Changes in P fractions and sorption in an Alfisol following crop residues application

With the emphasis on sustainable agriculture, attention has been increasingly turning to recycling of crop residues as a component of fertility management strategies for tropical soils. We assessed the effects of soybean residue (SR) and wheat residue (WR) applied either alone or in combination with fertilizer P (FP) on dynamics of labile P, distribution of P fractions, and P sorption in a semiarid tropical Alfisol by conducting a 16 w long incubation experiment. The amount of P added through crop residues, FP or their combinations was kept constant at 10 mg P (kg soil)^–1. Addition of SR or WR resulted in net increase of labile inorganic (P_i) and organic P (P_o) and microbial P throughout the incubation period, except that the WR decreased labile P_i during first 2 w due to P_i immobilization. The P immobilization associated with WR addition was, however, offset when fertilizer P was combined with WR. Generally, the increases in labile‐P fractions were larger with the SR and SR+FP than with the WR and WR+FP. The sequential fractionation of soil P at the end of 16 w indicated that a major part of added fertilizer P transformed into moderately labile and stable P fractions as evident from the increased NaOH‐P_i and HCl‐P in the FP treatment. In contrast, the addition of SR and WR alone or in combination with FP favored a build‐up in NaHCO₃‐P_i and ‐P_o and NaOH‐P_o fractions while causing a decrease in NaOH‐P_i and HCl‐P fractions. The addition of these crop residues also effectively decreased the P‐sorption capacity and hence reduced the standard P requirement of the soil (i.e., the amount of P required to maintain optimum solution P concentration of 0.2 mg P l^–1) by 24%–43%. Results of the study, thus, imply that soybean and wheat crop residues have the potential to improve P fertility of Alfisols by decreasing P‐sorption capacity and by redistributing soil P in favor of labile‐P fractions and promoting accretion of organic P.     

How does the Hedley sequential phosphorus fractionation reflect impacts of land use and management on soil phosphorus: A review

The Hedley sequential‐phosphorus (P)‐fractionation method has been used in many countries to study the effects of land‐use and management systems on soil P. Many data sets have been obtained but collectively never have been considered or to goal topic reviewed. Therefore, the objectives of this review were to compile and systematically evaluate these data. The data generated over many years were grouped into temperate, and subtropical and tropical soils of different land use and duration of soil‐management studies. In natural ecosystems, vegetation types and composition and percent of vegetation covers substantially affected all P fractions with pronounced impacts on the labile and moderately labile P. In short‐term studies (≤ 10 y), changes in the labile and moderately labile inorganic P (P_i) fractions were detected when more P (e.g., by factor 5) was applied than commonly recommended for agricultural crops. However, without P application the changes in all P fractions were subtle in temperate soils, but declines were significant in labile and moderately labile P in subtropical and tropical soils. In both temperate and tropical climates, medium (10–25 y) and long‐term (>25 y) cultivation without P application depleted all P fractions, whereas most of P fractions increased with continuous P application, regardless of the amount and source of P. Synthesis of data resulted in multiple‐regression functions which described differences in labile and moderately labile P fractions as function of differences in amount of P application and duration of the experiments. Moreover, the correlation analysis also showed strong association among most of the P fractions. Current limitations in data interpretation of Hedley fractionation can be overcome by the application of ³¹P nuclear–magnetic resonance (NMR) and X‐ray absorption near‐edge fine‐structure (XANES) spectroscopy.     

Soil phosphorus dynamics in a Vertisol as affected by cattle manure and nitrogen fertilization in soybean‐wheat system

Repeated application of phosphorus (P) as superphosphate either alone or in conjunction with cattle manure and fertilizer N may affect the P balance and the forms and distribution of P in soil. During 7 years, we monitored 0.5 M NaHCO₃ extractable P (Olsen‐P) and determined the changes in soil inorganic P (P_i) and organic P (P_o) caused by a yearly dose of 52 kg P ha^—1 as superphosphate and different levels of cattle manure and fertilizer N application in a soybean‐wheat system on Vertisol. In general, the contents of Olsen‐P increased with conjunctive use of cattle manure. However, increasing rate of fertilizer nitrogen (N) reduced the Olsen‐P due to larger P exploitation by crops. The average amount of fertilizer P required to increase Olsen‐P by 1 mg kg^—1 was 10.5 kg ha^—1 without manure and application of 8 t manure reduced it to 8.3 kg ha^—1. Fertilizer P in excess of crop removal accumulated in labile (NaHCO₃‐P_i and P_o) and moderately labile (NaOH‐P_i and P_o) fractions linearly and manure application enhanced accumulation of P_o. The P recovered as sum of different fractions varied from 91.5 to 98.7% of total P (acid digested, P_t). Excess fertilizer P application in presence of manure led to increased levels of Olsen‐P in both topsoil and subsoil. In accordance, the recovery of P_t from the 0—15 cm layer was slightly less than the theoretical P (P added + change in soil P — P removed by crops) confirming that some of the topsoil P may have migrated to the subsoil. The P fractions were significantly correlated with apparent P balance and acted as sink for fertilizer P.     

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.     

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).     

Effect of Long-Term Fertilizer Management and Crop Rotations on Accumulation and Downward Movement of Phosphorus in Semi-Arid Subtropical Irrigated Soils

Crop species and their varieties vary in phosphorus (P) requirements for optimum production and response to P application. As crop recovery of added P often ranges from 10 to 40%, the rest accumulates in soil and may create potential for P leaching, depending upon the soil characteristics, duration of P applications, and cropping systems. Accumulation and distribution of Olsen P (plant-available labile P), total inorganic P, and total organic P were investigated in soil profiles of three field experiments differing in rate (9–44 kg P ha^–1), frequency (applied once or twice annually), and duration (4–34 years) of fertilizer P applications, crop rotations, soil characteristics, and irrigation pattern (upland irrigated and flooded-rice crop) in a subtropical region. Profile samples were collected from soil depths of 0–15, 15–30, 30–60, 60–90, 90–120, and 120–150 cm of different treatments in these experiments and analyzed for different forms of P and soil characteristics. The results revealed that (i) annual applications of fertilizer P either to one crop (alternative-applied P) or to both crops (cumulative) led to the accumulation of residual fertilizer P in the form of Olsen P, varying from 44 to 148 kg P ha^–1, and the magnitude of accumulation was proportional to applied fertilizer P rate, frequency, and duration; (ii) majority of residual fertilizer P accumulated as inorganic P (74–89%) followed by organic P (11–26%) and Olsen P (9–19%), illustrating that the inorganic P pool is a major sink for fertilizer P; (iii) application of fertilizer nitrogen (N) and potassium (K) alone or in combination with fertilizer P did not affect residual fertilizer P accumulation in soil profile; (iv) incorporation of farmyard manure enhanced the P enrichment of soil profile; (v) irrigation pattern, soil pH (7.1–7.7), and calcium carbonate (CaCO₃) (trace–0.33%) did not influence P movement to deeper soil layers; silt, clay, and soil organic C (SOC) showed strong relationships with Olsen P (r = 0.827, 0.938, and 0.464, P < 0.01) and enhanced the retention of labile P in the plow layer; and (vi) only 6–29% total residual P moved beyond 30 cm deep in fine-textured soils under 22-year rice (Oryza sativa L.)–wheat (Triticum aestivum L.) and 34-year maize (Zea maize L.)–wheat rotations, whereas 41, 27, 20, 9, and 3% were located in soil layers 0–30, 30–60, 60–90, 90–120, and 120–150 cm deep, respectively, in coarse-textured soil profile under 4-year peanut (Arachis hypogaea L.)–sunflower (Helianthus annuus L.) field. These findings confirmed that interplay between the fertilizer P management (alternative vis-à-vis cumulative P application and optimal vis-à-vis excessive rates of fertilizer P in different crop rotations), amount of labile P accumulated in soil profile, and soil characteristics (silt, clay, and SOC) largely controlled the downward movement and resultant potential for P leaching in subtropical irrigated soils.     

Quantifying microbial biomass phosphorus in acid soils

 This study aimed to validate the fumigation-extraction method for measuring microbial biomass P in acid soils. Extractions with the Olsen (0.5 M NaHCO₃, pH 8.5) and Bray-1 (0.03 M NH₄F–0.025 M HCl) extractants at two soil:solution ratios (1 : 20 and 1 : 4, w/v) were compared using eight acid soils (pH 3.6–5.9). The data indicated that the flushes (increases following CHCl₃-fumigation) of total P (P_t) and inorganic P (P_i) determined by Olsen extraction provided little useful information for estimating the amount of microbial biomass P in the soils. Using the Bray-1 extractant at a soil:solution ratio of 1 : 4, and analysing P_i instead of P_t, improves the reproducibility (statistical significance and CV) of the P flush in these soils. In all the approaches studied, the P_i flush determined using the Bray-1 extractant at 1 : 4 provided the best estimate of soil microbial biomass P. Furthermore, the recovery of cultured bacterial and fungal biomass P added to the soils and extracted using the Bray-1 extractant at 1 : 4 was relatively constant (24.1–36.7% and 15.7–25.7%, respectively) with only one exception, and showed no relationship with soil pH, indicating that it behaved differently from added P_i (recovery decreased from 86% at pH 4.6 to 13% at pH 3.6). Thus, correcting for the incomplete recovery of biomass P using added P_i is inappropriate for acid soils. Although microbial biomass P in soil is generally estimated using the P_i flush and a conversion factor (k _P) of 0.4, more reliable estimates require that k _P values are best determined independently for each soil. Received: 3 February 2000     

Phosphorus fractions and profile distribution in newly formed wetland soils along a salinity gradient in the Yellow River Delta in China

Soil P availability has been identified as one of the key factors controlling wetland productivity, structure, and function. Soil P fractions at different depths in newly formed wetlands along a salinity gradient in Yellow River Delta (China) were studied using a modified Hedley fraction method. The total P (P_t) content ranged from 471.1 to 694.9 mg kg^–1, and diluted HCl‐extractable inorganic P (Dil‐HCl‐P_i) ranged from 324 to 524.2 mg kg^–1. The Dil‐HCl‐P_i is the predominant P form in all profiles, with on average 70% of the P_t extracted as P_i. Organic P (P_o) comprised (4.2 ± 2.0)% (mean ± SD) of the P_t, due to low organic‐matter content in coastal salt marsh ecosystems. The labile P (resin‐P, NaHCO₃‐P_i, and NaHCO₃‐P_o) and moderately labile P (NaOH‐P_i and NaOH‐P_o) concentrations were both low, ranged from 11.6 to 38.1 and 2.8 to 21.3 mg kg^–1, respectively, constituting (3.7 ± 1.1)% and (2.0 ± 0.7)%, respectively, of P_t, suggesting low availability of P to plants in these soils. Our results suggested that vegetation cover significantly influenced soil P dynamics and availability. In particular, the labile P content under Tamarix chinensis increased significantly by 23.2%–145.5% compared with adjacent soils. These findings have important implications for wetland conservation or restoration and long‐term sustainable management of newly formed wetland ecosystems in the Yellow River Delta.     

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.     

Distribution of Inorganic and Organic Phosphorus Fractions in Two Phosphorus-Deficient Soils as Affected by Crop Species and Nitrogen Applications

It is desirable to know the distribution of phosphorus (P) fractions in soil so that plants may use P efficiently. Here we report the dynamics of inorganic and organic P in P-deficient black and rice soil cropped by soybean, white lupin, and maize supplied with nitrogen (N) inputs by N fixation and urea fertilizer. Inorganic P fractions of the three cropped soils could be ranked as O-P (organic phosphorus) > Al-P (aluminum phosphorus) > Fe-P (iron phosphorus) > Ca₁₀-P (calcium-10 phosphorus) > Ca₈-P (calcium-8 phosphorus) > Ca₂-P (calcium-2 phosphorus), irrespective of soil type. The potential of various inorganic P fractions to plant nutrition differed between soybean and white lupin. The percentage of total P present as inorganic P was affected by crop, soil type, and N source. In black soil, the change of organic P fraction induced by N fixation was larger than by urea application. The moderately labile organic P (MLOP) concentration was not affected significantly by soil type and crop species, and it was probably the main P source to the inorganic P fraction because the correlation between the two pools was high (r = 0.945; P < 0.05). Crop species differed in their uptake of inorganic and organic P from soil. Though P fraction concentrations varied between black soil and rice soil, their response to crop species and N source was similar. The amounts of P removed from soil were affected by N source. The right choice of crop species and the application a suitable N source may increase crop yield and P uptake by plant in P-deficient soils.     

Transformation of fertilizer P in a Vertisol amended with farmyard manure

Availability, fixation, and transformation of added P were studied in a 16-week incubation experiment with a Vertisol amended with farmyard manure in pots with 500 g soil each. P availability, as measured by Olsen P, decreased for up to 8 weeks with various rates of added P, when no manure was applied. In the presence of farmyard manure, P availability decreased during the first 6 weeks and then showed a considerable increase from the 8th week onwards. P fixation increased for up to 8 weeks with the rates of P in the absence of manure. With manure application, P fixation increased only during the first 6 weeks and thereafter decreased continuously. Thus the presence of farmyard manure shortened the period of P fixation and promoted its availability. After 16 weeks of incubation, when manure and fertilizer P were applied together, P was transformed into labile organic (NaHCO₃–P), moderately labile organic P (NaOH-P), and calcium-bound inorganic P (HCl-P). When manure was not applied. P accumulated predominantly as labile inorganic (NaHCO₃–P), moderately labile inorganic (NaOH-P), and inorganic HCl-P. The application of farmyard manure enriched long-term P fertility through NaHCO₃–P and NaOH–P and a shortterm P supply as HCl-P. All fractions except inorganic NaOH-P showed good relationships with Olsen P.     

Soil phosphorus mobilization in different taxonomic orders

Changes in P fractions using Hedley's sequential fractionation of organic and inorganic soil P, were studied in soils covering a wide range of developmental stages and original materials. A greenhouse experiment was performed in order to make an exhaustive P uptake by Lolium perenne and to study soil phosphorus mobilization from different fractions. Samples were obtained at 30, 60 and 90 days from sowing, with two fertilization rates added as KH₂PO₄. The exhaustion produced by plants resulted in different patterns of mobilization according to soil characteristics. For control soils the contents of inorganic labile fraction (LIP) decreased at the end of the experience in Mollisol (31%), Vertisol (24%) and Andisol (17%). The mobilization of organic P was greater for Ultisol and Andisol (77 and 75% respectively) than for the other soils. Fertilization affected mainly inorganic P, with a significant increase in contents of LIP in Entisol (46%) and moderately resistant inorganic P (MRIP) in Andisol (15%). Inorganic P/organic P relationship tended to increase during the experiment, while labile P/moderately resistant P increased in Entisol and Mollisol.     

Land-use and fertilization effects on P forms in two European soils: resin extraction and 31P-NMR analysis

Macroporous anion-exchange resin extraction and ³¹P-NMR spectroscopy of dialysed NaOH extracts were used to investigate the effects of land use (Taubenberg, Bavaria: spruce forest, deciduous forest, permanent grass, arable) and fertilization (Askov, Denmark: unmanured, mineral fertilizer, animal manure) on forms of phosphorus in soil with emphasis on the potentially labile organic (P_o) and inorganic (P_i pools. Carbon content ranged from 12.5–118.1 g kg^?1 and total P (P_i) content from 511 to 2063 mg kg^?1. For all soils, the C:P_o ratios of SOM decreased in the order: whole soil, 150: 1–44:1; alkali extract, 57:1–41: 1; resin extract, 20:1–9:1; suggesting an increasing P functionality of the OM with increasing P_o lability. Analysis of functional relation showed a close relation between resin P_o and ³¹P-NMR estimates for diester-P including teichoic acid-P, indicating that these species contributed significantly to the labile P_o pool as determined by the resin method. The most marked effects of land-use were an increase in P_i under grass and arable, a concurrent sequestration of P_o and SOM under grass, and a depletion of P_o under arable. The amount of resin P_j appeared to be a function primarily of fertilization, and amounted to around 100 mg kg^?1 in the fertilized soils irrespective of the SOM content and P source. The forest soil and the unfertilized agricultural soil had much smaller resin P_j values. The soil under grass had the largest amounts in resin P_o and diester-P including teichoic acid-P, indicating a rapid turnover of P_o with build-up of a large potentially labile, microbially derived P_o pool. ³¹P NMR also showed large proportions of labile P_o species in soils where microbial activity is restrained by acidity (Taubenberg spruce forest, phosphonates) or where highly microbially altered OM is relatively enriched (Taubenberg arable, diester-P including teichoic acid-P). We conclude that the resin used in this study isolates a structurally and functionally reasonably uniform pool of potentially labile soil P_o.     

水磷一体化对磷素有效性与磷肥利用率的影响

水肥一体化是发挥水肥耦合效应提高养分效率的重要途径,然水磷一体化研究较少。本文在模拟滴灌条件下研究了液体磷肥和固体颗粒磷肥(TSP)及其不同施用方法对土壤磷移动性、各形态无机磷含量动态变化的影响,比较了玉米磷素营养与磷肥利用率对不同磷源及其施用方式的响应,旨在提出滴灌条件下磷肥高效利用的最优策略。研究结果表明:1)与TSP肥料分次施用相比,液体磷肥分次施用更能提高土壤磷素有效性,在各土层Ca2-P与树脂磷(resin-P)平均含量分别提高12.4%与21.6%,且可显著提高磷在土壤中的移动性(P0.05),resin-P含量的垂直下降幅度降低56.5%;2)与TSP分次施用相比,液体磷肥分次施用的土壤中高活性无机磷含量(Ca2-P、resin-P及Na HCO3-P之和)占无机磷总量的比例提高21.0%,而低活性无机磷含量(Ca10-P与residue-P之和)占无机磷总量的比例则下降10.1%,说明液体磷肥分次施用可减小磷肥在土壤中的固定转化;3)玉米地上部干物质、叶片吸磷量和植株磷素累积吸收量均对不同磷源与施用方式有明显响应(P0.05),液体磷肥分次处理的玉米生物量、吸磷量及肥料利用率分别比TSP肥料分次处理提高27.1%、34.6%及61.4%。水磷一体化施用可提高磷在土壤中的移动性和有效性,减少磷的固定转化,显著改善玉米磷素营养,并明显提高磷肥利用率。     

Legacy phosphorus in calcareous soil under 33 years of P fertilizer application: Implications for efficient P management in agriculture

Phosphorus (P) fertilizers have long been applied in agriculture. However, the influence of long-term P addition on the evolution of soil P fertility and legacy P characteristics have not been well-documented. Herein, literature data were collected from the Chinese National Knowledge Infrastructure Database (CNKI) to explore the evolution of soil P fertility after 33 years of application of P fertilizer; different soil samples were collected from cropland and adjacent uncultivated land to analyse the distribution of P fractions at different soil depths (0–0.8 m) using Guppy's sequential P extraction method. We found that soil Olsen-P significantly increased by 3.6-fold (from 7.2 mg kg⁻¹ in 1981 to 25.9 mg kg⁻¹ in 2013) after 33 years of P application, while total P increased slightly. The ratios of inorganic P fractions in cropland to those uncultivated land followed NaHCO₃-P (1.47) > NaOH-P (1.38) > resin-P (1.37) > residue-P (1.17) > HCl-P (1.11), suggesting that long-term P addition contributed more to labile and moderately labile P rather than non-labile P. Moreover, a principal component analysis could distinguish between cropland and uncultivated land, indicating that long-term application of P fertilizer changed soil P characteristics. Compared to uncultivated land, soil NaHCO₃-P in cropland was closely associated with soil organic C, total nitrogen and carbonate. Collectively, our findings highlight that soil legacy P was notably increased after long-term of P application, and a large portion of the applied P remained in labile and moderately labile forms. Therefore, soil legacy P can be recommended as a useful P management tool.     

旱地土壤微生物磷测定方法研究

介绍了国外关于土壤微生物磷测定方法的研究进展 ,讨论了常用的几种方法所存在的问题 ,介绍了主要操作过程要求。对我国 5种主要母质类型的土壤 (pH 3 .3～ 7.4,1molL- 1KCl)的对比研究表明 ,我国土壤采用氯仿熏蒸、0 .5molL- 1NaHCO3在 1∶2 0土水比提取测定无机磷 (Pi)、并以同时测得的培养土壤微生物的磷的回收率作为计算常数得到的结果最佳。测定的大多数南方土壤的微生物磷占土壤全磷的比例小于 1 .5 % ,微生物碳磷比值大于 3 0∶1 ,反映南方土壤磷的生物活性较低 ,土壤微生物对磷的作物供应调节能力不强。     

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     

Soil legacy phosphorus after 10 years of annual dairy liquid manure application in a no-tillage system

The benefits of manure as a source of nutrients for plants and to improve soil quality are well-known. Monitoring of manure application is needed if environmental issues are to be prevented. In particular, the availability and accumulation of phosphorus (P) has to be subject to rigorous monitoring. This study aims to both evaluate the efficacy of the resin method in extracting inorganic labile P in soils under the long-term application of dairy liquid manure (DLM), and verify the influence of DLM on the recovery of applied P and soil legacy P. To realize our objectives, two long-term field experiments were established under a no-tillage system with annual DLM application on sandy clay loam (sandy Oxisol) and clayey (clayey Oxisol) soils. Treatment consisted of DLM applications (0, 60, 120, 180 m³ ha⁻¹ year⁻¹), independent of mineral fertilizer. Soil samples were taken from the 0–5, 5–10 and 10–15 cm layers after 10 years from the beginning of the trial. A single extraction with resin underestimated inorganic labile P; however, successive extractions were able to take up 43% and 26% of the total P in sandy and clayey Oxisols, respectively, whereas in a single extraction the take-up was 17% and 8% from the same soils, respectively. The resin method was more effective in extracting P from the sandy Oxisol. Thus, when interpreting soil P contents for fertilizer planning, the soil texture should be taken into account. DLM application decreased P recovered from applied P, ranging from 54% to 83% (sandy), and 43% to 67% (clayey), and substantially increased soil legacy P.     

Seasonal effect of the exotic invasive plant Solidago gigantea on soil pH and P fractions

Invasions by alien plants can alter biogeochemical cycles in recipient ecosystems. We test if Early Goldenrod (Solidago gigantea) alters P fractions. To that end, we compare invaded plots and adjacent, uninvaded resident vegetation for specific fractions of organic and inorganic P, phosphomonoesterase (PME) activity in topsoil, and immobilization of P in above‐ and belowground organs and in soil microbial biomass. Invaded plots had lower soil pH and 20%–30% higher labile P fractions (resin‐P_i, bicarb‐P_i, NaOH‐Pi), and the difference was consistent across seasons. There was no difference in microbial P. Alkaline‐PME activity was 30% lower in topsoil of invaded plots. Annual P uptake in aboveground phytomass was not markedly higher in Solidago. In contrast, P in belowground organs steadily increased in autumn in invaded plots, due to both increased biomass and increased P concentrations. This indicated higher net P immobilization in Solidago, far in excess of both resorption from senescing shoots and P requirements for aboveground biomass in subsequent year. Higher turnover rates of P in belowground organs and mobilization of sparingly soluble P forms through rhizosphere acidification may be involved in the observed differences in soil P status between invaded and uninvaded plots.     

生物质炭施用对杉木幼苗土壤磷组分的影响

通过盆栽试验，采用Hedley连续浸提法研究不同生物质炭施用量处理（CK：0 t/hm²；B₁₂：12 t/hm²；B₃₆：36 t/hm²）对杉木幼苗土壤磷组分的影响。结果表明：与CK相比，试验180 d后B₁₂和B₃₆处理土壤全磷与有效磷含量分别增加了8.7%~26.0%和24.0%~101.7%，有效磷在全磷中的比例显著提高；土壤磷组分中，残余态磷在全磷及无机磷组分中的比例均最高，分别为48.5%~51.1%和58.7%~68.3%。B₃₆处理下，土壤各无机磷组分均显著增加，其中易分解态磷和中等易分解态磷在无机磷中的比例显著提高，而稳定态磷和残余态磷的比例显著降低。中等易分解态磷占总有机磷的比例最高，达69.3%~70.2%，生物质炭施用对各有机磷组分在总有机磷中的比例影响均不显著，仅在B₃₆处理下，土壤有机磷中易分解态磷和中等易分解态磷含量显著降低。冗余分析表明，土壤全碳与各无机磷组分呈显著正相关关系，与有机磷组分呈显著负相关关系，是影响土壤磷组分变化的关键因子。