Environmental Soil Test Research Articles

Soil Testing Indices for Phosphorus Leaching in Selected Vertisol and Inceptisol of India

Little information is available on P leaching potential of Indian soils. The degree of P saturation (DPS) relating the extractable P to the P sorption capacity governed by soil constituents (Al, Fe, Ca) has been widely used to predict the potential to adsorb or release P. The aim of the present study was to determine DPS in two major cultivable soils of India and to evaluate routine agronomic and environmental soil test P as indicators of P leaching through column leaching experiment with different levels of P fertilization. The results of the study showed the variation in leachate reactive P (RP) content which was significantly affected by P rates and increased significantly above threshold DPS values. For vertisol and inceptisol, threshold DPS Ol was 25.07 and 12.43%, DPSA.O. was 7.87 and 3.76%, and DPSM3 was 18.66 and 6.79%, respectively. The RP concentration showed a strong correlation with DPS and environmental soil test like 0.01 M CaCl2 and water extractable P (WEP) suggesting that soil 0.01 M CaCl2 and WEP can be used as surrogate for RP concentration for risk of P loss via leaching. Thus, the use of Olsen P, Mehlich 3 and ammonium oxalate P for calculating DPS provides reliable criteria for identifying soils having high risk of P loss to surface water bodies and works well in all soil types.

Deriving sorption indices for the prediction of potential phosphorus loss from calcareous soils

The aim of this study was to develop techniques to evaluate soil phosphorus (P) sorption capacity (PSC) and determine critical soil P levels to predict P loss potential for calcareous soils. Seventy-five soils mostly from Northern China were analyzed for soil P using four extraction methods (water, Pw; carbonate, POls; ammonium oxalate, Pox; and Mehlich 3, PM3) as well as PSC derived from single-point (PSC150) and multipoint sorption (S t) isotherms. Strong correlation was found between PSC150 and S t (r (2)=0.89, p<0.001). The sum of αCaM3 and βMgM3 as an index of PSC (PSC(CaM3 + MgM3)) was most closely related to the maximum amount of P sorbed (S max) as given by the sum of S t and soil initial P setting α=0.039 and β=0.462 (r (2)=0.80, p<0.001). The degree of P saturation (DPS) was thereafter calculated from PSC(CaM3 + MgM3) (DPS(CaM3 + MgM3)), to which Olsen P (POls) was significantly correlated (r (2)=0.82, p<0.001). In a split-line regression from Pw against DPS(CaM3 + MgM3) (r (2)=0.87, p<0.05), a change point was identified at 28.1% DPS(CaM3 + MgM3), which was equivalent to 49.2 mg kg(-1) POls and corresponded to a Pw concentration of 8.8 mg kg(-1). After the change point, a sharp increase in Pw was observed. Our results reveal a new approach to approximating DPS from CaM3 and MgM3 for calcareous soils without the need to generate a S max. We conclude that in the absence of an environmental soil test criteria for P, the DPS(CaM3 + MgM3) and POls could be used to predict P loss potential from calcareous soils.

Comparison of plant nutrient and environmental soil tests to predict Pb in urban soils

Most urban soils are not tested for Pb because of the high costs associated with sampling and laboratory analysis of soil contaminants. However, soil testing for plant nutrients is inexpensive and routinely performed for agricultural soils used for food production. The objectives of this study are to determine the ability of 1M HNO3, Mehlich 3, and Modified Morgan soil tests to predict total Pb and other contaminants in urban soils. Total Pb was determined from 65 urban vacant residential lots being considered for urban gardens and food production in Cleveland, OH. Extractable Pb was determined using common soil nutrient test methods Mehlich 3 and Modified Morgan extraction, and a 1M HNO3 extraction. Significant linear regressions between total Pb and Mehlich 3 (r2=0.83), 1M HNO3 (r2=0.92), and Modified Morgan (r2=0.77) in study soils were found. Most commercial and university soil testing labs use Mehlich 3 which could be implemented as a screening tool for soil Pb, Cu, and Zn. The Mehlich 3 soil test is widely used and is relatively inexpensive (<$15). Our results show that total Pb can be conservatively estimated by the following equation Total Pb (mgkg−1)=Mehlich 3 Pb (mgkg−1)×2.

Assessing soil erodibility and mobilization of phosphorus from Swedish clay soils – Comparison of two simple soil dispersion methods

Erodibility of Swedish clay soils estimated according to the existing methods is usually low, but high levels of suspended solids and attached unreactive phosphorus have been recorded in drainage water from fields and catchments dominated by clay soils. Inherent susceptibility to soil erosion is usually assessed through aggregate stability studies or dispersion tests. The latter are simple to perform and produce good results when compared against runoff lysimeter experiments. The environmental soil test to determine the potential for sediment and phosphorus transfer in runoff from agricultural land (DESPRAL) and soil suspension turbidity (SST) dispersion tests, which differ in soil–liquid ratio and shaking and settling times, were compared here for their ability to indicate the erodibility of 10 Swedish clay soils. The tests proved to be significantly correlated (r=0.78), but DESPRAL showed higher repeatability (r i =0.995) than SST (r i =0.824). Variation in soil dispersion was explained by clay, sand and organic matter content in DESPRAL and by clay and sand content in SST. An additional study on the effect of soil storage duration on dispersion (DESPRAL test) in 15 soil samples showed that storage had no effect on some soils, but significantly decreased dispersion in others after only 8 weeks. Therefore, soil dispersion tests should be performed as soon as possible after sample drying. The DESPRAL and SST tests proved to be a good option for estimating the erodibility factor K in the Revised Universal Soil Loss equation under Swedish conditions and were able to differentiate the susceptibility to sediment losses for different clay soils. They provided an indirect measure of the amounts of sediment and P mobilized, but further work is needed to calibrate them against measured values at field and catchment scale.

Phosphorus saturation of a tropical soil and related P leaching caused by poultry litter addition

Phosphorus deficiency is well known as a major agronomic constraint in the highly weathered Oxisols of Brazil and reasonable economic returns are not possible without application of high rates of phosphorus. Poultry litter, which is enriched in P, is increasingly being used in organic management of cultivated lands. Due to the great P fixing capacity of these soils, any limit to the soil sink of P is not recognized. The study was undertaken to evaluate the risk of P loss due to increase in phosphorus sorption saturation (PSS) from land application of poultry litter and to establish a relationship between PSS and water soluble phosphorus. No till corn-fallow rotation was followed for three years with annual application of 0, 5, 10, 25, 50 and 100Mgha−1 of poultry litter in a highly weathered clayey dystrophic red-yellow Argisol of Brazil. The effect of poultry litter application on soil was evaluated and Mehlich-3 P (PM-3) concentrations increased 3–134 times over control after three years of poultry litter application. Poultry litter application increased pH and decreased the concentration of exchangeable Al; whereas concentrations of K+, Na+, Zn2+, Mg2+ and Ca2+ increased substantially over control. Increase in soil pH and total organic carbon due to poultry litter application reduced the P sorption capacity of soils and P sorption. The PSS increased considerably at higher rates of poultry litter application (>10Mgha−1) and strongly increased the amount of desorbable P. Total water extractable P was mostly accounted for by reactive P forms and increased with poultry litter rates. In a plot of dissolved reactive P (DRP) against PSS, a change point was observed at 22.7% PSS corresponding to a dissolved reactive P (DRP) concentration of 0.92mgkg−1 soil after which a sharp increase in DRP was observed. P concentration >0.1mgL−1 was observed in soil solution at 60cm soil depth with increasing rates of poultry litter application, thus providing evidence of P leaching. In the absence of an environmental soil test criteria for P, the break point PSS of 22.7% could be used to practically monitor whether soils have reached a level of P loading that constitutes an environmental risk of P losses from soil to surface and ground waters.

Phosphorus in runoff from two highly weathered soils of the tropics

Ramírez-Ávila, J. R., Sotomayor-Ramírez, D., Martínez-Rodríguez, G. A. and Pérez-Alegría, L. R. 2011. Phosphorus in runoff from two highly weathered soils of the tropics. Can. J. Soil Sci. 91: 267–277. Agricultural fields with high soil phosphorus (P) content are important contributors to surface water degradation. Two consecutive simulated rainfall events were conducted on two Ultisols previously amended with inorganic P fertilizer or broiler litter. Soil test P (Bray 1 and Olsen) levels evaluated ranged from 1 to 350 mg kg−1. Surface runoff concentrations of total P (TP) and dissolved P (DP) generated by a 30-min runoff event were quantified. Runoff DP concentrations ranged from 0.08 to 3.98 mg L−1in fertilizer P-amended soils and from 0.08 to 4.93 mg L−1in broiler litter-amended soils. A single exponential model adequately described the relationships between soil test P and DP concentrations in runoff. For each soil, the soil test P-DP concentration relationships were positively influenced by soil organic matter and negatively influenced by antecedent soil moisture (P&lt;0.05). For both soils, the soil test P-DP concentration relationships were positively influenced by groundcover percentage and negatively influenced by slope. Environmental soil test P critical levels corresponding to a runoff threshold of 1 mg L−1DP, ranged between 176 and 296 mg kg−1(Olsen) and 143 to 276 mg kg−1(Bray 1) in soils amended with fertilizer-P. In broiler litter-amended soils, threshold values were 88 and 111 mg kg−1using Olsen and Bray 1, respectively. Differences in surface runoff-P concentrations due to amendment sources, antecedent soil moisture content, soil organic matter, groundcover and slope suggest that these factors need to be considered in P management decisions at the farm level.

Assessing extractable soil phosphorus methods in estimating phosphorus concentrations in surface run‐off from Calcic Hapludolls

AbstractUnderstanding soil test phosphorus (STP) and surface run‐off phosphorus (P) relationships for soils is necessary for P management. The objective of the study was to evaluate the efficacy of various soil test indices to predict P losses in surface run‐off. Selected sites were subjected to in situ rainfall simulations according to the protocol of the National Phosphorus Research Project (NPRP, 2001). P from a composite of twenty‐four 2.0‐cm‐diameter core soil samples (0–5 cm) was extracted using the Olsen, Bray–Kurtz, Mehlich III, distilled water and 0.01 m calcium chloride procedures. All of these P extraction methods explained a significant amount of variability in surface run‐off total dissolved P [TP (&lt;0.45)] (r2 ≥ 0.67; P ≤ 0.01), where 0.45 is the filter pore diameter in microns. Multiple regression models showed extractable P to be the best soil predictor of surface run‐off TP (&lt;0.45) among the studied soils. Despite extraction method or soil type, extractable P was the best soil predictor of surface run‐off TP (&lt;0.45). Either agronomic (0.92 ≤ r2 ≤ 0.96) or environmental (0.94 ≤ r2 ≤ 0.96) soil tests were effective in estimating surface run‐off TP (&lt;0.45) in select Mollisols.

Relationships Between Agronomic and Environmental Soil Test Phosphorus in Three Typical Cultivated Soils in China

A study was conducted to determine the relationships between agronomic soil test P and environmental soil test P in three soils predominately distributing in three typical agricultural production areas of China. Soil P was analyzed using Bray-1 (BP), Olsen (OP), and Mehlich-3 (MP) methods as agronomic tests, and using Fe-oxide impregnated filter paper (FeP), anion-exchange resin membrane (RP), and water (WP) as environmental tests. There were linear relationships between soil P extractable with all the tests evaluated. The regression coefficients, R 2, ranged from 0.8164 to 0.9409 between each two of the agronomic soil test P, and ranged from 0.4702 to 0.8990 between each two of the environmental soil test P, when the three soils were considered separately. When soil test P was analyzed across all the three soils, the highest regression R 2 was found between OP and MP (0.7940) amongst agronomic soil test P, and between FeP and RP amongst environmental soil test P (0.8842). While all of the three agronomic soil test P was linearly related to each of the environmental soil test P across the three soils, strongest relationships were found between OP and environmental soil test P. Agronomic OP may be adopted as an analytical tool for environmental prediction of soil P.

An environmental soil test to estimate the intrinsic risk of sediment and phosphorus mobilization from European soils

AbstractMethodologies are required to help identify soils that are vulnerable to both suspended sediment (SS) and phosphorus (P) transfer in land run‐off to combat the adverse impacts of agriculture on water quality. A laboratory test that quantifies dispersed particles and associated P in the same suspension was developed to estimate the potential mobilization of SS and P due to rainfall impact from 26 European soils with varied soil physical and chemical properties and P inputs. The test recovers an aliquot of the clay and fine silt (&lt;20 μm) fraction of soils after gently shaking in distilled water for 1 min at a 1:50 soil‐to‐solution ratio and measures the dry residue, total P and dissolved (&lt;0.45 μm) P content. The results of the test correlated well (r2 = 0.7–0.8) with the amounts of SS, total P and dissolved P in overland flow generated by indoor simulated rainfall (intensity 60 mm h−1 for 30 min and a 5° slope). Variation in SS and particulate P mobilization was linked to soil pH, organic matter (or clay) and sesquioxide content, although a multiple regression analysis showed these factors accounted for no more than 55% of this variation. Ranking showed that the soils generating the most sediment did not necessarily generate the most P loss due to variable degrees of P enrichment of the particulate fraction and variable contributions of dissolved P. Particulate P enrichment was related weakly (r2 = 0.5) to soil total P, while dissolved P fractions were predicted well (r2 = 0.8–0.9) by conventional soil P tests (water and Olsen). The environmental soil test has a potential role in identifying the comparative risk of sediment and P mobilization from critical source areas connected via both surface and subsurface pathways, and in providing data for incorporation into models predicting sediment and P transfer at the field and catchment scale.

Minimizing Confounding Factors in Phosphorus Leaching Assessment for Dairy‐and Poultry‐Manure‐Amended Soils

Soil phosphorus (P) concentrations have increased over the years, increasing P losses to surface waters. Phosphorus saturation ratios (PSR), used as environmental soil tests, have different relationships with conventional water‐soluble‐P (WSP) determinations for dairy and poultry‐manure‐amended soils. Objective was to develop a WSP procedure to characterize P leaching from manure‐amended soils. Soil samples were collected from dairy and poultry sites. WSP was determined using 1∶10 and 5∶1 soil–water ratios. Soils in columns were leached using unsaturated flow. Results showed that relationships between PSR and WSP 5∶1 were consistent for all soils. The 5∶1 ratio, closer to field moisture conditions, could be a good indicator of P leaching. There was good correlation between the WSP 1∶10, 5∶1, and column leachate, and a paired t test showed no difference between the last two. Thus, a single 5:1 extraction could be as useful in P leaching assessments as laborious column studies.

Agronomic and environmental soil test phosphorus in manured and non-manured Manitoba soils

Quantitative relationships between soil test phosphorus (STP) methods are needed to guide P management especially in manured soils with high P. Our objectives were: (i) to compare amounts of P extracted by different methods; (ii) to develop and verify regression equations to convert results among methods; and (iii) to establish environmental P thresholds for different methods, in manured and non-manured soils of Manitoba. We analyzed 214 surface soil samples (0–15 cm), of which 51 had previous manure application. Agronomic STP methods were Olsen (O-P), Mehlich-3 (M3-P), Kelowna-1 (original; K1-P), Kelowna-2 (modified; K2-P), Kelowna-3 (modified; K3-P), Bray-1 (B1-P) and Miller and Axley (MA-P), while environmental STP methods were water extractable (W-P), Ca Cl2 extractable (Ca-P) and iron oxide impregnated filter paper (FeO-P) methods. The different methods extracted different amounts of P, but were linearly correlated. For an O-P range of 0–30 mg kg-1, relationships between O-P and other STP were similar for manured and nonmanured soils, but the relationships diverged at higher O-P levels, indicating that one STP cannot be reliably converted to another using a single equation for manured and non-manured soils at environmentally critical P levels (0–100 mg kg-1 O-P). Suggested environmental soil P threshold ranges, in mg P kg-1, were 88–118 for O-P, 138–184 for K1-P, 108–143 for K2-P, 103–137 for K3-P, 96–128 for B1-P, 84–111 for MA-P, 15–20 for W-P, 5–8 for Ca-P and 85–111 for FeO-P. Key words: Phosphorus, soil test phosphorus, manured soils, non-manured soils, environmental threshold

Path and Multiple Regression Analyses of Phosphorus Sorption Capacity

Soil P saturation indices and P Langmuir adsorption maximum (Smax) are two environmental soil tests that provide valuable information for the proper management P in soils to avoid the overapplication of P. The objectives of this study were to determine Smax and develop P saturation indices for 28 Oklahoma benchmark soils and to use path analysis and multiple regression to examine the relationships between Smax and soil properties. Soil samples were analyzed for pH, clay content, oxalate extractable P (Pox), Al (Alox), Fe (Feox), and Mehlich-3 (M3) extractable P (PM3), Al (AlM3), Fe (FeM3), Ca (CaM3), and Mg (MgM3). The Smax value and saturation indices based on oxalate and M3 extractions were determined. The Smax value ranged from 34 to 500 mg kg−1 and was highly correlated with clay content (r = 0.79), organic C (r = 0.80), Alox (r = 0.88), and Feox (r = 0.83). Soil pH was not correlated (p> 0.05) with Smax Path analysis showed significant direct effects (p< 0.01) between Alox and Smax and between Feox and Smax but these relationships were highly influenced by indirect effects of Alox and Feox Multiple regression agreed well with path analysis and found that the combination of Alox and Feox were the two most important soil properties related to Smax of the soils studied. Significant relationships existed between AlM3 (r = 0.54) and Smax and between FeM3 (r = 0.54) and Smax Three P saturation indices studied were highly correlated (p< 0.05) with each other. Our results show that Smax of Oklahoma soils may be predicted with oxalate extractable Al and Fe or M3 extractable Al, Fe, and Ca.

Evaluation of the Phosphorus Source Component in the Phosphorus Index for Pastures

A phosphorus (P) index for pastures was developed to write nutrient management plans that determine how much P can be applied to a given field. The objectives of this study were to (i) evaluate and compare the P index for pastures, particularly the P source component, and an environmental threshold soil test P level by conducting rainfall simulations on contrasting soils under various management scenarios; and (ii) evaluate the P index for pastures on field-scale watersheds. Poultry litter was applied to 12 small plots on each of six farms based on either an environmental threshold soil test P level or on the P index for pastures, and P runoff was evaluated using rainfall simulators. The P index was also evaluated from two small (0.405 ha) watersheds that had been fertilized annually with poultry litter since 1995. Results from the small plot study showed that soil test P alone was a poor predictor of P concentrations in runoff water following poultry litter applications. The relationship between P in runoff and the amount of soluble P applied was highly significant. Furthermore, P concentrations in runoff from plots with and without litter applications were significantly correlated to P index values. Studies on pastures receiving natural rainfall and annual poultry litter applications indicated that the P index for pastures predicted P loss accurately without calibration (y = 1.16x - 0.23, r(2) = 0.83). These data indicate that the P index for pastures can accurately assess the risk of P loss from fields receiving poultry litter applications in Arkansas and provide a more realistic risk assessment than threshold soil test P levels.

Soil testing to predict phosphorus leaching.

Subsurface pathways can play an important role in agricultural phosphorus (P) losses that can decrease surface water quality. This study evaluated agronomic and environmental soil tests for predicting P losses in water leaching from undisturbed soils. Intact soil columns were collected for five soil types that a wide range in soil test P. The columns were leached with deionized water, the leachate analyzed for dissolved reactive phosphorus (DRP), and the soils analyzed for water-soluble phosphorus (WSP), 0.01 M CaCl2 P (CaCl2-P), iron-strip phosphorus (FeO-P), and Mehlich-1 and Mehlich-3 extractable P, Al, and Fe. The Mehlich-3 P saturation ratio (M3-PSR) was calculated as the molar ratio of Mehlich-3 extractable P/[Al + Fe]. Leachate DRP was frequently above concentrations associated with eutrophication. For the relationship between DRP in leachate and all of the soil tests used, a change point was determined, below which leachate DRP increased slowly per unit increase in soil test P, and above which leachate DRP increased rapidly. Environmental soil tests (WSP, CaCl2-P, and FeO-P) were slightly better at predicting leachate DRP than agronomic soil tests (Mehlich-1 P, Mehlich-3 P, and the M3-PSR), although the M3-PSR was as good as the environmental soil tests if two outliers were omitted. Our results support the development of Mehlich-3 P and M3-PSR categories for profitable agriculture and environmental protection; however, to most accurately characterize the risk of P loss from soil to water by leaching, soil P testing must be fully integrated with other site properties and P management practices.

Soil phosphorus dynamics: agronomic and environmental impacts

Phosphorus (P) related eutrophication of surface water is of increasing concern in many areas of the U.S. This concern has arisen where inputs of P in fertilizer and manure to agricultural systems have exceeded output in harvested crops for several years. As the loss of P in surface ( r 2 0.85 to 0.96) and subsurface drainage ( r 2 0.86) have been shown to be related to soil P content, measures to minimize nonpoint source losses of agricultural P are most effective when implemented at the source. To achieve this, identification of soils and management systems vulnerable to P loss and an understanding of the main factors controlling soil P bioavailability is essential. Soil P bioavailability is determined by reaction with hydrous oxides, amorphous and crystalline complexes of Al, Fe and Ca, and organic matter. The rate and extent of these reactions is influenced by soil management and drainage. In wetlands for example, Fe redox dominates P solubility, while organic P mineralization can contribute up to 25 kg P ha −1 yr −1 in temperate mineral soils and up to 160 kg P ha −1 t yr −1 in organic soils. However, it is critical that we are able to reliably determine threshold soil P values at which agronomic issues become environmental concerns. Agronomic soil P tests may target problem soils on which environmental soil tests will assess P bioavailability and P sorption capacity. Clearly, soil P dynamics are of agronomic and environmental importance, influencing both crop productivity and eutrophication and thus, must be considered in developing effective management plans.