History Of Manure Application Research Articles

Increased soil-derived N2O production following a simulated fall-freeze–thaw cycle: effects of fall urea addition, soil moisture, and history of manure applications

Increased soil-derived N2O production following a simulated fall-freeze–thaw cycle: effects of fall urea addition, soil moisture, and history of manure applications

Phosphorus release from intact soil monoliths of manure-amended fields under simulated snowmelt flooding.

Anaerobic conditions developed in soils with flooding can enhance the release of soil P to overlying water, but little information is available for soils with a long history of manure application. We examined the P release from manure-amended soils under simulated snowmelt flooding. Intact monoliths from manured (solid swine manure [SSM] or liquid swine manure [LSM]) and unamended (control) field plots were collected from Carman, Manitoba. Monoliths were frozen for 7 d, thawed, flooded, and incubated at 4±1°C. Redox potential, pH, and concentrations of dissolved reactive P (DRP), Ca, Mg, Fe, and Mn in pore water and floodwater were determined weekly up to 56 d after flooding (DAF) and at 84 DAF. Redox potential decreased with DAF with a greater and more rapid decrease in SSM (from ∼300 to<0mV by 84 DAF) compared with LSM and control (∼100mV by 84 DAF). Pore water and floodwater DRP concentrations were significantly greater in manured treatments than in the control at all DAFs and in SSM than in LSM for most DAF. Whereas floodwater DRP concentrations remained relatively stable in the control treatment, concentrations in manured treatments increased substantially from the onset of flooding to 35-42 DAF (threefold to fourfold increase) and remained relatively stable thereafter. Significantly greater P release from SSM- than from LSM-treated monoliths was due to greater input of P and the higher organic matter content in SSM-treated soils. These favored the rapid development of anaerobic conditions that further induced P release.

The long-term effects of cattle manure application to agricultural soils as a natural-based solution to combat salinization

Excessive exchangeable sodium and high soil pH result in structural destabilization of sodic soil. The long-term application of cattle manure is an important management practice that can affect the physical properties of sodic soil. Experiments were carried out using a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays L.) fields with annual manure application since 2011 (M2011), 2006 (M2006), 2001 (M2001) and 1995 (M1995) were used as the experimental treatments; manure was applied at a rate of 10,000 kg ha−1 yr−1 on an oven-dry weight basis, and corn without manure application was used as the control. The results indicated that long-term application of manure to sodic soil resulted in significant increases in soil porosity, water-holding capacity, and saturated hydraulic conductivity (Ks) and a decrease in bulk density in comparison to the control treatment. In addition, manure application significantly increased macro-aggregate formation and the mean weight diameter (MWD). Based on stepwise regression analysis, the dominant independent variable that affected aggregate stability was water-stable aggregates (WSAs) of 0.5–1 mm, and the dominant independent variable that affected both capillary porosity (ƒc) and non-capillary porosity (ƒn) was WSAs of 0.25–0.5 mm. MWD, ƒn and especially soil organic matter (SOM) were the dominant attributes that affected Ks. It was concluded that improved soil physical properties are related to soil aggregation, resulting mainly from macro-aggregate formation, particularly WSAs of 0.25–0.5 and 0.5–1 mm. This is due to binding-agent production and increased SOM from annual manure application.

Assessment of long-term soil dynamics at manured fields with field measurement and interviews: a case study in the semi-arid Ethiopian Rift Valley

ABSTRACTAssessment of long-term (more than 20 years) soil fertility dynamics is rare in Sub-Saharan Africa (SSA). It is because soil quality assessments have been conducted in research stations, which are difficult to continue in the long term mainly due to lack of funds in SSA. Farmers in the semi-arid Ethiopian Rift Valley (NERV) cultivate maize with long-term manure application to the fields (aradas). The history of manure application was carefully ascertained from farmers, and 40 manured aradas for 20 years and more and 40 unmanured fields were selected. Soil chemical properties (SOC, total N, Olsen P, CEC, exchangeable cations, EC, and pH) were analyzed, while on-site NO3-N and soil physical properties (soil compaction, saturated hydraulic conductivity, and water retention capacity) were measured. The manured aradas increased SOC, total N, P, CEC, K, Na, Mg, EC, and NO3-N and lowered Ca and pH. The arada soils lowered soil compaction and bulk density and increased porosity. No consistent changes in hydraulic conductivity and water retention capacity were observed, probably because of plough pans underlying the surface soil layer across NERV. Soil quality assessment to diagnose farmers’ long-term manure application based on field measurement and interviews can be an appropriate approach in SSA.

Effects of Manure History and Nitrogen Fertilizer Rate on Sugar Beet Production in the Northwest US

Core Ideas Manure can have a lasting effect on soil fertility and crop production. Sugar beet yields are increased on soils with a manure history. Sugar beet quality can be decreased under heavy past manure applications. Past manure applications effects on sugar beet (Beta vulgaris L.) production needs to be assessed in the areas where manure applications to crop land are common. A study was conducted in Kimberly, Idaho in 2014 and 2016 to assess the effects of manure application history and N rates on sugar beet production on a Portneuf silt loam (coarse‐silty mixed mesic Durixerollic Calciorthid) soil. From 2004 to 2009, manure was applied to plots every 2 years (M1, total application = 60 tons/acre), every year (M2 total application = 106 tons/acre), or no manure (F, commercial fertilizer only). In spring 2014, the manure main plots were split in half with half receiving a commercial fertilizer N rate treatment superimposed on the main plots in 2014 and the other half receiving the superimposed N rate treatments in 2016. In 2014 and 2016, the commercial fertilizer N rates were 0, 30, 56, 77, 100, 141, 180, and 202 lb/acre. The study design was a randomized block split‐plot with manure history as the main plot and N rate as the subplot. During both years of the study, N rate did not affect sugar beet yields, but M1 and M2 treatments had higher sugar beet root yields compared to the F treatment. Averaged across all N rates, root yields from both manured treatments were 12 and 36% greater than the F treatment in 2014 and 2016, respectively, although sugar yield was only significantly greater in 2016. Manure applications will impact sugar beet production for several years after manure applications have ceased.

Phytoextraction of nitrogen and phosphorus by crops grown in a heavily manured Dark Brown Chernozem under contrasting soil moisture conditions

ABSTRACTPhytoextraction of excess nutrients by crops in soils with a long history of manure application may be a viable option for reducing the nutrient levels. This greenhouse study examined the effectiveness of six growth cycles (40 d each) of barley, canola, corn, oat, pea, soybean, and triticale at extracting nitrogen (N) and phosphorus (P) from a Dark Brown Chernozem that had received 180 Mg ha−1 (wet wt.) of beef cattle feedlot manure annually for 38 years. Moisture content during the study was maintained at either 100% or 50% soil field capacity (SFC). Repeated cropping resulted in an overall decrease in dry matter yield (DMY). The decrease in N and P uptake relative to Cycle 1 was fastest for the cereal grains and less pronounced for the two legumes. However, cumulative N uptake values were significantly greater for corn than the other crops under both moisture regimes. The reduction in soil N was greater under the 100% than the 50% SFC. These results indicate that repeated cropping can be a useful management practice for reducing N and P levels in a heavily manured soil. The extent of reduction will be greater for crops with high biomass production under adequate moisture supply.

Nitrogen Mineralization as Affected by Temperature in Calcareous Soils Receiving Repeated Applications of Dairy Manure

Core Ideas Prediction of N mineralization is dependent on accurate rate correction factors and the ratio of the change of the rate coefficient of mineralization for every increase in temperature of 10°C (Q10) based on temperatures observed in the region. Few studies have investigated N mineralization in soils receiving repeated applications of manures at low temperatures. This study determined that manure additions may lead to larger Q10 values at low temperatures and growing degree‐days may aid in predicting N release from these soils. There are currently no tools available to help predict N mineralization for the silty soils found in southern Idaho receiving repeated manure applications. This experiment aimed to determine the effect of temperature on N mineralization from control and manured soils, develop N mineralization rate correction factors for temperature [ratio of the change in the rate coefficient of mineralization for every 10°C increase (Q10) and temperature factors], and create a simple model for predicting N mineralization as a function of growing degree‐days. Manured and control soils underwent a 49‐d laboratory incubation at five temperatures (–14, 4, 10, 23, and 30°C); soil inorganic N concentration was determined at 0, 1, 3, 5, 7, 13, 20, 28, 35, 42, and 49 d. Net N mineralization was fitted to a zero‐order model, where the rate coefficient (k) values for the manured soil ranged from 0.017 to 1.28 mg kg–1 soil d–1 over the five temperature treatments, whereas k in the control measured 0.028 to 0.53 mg kg–1 soil d–1. The calculated Q10 values from –14 to 30°C were 2.7 and 2.0 for the manured and control soils respectively. At low temperatures (–14 to 4°C), the Q10 for manured soil was 5.1 compared with 1.5 for the control. This suggests that manure additions may lower the temperature threshold for N mineralization under near frozen soil conditions. Manure treatment effects on the temperature factor were not observed, suggesting that manure application history may not need to be considered when developing temperature factor coefficients for N mineralization models.

Net Greenhouse Gas Budget and Soil Carbon Storage in a Field with Paddy–Upland Rotation with Different History of Manure Application

Methane (CH4) and nitrous oxide (N2O) fluxes were measured from paddy–upland rotation (three years for soybean and three years for rice) with different soil fertility due to preceding compost application for four years (i.e., 3 kg FW m−2 year−1 of immature or mature compost application plots and a control plot without compost). Net greenhouse gas (GHG) balance was evaluated by integrating CH4 and N2O emissions and carbon dioxide (CO2) emissions calculated from a decline in soil carbon storage. N2O emissions from the soybean upland tended to be higher in the immature compost plot. CH4 emissions from the rice paddy increased every year and tended to be higher in the mature compost plot. Fifty-two to 68% of the increased soil carbon by preceding compost application was estimated to be lost during soybean cultivation. The major component of net GHG emission was CO2 (82–94%) and CH4 (72–84%) during the soybean and rice cultivations, respectively. Net GHG emissions during the soybean and rice cultivations were comparable. Consequently, the effects of compost application on the net GHG balance from the paddy–upland rotation should be carefully evaluated with regards to both advantages (initial input to the soil) and disadvantages (following increases in GHG).

Effects of chlortetracycline on soil microbial communities: Comparisons of enzyme activities to the functional diversity via Biolog EcoPlates™

Veterinary antibiotics (VAs) can enter agricultural soil by the application of animal excrements. However, the response of soil microorganisms to VAs is not well understood. Therefore, a 45-day microcosm experiment was conducted to ascertain the impact of chlortetracycline (CTC) on soil microbial communities. In this study, CTC was applied to soil samples with no previous antibiotic-containing manure application history at three concentrations of 1, 10, and 100 mg/kg soil. Soil samples were taken after 1, 6, 12 and 45 day(s) of incubation to determine the dissipation of CTC using HPLC. Meanwhile, to investigate the effect of CTC on microorganisms, microbial activities in the cultivable and the actual community were determined using Biolog EcoPlates™ and enzyme activities, respectively. It was demonstrated that CTC dissipated faster at lower spiking levels. At the end of the experiment, no CTC could be extracted in all treatments, except for C100. The enzyme activities were enhanced on the first day and then were significantly inhibited by CTC for up to 45 days. This inhibition was especially true for activities of dehydrogenase and urease, whereas phosphatase activities were slightly affected. The results demonstrated that CTC contamination could pose a selective pressure on soil microorganisms, despite its rapid decline in the extractable concentration. However, community-level physiological profiles (CLPP) that were assessed using Biolog EcoPlates™ displayed different susceptibilities to the addition of CTC: it responded rapidly to CTC-amendment and were improved strongly by CTC on the first day, whereas no effect was detected thereafter. It was suggested that the Biolog EcoPlates method was more suitable for short-term toxicity tests than for the relatively long-term effects of pollutants on microbial communities.

Distribution of carbon and nitrogen in water-stable aggregates and soil stability under long-term manure application in solonetzic soils of the Songnen plain, northeast China

Excessive exchangeable sodium and high pH significantly decrease soil structural stability and permeability. Long-term application of cattle manure is an important management practice that can affect water-stable aggregates (WSAs), as well as aggregate stability and distribution of soil organic carbon (SOC) and total nitrogen (TN) in solonetzic soils. Experiments were carried out in a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays) with manure applied for 1, 5, 12, and 17 years were used as the experimental treatments and corn without manure application was used as a control. Soil properties, including WSAs, mean weight diameter (MWD), and SOC and TN concentrations in bulk soils and WSAs, were measured across all treatments. The relationships among the measured soil attributes were determined using stepwise regression analysis. Results indicated that micro-aggregates mainly accumulated in soils without manure application, while manure application significantly increased macro-aggregates formation. MWD was highest when manure was applied to the soil for 1 year, decreased after 5 years, and increased again after 12 years. SOC and TN concentrations in bulk soils and WSAs increased with the number of years of manure application, with the highest concentrations observed for 17 years in bulk soils. Stepwise regression analysis showed that WSAs 2–5 mm, SOC in WSAs 0.25–0.5 mm, and TN in WSAs 0.1–0.25 mm were dominant independent variables affecting aggregate stability, and that SOC in WSAs 0.25–0.5 mm and TN in WSAs <0.1 mm were dominant independent variables affecting SOC and TN concentrations in bulk soils, respectively. Long-term application of manure to a solonetz significantly increased macro-aggregates and aggregate stability as well as SOC and TN in bulk soils and all aggregate sizes. These results are likely related to binding agent production as well as C and N accumulation from manure application.

Carbon mineralization kinetics and soil biological characteristics as influenced by manure addition in soil incubated at a range of temperatures

This study was conducted to investigate the effects of incubation temperature on mineralization of native pools of C from a soil with a history of manure application, compared to a non-manured soil. Net C mineralization, microbial community structure, biomass size, and metabolic quotient ( qCO 2) were measured. Mineralization at cooler temperatures followed zero-order kinetics, indicating a non-limiting supply of substrate. First-order kinetics dominated at warmer temperatures as substrate supply increasingly limited microbial respiration. The soil with a history of manure application had a larger microbial biomass than the non-manured soil, and higher rates of C mineralization. There was a trend toward decreased biomass sizes with increasing incubation temperature. Bacterial DNA T-RFLP profiles were affected by incubation temperature and time with a significant difference in community structure detected after soils had been incubated for 120 days, as well as after incubation at 35 °C. Fungal DNA T-RFLP profiles indicated a distinct community in soils incubated at 35 °C, regardless of the length of the incubation. The key findings from the study were that C mineralization from native pools of organic matter does not follow Arrhenius kinetics at high temperatures, and that incubation of soils outside of their normal temperature range can alter soil biological characteristics which may impact estimates of mineralization parameters.

Influence of manure from pigs fed chlortetracycline as growth promotant on soil microbial community structure

Chlortetracycline (CTC), an antimicrobial compound used in animal production, is not sorbed or degraded in the animal, and may enter the field environment through manure land-spreading. This study determined the influence of a single application of manure with or without CTC on field soil microbial community characteristics. Manures from swine fed unamended or CTC-amended rations were applied at 7,000 kg solid ha−1 to a Brandt silty clay loam soil that had no known prior history of manure application. Soil samples taken 1, 7, 28, or 42 days after treatment (DAT) were analyzed for aerobic culturable counts on R2A agar and most probable number using 2,4-D as sole carbon source. Soil extracts of 1, 7, and 42 DAT samples were subjected to polymerase chain reaction followed by denaturing gradient gel electrophoresis (DGGE) analysis of the V3 region of the 16S rRNA gene pool. Gels were analyzed by Neighbor Joining based on Euclidean distance and Raup–Crick multivariate statistical analysis, and selected bands were extracted to identify predominant community members. Both manure applications initially changed soil microbial diversity, however, communities appeared to converge over time, so that no long-term significant effect was detected with this single application.

Long‐Term Changes in Mollisol Organic Carbon and Nitrogen

Conversions of Mollisols from prairie to cropland and subsequent changes in crop production practices in the Midwestern USA have resulted in changes in soil organic matter. Few studies have used archived samples, long-term resampling of soils to a depth of 1 m, and space for time studies to document these changes. We resampled soils by depth (0-100 cm) in fields at 19 locations in central Illinois on poorly drained Mollisols that were in corn (Zea mays L.) and soybean (Glycine max L. Merr.) rotations, were tile drained, and had no known history of manure application in recent decades. Three fields were paired with virgin prairie remnants, two had grass borders that were sampled, and 16 had been previously sampled in 1901 to 1904 or 1957 under various land uses (virgin prairie, cultivation, grass cover). The soils had large amounts of C and N in the profile, with mean values of 175 [corrected] Mg C ha(-1) and 16.1 Mg N ha(-1) for the 18 cultivated fields sampled in 2001 and 2002. We confirmed a large reduction in organic C and total N pools from conversion of prairies to annual cultivation and artificial drainage and documented no change in these organic matter pools of cultivated soils during the period of synthetic fertilizer use (1957--2002). Cultivated fields had soil C and N concentrations typically 30 to 50% less than virgin prairie soils. Smaller but significant declines in C and N concentrations were found when comparing 1900s cultivated fields to concentrations in 2002, after another 100 yr of cultivation, and in comparing 1957 grass covered fields that had been converted to annual cultivation before 2002. The reduction in organic matter after cultivation of prairies occurred mostly in the top 50 cm of soil, with evidence of translocation of C and N from these upper layers to the 50- to 100-cm depth, possibly enhanced by tile drainage. For these Mollisols, declines in organic matter were likely completed by the 1950s, with organic matter pools in a steady state under the production practices in place from the late 1950s through 2002.

Estimating Yield and Yield Response using Computer Simulation of Plant Available Nitrogen from Soil Organic Matter and Manure

The amount of organic N mineralized as plant available nitrogen (PAN) from soil organic matter (SOM) during a crop growing season has proved difficult to assess using traditional soil testing. It was the objective of this study to evaluate the potential for computer simulation in the estimation PAN from SOM during the growing season. A secondary objective was to evaluate this approach as a way to identify soils where crops would be non‐responsive to fertilizer N. Plant available N from SOM was estimated using a simple, first‐order kinetic equation. Plant available N from manure was estimated using the computer model, DECOMPOSITION. Plant available N from the previous crop and from preplant fertilizer N were taken from published data. No additional fertilizer N was applied. Corn (Zea mays L.) yield was significantly related to total PAN (sum of SOM N, manure N, crop residue N, and preplant N) and the response of corn to total PAN was typical of previously published values. Total PAN was not a good predictor of soils where corn was nonresponsive to fertilizer N, while a history of manure applications was a good predictor of nonresponsiveness.

Evaluation of phosphorus retention equations for Manitoba soils

One of the key factors in phosphorus management is the P retention capacity (PRC) of the soil. In our previous study, we formulated several equations for estimating the phosphorus retention capacity of Manitoba soils. The objectives of the current study were to evaluate these equations using independent soil samples and to evaluate the influence of manure application on the predictive ability of these equations. Forty representative surface soil samples (20 soils with history of manure application and 20 without manure application history) were collected from across Manitoba. The P retention index (P150) and Langmuir adsorption maximum (Smax) were determined in the laboratory. The measured P retention capacities were then compared with those estimated using the formulated equations. Surprisingly, P150, which was obtained from a single measurement, was more robust than Smax that was obtained from at least 17 measurements as the equations provided a better estimate of P150 than Smax. Equations that were based on soil particle sizes (either percent clay or percent sand) provided poor estimates of soil PRC for the whole soil collection. However, when the soils were grouped on a pH basis, soil particle size worked better for soils with pH &lt;7 than for soils with pH ≥7. The equations also worked better for soils with pH similar to those of the soils that were used to formulate the P retention equations. The accuracy of the predicted P sorption capacity improved with the manured soils due to the direct influence of manure application on soil properties that influence P retention such as Ca and Mg. Overall, the combination of CaM3, MgM3 and AlOx provided the best estimate of the PRC of Manitoba soils. Key words: Soil phosphorus, calcareous soils, phosphorus sorption, phosphorus retention, phosphorus retention capacity, estimating phosphorus retention capacity

Effect of amendment of manure and corn residues on soil N mineralization and enzyme activity

Understanding the effect of manure and crop residue application on N mineralization in soil is crucial in order to minimize nitrate contamination of surface and groundwater. Besides, developing an alternative management practice for corn residue burning is of great importance and needs more knowledge about inorganic N dynamics. Here we conducted a laboratory experiment to study the effect of corn residue application on inorganic N dynamics and soil enzyme activities in soils with different manure fertilization histories. The laboratory experiment was a combination of 3 fertilization histories of: 0, 50 and 100 Mg cow manure ha−1 year−1 for five consecutive years; and 3 residue treatments including: no residue, corn shoot and corn root application. We monitored inorganic N periodically during 20 weeks of incubation. We also monitored the activities of urease, L-asparaginase, L-glutaminase and β-glucosidase before and after incubation. Our findings show that for residue-amended soils, inorganic N decreased in the first 2 weeks of incubation by 50 to 86%, followed by a gradual increase. In contrast, for control soils without residue amendment, the inorganic N concentration increased from 64 to 86% during the first week of incubation. Our results thus show that the application of corn residues can control the flush of inorganic nitrogen and reduce the potential of nitrate leaching in manure-applied soils. Furthermore, manure application at the highest rate increased the activity of urease by 47%, L-asparaginase by 70%, L-glutaminase by 60% and β-glucosidase by 78%. β-glucosidase increased due to corn shoot application by about 8% and was the most responsive enzyme to the treatments. Overall, the enzyme activities were more influenced by manure application history than corn residue application.

Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application

Indicators of soil fertility are needed for the effective management of organic farming systems. Sustainable management hinges upon our gaining an improved understanding of C and N dynamics. The influence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG Org-CG > Conv. Amino sugar-N (AS-N) contents, which reflect microbially derived N, did not differ among systems and concentrations were quite high (346.5 mg AS-N/kg soil in the 0–50 cm depth). This, and soil variability were attributed to the sites’ history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (≈7.5% of total SOC) of POM-C were quite low and did not differ among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.

Assessment of the Amino Sugar–Nitrogen Test on Iowa Soils: I. Evaluation of Soil Sampling and Corn Management Practices

A soil N test capable of measuring the soil organic N fraction that contributes to plant available N would be useful to corn (Zea mays L.) producers as they make N fertilizer rate decisions. The objectives of this study were to evaluate the effects of soil sampling time, sampling depth, long‐term crop rotation, and long‐term N fertilizer application on the amino sugar–N test (ASNT). Soil samples from 43 N rate trials were analyzed using the ASNT procedure. The ASNT was also determined on soil samples from two sites having several crop rotations and N fertilizer rates in place for the past 18 and 24 yr. The ASNT results were consistent over time but show variation from week to week and were more variable at sites with high soil organic C or manure application history. Amino sugar–N test values from the 0‐ to 15‐cm soil depth were usually greater than the 15‐ to 30‐cm or 0‐ to 30‐cm depths. Crop rotations that included alfalfa (Medicago sativa L.) resulted in greater ASNT values than continuous corn and corn rotated with soybean [Glycine max (L.) Merr.]. Therefore, sampling depth and rotation should be taken into consideration when calibrating the ASNT. Long‐term N fertilization rate did not consistently influence ASNT values. Differences between soils had larger effects on the ASNT than corn management practices. Sampling before N application in the fall, early spring before planting, or late spring during the growing season should provide similar ASNT results and flexibility in sample collection before N application.

Phosphorus Speciation in Manure and Manure-Amended Soils Using XANES Spectroscopy

Previous studies suggested an increase in the proportion of calcium phosphates (CaP) of the total phosphorus (P) pool in soils with a long-term poultry manure application history versus those with no or limited application histories. To understand and predict long-term P accumulation and release dynamics in these highly amended soils, it is important to understand what specific P species are being formed. We assessed forms of CaP formed in poultry manure and originally acidic soil in response to different lengths of mostly poultry manure applications using P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. Phosphorus K-edge XANES spectra of poultry manure showed no evidences of crystalline P minerals but dominance of soluble CaP species and free and weakly bound phosphates (aqueous phosphate and phosphate adsorbed on soil minerals). Phosphate in an unamended neighboring forest soil (pH 4.3) was mainly associated with iron (Fe) compounds such as strengite and Fe-oxides. Soils with a short-term manure history contained both Fe-associated phosphates and soluble CaP species such as dibasic calcium phosphate (DCP) and amorphous calcium phosphate (ACP). Long-term manure application resulted in a dominance of CaP forms confirming our earlier results obtained with sequential extractions, and a transformation from soluble to more stable CaP species such as beta-tricalcium calcium phosphate (TCP). Even after long-term manure application (> 25 yr and total P in soil up to 13,307 mg kg(-1)), however, none of the manure-amended soils showed the presence of crystalline CaP. With a reduction or elimination of poultry manure application to naturally acidic soils, the pH of the soil is likely to decrease, thereby increasing the solubility of Ca-bonded inorganic P minerals. Maintaining a high pH is therefore an important strategy to minimize P leaching in these soils.

Long-Term Dynamics of Phosphorus Forms and Retention in Manure-Amended Soils

Phosphorus (P) leaching from soils with elevated P levels due to manure applications is increasingly becoming a concern as a source of eutrophication of streams and lakes. This study investigates the relationship between organic and inorganic P in soil pools and equilibrium leachate along a chronosequence of poultry and dairy manure additions in New York state. Resin-extractable P (molybdate-reactive P, RP) and total soil P reached very high levels of 2330 and 7343 mg of P kg(-1), respectively, after more than 25 years of continuous manure applications. After long-term manuring, the ability of these soils to retain additional P was low (Langmuir maximum sorption potential of 51-59 g of P kg(-1)) and equilibrium leachate concentrations of total dissolved P (TDP) were high (5.5-7.6 mg L(-1); saturated conditions, 0.15-m lysimeters in closed loop). Total dissolved P concentrations in equilibrium leachate increased linearly (r= 0.737) to a total soil P of 4500 mg kg(-1) and increased to a greater extent above 4500-5500 g kg(-1) (change point equivalent to about 1500 mg kg(-1) Mehlich 3-extractable RP). The proportion of dissolved unreactive P (DUP) in equilibrium leachate decreased from 90% of TDP in fields with a short manure application history to 2% of TDP where mainly poultry manure had been applied for >25 years, while unreactive P (UP) in soil decreased from 44% to 6%. Dissolved RP (DRP) was less mobile than DUP in soils with short duration of manure applications (p < 0.05), while differences between DUP and DRP mobility disappeared with longer duration of manure application and greater total soil P. Organic P forms in NaOH/NaF extracts determined by 31P NMR did not change with manure history, but sequential fractionation showed that the relative distribution of RP pools in soils changed. Dilute acid Pi increased from 10% to 62% with longer poultry manure additions, suggesting the formation of calcium phosphates as the soil pH increased from 4.1 to 6.0-7.2. The precipitation of P as calcium phosphates appeared to influence leachable P upon high and long-term applications of manure dominated by poultry litter.