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

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

An evaluation of Colwell‐P as a measure of plant‐available phosphorus in soils of volcanic and non‐volcanic origins in the highlands of Papua New Guinea

Various soil test methods including Olsen, Colwell, Bray and Truog have been used to assess the levels of plant‐available P (PAP) in soils situated in the highlands of Papua New Guinea (PNG). Up until now, though, there has been no guarantee that these tests provide valid assessments of PAP in these somewhat atypical organic matter‐rich tropical soils. Furthermore, the critical soil‐P concentrations associated with the tests have been based on studies conducted elsewhere in sub‐tropical and temperate latitudes and as such may or may not be valid for soils or cropping situations in PNG. Soil (Colwell)‐P and leaf‐P data collected during a recent survey of sweet potato gardens in the highlands of PNG were therefore used to determine if useful relationships existed between these variables for different groups of soils, and if they do, to use these relationships to evaluate critical soil Colwell‐P concentrations corresponding to a known critical concentration of P in sweet potato index leaf tissue. Separate, highly significant linear relationships were obtained between leaf‐P and Colwell‐P for soils of volcanic and non‐volcanic origins. Based on these relationships, the critical Colwell‐P concentration for volcanic soils was found to be four times greater than that for non‐volcanic soils, presumably because much of the P extracted from the former soils with alkaline sodium bicarbonate had been chemically ‘fixed’ via sorption and precipitation reactions with sesquioxides and rendered unavailable to plants at ambient soil pH. These critical Colwell‐P concentrations if adopted as benchmark values for the soil groups in question should ensure that the results of future soil fertility surveys involving Colwell‐P assessments are correctly interpreted.     

The ability of the DGT soil phosphorus test to predict pasture response in Australian pasture soils – a preliminary assessment

Diffusive gradients in thin‐films (DGT) technology provides an alternative assessment of available phosphorus (P) for a range of crops, suggesting a preliminary examination of the performance of the new DGT‐P test, compared to existing bicarbonate extractable Olsen and Colwell P tests, for pastures is justified. This study utilized historic data from the Australian National Reactive Phosphate Rock (NRPR) study (1992–1994) that included 25 experimental sites representing a wide range of soil types and climates used for pasture production. Stored (~19 yr) soil samples were analysed for DGT‐P, Olsen P and a single point P buffering index (PBI) and re‐analysed for Colwell P. Results showed the traditional bicarbonate extractable Colwell (r² = 0.45, P < 0.001) and Olsen P (r² = 0.27, P < 0.001) methods predicted relative pasture P response more accurately, compared to the novel DGT‐P test (r² = 0.09, P = 0.03) when all 3 yr of data were examined. We hypothesize that the harsher bicarbonate extraction used for the Olsen and Colwell methods more accurately reflects the ability of perennial pasture roots to access less labile forms of P, in contrast to the DGT‐P test, which does not change the soil pH or dilute the soil and appears unable to fully account for a plants ability to solubilize P. Further studies are needed to compare the capacity of DGT‐P to measure P availability in perennial pasture systems and to better understand the soil chemical differences between pasture and cropping systems.     

Assessment of co‐blending water treatment residual with dairy manure to reduce phosphorus concentrations in run‐off in Northern Ireland

Losses of phosphorus (P) to water that follow manure applications can be high while water treatment residuals (WTR) have an appreciable capacity to sorb soluble P which is an important risk factor in determining the susceptibility of manure P to run‐off losses. The objective of this study was to assess whether co‐blending WTR with dairy cow manure prior to surface application would reduce P concentrations in run‐off from grassland. An alum‐derived WTR was collected from a water treatment works (WTW), dried and characterized for its phosphorus sorption capacity (PSC) based on oxalate‐extractable Al and Fe. Multipoint P sorption isotherms were used to calculate the Langmuir P sorption maximum (P_max) and equilibrium P concentration (EPC₀). The WTR contained 170 g Al_ox/kg and 2.2 g Fe_ox/kg with a nominal long‐term PSC of 118 g/kg. Following a 6 day incubation of WTR, the Langmuir P_max was 82.6 g/kg and the EPC₀ of 0.13 mg P/L. Laboratory incubations of manure co‐blended with WTR indicated that 144 g WTR/kg dry matter (DM) manure significantly lowered (P < 0.001) manure WSP by 71.5 ± 16.6% after 108 h, but lower WTR mixing rates of 72 and 36 g WTR/kg had no statistical effect on manure WSP. Results from a field experiment using simulated rain on 0.5‐m² grassland plots showed no significant effect on run‐off P 2 days after applying 50 m³/ha of 6% DM manure co‐blended WTR at rates of 150 and 250 g WTR/kg.     

Relation between soil P test values and mobilization of dissolved and particulate P from the plough layer of typical Danish soils from a long‐term field experiment with applied P fertilizers

Accumulation of phosphorus (P) in agricultural topsoils can contribute to leaching of P which may cause eutrophication of surface waters. An understanding of P mobilization processes in the plough layer is needed to improve agricultural management strategies. We compare leaching of total dissolved and particulate P through the plough layer of a typical Danish sandy loam soil subjected to three different P fertilizer regimes in a long‐term field experiment established in 1975. The leaching experiment used intact soil columns (20 cm diameter, 20 cm high) during unsaturated conditions. The three soils had small to moderate labile P contents, expressed by water‐extractable P (3.6–10.7 mg/kg), Olsen P (11–28 mg/kg) and degree of P saturation (DPS) (25–34%). Mobilization of total dissolved P (TDP) increased significantly (P < 0.05) from the intact soil columns with increasing labile P, whereas the increase in particulate P (PP) with increasing labile P content was modest and statistically insignificant. We found concentrations up to 1.5 mg TP/L for the plough layer of this typical Danish sandy loam soil. This highlights that even a moderate labile P content can be a potential source of TDP from the plough layer, and that a lower concentration margin of optimum agronomic P levels should be considered.     

Availability of P from 32P-labelled endogenous soil P and 33P-labelled fertilizer in an alkaline soil producing cotton in Australia

Yield responses of irrigated, field‐grown cotton to phosphorus fertilizer application in Australia have been variable. In an attempt to understand better this variability, the distribution of fertilizer P within soil P fractions was identified using ³²P and ³³P radioisotopes. The soil chosen, an alkaline, grey, cracking clay (Vertosol), was representative of those used for growing cotton in Australia. Chang and Jackson fractionation of soil P from samples collected within 1 h of application indicated that 49, 7 and 13% of the P fertilizer was present as 0.5 m NH₄F, 0.1 m NaOH and 1 m H₂SO₄ extractable P, respectively. Over 89% of the P fertilizer was recovered as Colwell extractable P in these samples, suggesting that the majority of these reaction products was in a highly plant‐available form. Fertilizer‐P remained in an available form within the band 51 days after application, and 68% of the applied fertilizer‐P was recovered as Colwell‐P (1071 mg kg^?1). The Colwell‐P concentration in the band was 35 times that in the unfertilized soil. Thus, the variability in crop response to P fertilizer application in these soils is not a consequence of fertilizer‐P becoming unavailable to plants. These results confirm the suitability of the Colwell (1963) sodium bicarbonate extraction method for measuring available P in these soils.     

Assessing the Feasibility of Olsen P and P Sorption Parameters in Acidic Soils

Plant-available phosphorus (P) and P adsorption capacities are important for crop growth in acidic soils. Olsen P test, which is based on extraction with bicarbonate for predicting the amount of soil P available to plants, was used in this work. Soil P-adsorption capacities were determined by Langmuir line equation. The purpose of this work was to examine the suitability of Olsen P for predicting phytoavailable P and P sorption parameters in acid soil. To this end, we (i) assessed the phytoavailable P by successively pot-cropping rice and (ii) P adsorption characteristics of soil and their relation with Olsen P. Plant-available P, estimated by Olsen P in tested soil, was correlated to labile P. Qm (phosphorus sorption maximum) was negatively correlated with K (P sorption strength). P buffering capacity of soils was P3 (the highest P rate) >P2 (the second highest P rate) >P1 (the lowest P rate) >P0 (no P adding) after 75 day’s rice growth, which indicated P replenishment capacity was different among P treatments. This also suggested that P of plant uptake may decrease soil buffering capacity, especially for soils that contained relatively lower amounts of P. Qm and K were not significantly correlated to Olsen P. Degree of P saturation and Olsen P shared the similar trend with the change of P application rates and sampling dates. We concluded P status in soil can be characterized by degree of P saturation and Olsen P in tested soil. They were able to explain P status from both agronomic and environmental aspects.

Abbreviations: Qm, P sorption maximum; K, P sorption strength; P3, highest P rate in soil; P2, second highest P rate in soil; P1, lowest P rate in soil; P0, P adding in soil.     

Phosphorus Adsorption and Bioavailability in a Paddy Soil Amended with Pig Manure Compost and Decaying Rice Straw

Phosphorus (P) availability in soil is closely related not only to soil P content but also to soil physicochemical and biological properties, which are closely associated with P sorption and biochemical transformation. The aims of this study were to determine the effects of pig manure compost (PMC) or decaying rice straw (DRS) added to a paddy soil on soil pH, soil organic carbon (SOC), dissolved organic carbon (DOC), acid phosphatase, microbial biomass P, soil test P (Olsen P), and P uptake by rice (Oryza sativa L. cv. ‘Liaoyan’). Phosphorus adsorption characterization affected by PMC‐ or DRS‐derived DOC was also studied. Compared with the control, both PMC and DRS treatments increased soil pH, SOM, DOC, microbial biomass P, and Olsen P, and the activity of acid phosphatase during the 110‐day incubation period. Phosphorus adsorption in soil decreased with DOC extracted from PMC and DRS and was well fit by the Langmuir equation. The Olsen P in the PMC‐ and DRS‐treated soil was correlated with both DOC content and acid phosphatase activity. Both PMC and DRS treatments significantly increased dry‐matter yield and P uptake in rice shoot. In conclusion, the increased P availability in the paddy soil was not only a result of direct P supplied following organic manure incorporation, but also an indirect result of reduction in P sorption on the solid phase of the paddy soil by DOCs which were derived from DRS or PMC.     

Changes in the Soil Phosphorus Content of a Long‐Term Fertilization Field Trial Studied in Laboratory Incubations

Abstract

The importance of different soil phosphorus (P) compounds and their transformation influenced by several soil and other factors is well established. However, the dynamics of short‐term processes taking part in the long‐term changes of soil P including immobilization and mobilization is still not completely documented. Laboratory incubation experiments were carried out at 10°C and 40°C for studying the influence of incubation on the availability of residual and freshly applied P in samples of a long‐term fertilization field trial conducted on a brown forest soil (U.S. taxonomy: Orthic Eutrochrept; FAO taxonomy: Eutric Cambisol). Samples showing three levels of P resulting from 10 years of intensive P fertilization (referred as P0, P1 and P2, respectively), were collected 30 years after fertilization ceased. Available P contents of soil samples were determined using three approaches: in water (modified Murphy–Riley method), sodium bicarbonate (Olsen, pH=8.5), and ammonium lactate (AL, pH=3.7) extract. Changes in the amounts of P were determined after 2 and 60 days of incubation in four freshly applied new treatments with increasing additions of P: 0, 100, 500, and 1000 mg of P₂O₅ per kg of soil, representing agronomic and extreme P rates. From the results of our experiments, it was suggested that after 2 days of incubation, at 10°C, both agronomic and extreme P rates resulted in significant increases in P content in each extract. On the other hand, after 60 days, even higher values were obtained. Decreases found in water‐P values after 60 days of incubation were considerable compared to either the Olsen‐P or the AL‐P values, indicating the decline of water‐soluble P forms and further evidence of immobilization with increasing incubation time and temperature. Correlation between water‐P, Olsen‐P, and AL‐P values were significant at both temperatures.     

Structure and hydraulic properties of the boreal clay soil under differently managed buffer zones

Vegetated buffer zones (BZs) between arable fields and bodies of water are commonly established to reduce erosion and run‐off of particle‐bound nutrients. Functioning of a BZ depends on soil structure, as it is important for water infiltration. Therefore, it is vital to understand how varying management practices affect soils of BZs. We studied the structural and hydraulic properties of three differently managed BZs established in a boreal Vertic Stagnic Cambisol (clay, 51%). The three management practices for vegetation were as follows: natural with no treatment, harvested yearly and grazed by cattle. We used bulk density and macroporosity, together with a pore geometry index (air permeability per unit air‐filled porosity), to describe the soil structural properties. Hydraulic properties were measured at different length scales by means of an aggregate sorptivity test, saturated hydraulic conductivity of the core samples and field‐saturated hydraulic conductivity. Vegetation management markedly affected the physical properties in the top 5 cm of the soil. Properties were least favourable for infiltration at the grazed site, with the greatest bulk density, least macroporosity and hydraulic conductivity or greatest pore tortuosity. In general, spatial variation in zones with restricted and good hydraulic conductivity together with reduced aggregate sorptivity in the deeper horizons made the soil prone to preferential flow when initially dry. Prolonged wetness, on the other hand, reduced saturated hydraulic conductivity significantly, resulting in surface run‐off. Harvesting was considered the best management practice due to its inherent capacity for reducing the soil nutrient content and because it has minor implications for soil physical properties.     

Effects of compaction on soil surface water repellency

Water repellency can reduce the infiltration capacity of soils over timescales similar to those of precipitation events. Compaction can also reduce infiltration capacity by decreasing soil hydraulic conductivity, but the effect of compaction on soil water repellency is unknown. This study explores the effect of compaction on the wettability of water repellent soil. Three air‐dry (water content ～4 g 100 g^?1) silt loam samples of contrasting wettability (non‐repellent, strongly and severely water repellent) were homogenized and subjected to various pressures in the range 0–1570 kPa in an odeometer for 24 h. Following removal, sample surface water repellency was reassessed using the water drop penetration time method and surface roughness using white light interferometry. An increase in compaction pressure caused a significant reduction in soil surface water repellency, which in turn increases the soil's initial infiltration capacity. The difference in surface roughness of soils compacted at the lowest and highest pressures was significant (at P > 0.2) suggesting an increase in the contact area between sessile water drops and soil surfaces was providing increased opportunities for surface wetting mechanisms to proceed. This suggests that compaction of a water repellent soil may lead to an increased rate of surface wetting, which is a precursor to successful infiltration of water into bulk soil. Although there may be a reduction in soil conductivity upon compaction, the more rapid initiation of infiltration may, in some circumstances, lead to an overall increase in the proportion of rain or irrigation water infiltrating water repellent soil, rather than contributing to surface run‐off or evaporation.     

The relationship between water‐soluble P and modified Morgan P: results based on data and chemical modelling.

An improved understanding of potential soluble phosphorus (P) loss in run‐off and leachate from agriculturally managed soils presents practical and theoretical challenges. Our study aimed to discover whether modified Morgan extractable P (MMP) can be used to predict water‐soluble P (WSP). We first addressed the relationship between MMP and WSP, and whether MMP is useful for predicting the WSP concentrations demanded by water quality regulations. Secondly, we applied novel soil chemical models to explain why the relationship between MMP and WSP depends upon soil properties. Thirdly, we explain how soil properties relate to potential soluble P loss in situations in which soil is subjected to a wide liquid‐to‐soil ratio (e.g. run‐off and rivers) compared with those with a narrow ratio (e.g. soil porewater). To address these P loss scenarios, 60 agricultural topsoils (0–10 cm) were collected from a mixed‐farming catchment (Lunan catchment, northeast Scotland) and chemically characterized. Theoretical understanding of P solubility was obtained with a P sorption model. The data showed variability in the relationship between MMP and WSP. Modelling shows the MMP versus WSP relationship is nonlinear, depending on several confounding factors (P sorption capacity (PSC), Ca, pH) and the liquid‐to‐soil ratio (L:S) employed for WSP determination. Consequently, the slope of the relationship is not unique but depends subjectively on the set of soils surveyed. MMP versus WSP at large L:S (e.g. in run‐off or rivers) is positively correlated to PSC, whereas at narrow L:S (e.g. porewater) there is a negative correlation with PSC. The study provides new ideas for the interpretation and extrapolation of agronomic soil test data for soils of varied properties and highlights the need to utilize insights from soil chemistry.     

Simple phosphorus saturation index to estimate risk of dissolved P in runoff from arable soils

Abstract. There is increasing evidence that phosphorus has been accumulating in the surface horizons of agricultural soils to the extent that some soils represent a potential diffuse source of pollution to surface waters. The relationships between equilibrium phosphorus concentration at zero sorption (EPC ₀) of soil and a number of soil physicochemical variables were investigated in the surface layers of arable and grassland agricultural soils sampled from the Thame catchment, England. Soil EPC₀ could be predicted from an equation including soil test (Olsen) P, soil phosphate sorption index (PSI) and organic matter content (OM) (R²=0.88; P <0.001) across a range of soil types and land use. The simple index Olsen P/PSI was found to be a good predictor of EPC₀ (R²=0.77; P <0.001) and readily desorbable (0.02 m KCl extractable) P (R²=0.73; P <0.001) across a range of soil types under arable having soil organic matter contents of <10%.     

Changes in some soil phosphorus availability parameters as induced by phosphorus addition and soil sorption properties

Abstract

Changes in agronomic and environmental soil phosphorus (P) availability parameters, i.e., Mehlich‐ and Olsen‐extractable P, reversibly‐adsorbed P, soil‐solution P, and equilibrium‐P concentration were determined following equilibration of 13 Italian soils with five rates of P application (0, 12.5, 25, 50, and 100 mg P kg^‐1 soil). Soil P availability as determined by each parameter increased with added P. The relative change in soil P availability with added P was a function of soil sorption index silicon (SI), according to the equation DP=(P_added)^a*exp(b+g*SI). This equation accounted for 94 to 98% of the variance in soil‐P availability. The inclusion of SI in a soil testing program may increase the reliability in assessing both soil‐P fertilizer requirements and the vulnerability of a soil to P loss in runoff following land application of fertilizer or manure P.     

Evaluation of two soil conditioners for limiting post‐fire erosion as part of a soil conservation strategy

Soil conservation is a major concern for catchments affected by forest fires. The lack of vegetation cover and the development of soil water repellency increase the risk of topsoil erosion. This paper evaluates two soil conditioners (a wetting agent and a polyvinyl acetate) for limiting overland flow and erosion in inter‐rill areas. Unburned and burned soil samples were treated with one or both soil conditioners. The effects of these treatments on run‐off, water retention, erosion and plant growth were assessed using laboratory rainfall simulations. Polyvinyl acetate had little impact on water retention but was effective in reducing soil loss. The surfactant had little impact on water run‐off or soil loss but substantially improved water retention and plant biomass production. Application of soil conditioners on post‐fire areas could be a valuable technique in a soil conservation strategy. To maximize their benefits, soil conditioners could be applied with seeding using hydroseeding techniques and be limited to particular areas, such as paths and roadsides. Laboratory results indicate that field testing should also be carried out.     

Predicting the changes in environmentally and agronomically significant phosphorus forms following the cessation of phosphorus fertilizer applications to grassland

Phosphorus (P) loss from soil can impair surface water quality. Losses from soil are related to soil P concentrations, but agronomic measures such as Olsen P do not in many cases predict the potential for P loss. One possible strategy to decrease P loss is to stop applying P fertilizers. We examined the changes in both agronomic (Olsen P) and environmental [water‐extractable P (WEP) and calcium chloride‐extractable P (CaCl₂‐P)] P tests, and the potential implications following a halt to P fertilizer application to four long‐term grassland field trials on different soil types. Exponential decreases in Olsen P and WEP concentration over time were observed in three of the four trials, but only in one trial for CaCl₂‐P. The rates of decrease in Olsen P (OP) and WEP concentration were best correlated with initial WEP (WEP_i) concentration and the quotient of Olsen P_i/P retention (PR, a measure of Al‐ and Fe‐oxides), respectively. The equation t = 1/(?0.035 × ln OP_i/PR ? 0.0455) × (ln WEP_t ? ln WEP_i) was used to predict the time (t) taken for WEP concentrations at the sites to decrease to 0.02 mg/L (WEP_t), which is proposed as a limit for dissolved reactive phosphorus in overland flow, and the result was 23–44 yr. Results from a similar equation for Olsen P predicted a quicker rate of WEP. A significant decline in dry matter (DM) yield was observed at one trial site. For this site, the rate of decline in DM yield was of a similar magnitude to the rate of decline in WEP concentration. This suggests that halting P fertilizer application to decrease P loss as measured by WEP concentration may decrease farm productivity. An alternative, more financially acceptable, strategy is required, such as a negative P balance while maintaining yields with N fertilizer, but further work is required to assess both the agronomic and environmental implications of this strategy.     

Comparison of standard and total Colwell procedures for measuring soil test phosphorus

Abstract

When soils are extracted with sodium bicarbonate to measure soil test phosphorus (P) by the standard Colwell procedure, the concentration of P in the extract solution is measured using the Murphy and Riley procedure. This measures P as orthophosphate (PO₄) and most of the organic P extracted is not measured. The total (inorganic plus organic) P extracted can be measured by digesting an aliquot of the extract solution with perchloric acid to convert all the extracted P to PO₄ before measuring the P concentration by the Murphy and Riley procedure. This is called total Colwell P. Data from one crop and two pasture field experiments in Western Australia are presented in which soil test P measured in 1991 and 1992 by the standard and total Colwell procedures were compared. Fertiliser P residues, including organic P, accumulate in the topsoil because, (i) the fertiliser is applied to the surface of pastures, and (ii) crops are being increasingly sown by minimum (conservation) tillage when P is concentrated in the top approximate 5 cm of the soil compared with about 10 cm when crops are sown conventionally. Consequently, to measure soil test P in the present study, soil samples were collected in February 1991 to either 5 or 10 cm depth. For the two Colwell procedures and both sampling depths, soil test P was related to: (i) the level of P applied in previous years and to (ii) plant yield measured later on that year (the soil test P calibration). Soil test P was larger for the total Colwell procedure and for soil samples collected to 5 cm depth. Total Colwell P as the dependent variable was closely correlated with standard Colwell P as the independent variable. The relationship between soil test P and the level of P applied, and the calibration relating yield to soil test P, were different for standard and total Colwell P. Neither method can be claimed to be significantly better than the other. It is concluded that use of the total Colwell procedure instead of the standard procedure is not warranted. Likewise, there was no evidence that collecting soil samples to 5 cm to measure soil test P provided better estimates of the current P status of soils than collecting soils to the standard 10 cm depth. There is therefore no need to change the sampling depth.     

长期施肥红壤性水稻土磷素演变特征及对磷盈亏的响应

研究双季稻种植制度下长期不同施肥红壤性水稻土磷素含量及磷素有效性演变特征及其对土壤磷盈亏(磷平衡)的响应,为南方双季稻区红壤性水稻土科学施磷提供依据。以35年长期肥料定位试验为平台,研究不同施肥处理土壤全磷、有效磷及磷活化系数(PAC)的演变规律,计算不同处理土壤-作物系统每年磷素盈亏量及累积磷素盈亏量,探讨土壤全磷、有效磷及PAC与累积磷盈亏量的响应关系。结果表明,不施磷肥的CK和NK处理土壤全磷、有效磷和PAC随试验年限呈持平或下降趋势;不施磷肥仅施猪粪的NK+PM处理土壤全磷呈缓慢上升趋势,有效磷和PAC呈下降趋势;施化学磷肥或化学磷肥配施稻草的NP、NPK、NP+RS和NPK+RS处理土壤全磷在试验前10年上升速率较快,之后25年上升速率变缓或随时间变化不显著,土壤有效磷在试验前5年急剧升高,之后随时间变化速率减缓或基本持平。CK、NK和NK+PM处理35年土壤PAC平均值较试验初始值分别下降33.2%、29.7%和16.6%,NP、NPK、NP+RS和NPK+RS土壤PAC较初始值分别提高66.2%、60.6%、65.6%和52.9%。不施磷肥导致红壤性水稻土磷素亏缺,不施化学磷肥仅施猪粪土壤磷素基本持平,施用化肥磷及化肥磷配施稻草土壤磷素盈余。土壤全磷、有效磷及PAC与土壤磷累积盈亏量均呈极显著正相关关系,土壤每盈余磷100 kg hm-2,全磷含量提高0.03 g kg-1,有效磷提高1.20 mg kg-1,土壤PAC上升0.09%。外源磷投入是影响土壤磷素及磷有效性的重要因素,在本试验条件下,长期不施磷或磷投入不足导致土壤磷亏缺,进而导致土壤磷及磷有效性降低,而化肥磷及有机无机磷配施促进了土壤磷盈余及土壤磷素肥力的提高。     

Effects of soil‐surface microbial community phenotype upon physical and hydrological properties of an arable soil: a microcosm study

The nature of the first few millimetres of the soil surface strongly affects water infiltration rates, generation of run‐off, soil detachment and sediment transport. We hypothesized that the phenotypic community structure of the soil‐surface microbiota affects the physical and hydrological properties of an arable soil. A range of contrasting microbial community phenotypes were established in microcosms by manipulating the wavelength of light reaching the soil surface, with the microcosms being incubated in the field for approximately 6 months. Phenotypes were characterized by phospholipid fatty acid (PLFA), ergosterol and chlorophyll analysis. The microcosms were then subjected to simulated rainfall at an intensity of 60 mm hour⁻¹ for 20 minutes at a slope gradient of 9°. Water infiltration rates, run‐off generation, soil loss (including a particle‐size analysis of the sediment) and soil‐surface shear strength were quantified. Distinct microbial phenotypes developed on the soil surfaces with UV‐A and restricted‐UV treatments when compared with subsurface layers. There was significantly greater fungal biomass in the no‐light treatment when compared with all other treatments, with approximately 4.5 times more ergosterol being extracted from the subsurface layer of the no‐light treatment when compared with other treatments. The no‐light treatment produced the greatest amount of run‐off, which was approximately 15% greater than the restricted photosynthetically‐active radiation (PAR) treatment. Significant differences between treatments were also found in shear strengths, with increasing strength being correlated with increasing ergosterol concentration. Water infiltration, erosion and the sediment concentrations in run‐off were not significantly different between treatments. This work demonstrates that the quality of light reaching the soil surface affects the microbial phenotype, in turn producing functional consequences with regard to the physical and hydrological properties of arable soil surfaces.     

施用常规磷水平的80%可实现玉米高产、磷素高效利用和土壤磷平衡

【目的】近年来,黑土有效磷含量呈逐年增加趋势。研究田间条件下,黑土的玉米产量及构成因素、磷素的吸收利用和土壤有效磷含量变化对不同施磷水平的响应,为黑土区的磷肥合理施用和地力培育提供理论依据。【方法】在土壤有效磷初始含量较高（30.15 mg/kg）的吉林公主岭黑土区,进行了3年的田间试验,以不施磷肥为对照（P0）,设置当地磷肥用量的80%（P₂O₅ 60 kg/hm2,P60）和当地施肥量（P₂O₅75 kg/hm2,P75）,研究不同施磷水平对玉米产量及产量性状、磷素吸收分配、磷肥利用效率的影响,并分析了土壤表观磷平衡和有效磷含量的变化。【结果】连续三年（2009~2011年）不同施磷水平下,玉米的产量随施磷水平的提高而增加,到第三年施磷处理的玉米产量显著高于不施磷处理,随施肥年限增加,P60与P75处理的增产效应差距缩小。P75处理吸收的磷素高于P60,但分配到籽粒中的磷素比例逐年下降,说明其吸收的磷素未高效转移到籽粒中,存在磷素奢侈吸收现象。两个施磷处理的磷肥利用率均为P75>P60,磷肥偏生产力均为P60>P75,说明P60处理中土壤基础养分和施入磷肥的综合效应更大。2009~2011年,土壤的表观磷平衡,P0处理一直处于亏缺状态,P60和P75处理均有盈余。P0、P60和P75处理的土壤有效磷的变化量为-15.4、-0.19和3.50 mg/kg。有效磷含量变化与表观磷盈余量呈极显著线性正相关,土壤P盈余每增加100 kg/hm2,有效磷含量增加9.6 mg/kg。【结论】在有效磷含量较高的黑土区,适当减少磷肥用量（60 kg/hm2 P₂O₅,比传统施肥减少20%）能获得与传统施磷相当的产量,维持土壤适宜的有效磷含量和供磷水平,并能保证磷肥的高效利用。可以考虑将P₂O₅ 60 kg/hm2作为黑土区的推荐施磷水平。