Soil Test Phosphorus Research Articles

High Soil Test Phosphorus Effect on Corn Yield

Core Ideas High soil test P levels are often recommended for high yield corn. Many states recommend a deficiency correction approach for P application. Application of P to replace removal in the previous harvest was marginally superior. Maintenance of Bray‐1 P at > 25 ppm was not justified. Phosphorus removal in crop harvest has increased as yields have increased. Fertilizer P use guidelines are based on calibrations often developed for much lower yield levels and may need recalibration. Corn yields may be greater with higher than recommended soil test P when springs are relatively wet and cool. Research was conducted across 12 irrigated and five rainfed site‐years in Nebraska with initial Bray‐1 P ≤ 11 mg kg–1 to evaluate P application strategies for yield and P uptake of continuous corn (Zea mays L.) with and without tillage. The fertilizer P treatments were maintained on the same plots and included: (i) no P applied (0P); (ii) P applied according to the University of Nebraska‐Lincoln deficiency correction recommendation (UNL_P); (iii) P applied to replace P removed in the previous harvest (Replace_P); (iv) Bray‐1 P increased and maintained at 25 mg kg–1 (Bray_25); and (v) Bray‐1 P increased and maintained at 35 mg kg–1 (Bray_35). Interactions of P practice with other factors were not significant indicating consistency of P practice effects across varied climate conditions near planting and plant emergence. Grain yield was 9.3% and 0.89 Mg ha–1 more with the P‐applied treatments compared with 0P. Grain yield was 3.3% more due to the additional 5.9 kg ha–1 yr–1 P applied with Replace_P compared with UNL_P. Grain yield did not differ for Replace‐P, Bray_25, and Bray_35. Plant P uptake was on average linearly increased by 0.27 kg kg–1 P applied. Fertilizer P application for continuous corn should be by Replace_P.

Transforming soil phosphorus fertility management strategies to support the delivery of multiple ecosystem services from agricultural systems

Despite greater emphasis on holistic phosphorus (P) management, current nutrient advice delivered at farm-scale still focuses almost exclusively on agricultural production. This limits our ability to address national and international strategies for the delivery of multiple ecosystem services (ES). Currently there is no operational framework in place to manage P fertility for multiple ES delivery and to identify the costs of potentially sacrificing crop yield and/or quality. As soil P fertility plays a central role in ES delivery, we argue that soil test phosphorus (STP) concentration provides a suitable common unit of measure by which delivering multiple ES can be economically valued relative to maximum potential yield, in $ ha−1 yr−1 units. This value can then be traded, or payments made against one another, at spatio-temporal scales relevant for farmer and national policy objectives. Implementation of this framework into current P fertility management strategies would allow for the integration and interaction of different stakeholder interests in ES delivery on-farm and in the wider landscape. Further progress in biophysical modeling of soil P dynamics is needed to inform its adoption across diverse landscapes.

Rejoinder to the comment on: S. Nawara, T. van Dael, R. Merckx, F. Amery, A. Elsen, W. Odeurs, H. Vandendriessche, S. McGrath, C. Roisin, C. Jouany, S. Pellerin, P. Denoroy, B. Eichler‐Löbermann, G. Börjesson, P. Goos, W. Akkermans & E. Smolders. A comparison of soil tests for available phosphorus in long‐term field experiments in Europe

European Journal of Soil ScienceVolume 69, Issue 4 p. 749-751 Letter to the Editor Rejoinder to the comment on: S. Nawara, T. van Dael, R. Merckx, F. Amery, A. Elsen, W. Odeurs, H. Vandendriessche, S. McGrath, C. Roisin, C. Jouany, S. Pellerin, P. Denoroy, B. Eichler-Löbermann, G. Börjesson, P. Goos, W. Akkermans & E. Smolders. A comparison of soil tests for available phosphorus in long-term field experiments in Europe S. Nawara, S. Nawara orcid.org/0000-0003-0867-2162 Department of Earth and Environmental Sciences, KU Leuven, Leuven 3001, BelgiumSearch for more papers by this authorF. Amery, F. Amery Institute for Agricultural and Fisheries Research, Plant Sciences Unit – Crop Husbandry and Environment, Merelbeke 9820, BelgiumSearch for more papers by this authorE. Smolders, E. Smolders Department of Earth and Environmental Sciences, KU Leuven, Leuven 3001, BelgiumSearch for more papers by this author S. Nawara, S. Nawara orcid.org/0000-0003-0867-2162 Department of Earth and Environmental Sciences, KU Leuven, Leuven 3001, BelgiumSearch for more papers by this authorF. Amery, F. Amery Institute for Agricultural and Fisheries Research, Plant Sciences Unit – Crop Husbandry and Environment, Merelbeke 9820, BelgiumSearch for more papers by this authorE. Smolders, E. Smolders Department of Earth and Environmental Sciences, KU Leuven, Leuven 3001, BelgiumSearch for more papers by this author First published: 02 July 2018 https://doi.org/10.1111/ejss.12681Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume69, Issue4July 2018Pages 749-751 RelatedInformation

Effect of Diammonium Phosphate as In‐Furrow Starter Fertilizer on Winter Canola Grain Yield and Quality

Core Ideas In‐furrow application of diammonium phosphate (DAP) as a starter fertilizer could be a beneficial component of a comprehensive soil fertility program for winter canola production. Effect of in‐furrow starter, DAP, on the oil and protein content of winter canola was not significant. It is important to account for both soil test P (STP) and soil pH completely when providing nutrient recommendations in winter canola. Winter canola is a valuable rotational crop in Oklahoma. Starter fertilizer application is viewed as a way to improve canola yields. Field experiments were conducted in Dacoma, El Reno, Fairview, Fort Cobb, Kingfisher, Lahoma, Lamont, Miami, and Perkins, OK to evaluate the effect of applying diammonium phosphate (DAP, 18–46–0: N–P2O5–K2O) in‐furrow on winter canola grain yield and quality. Diammonium phosphate was applied with the seed at planting at 22 and 30 lb/ac in no‐till (NT) and minimum/conventional till (CT) systems, respectively. Canola variety ‘DKW 46–15’ was seeded from September 10 to October 10, 2016 at 3.75 lbs/ac spaced at 7.5 (CT) and 15 in (NT). Four of the 10 locations responded to in‐furrow application of DAP. Yield response ranged from 1 to 6 bu/ac. Locations that had low soil test phosphorus and low soil pH generally had higher yield response (3–6 bu/ac) than all other locations. Effect of in‐furrow DAP on the oil and protein content of winter canola was not significant. Results indicated the importance of accounting for both soil test phosphorus and soil pH completely when providing nutrient recommendations in winter canola.

Nitrogen- or phosphorus-based pig manure application rates affect soil test phosphorus and phosphorus loss risk

Pig manure is an effective source of plant nutrients that must be properly managed to prevent these nutrients from reaching surface and ground water. We conducted a 3-year study in southern Manitoba to investigate how the choice of cropping system and manure management practices affect soil test phosphorus (STP) concentration and loss of phosphorus (P) to groundwater. The experiment had a split-plot design with two cropping systems (annual and perennial) as main plots, and five nutrient management treatments as subplots: N-based liquid pig manure, P-based liquid pig manure, N-based solid pig manure, P-based solid pig manure and an unfertilized control. We did not measure an appreciable increase in STP concentration below the 0.15 m depth. However, manure application at an N-based rate resulted in increased STP concentration in the 0–0.15 m depth interval. After 3-year, STP concentration in the N-based treatments (48 and 43 mg Olsen P kg−1 for solid and liquid respectively) were significantly greater than for the P-based treatments (26 and 17 mg Olsen P kg−1 for solid and liquid respectively). The mass of P in the leachate was small, ranging from a low of 1 g P ha−1 in 2009 to a high of 100 g P ha−1 in 2011. Both P- and N-based manure application rates produced no apparent risk of P leaching at our site, but the N-based manure application rate increased STP concentration in the surface soil, which could lead to the loss of P in surface runoff.

Effects of Land-Applied Ammonia Scrubber Solutions on Yield, Nitrogen Uptake, Soil Test Phosphorus, and Phosphorus Runoff.

Ammonia (NH) scrubbers reduce amounts of NH and dust released from animal rearing facilities while generating nitrogen (N)-rich solutions, which may be used as fertilizers. The objective of this study was to determine the effects of various NH scrubber solutions on forage yields, N uptake, soil-test phosphorus (P), and P runoff. A small plot study was conducted using six treatments: (i) an unfertilized control, (ii) potassium bisulfate (KHSO) scrubber solution, (iii) aluminum sulfate [Al(SO) ⋅14HO, alum] scrubber solution, (iv) sodium bisulfate (NaHSO) scrubber solution, (v) sulfuric acid (HSO) scrubber solution, and (vi) ammonium nitrate (NHNO) fertilizer. The scrubber solutions were obtained from ARS Air Scrubbers attached to commercial broiler houses. All N sources were applied at a rate of 112 kg N ha. Plots were harvested approximately every 4 wk and soil-test P measurements were made, then a rainfall simulation study was conducted. Cumulative forage yields were greater ( < 0.05) for KHSO (7.6 Mg ha) and NaHSO (7.5 Mg ha) scrubber solutions than for alum (6.7 Mg ha) or HSO (6.5 Mg ha) scrubber solutions or for NHNO (6.9 Mg ha). All N sources resulted in higher yields than the control (5.1 Mg ha). The additional potassium in the KHSO treatment likely resulted in higher yields. Although Mehlich-III-extractable P was not affected, water-extractable P in soil was lowered by the alum-based scrubber solution, which also resulted in lower P runoff. This study demonstrates that N captured using NH scrubbers is a viable N fertilizer.

Soil test phosphorus as affected by phosphorus budgets in two long-term field experiments in Germany

Phosphorus (P) is a limited resource but plays an important role in crop production. Because of the high P binding capacity in soils, changes in soil P availability due to different P management practices generally occur slowly. This study evaluated data of two long-term field experiments in Germany, which both focus especially on P management strategies. The Rostock field experiment (established in 1998, north-east Germany) considers organic and inorganic P sources in single and combined application and the Freising field experiment (established in 1978, south Germany) comprises different levels of inorganic P sources in combination with liming. Soil tests for available P were performed using double-lactate (DL) and calcium-acetate-lactate (CAL) extraction. For calculations of P budgets, the P removal with the harvest and the P supply through fertilizers were considered. Crop yields depended only partly on P supply and differences regarding crops sensitivity to P supply were found in the following order: beet > maize > spring cereals > winter cereals. Omitted P supply resulted in reductions of soil test P from about 42 to 29 mg kg−1 within 18 years in Rostock and from about 44 to 17 mg kg−1 within 38 years in Freising. Contents of soil test P were positively related with P budgets (Rostock: R2 = 0.70, Freising: R2 = 0.69). However, variations of soil test P occurred at both sites, a finding which could not be explained by P budgets and might be reasoned with vertical P transport. Our study shows that results of long-term experiments are important for the interpretation of soil P tests. The different responses of crops to P supply and the temporal variations in soil test P should be considered more in P fertilizer recommendations.

Use of manure nutrients from concentrated animal feeding operations

Abstract Over the past few decades, there has been a nationwide trend away from small livestock farms and toward large Concentrated Animal Feeding Operations (CAFOs). This shift results in concentrated manure production and introduces potential problems associated with its disposal. We analyzed data from 13 permitted CAFOs in southeastern Michigan, including 1187 occurrences of manure application from 12 of the CAFOs with available field-level data. CAFOs applied excess manure nutrients to cropland by applying to fields with soil phosphorus test levels >50 ppm (42% of all cases), applying to soybeans (7% of all cases), over-estimating crop yields in calculating plant nutrient requirements (67% of all cases), and applying beyond what is allowed by state permits (26% of all cases). This represents significant potential for redistribution of manure nutrients. The total amount of manure from all instances of over-application could be redistributed to fertilize over 4775 ha (11,800 acres) per year. Significant barriers to redistribution of manure exist, however, including cost, land availability, crop and soil need, transport logistics, and farmers' reluctance to use manure instead of inorganic fertilizer due to its variable composition. These findings are relevant to the harmful algal bloom and hypoxia issues in Lake Erie, which are driven by excess nutrients, and can be used to better inform science, modeling, and policy in the region.

Over‐Fertilization Does Not Build Soil Test Phosphorus and Potassium in Ohio

Core IdeasCorn and soybean yield seldom responded to P and K fertilization over 9 yr.Soil test P and soil test K significantly decreased from values initially in the recommended maintenance range.Corn Leaf P and Leaf K was often below the sufficiency concentration.Appropriate P and K fertilizer recommendations for corn (Zea maysL.) and soybean [(Glycine max(L.) Merr.] in Ohio are essential, as water quality and nutrient management issues in the region have intensified over the last several years. The objectives of this study were to: (i) evaluate corn and soybean grain yield response to P and K fertilization, (ii) examine soil test phosphorus (STP) and potassium (STK) and corn Leaf P and Leaf K trends, and (iii) compare the ability of soil and leaf tissue testing to reflect corn and soybean response to fertilization. We evaluated three P and K fertilizer rates, no fertilizer (0×), an estimated nutrient removal rate (1×), and twice the estimated nutrient removal rate (2×), in corn–soybean rotations at three sites over 9 yr. Grain yield was generally non‐responsive to P and K fertilization, with only 9 of 42 site‐years yielding significantly positive responses. Soil test P and K started in the maintenance range, but significantly declined with the 1× rate at two of three sites for P and at all sites for K. Furthermore, the 2× rate of P and K failed to build STP and STK at any site, with significant declines at one site. The results revealed an inability to maintain initial STP and STK levels with the 1× rate and call into question the suitability of current fertilizer P and K recommendations aimed at maintaining STP and STK. These recommendations require updating to better reflect fertilizer needs of modern corn and soybean.

Assessing edge-of-field nutrient runoff from agricultural lands in the United States: How clean is clean enough?

Excess nutrient loading from numerous sources (e.g., agricultural and urban runoff, treatment plant discharge, and streambank erosion) continues to adversely impact water resources, and determination of the cause(s) of accelerated nutrient enrichment has become a contentious and litigious issue in several US regions. This paper addresses one fundamental question: What are acceptable levels of nutrients in runoff from agricultural fields? It focuses on the field scale where farmers and ranchers make management decisions. Not answering this question limits the effectiveness of on-farm management and policy alternatives to address agriculture9s contribution. To answer the question, some might suggest “direct comparison” with reference site data, existing criteria/standards, or measured data compilations. Alternatively, “indirect assessments” using soil test phosphorus (P) levels, P indices, field-scale models, or certainty programs might be suggested. Thus, to provide a scientific basis for policy debate and management decisions related to nutrient runoff from agricultural fields, we evaluated “direct comparisons” with measured data from case studies and evaluated “indirect assessment” alternatives. While acknowledging that scientific challenges and practical realities exist for each alternative, we concluded that certainty programs offer the most promise for ensuring acceptable nutrient runoff, and that field-scale models linked with watershed decision support tools are the most promising for assessing impacts on downstream water quality. Recognizing the reality that some nutrient loss is unavoidable from natural and anthropogenic sources, agriculture, industry, and municipalities are each encouraged to commit to implementing enhanced management where needed to minimize their sector9s contribution to excess nutrients in our nation9s waters.

AVAIL Phosphorus Fertilizer Enhancer: Meta‐Analysis of 503 Field Evaluations

Core Ideas Meta‐analysis shows a significant yield increase of 2.1% with AVAIL+P fertilizer.Many AVAIL studies were not conducted under P responsive conditions.Likelihood of response increases with low soil test P and P rate and extreme pH.Average yield response increases to 4.6% when only likely to respond sites included.Enhanced efficiency fertilizer should be evaluated under P responsive conditions. AVAIL, a maleic‐itaconic copolymer acid marketed to enhance P fertilizers, has been studied on a variety of crop species. Data from all known field studies comparing P fertilization with and without AVAIL was amassed into a meta‐analysis of 503 field observations. The average yield increase was a modest, although statistically significant, 2.1% (P &lt; 0.0001). However, only 116 of these observations were conducted under conditions where a positive yield response to a P enhancement product would be expected– that is, low soil test phosphorus (STP), strong alkaline or acid pH, and low P fertilizer rate. As such, the data was parsed into a subset of only those observations that were evaluated under responsive conditions, resulting in a greater magnitude of a yield response to AVAIL at 4.6% (P &lt; 0.0001). Further parsing of the data, by eliminating any data not published in refereed or thesis/dissertation sources resulted in an average increase of 5.8% (P = 0.0039). AVAIL effectively increased yields when used appropriately under conditions where a P response was expected. Testing enhanced efficiency fertilizer products in a variety of conditions is useful, but the conclusions from the multitude of studies with AVAIL in environments where no response to P fertilizer enhancement product would be expected may lead to erroneous conclusions if the data is not further parsed and categorized. These data demonstrate the importance of applying fundamental soil fertility principles when designing and evaluating fertilizer crop response studies.

A comparison of soil tests for available phosphorus in long‐term field experiments in Europe

SummaryMost soil tests for available phosphorus (P) perform rather poorly in predicting crop response. This study was set up to compare different established soil tests in their capacity to predict crop response across contrasting types of soil. Soil samples from long‐term field experiments, the oldest &gt;100 years old, were collected in five European countries. The total number of soil samples (n = 218), which differed in cropping and P treatment, and originated from 11 different soil types, were analysed with five tests: ammonium oxalate (Ox), ammonium lactate (AL), Olsen P, 0.01 m CaCl2 and the diffusive gradient in thin film (DGT). The first three tests denote available P quantity (Q), whereas the last two indicate P intensity (I) of the soil solution. All five tests were positively related to the crop yield data (n = 317). The Q‐tests generally outperformed I‐tests when evaluated with goodness of fit in Mitscherlich models, but critical P values of the I‐tests varied the least among different types of soil. No test was clearly superior to the others, except for the oxalate extraction, which was generally poor. The combination of Q‐ and I‐tests performed slightly better for predicting crop yield than any single soil P test. This Q + I analysis explains why recent successes with I‐tests (e.g. DGT) were found for soils with larger P sorption than for those in the present study. This systematic evaluation of soil tests using a unique compilation of established field trials provides critical soil P values that are valid across Europe.Highlights We compared soil P tests for predicting crop response across contrasting soil types. No test was clearly superior to the others except for the oxalate extraction, which was generally poor. This study suggests that intensity tests do not perform markedly better than quantity tests. The evaluation of soil P tests on this unique dataset provided critical soil P values across Europe.

Using Topsoil Thickness to Improve Site‐Specific Phosphorus and Potassium Management on Claypan Soil

Core Ideas Topsoil depth influences P and K dynamics on claypan soils. Most P and K dynamics were inversely affected by depth to claypan. Accounting for depth to claypan could improve P and K fertilizer management. Precise P and K fertilizer management on claypan soils can be difficult due to variable topsoil thickness, or depth to claypan (DTC), across landscapes, nutrient supply from subsoils, and crop removal. Therefore, a study was performed to determine if DTC could be used to improve P and K management for corn (Zea mays L.), soybean [Glycine max (L.)], and switchgrass (Panicum virgatum L.). Research was conducted on a claypan soil at the University of Missouri's (MU) South Farm Research Center in Columbia, MO, from 2009 to 2016. Corn, soybean, and switchgrass were grown each year on 16 plots with constructed DTC ranging from 0 to 94 cm. Surface soil samples for soil test phosphorus (STP) and potassium (STK) were collected in the early spring of 2009, 2015, and 2016. Fertilizer was applied shortly after soil sampling in 2009 and 2015 based on the MU buildup recommendation. Results in the spring of 2015 showed that STP increased 0.53, STK decreased 4.4, and the phosphorus buffering index (BIP) decreased 0.94 kg ha−1 with each 1 cm increase in DTC. Most importantly, across the 2015 growing season the amount of fertilizer K needed to raise soil test potassium by 1 kg ha−1 (REQK) was four times greater at DTC of 44 than 0 cm. These relationships show that accounting for DTC could improve current fertility guidelines by applying more, or more frequent P, and less K on shallow soils.

Modeling Soil Test Phosphorus Changes under Fertilized and Unfertilized Managements Using Artificial Neural Networks

Core Ideas An artificial neural network was developed to describe soil P dynamics. The model accurately predicts soil test P increases and decreases. A meta‐model was derived to apply the build‐up and maintenance philosophy. The build‐up and maintenance criteria have been introduced for P fertilizer management in the Pampas of Argentina. However, methods for predicting soil test P changes under contrasting fertilizer rates are not available. We performed a meta‐analysis using results from 18 local field experiments performed under the most common crop rotations, in which soil test P changes with and without P fertilization and soil P balance were assessed. We assembled 329 soil test P variation data sets corresponding to a period 12 yr and 129 P balance records. The P balance was not a good predictor of annual soil test P changes (R2 = 0.33). In 38% of the cases, the P balance and soil test P changes showed opposite trends. Polynomial regression and artificial neural networks were tested for soil test P modeling. The neural networks performed better than the regressions (R2 = 0.91 vs. 0.83; P &lt; 0.01). The network that yielded the best results used the initial soil test P level, the P fertilization rate and time as inputs. According to the model, unfertilized crops growing in soils with low initial P levels (soil test P = 10 mg kg−1 or lower) were subjected to only small decreases in soil test P levels, whereas greater decreases occurred in soils with initial high P levels. For fertilized crops, the model showed that P‐rich soils were less enriched in P than P‐poor soils. A simple meta‐model was developed for the prediction of soil test P changes under contrasting fertilizer managements.

Investigation of acid hydrolysis reactions of polyphosphates and phytic acid in Bray and Mehlich III extracting solutions

Soil test phosphorus (STP) (Bray P-1, Mehlich III) was developed to predict the plant available P in agricultural soils in the USA. The acidic STP extracting solutions were intended to extract phosphate from alkaline earth metal-based solubility products and or adsorbed species on amorphous metal hydroxides or phyllosilicates in soils. However, the accuracy of STP in predicting plant available phosphate has often been questioned due to potential acid hydrolysis of poly- and organic-P in soils during the STP extraction. The objective of the study was to investigate the acid hydrolysis reaction of reference poly- and organic-P compounds (1.25–3.75 mM) in Bray and Mehlich III extraction solutions using spectrophotometric methods. The results showed that both tripolyphosphate and pyrophosphate readily underwent the acid hydrolysis reaction over 2 h, whereas phytic acid did not hydrolyze. The results suggest an overestimation of dissolved reactive phosphate from these polyphosphates should be considered when evaluating the STP data.

Switchgrass forage yield and biofuel quality with no-tillage interseeded winter legumes in the southern Great Plains

ABSTRACTInformation is limited on using winter legumes as a source of nitrogen (N) intercropped with switchgrass in the southern Great Plains of the United States. The objectives of this study were to evaluate N contribution of several winter legumes to switchgrass, and to determine the influence of winter legumes on biofuel quality and soil fertility status. Field experiments were conducted at two locations in Oklahoma in which six winter legumes and four rates of N fertilizer were studied over a 3-year period. Winter legumes did not increase switchgrass forage yield, cellulose, lignin, and hemicellulose concentrations at any location. Soil organic matter (OM), nitrate-N (NO3-N), soil test phosphorus (P), soil test potassium (K), and soil pH remained unchanged. In contrast, applying inorganic N only increased switchgrass yield. This study demonstrated that southern Great Plains may not be conducive to utilizing legumes as the primary N source for switchgrass.

Vegetative Composition, Arbuscular Mycorrhizal Fungi Root Colonization, and Biological Nitrogen Fixation Distinguish Organic and Conventional Perennial Forage Systems

Core Ideas Conventional and organic forage fields did not differ in total forage yield. Legume content was more than two times greater under organic management. Total forage biological nitrogen fixation was greater under organic management. Arbuscular mycorrhizal fungi root colonization was greater under organic management. Arbuscular mycorrhizal fungi root colonization was inversely related to soil test P concentrations. Low concentrations of Olsen soil test phosphorus (STP) on organic dairy farms in Canada have been reported, however, the resulting impact on crop productivity is unclear. This study evaluated mixed forage (alfalfa [Medicago sativa L.]/timothy [Phleum pratense L.]) productivity, nutrient uptake, and related soil biological and biochemical properties on organic and conventional dairy farms in Ontario, Canada. Despite a lower STP concentration, mean organic forage yield (8.0 Mg DM ha−1) did not significantly differ from conventional (9.5 Mg DM ha−1). The proportion of N derived from biological nitrogen fixation (BNF) in alfalfa did not differ by management system, however the total forage BNF‐N was greater in the organic fields due to a twofold increase in legume proportions. Alfalfa tissue P concentrations, above the suggested critical value of 2.0 g kg−1 in all systems, were positively correlated with STP (r = 0.82, P = &lt; 0.0001) and significantly greater in conventional (3.3 g kg−1) than organic (2.4 g kg−1). Mean arbuscular mycorrhizal fungi (AMF) root colonization of alfalfa was greater in organic systems (37 vs. 23%) and was negatively correlated with STP (P = 0.0006). Management systems did not differ in soil alkaline and acid phosphatase activity, or phytase‐labile P. It was concluded that legume‐based forages can produce acceptable yields at low STP concentrations (&lt;10 mg kg−1) and supports the importance of legumes, legume BNF, and biological processes linked to soil P cycling in maintaining productivity in organic dairy farming systems.

Effects of extraction time and phosphorus speciation on soil test phosphorus data: A case study of Illinois agricultural soils

Bray P-1 and Mehlich III STP extractions aim to assess the concentrations of labile P in soils. It is unknown, however, how the observed quantity of labile P is affected by the release of variable P species. The kinetics of orthophosphate (Pi), organic-P (Po), and colloidal P were evaluated in manure-amended and chemical fertilizer-amended Central Illinois agricultural soils using Bray-1 and Mehlich III extractants. In both soils, Bray and Mehlich III extractable P increased with increasing time. The extracted P species are not only Pi but also Po and colloidal P. Between 10 and 15% of total Po was extracted from each soil with manure amended soils releasing more total Po than fertilizer amended soils. BrayP-1 and Mehlich III extracted colloidal P from manure-amended and fertilizer-amended soils, but concentrations were only significant after 1–3h. The results indicate that P speciation and extraction time have major impacts on the results of STP extractions, therefore, to fertilizer recommendation.

Changes in Soil Phosphorus Fractions Resulting from Crop Residue Removal and Phosphorus Fertilizer

ABSTRACTIt is crucial to know how management factors influence soil test phosphorus (P) since non-point P sources for surface waters are becoming recognized as a problem throughout the USA. Phosphorus fertilizer and crop residue can impact the cycling of P in soils. An eight-year crop residue removal and P fertilization (0, 7.3, 14.7 and 29.4 kg P/ha) as triple superphosphate (TSP) experiment were conducted to determine the effect of P applications on soil P fractions. Significant differences in Bray-l extractable P were observed after only one year of P applications. Extractable P at the highest P rate was significantly higher than all the other rates. For each 5.6 kg P/ha added or removed, Bray-l P changed by 1 mg/kg. Fertilizer P applications did not significantly change the organic P (Po) levels, microbial P (Pm) or soil pH, whereas residue treatments had effects on them except for soil pH. Residue-retained plots had significantly higher Pm in the last two years of study, and Po in the 8th year, compared with residue-removed plots.

Shifting from N-based to P-based manure management maintains soil test phosphorus dynamics in a long-term corn and alfalfa rotation

Multiyear repeated dairy manure application based on nitrogen (N) needs of corn (Zea mays L.) increases soil test phosphorus (P) concentration and risk of P runoff over time. A P removal based application of manure adds less P but could impact yield. A corn field trial was implemented in New York in 2001 and rotated into alfalfa (Medicago sativa L.) in 2006 to examine soil test P dynamics over a corn-alfalfa rotation (2001 to 2011). Treatments were annual spring applications of N-based versus P removal based compost (74 and 46 Mg ha−1, respectively), liquid dairy manure (196 and 68 m3 ha−1, respectively), and two control treatments (0 N and 112 kg ha−1 sidedress N). No manure or compost was applied during the alfalfa years. In the five corn years, Morgan-extractable soil test P concentrations increased 4- and 2-fold for N-based and P-based manure and 6- and 4-fold for N-based and P-based compost, respectively, consistent with greater P balances possibly combined with differences in P fractions in each source. Soil test P concentrations declined in the alfalfa years but reached initial concentration only in the P-based manure system. Our findings show, for the first time in dairy forage rotations, the long-term sustainability benefits of P-based manure management and emphasize the importance of rotation fertility management rather than single-year P management. In conclusion, we demonstrated that a shift from N- to P-based manure allocation in corn years is a good approach to maintaining soil test P concentrations over the rotation while for higher application rates, a greater number of years in alfalfa than corn might be needed to prevent soil test P from building over the rotation.