted by four soil P tests. Linear-plateau model fits excluded a site with the highest pH (8.1), which is indicated by an arrow.

 
Table 1 shows critical soil-test P concentrations calculated with CN, LP, and QP models. Critical concentrations varied considerably depending on the model used, a result that was shown before for other data sets and additional models (Dahnke and Olson, 1990; Mallarino and Blackmer, 1992). Models fits in Table 1 excluded the site with the highest soil pH (8.1). Excluding this site significantly affected only the fit for BP (the R2 was reduced) but did not affect the critical concentrations. Critical concentrations determined for BP, M3P, and RMP were approximately similar, and differences between models were much higher than differences between tests. Critical concentrations for OP were lower, which agrees with less P extracted by this test. The minor difference between BP and M3P coincides with results from Pennsylvania soils (Beegle and Oravec, 1990) and with previous results from Iowa (Mallarino and Blackmer, 1992; Mallarino, 1997). The fits for all models across all soils indicate that M3P was slightly more effective at predicting corn response to P than the other tests, while BP, RMP, and OP were approximately similar. Plots of distribution of residuals did not add more meaningful information and are not shown. The results for the BP test can be misleading, however, and its efficacy will likely be lower in areas with more abundant CaCO3–affected soils.


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  		Table 1. Critical concentrations of soil-test P for corn estimated by four tests and three models.

 
There is no clearly superior or widely accepted method for defining agronomically optimum critical concentration ranges (Dahnke and Olson, 1990; Mallarino and Blackmer, 1992). Mallarino and Blackmer (1992) showed that short-term (for one crop) economically optimum soil-test P critical concentrations usually are within the range of concentrations defined by the CN and LP models. These researchers showed that critical concentrations defined by the quadratic and QP models usually are much higher than those defined by the CN and LP models, and their use resulted in smaller returns to fertilization across fields. Critical concentration ranges defined by the CN and LP models in this study were 13 to 20 mg kg–1 for BP; 16 to 21 mg kg–1 for M3P; 13 to 19 mg kg–1 for RMP; and 7 to 10 mg kg–1 for OP. Calculations from response data in Fig. 4 indicated that the ranges for BP, M3P, and RMP correspond to a 94 to 96% mean relative yield response. Similar calculations for OP showed a slightly lower (92%) mean relative yield response.

Critical concentration ranges identified in this study and current Iowa interpretations for the BP, M3P, and OP tests are within the variation range of interpretations in neighboring states such as Illinois, Minnesota, Nebraska, and South Dakota (Hoeft and Peck, 2001; Rehm et al., 2001; Gerwing and Gelderman, 2002; Shapiro et al., 2003). Critical concentration ranges defined in this study by the CN and LP models for BP and M3P tests match well with the optimum category (16–20 mg P kg–1 for both tests) of current interpretations for corn and soybean for most Iowa soils (Sawyer et al., 2002). Only P fertilization to maintain soil-test P based on crop P removal is recommended for this category. However, the critical concentration range defined by the CN and LP models for OP (7–10 mg P kg–1) is lower than the optimum category for this test in current Iowa interpretations (11–14 mg P kg–1) and matches better the low category (6–10 mg P kg–1). Calculations of moving averages from data for OP in Fig. 4 for a range width of 4 mg P kg–1 indicated that a range of 8 to 11 mg kg–1 corresponded to a mean relative yield response approximately similar to those of other tests (96%). Therefore, current Iowa interpretations for the OP test could be adjusted to better predict P fertilization needs.

This study focused on corn yield response to P, and research is needed for other crops. However, because the correlations of yield response and soil-test values confirmed relationships between amounts of P extracted, it is reasonable to assume that interpretations for RMP and OP for corn derived from this study would approximately apply to other Iowa crops for which similar interpretation classes and P fertilization criteria are currently used. For example, the same Optimum category and only maintenance fertilization (based on expected P removal in harvested products) are used in Iowa for corn grown for grain or silage, soybean, sorghum [Sorghum bicolor (L.) Moench], oat (Avena sativa), sunflower (Helianthus annus), and several forages except alfalfa (Medicago sativa L.).


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Results showed that RMP and OP had a similar capacity to predict corn response to P fertilization, which was only slightly lower than for M3P. Although the efficacy of BP was as good as that for M3P except for a site with the highest soil pH (8.1) and calcareous content, the BP efficacy will likely be lower than for other tests in areas with abundant CaCO3–affected soils. Study of critical concentration ranges defined by the CN and LP models and mean relative yield response for various ranges indicated that critical concentration ranges of 13 to 20 mg kg–1 for BP, 16 to 21 mg kg–1 for M3P, 13 to 19 mg kg–1 for RMP, and 8 to 11 mg kg–1 for OP corresponded to a 94 to 96% mean relative yield response. The sink-based RMP test was as effective as commonly used routine P tests based on a chemical extraction at predicting corn response to P fertilization. Therefore, it would be a useful tool for both agronomic and environmental soil P testing if new research confirms previous suggestions in that it may be more reliable than routine P tests to assess soil P that promotes algae growth in surface water bodies when there is soil loss with surface runoff.

Received for publication April 12, 2004.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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[Abstract] [Full Text] [PDF]

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