Phosphorus fractions in an acid soil continuously fertilized with mineral and organic fertilizers

The effect of different treatments on the fate of applied P was investigated in a long-term field experiment started in 1972–1973 following a maize–wheat sequence. The soil samples were collected after 29 years of continuous addition of mineral fertilizers and amendments such as farmyard manure (FYM) and lime. The total P content of all the treatments increased compared to the original soil; NaOH-inorganic P (P_i) (NaOH-P_i) representing Fe and Al-bound P was the dominant P_i fraction. At the beginning of the experiment (1972–1973), the various P pools could be quantitatively ranked in the following order: residual P>NaOH-organic P (P_o)>NaOH-P_i>NaHCO₃-P_o>NaHCO₃-P_i>HCl-P>H₂O-P. As a result of continued P fertilization and cropping, the order changed as follows: residual P>NaOH-P_i>NaOH-P_o>NaHCO₃-P_i>NaHCO₃-P_o>HCl-P>H₂O-P. Compared to the imbalanced mineral fertilizer application, the balanced as well as integrated application of nutrients resulted in significantly lower P adsorption capacity of soils. The Olsen extractable-P fraction (plant-available P) increased from about 12 mg kg^–1 soil in 1972 to about 81 mg kg^–1 soil in the treatments receiving P for the last 29 years.     

低分子量有机酸对土壤磷活化影响的研究

研究两种低分子量有机酸（柠檬酸和苹果酸）对土壤磷活化影响,并用修正的Hedley法测定土壤磷活化前后磷组分的变化。结果表明,低分子量有机酸能持续活化土壤磷,活化强度随低分子量有机酸浓度的增大而增强,并且柠檬酸活化土壤磷的能力强于苹果酸。低分子量有机酸能促进作物有效态无机磷组分（H2O-P和NaHCO3-Pi）的释放;同时还促进有机磷组分（NaHCO3-Po和NaOH-Po）的矿化。在低分子量有机酸浓度达到0.5 mmol/L以上时,其对土壤磷组分的活化量的顺序为:NaOH-Pi HCl-P NaHCO3-Pi H2O-P,即铁铝结合态磷 钙结合态磷 作物有效态磷。低分子量有机酸活化土壤磷的过程中伴有大量铁、铝释放,且铁或铝的释放量与磷活化量之间显著正相关（P0.05）。说明铁、铝结合态磷是低分子量有机酸活化土壤磷的主要磷源,并且其活化机制可能与铁、铝结合态磷的螯合溶解有关。     

Long-Term Wheat Residue Management and Supplementary Nutrient Input Effects on Phosphorus Fractions and Adsorption Behavior in a Vertisol

The management of crop residues coupled with external nutrient inputs is important for improving and conserving soil fertility and productivity. We assessed the long-term effects of three wheat residue management options (RMO) (residue burning, incorporation, and surface retention) in combination with three supplementary nutrient inputs (SNI) [control, fertilizer, and farmyard manure (FYM)] on phosphorus (P) fractions and adsorption behavior of a Vertisol under soybean–wheat system. Wheat residue incorporation and retention improved the labile inorganic P [sodium bicarbonate (NaHCO₃-P_i)] by 3.2 and 5.0 mg kg^?1 and the labile organic P (NaHCO₃-P_o) by 2.4 and 4.2 mg kg^?1, respectively, as compared to residue burning. The soils under residue incorporation and retention had 38 and 26% more moderately labile organic P [sodium hydroxide (NaOH-P_o)], respectively, than the soil under residue burning. The SNI either as fertilizer or FYM further enhanced NaHCO₃-P_i, NaHCO₃-P_o, and NaOH-P_o. In contrast, less labile P fractions [hydrochloric acid (HCl)-P and residual-P] remained unaffected by RMO and SNI treatments. Residue retention or incorporation decreased P adsorption over the residue burning for all the three nutrient inputs. The P-adsorption data fitted well to the Langmuir equation (R² ranged from 0.970 to 0.994). The P-adsorption maximum (b), bonding energy constant (k), differential P-buffering capacity (DPBC), and standard P requirement (SPR) were lower with residue incorporation or surface retention than with residue burning. The SPR followed the order residue burning > incorporation > retention for RMOs and control > fertilizer > FYM for SNI treatments. The NaHCO₃-P_i, NaHCO₃-P₀, and NaOH-P_o had negative correlation with P-adsorption parameters and showed positive correlation with soybean P uptake. Wheat residue incorporation or retention plus FYM could be an effective strategy for enhancing the P fertility of Vertisols under a soybean–wheat system.     

Effects of repeated manure and fertilizer phosphorus additions on soil phosphorus dynamics under a soybean-wheat rotation

 Soil P availability and efficiency of applied P may be improved through an understanding of soil P dynamics in relation to management practices in a cropping system. Our objectives in this study were to evaluate changes in plant-available (Olsen) P and in different inorganic P (P_i) and organic P (P₀) fractions in soil as related to repeated additions of manure and fertilizer P under a soybean-wheat rotation. A field experiment on a Typic Haplustert was conducted from 1992 to 1995 wherein the annual treatments included four rates of fertilizer P (0, 11, 22 and 44 kg ha^–1 applied to both soybean and wheat) in the absence and presence of 16 t ha^–1 of manure (applied to soybean only). With regular application of fertilizer P to each crop the level of Olsen P increased significantly and linearly through the years in both manured and unmanured plots. The mean P balance required to raise Olsen P by 1 mg kg^–1 was 17.9 kg ha^–1 of fertilizer P in unmanured plots and 5.6 kg ha^–1 of manure plus fertilizer P in manured plots. The relative sizes of labile [NaHCO₃-extractable P_i (NaHCO₃-P_i) and NaHCO₃-extractable P₀ (NaHCO₃-P₀)], moderately labile [NaOH-extractable P_i (NaOH-P_i) and NaOH-extractable P₀ (NaOH-P₀)] and stable [HCl-extractable P (HCl-P) and H₂SO₄/H₂O₂-extractable P (resisual-P)] P pools were in a 1 : 2.9 : 7.6 ratio. Application of fertilizer P and manure significantly increased NaHCO₃-P_i and -P₀ and NaOH-P_i, and -P₀ fractions and also total P. However, HCl-P and residual-P were not affected. The changes in NaHCO₃-P_i, NaOH-P_i and NaOH-P₀ fractions were significantly correlated with the apparent P balance and were thought to represent biologically dynamic soil P and act as major sources and sinks of plant-available P. Received: 23 October 1997     

Phosphate Amendments to Compost for Improving P Bio-Availability

This study was conducted to investigate changes in P-fractions, bio-available P (CAL-P), citric acid extractable P, acid phosphatase activity and microbial biomass C and N during incubation of mature biogenic compost (MBC), immature biogenic compost (IBC) or immature sheep manure compost (ISC) not amended with P or amended with rock phosphate (RP, 7.6% P) or triple-superphosphate (TSP, 19.5% P). Incubation was performed at 20?°C in darkness under aerobic conditions. Samples were collected for laboratory analysis at the start of incubation (D-0) and after one, six and 26?days during incubation (D-1, D-6, D-26). Addition of soluble P fertilizer (TSP) led to a threefold increase in all P fractions in comparison to compost without TSP; even a “priming effect” could be observed, promoting conversion of non-labile to labile P. Moreover, addition of TSP lowered biological activity, especially acid phosphatase activity (P-ase), due to already high concentrations of readily available P. In general, P fractions (bicarbonate extractable P_i (NaHCO₃-P_i) and bicarbonate extractable P_o (NaHCO₃-P_o) and sodium hydroxide extractable P_o (NaOH-P_o)) increased during incubation until day 6 at the expense of NaOH-P_i fraction, which decreased. Generally, RP-derived P showed little or no effect on P fractions during the entire incubation period and only led to slightly increased CAL-P and Citric-acid-P levels. Fertilizer effects on labile P fractions were most enhanced with ISC. IBC enhanced microbial growth and P-ase, thereby enhancing conversion of labile into moderate labile NaOH-P_o.     

Effects of long-term phosphorus fertilization and winter cover cropping on soil phosphorus transformations in less weathered soil

Information concerning sources and sinks of available P in soil is needed to improve soil P management and protect water quality. This study, conducted from 1989 to 1998 on a Sultan silt loam soil (Aquantic Xerochrept), determined the annual P removal rate by corn (Zea mays L.) and P transformation as affected by P rate and winter cover cropping. Treatments included two P rates (0 and 44 kg P ha^–1) applied to corn at planting each year. All cover crops received 19.6 kg P ha^–1 at seeding each fall. Also included was a control without any cover crop and with no P addition. Corn yield and P uptake were affected by P fertilizer additions, but not by cover crops. A fairly constant amount of P was supplied from indigenous soil P when no external P was added. When the amount of P added exceeded that removed by corn, the excess P was converted mainly to NaOH-extractable inorganic P (NaOH-P_i). When the amount of P applied was below that removed by corn, indigenous soil NaOH-P_i acted as a source of available P for the plant. With no reduction of organic P (P_o) extractable by NaOH or NaHCO₃, the contribution from P_o to the available P pool appeared limited. The role of NaOH-P_i in P availability in the soil was substantiated by its significant correlation with labile NH₄Cl-extractable P (NH₄Cl-P; r² =0.60, P <0.001) or NaHCO₃-P_i (r² =0.81, P <0.001) pools. The NaOH-P_i for the soil reflected the changes in soil P resulting from past fertilizer P input and P removal by the crops.Scientific Paper Number 0005-34     

Changes in phosphorus fractions in three tropical soils amended with corn cob and rice husk biochars

ABSTRACT

The formation of phosphorus (P) compounds including iron-P, aluminum-P and calcium-P in highly weathered tropical soils can be altered upon biochar addition. We investigated the effect of corn cob biochar (CC) and rice husk biochar (RH) pyrolyzed at three temperatures (300°C, 450°C and 650°C) on phosphorus (P) fractions of three contrasting soils. A 90d incubation study was conducted by mixing biochar with soil at a rate of 1% w/w and at 70% field capacity. Sequential P fraction was performed on biochar, soil and soil-biochar mixtures. Increase in most labile P (resin-P_i, NaHCO₃-P_i) and organic P fraction (NaHCO₃-P_o + NaOH-P_o) in CC and RH biochars were inversely related to increasing temperature. HCl-P_i and residual P increased with increasing temperature. Interaction of CC and RH with soils resulted in an increase in most labile P as well as moderately labile P (NaOH-P_i) fractions in the soils. CC increased most labile P in the soils more than RH. The increase in most labile P fraction in soils was more significant at relatively lower temperatures (300°C and 450°C) than 650°C. However, the increase in HCl-P_i and residual P of the soils was more predominant at high temperature (650°C). The study suggested that biochar pyrolyzed at 300–450°C could be used to increase P bioavailability in tropical soils.     

Transformation and recovery of fertilizer phosphorus applied to five Quebec Humaquepts

Abstract

Improving phosphorus (P) fertilizer efficiency while minimizing environmental impacts requires better understanding of the dynamics of applied P in soils. This study assessed the fate of fertilizer P applied in Quebec Humaquepts. A pot experiment with five textural Humaquepts, each receiving 0 (P0), 10 (P10), 20 (P20) and 40 (P40) mg P kg^?1 soil was conducted under barley (Hordeum vulgare L.)-soybean (Glycine max L.) rotations. A modified Hedley procedure was used for soil P fractionation. The clayey soils reached a plateau of dry matter at less P applied than the coarser-textured soils. Plant P uptake, soil labile inorganic P (resin-P?+?NaHCO₃-P_i) and moderately labile inorganic P (NaOH-P_i) increased proportionally with P rate. The coarser-textured soils had lower contents of labile and moderately labile P_i, but a larger increase in labile P_i than the finer-textured soils after receiving P additions. The applied P was retained primarily as soil labile P_i, accounting for 43–69% of total soil recovery of applied P, compared to 20–30% recovered as moderately labile P_i, and 7–29% assumed to be sparingly soluble P (HCl-P?+?H₂SO₄-P). The labile P_i recovery of applied P was linearly depressed with clay content, compared to a quadratic relation for the moderately labile P_i recovery. The results suggest the importance of accounting for soil texture along with soil P adsorption capacity when assessing the efficiency of applied P, P accumulation in soils and subsequently P nutrient management.     

Long-Term Effects of Tillage and Manure Applications on Soil Phosphorus Fractions

Application of manure on the basis of crop nitrogen (N) need increases the level of soil phosphorus (P), which is concern for deterioration of surface water quality. Soil samples were collected from a long-term field study to investigate the impact of crop N need–based manure application on soil P fractions and P adsorption and release kinetics. The field experiment was initiated in 1990. The soil was moderately well-drained Kennebec (fine silty, mixed, mesic Cumulic Hapludolls). No-tillage (NT) and conventional-tillage (CT) treatments were established in main plots, and subplots had five N treatments, including a control, and annual application of 84 or 168 kg N ha^?1 applied as ammonium nitrate (NH₄NO₃) or beef (Bos taurus) manure. Manure at the high N application rate had significantly greater Bray 1 P under NT than under CT at 0- to 5-cm soil depth. Nitrogen fertilizer treatments were not significantly different than the control for Bray 1 P. Continuous application of manure at the high N rate significantly increased all Hedley P fractions; however, the major increase was observed in high bioavailable P pools [iron oxide (FeO) P and sodium bicarbonate (NaHCO₃) P_i] and hydrochloric acid (HCl) P fractions. Soil organic P (P_o) pools, including both labile (NaHCO₃-P_o) and resistant [sodium hydroxide (NaOH) P_o], were increased by application of N from any source, suggesting biomass production and return of residue to soil surface was the responsible factor. Continuous application of manure based on N need also significantly increased FeO-P, NaHCO₃-P_i, and HCl-P fractions at lower soil depths (5–15 and 15–30 cm). Results from the P-adsorption study suggest that ability of soil to adsorb additional P was decreased by manure application and that EPC₀ was increased. Maximum desorbable P was observed for manure treatments under NT, although the release constant k (h^?1) was significantly less than with fertilizer N treatments.     

Organic amendments differ in their effect on microbial biomass and activity and on P pools in alkaline soils

Organic amendments could be used as alternative to inorganic P fertilisers, but a clear understanding of the relationship among type of P amendment, microbial activity and changes in soil P fractions is required to optimise their use. Two P-deficient soils were amended with farmyard manure (FYM), poultry litter (PL) and biogenic waste compost (BWC) at 10 g?dw?kg^?1 soil and incubated for 72 days. Soil samples were collected at days 0, 14, 28, 56 and 72 and analysed for microbial biomass C, N and P, 0.5 M NaHCO₃ extractable P and activity of dehydrogenase and alkaline phosphomonoesterase. Soil P fractions were sequentially extracted in soil samples collected at days 0 and 72. All three amendments increased cumulative CO₂ release, microbial biomass C, N and P and activity of dehydrogenase and alkaline phosphomonoesterase compared to unamended soils. The increase in microbial biomass C and N was highest with PL, whereas the greatest increase in microbial biomass P was induced with FYM. All three biomass indices showed the same temporal pattern, with the highest values on day 14 and the lowest on day 72. All amendments increased 0.5 M NaHCO₃ extractable P concentrations with the smallest increase with BWC and the greatest with FYM, although more P was added with PL than with FYM. Available P concentrations decreased over time in the amended soils. Organic amendments increased the concentration of the labile P pools (resin and NaHCO₃-P) and of NaOH-P, but had little effect on the concentrations of acid-soluble P pools and residual P except for increasing the concentration of organic P in the concentrated HCl pool. Resin P and NaHCO₃-P_i pools decreased over time whereas NaOH-P_i and all organic P pools increased. It is concluded that organic amendments can provide P to plants and can stimulate the build-up of organic P forms in soils which may provide a long-term slow-release P source for plants and soil organisms.     

Phosphorus status of a Humic Cryaquept profile in a frigid continental climate as influenced by cropping practices

Most previous studies have limited the assessments of soil phosphorus (P) status within the plow layer. This study was to assess the impacts of crop sequences and nutrient sources on P status of a Labarre silty clay (Humic Cryaquept) profile in a frigid continental climate. Soil of the 0- to 15-, 15- to 30-, 30- to 60-, and 60- to 90-cm layers was sampled from a split-plot experiment comprising a barley (Hordeum vulgare L.) monoculture and a 3-year barley-forage rotation as main plots, and receiving mineral fertilizers (MIN) or liquid dairy manure (LDM) as subplots. A modified Hedley sequential fractionation was used to characterize soil P status. Labile P pools were more affected than stable ones by the investigated treatments. After 10 years, the MIN resulted in larger resin-P and NaHCO₃-P_i, and lower NaHCO₃-P_o and NaOH-P_o pools than the LDM in the top 30 cm of soil. The rotation resulted in larger labile P_i and P_o pools than the monoculture in the 30- to 60-cm layer. The rotation associated with LDM produced the largest total labile P pool, whereas the LDM resulted in an about 20% higher degree of soil P saturation as expressed by the P_ox/(Fe_ox + Al_ox) molar ratio than the MIN in the 0- to 30-cm layer. Our observations stressed that the impacts of crop sequences and nutrient sources on soil labile P extended deeper into the profile than the disturbance caused by primary tillage.     

Transformation of added phosphorus to acid upland soils with different soil properties in Indonesia

Abstract

The transformation of added phosphorus (P) to soil and the effect of soil properties on P transformations were investigated for 15 acid upland soils with different physicochemical properties from Indonesia. Based on oxide-related factor scores (aluminum (Al) plus 1/2 iron (Fe) (by ammonium oxalate), crystalline Al and Fe oxides, cation exchange capacity, and clay content) obtained from previous principal component analyses, soils were divided into two groups, namely Group 1 for soils with positive factor scores and Group 2 for those with negative factor scores. The amounts of soil P in different fractions were determined by: (i) resin strip in bicarbonate form in 30 mL distilled water followed by extraction with 0.5 mol L^?1 HCl (resin-P inorganic (P_i) that is readily available to plant), (ii) 0.5 mol L^?1 NaHCO₃ extracting P_{i and} P organic (P_o) (P which is strongly related to P uptake by plants and microbes and bound to mineral surface or precipitated Ca-P and Mg forms), (iii) 0.1 mol L^?1 NaOH extracting P_i and P_o (P which is more strongly held by chemisorption to Fe and Al components of soil surface) and (iv) 1 mol L^?1 HCl extracting P_i (Ca-P of low solubility). The transformation of added P (300 mg P kg^?1) into other fractions was studied by the recovery of P fractions after 1, 7, 30, and 90 d incubation. After 90 d incubation, most of the added P was transformed into NaOH-P_i fraction for soils of Group 1, while for soils of Group 2, it was transformed into resin-P_i, NaHCO₃-P_i and NaOH-P_i fractions in comparable amounts. The equilibrium of added P transformation was reached in 30 d incubation for soils of Group 1, while for soils of Group 2 it needed a longer time. Oxide-related factor scores were positively correlated with the rate constant (k) of P transformation and the recovery of NaOH-P_i. Additionally, not only the amount of but also the type (kaolinitic) of clay were positively correlated with the k value and P accumulation into NaOH-P_i. Soils developed from andesite and volcanic ash exhibited significantly higher NaOH-P_i than soils developed from granite, volcanic sediments and sedimentary rocks. Soil properties summarized as oxides-related factor, parent material, and clay mineralogy were concluded very important in assessing P transformation and P accumulation in acid upland soils in Indonesia.     

免耕和秸秆覆盖对黑垆土磷素形态组分的影响

[目的]探究免耕及添加秸秆条件下黑垆土土壤磷组分特征及其与AM真菌侵染的关系,了解雨养农业区农业系统磷素利用效率。[方法]在陇东黄土高原黑垆土区域,测定传统耕作、传统耕作+秸秆覆盖、免耕和免耕+秸秆覆盖4种处理小麦—玉米—大豆轮作系统中玉米阶段土壤全磷、速效磷组分及AM真菌菌根侵染率。[结果]水土保持耕作处理实施9a后,免耕和秸秆覆盖处理下0—5cm土壤磷素含量显著提高,活性磷组分H2O—Pi,NaHCO3—Pi,NaOH—Pi分别比对照提高84.6%,85.2%和56.6%;活性无机磷(H2O—Pi,NaHCO3—Pi之和)和潜在活性磷(NaOH—Pi)分别占总无机磷的11.4%和4.5%,全磷含量与磷组分、速效磷与磷组分呈显著正相关,2个免耕处理菌根侵染率分别比对照增加20.8%和16.5%。[结论]免耕和秸秆覆盖显著提高了土壤磷含量,免耕对AM真菌菌根侵染率有积极影响。     

Addition of organic and inorganic P sources to soil – Effects on P pools and microorganisms

Phosphorus deficiency is wide-spread due to the poor solubility of soil P and the rapid formation of poorly available P after P addition. Microbes play a key role in soil P dynamics by P uptake, solubilisation and mineralisation. Therefore a better understanding of the relationship between type of P amendment, microbial activity and changes in soil P pools is important for a better management of soil P. A P deficient soil was amended with two composts (low P or high P), two crop residues (low P or high P), and inorganic P (KH₂PO₄) at low and high P, and incubated for 56 days. Composts were added at 20 g kg⁻¹ resulting in a total P addition of 4.1 mg kg⁻¹ soil with the low P compost and 33.2 mg kg⁻¹ soil with the high P compost. The same amount of P was added with the other amendments (residues and inorganic P). All amendments increased cumulative respiration, but microbial biomass and the abundance of bacteria and fungi (assessed by phospholipid fatty acid analysis) increased significantly only in soils with organic amendments, with greater increases with residues. The concentration of the inorganic P pools NaHCO₃-P_i, NaOH-P_i and HCl-P increased significantly within 5 h after amendment, particularly with high P amendments. Over the following 56 days, labile inorganic P was converted mainly into non-labile inorganic P with inorganic P addition whereas labile and non-labile organic P was formed with organic amendments. It is concluded that organic P sources, particularly those with high P concentration can stimulate the formation of organic P forms in soils which may provide a long-term slow release P source for plants and soil organisms.     

Phosphorus Fractionations in Acidic Piedmont Rice Soils

Piedmont lands in Bangladesh, India, Nepal, and many other Asian countries are important rice-growing soils, but most of the soils are potentially phosphorus (P) deficient because of low pH. Phosphorus fractions of rice-growing acidic piedmont soils were determined. Soil samples were amended with 100 and 200 mg P kg^?1 soil, and a control soil without P amendment was maintained. The samples were analyzed for the following fractions: solution P, labile pool [sodium bicarbonate (NaHCO₃) P], alkali-extracted inorganic pool [sodium hydroxide (NaOH) P_i], organic pool (NaOH P_o), acidic pool [sulfuric acid (H₂SO₄)?hydrochloric acid (HCl) P], and residual P. About 98% of the applied P in soils was extracted by the sequential extraction employed in the present experiment. The mean total P concentration in 10 acidic Piedmont soils was 247 ppm, of which only 0.12% was in solution, 8% labile (NaHCO₃), 16% NaOH-extracted inorganic, 32% resistant organic, 18% relatively recalcitrant acidic, and 25% residual. Application of P fertilizer increased mainly the labile P fraction, which would be easily available to wetland rice. Solution P was positively and significantly correlated with pH_KCl (r = 0.64, P < 0.05) and negatively correlated with clay (r = ?0.77, P < 0.01). A negative and significant correlation of NaHCO₃-P was observed with pH_H2O (r = ?0.62, P < 0.05). Solution P showed a negative and significant relationship with NaOH-P_i (r = ?0.63, P < 0.05). A significant and negative relationship of solution P was also observed with acid P (r = ?0.78, P < 0.01) and residual P (r = ?0.82, P < 0.01). The relationship of NaHCO₃-P with NaOH-P_i was positive (r = 0.70, P < 0.05) and significant. Similarly, a positive and significant relationship (r = 0.89, P < 0.01) between NaOH-P_i and acid P was observed, and acid P was positively and significantly correlated with residual P (r = 0.84, P < 0.01).     

Correlations between Phosphorus Fractions and Total Leachate Phosphorus from Cattle Manure– and Swine Manure–Amended Soil

Although many studies have examined the effect of different application rates of cattle manure, swine manure, and urea fertilizer on the distribution of phosphorus (P) fractions in soil, few studies have correlated P fractions in soil with inorganic P (P_i) and organic P (P_o) in leachates. As part of a long-term field study, cattle and swine manures were applied to a loamy soil based on a nitrogen (N) content equivalent of 100 (low) and 400 (high) kg total N ha^?1 yr^?1 and were compared to urea fertilizer at 100 kg N ha^?1 yr^?1 and an unamended control soil. Readily available P_i [resin and sodium bicarbonate (NaHCO₃)] was significantly greater in cattle manure– and swine manure–amended soil at a high application rate than in the control. With some exceptions, urea did not significantly affect P fractions in sequentially extracted P pools. Leaching of P_i and P_o was at levels of environmental concern when cattle and swine manures were applied at the high application rate but not at the low application rate. Cattle manure had significantly greater concentrations of P_i and P_o removed by leaching compared to swine manure, most likely because of its narrow N/P ratio and greater amount of P added. Positive correlations were observed between resin P_i and total leachate P_i and between NaHCO₃-P_i and total leachate P_i, indicating the value of these measurements in predicting P mobility. The results suggest that a threshold (40 μg P g^?1 of soil) must be exceeded before a positive correlation occurs.     

The Size of P Pools in Soils is Affected by Soil Properties and Compost Addition

It is well known that compost amendment can improve soil phosphorus (P) availability, but there are few studies comparing the effect of one compost type on soil P pools of soils which differ in properties. The aim of this glasshouse experiment was to determine the effect of compost (derived from garden waste) application on P pools in soils with different properties planted with wheat. Four soils from two sites were used, with a heavier and a lighter textured soil from each site. The compost was applied as a 2.5 cm thick layer on the soil surface and wheat plants were grown for 63 days. The treatments also included soil without compost and plants. All pots were regularly watered. The soils were sampled on day 0 in the unamended soils and on day 63 in soil without compost and with compost, and plants after removal of the compost layer. Without and with compost the concentrations of most P pools were higher in the two heavier textured soils (16% and 35% clay) than in the two lighter textured soils (8% and 13% clay). Principal component analysis (PCA) showed that the concentrations of most P pools were positively correlated with organic matter, clay, and silt content of the soils. Only the concentration of water-soluble P was positively correlated with sand content. Compost addition increased the concentration of microbial P, sodium bicarbonate (NaHCO₃)-Pi, sodium hydroxide (NaOH)-Pi, hydrochloric acid (HCl)-P, and residual P in all soils, whereas the concentration of NaHCO₃-Po was reduced and the concentration of NaOH-Po little affected by compost addition indicating that P was transferred from the compost layer with watering. Compared with the unamended soil on day 0, the concentrations of microbial P, NaHCO₃-Pi, NaOH-Pi, HCl-P, and residual P on day 63 were higher, whereas the concentrations of the two organic pools (NaHCO₃-Po and NaOH-Po) were lower. This suggests mineralization of organic P pools and formation of inorganic P as well as microbial P uptake. These changes occurred in the unamended and compost-amended soils with greater increases over time in the compost-amended soils. It can be concluded that the size of the P pools is predominately affected by soil texture. Compost amendment increases P availability and microbial P uptake but also leads to the formation of less labile P pools such as HCl-P and residual P which could serve as plant P sources in the long term.     

Soil genesis and heterogeneity of phosphorus forms and carbon below mounds inhabited by primary and secondary termites

Termite activities are known to significantly influence small-scale soil properties in tropical savannas. The lateral and vertical extent of the alterations to the nest's surrounding, and particularly resulting impacts on diagnostic soil horizons remain largely unresolved until today. We examined the effects of mound-building termites on soil genesis and constitutive chemical soil properties in and below their nests. Two transects to a soil depth of 100 cm were dug below three younger mounds of Cornitermes silvestrii (the primary nest builder), three older mounds in which C. silvestrii had died out and which were secondarily colonized mainly by Nasutitermes kemneri, and three reference sites in the Brazilian Cerrado. The samples were characterized by standard procedures for soil classification; in addition, phosphorus extractions were conducted on selected samples using NaHCO₃ for labile P forms, and concentrated HCl for stable P forms. This data set was then used to build calibration models for the prediction of labile and stable inorganic (P_i) and organic (P_o) P forms, as well as for contents of organic carbon (OC), for the remaining samples applying mid-infrared spectroscopy in combination with partial least squares regression (MIRS-PLSR). We can show that the termite influence on the soil was sufficiently large to change diagnostic characteristics of the soils under termite mounds. The MIRS-PLSR predictions were suitable for quantifying organic carbon and most of the labile and stable phosphorus fractions. They showed an enrichment of OC, NaHCO₃-P_o and NaHCO₃-P_i contents in nests inhabited by primary and secondary termites by factors of 1.6–2.0 and 1.4–1.5, respectively. The soils surrounding the nests had higher contents of OC and NaHCO₃-P under both nest types vertically down to 30 cm below the lower nest border, and OC and NaHCO₃-P_i contents were elevated at minimum to a lateral distance of 60 cm away from the nest border. As the pattern of HCl_conc-P_i, which comprised 95% of total P, showed no variations, we conclude that the higher NaHCO₃-P_i amount was formed in termite nests by changing the availability of the more stable HCl_conc-P_i. In contrast to the contents, the OC and NaHCO₃-P stocks below the mounds inhabited by primary termites were comparable to those inhabited by secondary ones, because the bulk density of the secondarily inhabited nests was elevated. This was due to a transport of clay-rich material from the subsurface argic horizons into the nests. Here, the secondary termites even reverted the lessivation observed in the reference soils and under mounds inhabited by primary termites, thus causing the soil types to change from Alisols and Acrisols to the properties of Umbrisols.     

Effects of poultry manure amendment on phosphorus uptake by ryegrass,soil phosphorus fractions and phosphatase activity

Poultry manure (PM) contains a large proportion of phosphorus (P) in mineral-associated forms that may not be readily available for plant uptake. In addition, PM application influences both chemical and biotic processes, and can affect the lability of native soil P. To investigate the effects of PM on soil P availability, we grew ryegrass (Lolium perenne) in greenhouse pots amended with poultry manure. Biomass was harvested at 4, 8, and 16 weeks following PM application, with soil separated into rhizosphere and bulk fractions. Soil was sequentially extracted by H₂O, 0.5 M NaHCO₃, 0.1 M NaOH, and 1 M HCl, and inorganic P (P_i) and enzymatically hydrolyzable organic P (P_oe) were quantitated. Root P concentrations were 37% higher and total P uptake 59% higher with PM application than Control. At week 16, there was 30% more labile-P_i (H₂O- plus NaHCO₃-P_i) in the rhizosphere with PM than in Control. Phosphodiesterase activity increased with PM application. Furthermore, acid phosphomonoesterase, alkaline phosphomonoesterase, and phosphodiesterase activities were all higher in the rhizosphere than in bulk soil at week 16 with PM, indicating that increased labile-P_i was due primarily to stimulation of soil phosphatases to mineralize NaOH-P_oe. Soil pH increased with PM application and plant growth, and may have promoted P availability by decreasing sorption of Al- and Fe-associated inorganic and organic phosphates. These results demonstrate that whereas PM application may initially increase NaOH and HCl-P_i, these fractions can be readily changed into labile-P and do not necessarily accumulate as stable or recalcitrant P in soil.     

Soil phosphorus fractions after seven decades of fertilizer application in the Rengen Grassland Experiment

Declining global P reserves require a better understanding of P cycling in soil and related plant uptake. On managed grasslands, application of lime and fertilizer affects not only soil nutrient status, but also plant‐species composition of the sward. We examined the P fractionation in the Rengen Grassland Experiment (RGE) on a naturally acid Stagnic Cambisol in the Eifel Mts. (Germany) 69 y after the setup of the experiment. A modified sequential Hedley fractionation was carried out for samples from 30 plots at 0–10 cm depth. Application of inorganic phosphorus fertilizer had diverse effects on inorganic (P_i) and organic P (P_o) fractions. Resin‐P_i, NaHCO₃‐P_i, NaHCO₃‐P_o, NaOH‐P_i, HCl_dil‐P_i, HCl_conc‐P_i, and HCl_conc‐P_o contents increased, while NaOH‐P_o significantly decreased and residual‐P remained unaffected. Strongest enrichment occurred in the HCl_dil‐P_i fraction, probably due to the chemical nature of the basic Thomas slag applied as P fertilizer. Without P fertilization, all fractions except residual‐P were more or less depleted. Strong P limitation of the vegetation in the limed treatments without P led to lowered contents also for NaOH‐P_i and NaOH‐P_o. However, NaOH‐P_o was largest in the Control and even exceeded the respective content in the treatments with P. It remained unclear why species adapted to a low soil P status did not access this P fraction though being P‐limited. Published theory on the availability of Hedley P fractions does neither match P exploitation nor P nutritional status of the vegetation in the RGE. Regarding NaOH‐P_o as stable and HCl_dil‐P_i as moderately labile led to a more realistic evaluation of plant P uptake. Evaluation of P availability on the basis of chemical extractions alone is questionable for conditions like in the RGE. On long‐term grassland, plant‐species composition has to be taken into account to estimate access of plants to soil P.