Assessing phosphorus bioavailability in agricultural soils and runoff

Bioavailable phosphorus (BAP) transported in agricultural runoff can accelerate surface water eutrophication. Although several algal assays and chemical extractions have been proposed to estimate BAP, procedural and theoretical limitations have restricted widespread BAP measurement. Thus, a routine method was developed to estimate BAP, which uses iron oxide-impregnated paper strips (Fe-oxide strips) as a P-sink for BAP in runoff. In the proposed method BAP is determined by shaking 50 mL of unfiltered runoff with one Fe-oxide strip for 16 h. Phosphorus is removed from the strip by 0.1M H₂SO₄ and measured. The BAP content of runoff from 20 agricultural watersheds in the Southern Plains was related to the growth of P-starved algae incubated for 29 d with runoff as the sole source of P. Acting as a P sink, Fe-oxide strips may have a stronger theoretical basis than chemical extraction in estimating BAP. The method may also have potential use as an environmental soil P test to indicate soils liable to enrich runoff with sufficient P to accelerate eutrophication. Bioavailable P loss in runoff was lower from no till (438 g ha^–1 yr^–1) than from conventional till (1288 g ha^–1 yr^–1). Kinetic and enrichment ratio approaches accurately predicted (r² of 0.93) BAP transport in runoff during 1988 to 1990. Use of the Fe-oxide strip method will facilitate estimation of BAP transport in runoff and thereby, improve assessment of the resultant impact on the biological productivity of receiving surface waters.Abbreviations A Degree of soil aggregation (unitless) - B Soil bulk density (Mg m^–3) - BAP Bioavailable P content of runoff (mg L^–1 and kg ha^–1) - BIOP Bioavailable P content of soil (mg kg^–1) - BPP Bioavailable particulate P content of runoff (mg L^–1 and kg ha^–1) - D Effective depth of interaction between runoff and surface soil (mm) - DP Dissolved P content of runoff (mg L^–1 and kg ha^–1) - ER Enrichment ratio (unitless) - P Phosphorus - P_a Bray I available P content of 0-50 mm depth of soil (mg kg^–1) - PP Particulate P content of runoff (mg L^–1 and kg ha^–1) - STP Soil test P, plant available (mg kg^–1) - TP Total P content of runoff (mg L^–1 and kg ha^–1) - t Duration of runoff event (min) - W Runoff water/soil (suspended sediment) ratio (L g^–1) - K,, ß, i Constants of the equation describing the kinetics of soil P desorption     

Evaluating the spatial and temporal dynamics of farm and field phosphorus and potassium balances on a mixed crop and livestock farm

Methods to track P and K on farms over time at varying spatial scales can improve farm agronomic and environmental performance monitoring. An annual nutrient balance was used to determine P and K balances at varying spatial scales on a 128 ha mixed crop and dairy farm in a central Pennsylvania limestone valley for each of nine years. Alfalfa (Medicago sativa L.) and corn (Zea mays L.) occupied 60% and 40% of the cropland, respectively. Inputs of P and K to the farm exceeded outputs over the study period. Net increases of P and a decrease in K were determined in the aggregate of all fields over the 9-yr period. The balance of P and K varied with time within a field, and by field within a year because nutrient inputs and removals varied with crop selection, management tactics, and year in the rotation. Recognizing that increases in field P are in proportion to P entering the farm can help reduce P accumulation in fields by addressing surpluses at their source or balancing managed flows for the farm. Conversely, decreases in field K associated with forage crops may be the reason for additional supplemental K inputs to the farm. Monitoring nutrient stocks (soil testing) and flows (input/output balances) at different scales in conjunction with spatial patterns of nutrient balances can be the foundation for integrating farm activities and information technologies in a new generation of performance enhancing tools.     

表面活性剂对料浆法重钙水溶磷影响的实验研究

为了提高重钙产品水溶磷含量,模拟料浆法重钙生产工艺,在实验过程中添加表面活性剂,研究其对重钙产品水溶磷的影响。从21种单一及其复配型中筛选出了可以有效提高重钙水溶磷的6种表面活性剂。实验表明,通过添加表面活性剂,改善料浆反应状况,提高重钙水溶磷含量是可行的。     

Agro-farming systems determine phosphorus budget characteristics at the farm and catchment scales in subtropical China

Agricultural and economic activities may profoundly determine phosphorus (P) budget characteristics that affect environmental quality; therefore, P budget characteristics were investigated at the farm and catchment scales, and the total-phosphorus (TP) concentrations in stream water were observed to examine their relationships in eight Chinese subtropical catchments. The results showed that chemical fertilizer accounted for 67–76% of the total P input and cereal grain comprised of 60–62% of the output in the planting farms, while animal feed and animal product accounted for 62–95 and 48–71% in the planting–livestock farms and livestock farms, respectively, indicating that agro-farming systems determined the P budget characteristics at the farm scale. The P input, output, and surplus intensities linearly increased with agricultural incomes in the agro-farming systems, suggesting that economic activities greatly affected the P budget characteristics at the farm scale. The catchment P budget characteristics were largely shaped by the characteristics at the farm scale; the planting–livestock farm proportion was negatively correlated (R²?>?0.55) while the livestock farm proportion was positively correlated (R²?>?0.59) with catchment P budget items. These effects on catchment P budget characteristics greatly deteriorated stream water quality; both the TP concentrations and loadings in stream water were significantly correlated to catchment P input, output, and surplus intensities. Considering the higher economic benefits and lower P input and surplus intensities due to the closed P cycle loop between cropping and husbandry, planting–livestock system should be promoted at the farm scale to protect catchment water environmental quality in subtropical China.     

Dietary and developmental influences on induced detoxification in an oligophage

Many plant secondary compounds induce detoxification activity in herbivorous insects. Although inducibility may be advantageous as a means of reducing costs associated with maintenance of metabolism, another benefit of inducibility is that it may allow insects to tailor their detoxification profiles to multiple substrate toxins in their diets. The parsnip webworm, Depressaria pastinacella, must contend with many types of furanocoumarins, toxins present in abundance in all of its host plants. Previous studies have documented that cytochrome P-450s are responsible for metabolism of furanocoumarins in this species and that this overall activity is inducible. In this study, we examined the effects of ingestion of single furanocoumarins on metabolism of multiple furanocoumarins and the ability of webworms to adjust their metabolism profiles to match artificial diets with furanocoumarin content differing qualitatively and quantitatively from the average content found in their principal host. That detoxification rates of newly molted sixth instars prior to feeding did not differ from those of actively feeding fifth or sixth instars suggests that constitutive activities of furanocoumarin-metabolizing enzymes are maintained in the absence of substrates. All of the induction assays in this study were performed with ultimate instars. Each of the furanocoumarins assayed was found to induce metabolism of five different furanocoumarin substrates; however, the induction profile was independent of the inducing agent. Consistent with this finding, webworms were incapable of matching their detoxification profiles to diets with different furanocoumarin compositions. Thus, the profile of detoxification within individuals of this species appears to be genetically fixed, although there is considerable variation in profiles among individuals.     

芦荟凝集素的理化性质及其对动物细胞生长的影响

对分别从中华芦荟、库拉索芦荟和木立芦荟叶肉组织中分离提取得到的 3种凝集素 (命名为Lec1、Lec2和Lec3)进行了理化性质的比较研究 ,考察了三者的分子质量 ,对糖抑制的专一性和糖基组成。结果表明Lec1和Lec3的相对分子质量为2 3 0 0 0 ,而Lec2为 2 6 0 0 0 ,只有Lec3能被麦芽糖抑制。糖基组成分析结果表明 ,三者的糖链部分主要由甘露糖、葡萄糖和N 乙酰氨基葡萄糖构成。三种芦荟凝集素能够识别并抑制K562乳腺癌细胞的生长 ,中华凝集素、库拉索凝集素、木立凝集素的抑瘤率IC50值分别为 4 1 93、2 30 5、1 41 8mg/ml。而在质量浓度 >2 5mg/ml时它们对成纤维细胞FC的生长有一定的促进作用。动物体内实验进一步证实了芦荟凝集素的抑瘤作用 ,同时表明芦荟凝集素能够激发机体的免疫功能来抵御癌细胞的入侵     

A phosphorus budget of a poultry farm and a dairy farm in the southeastern U.S., and the potential impacts of diet alterations

Current and potential environmental problems associated with P transport from lands receiving high application rates of animal waste are a major concern. Phosphorus management strategies are needed to reduce P loading on land. This study was conducted to compare on-farm P budgets for a modern broiler farm and a dairy farm under traditional diets and management practices. Phosphorus inputs, recycling and outputs were assessed for both farms. A typical broiler and a dairy farmer from North Carolina were interviewed and pertinent information for the study was obtained, in cooperation with extension agents, and other professionals associated with the farms. The annual on-farm P surplus for the broiler farm was 6,380 kg, while that for the dairy farm was 1,141 kg. This corresponds to an annual application of 65 kg P ha^–1 for the broiler farm and 20 kg P ha^–1 for the dairy farm in excess of removal. The potential for reducing P surpluses by the addition of phytase enzymes and/or the use of low phytic acid corn (Zea mays L.) feed in the broiler farm diet was also assessed. Estimates by animal nutritionists indicate that feed supplementation with phytase enzyme can reduce the broiler farm's P surplus by 33%. The use of low phytic acid corn can reduce the surplus by 49% and a combination of the two can reduce the surplus by 58%. In this study, the incorporation of soybean (Glycine max (L.) Merr.) and alfalfa (Medicago sativa) land into the waste utilization plan of the dairy farm decreases the annual P surplus from 20 to 9 kg P ha^–1. The use of new feed technology and expanding waste application to a larger land base can significantly alter the P budgets of broiler and dairy farms and reduce P surpluses, minimizing the risk of environmental problems.     

Direct and residual fertilizer phosphorus effects on yield and phosphorus efficiency of upland rice in an Ultisol

Phosphorus (P) deficiency is one of the major limiting factors for crop production in highly weathered soils in the humid zone of West Africa. Very few studies have evaluated the residual value of fertilizer P to rice in these soils. Field experiments were conducted for three years (1993–1995) to determine the response of four upland rice cultivars to fertilizer P applied at 0, 45, 90, 145 and 180 kg P ha^-1 only once in 1993, and to fertilizer P residues in 1994 and 1995. The soil at the experimental site, in the humid forest zone of Ivory Coast (West Africa), was an Ultisol, low in available P. Grain yields of the rice cultivars were significantly increased by fertilizer P in 1993, and by the fertilizer P residues in 1994 and 1995 although the magnitude of response decreased with time since the fertilizer was applied. The cultivars differed in cumulative agronomic and physiological efficiencies, and the efficiencies were higher at the lower rates of P. The amounts of total P removed in three successive crops were similar for all the four rice cultivars although P harvest index was 10–12% higher in the P efficient than inefficient cultivars. The results suggest that the differences observed in the P efficiency of rice cultivars are due to differences in the internal efficiency of P. This revised version was published online in August 2006 with corrections to the Cover Date.     

Assessing phosphorus management among organic farming systems: a farm input,output and budget analysis in southwestern France

Organic farming is gaining interest worldwide due to its low environmental impact. However, questions still remain about its long-term sustainability, particularly in terms of nutrient management. There is debate about the ability of organic farming systems to compensate for nutrient exports due to crop and animal production. Stockless systems are considered as the most critical and they are generally associated with negative farm-gate nutrient budgets. In this study, we examined the farm-gate nutrient budgets of 23 organic farms located in southwestern France, with special focus on stockless farming systems. Phosphorus (P) was taken as a case study due to the issue of its critical management in organic farming systems. The farms were characterised on the basis of interviews with farmers and the soil nutrient status was assessed through soil sampling. Results showed that none of the farms imported rock phosphate fertiliser. On the contrary, most farms imported organic fertiliser and/or compost and manure, the latter from neighbouring farms or urban areas. As a consequence, stockless farm P budgets were not necessarily negative and options existed from achieving better nutrient cycle closure. However, soil P test was low to moderate in many cases. These results suggested that P management in organic farming systems is not simply related to the mixed versus specialised characteristics of the farms and that nutrient cycling should be addressed and assessed at a larger, e.g., district, scale.     

纳米银在饱和多孔介质含水层中迁移主控机理和影响特征

纳米银（AgNP）作为应用最广、生态毒性最强的工程纳米材料之一,一旦进入地下水环境,将引发环境问题。目前,环境因素对纳米银在地下水环境中运移的影响机理尚不清楚。通过室内柱实验,研究了流速（1、2 ml·min^-1）和介质粒径特征（0.605、0.115 mm以及混合粒径的玻璃珠）对纳米银在饱和多孔介质中迁移的影响。研究结果表明纳米银在粒径较大（0.605 mm）的介质中的迁移主要受吸附沉降控制;在小粒径介质中（0.115 mm以及混合粒径玻璃珠）,迁移过程同时受吸附沉降和阻塞沉降两种机理的控制,且阻塞效应主要受小粒径部分介质控制。水流速度提高能降低大粒径介质中纳米银颗粒的沉降效率,从而提高其迁移能力。而对于小粒径介质和混合粒径介质,流速提高除了降低纳米银的沉降效率,还能降低阻塞效应和促进尺寸排除效应,不但能更显著地降低纳米银在介质中的衰减,还能提高纳米银在介质中的穿透速度。研究成果对于理解复杂的场地条件下纳米材料的迁移分布动态具有理论价值。     

The effect of particle size on North Carolina phosphate rock on its dissolution in soil and on levels of bicarbonate-soluble phosphorus

The effect of the particle size of North Carolina phosphate rock on its dissolution in soil was investigated in the laboratory using four size fractions (150–250, 106–125, 45–53 and < 38µm) and two levels of application. Dissolution as measured by soil-exchangeable Ca increased to a minor extent with both decreasing particle size and incubation period. For a PR application of 400µg P/soil the percentage dissolution ranged with decreasing particle size from 13 to 18% and 14 to 20% of applied P for 7 and 35 days incubation periods respectively. The highest percentage dissolution occurred for the smallest particle size. The percentage dissolution was much lower (6–7% and 7–8% of applied P for 7- and 35-day incubation respectively) for the higher application level of 1600µg P/g soil although the absolute amounts of dissolution were larger. Amounts of bicarbonate-soluble p in the soil also increased with decreasing particle size and were about 3–4% and 1% of applied P for 400 and 1600µg P/g levels of application respectively for the 35-day incubation.     

Experimental investigation on the mean drop size and drop size distribution in an L-shaped pulsed sieve-plate column

Vertical pulsed extraction columns cannot be employed in applications with height limitations. On the other hand, the horizontal extraction columns have low throughput, which affects their applicability in industrial applications. Therefore, there is a need to design a new type of extractors for such circumstances. In this paper, an experimental study on drop sizes has been implemented in a novel L-shaped pulsed sieve-plate extraction column in the absence and presence of mass transfer. Moreover, new correlations are developed for prediction of the mean drop size and size distribution using the log-normal probability density function.     

缺氧环境对颗粒污泥强化除磷系统释磷的影响

以除磷颗粒污泥为研究对象,采用批次试验,以混合丙酸和乙酸（2∶1）为外加碳源,在厌氧起始阶段投加不同浓度的NO^-₃-N（0, 20, 30, 50和75 mg·L^-1, pH=8.0）和NO^-₂-N（10,20,40和60 mg·L^-1, pH=7.0, 7.5和8.0）,研究缺氧环境对颗粒污泥强化除磷系统释磷的影响。结果表明,硝态氮的投加对聚磷菌释磷无明显抑制,系统中VFA的吸收、磷的释放和硝态氮的反硝化同时发生,挥发性脂肪酸（相似文献   

Fertilizer rate and hedging intensity influences on the yield and fruit size of rabbiteye blueberry,cultivar Tifblue

A field study was initiated to investigate the effects of two rates of N-P-K fertilizer, summer vs. winter hedging time, and three hedging intensities on yield and fruit size of mature rabbiteye blueberry (Vaccinium ashei Reade), cv. Tifblue. Yields were reduced by 45% the first year when no fertilizer was applied and 21% the fifth year of the experiment when half-rate fertilizer was used. No significant differences between full- and half-rate fertilizer effects were observed during the 2nd, 3rd, or 4th year of the study. However, the difference between the 5-year yield averages of full- and half-rates approached the 0.05 significance level indicating higher yield with the full rate of fertilizer. Winter hedging of 33 and 50% produced more fruit the last three years than the same hedging intensities in the summer. Fertilizer rate and hedging intensity interaction was significant for yield and fruit size for some years. Full-rate fertilizer produced more fruit on 100% hedging intensity than on 33% hedged plants. Half-rate fertilizer produced higher yields on 33% hedged plants compared to those hedged 100%. Fruit size was not significantly affected by the rate of fertilizer or the time of hedging. Hedging intensity did influence fruit size which varied from one year to another.     

Electrtic transport properties and the size effect in ZrO2-based ceramic materials

Amorphous nanomaterials in the ZrO₂-CeO₂ system are synthesized. The aging and crystallization processes in a complex zirconium-cerium hydrogel are investigated. Powders with a crystal size of 45–100 nm are prepared. Samples having a porosity of less than 2.2% are produced from the powders. It is demonstrated that tetragonal zirconia-based solid solutions Zr_1?x Ce_xO_2?δ sintered at a temperature of 1500°C possess ionic conductivity in air and in noble gasses. The assumptions are made regarding the mechanisms of ionic (surface anionic) and electronic (hopping) conduction in samples of the 88ZrO₂ · 12CeO₂ (mol %) composition. The solid solutions prepared can be used at a temperature of 720°C as high-strength inexpensive solid electrolytes.     

Influence of soil phosphorus and manure on phosphorus leaching in Swedish topsoils

In Sweden, subsurface transport of phosphorus (P) from agricultural soils represents the primary pathway of concern for surface water quality. However, there are mixed findings linking P in leachate with soil P and limited understanding of the interactive effects of applied P sources and soil test P on P leaching potential. Identifying soils that are susceptible to P leaching when manure is applied is critical to management strategies that reduce P loadings to water bodies. Intact soil columns (20 cm deep) from five long-term fertilization trials across Sweden were used in leaching experiments with simulated rainfall to explore the interactive effects of dairy cow (Bos taurus L.) manure application, soil test P and cropping system. Strong relationships were observed between ammonium lactate-extractable P in soil and dissolved reactive P (DRP) concentrations in leachate, although regression slopes varied across soils. For three soils, application of manure (equal to 21–30 kg P ha^?1) to the soil columns significantly increased DRP leaching losses. The increase in DRP concentration was correlated to soil test P, but with wide variations between the three soils. For two soils leachate P concentrations after manure addition were independent of soil P status. Despite variable trends in P leaching across the different soils, P concentrations in leachate were always moderate from soils at fertilization rates equivalent to P removal with harvest. Results clearly stress the importance of long-term P balance to limit P leaching losses from Swedish agricultural soils.     

Water vapor transport in an epoxy resin based on TGMDA and DICY

Water uptake has been measured in an epoxy resin based on tetraglycidylmethylenedianiline curved with dicyanidamide. The curing behavior of this system as elucidated by differential scanning calorimetry and Fourier transform infrared is complex. Based upon this information we selected curing temperatures and times in addition to the “standard” cure. The kinetics of the sorption of water by the materials which have undergone the standard cure indicate that the two modes of sorption are involved at high humidity and only a single mode at lower humidity (as seen by changes in the slope of the log M_t vs log t plots). The kinetics of the sorption in the resins which have undergone post cure at higher temperatures also indicate two or more modes of sorption at high humidities. However the slopes of the log M_t vs log t plots differ from those for the resin with standard cure. Subsequent sorption/desorption cycles on the standard cure resin showed marked increases in the initial sorption rate as well as changes in mode, suggesting that irreversible changes in the resin had occurred.     

Rates and controls on denitrification in an agricultural soil fertilized with liquid lagoonal swine waste

Under laboratory conditions, we studied rates and controls on denitrification and denitrification potential (denitrifying enzyme activity, DEA) in agricultural soils in the southeastern United States that had been repeatedly fertilized with liquid lagoonal swine effluent. This is a waste management practice commonly employed by large-scale swine production facilities that have proliferated regionally in the past 10 years. The microbial community was rapidly responsive to the added waste, as denitrification N flux (N₂ + N₂O) from intact soil cores increased from about 200 to as high as 2850 g N m^–2 h^–1, usually within 1 day of application. Elevated rates of denitrification were short-lived (3 days), as the combination of coarse soil texture (rapid drainage) and low mineralization potential (low organic content) of the waste rapidly restored aerobic conditions. Although <2% of the fertilizer-N was lost to denitrification by the time rates had returned to pre-fertilization values after 8–12 days, soil NO₃^––N levels increased from 5 g N g_dw soil^–1 to as high as 43 g N g_dw soil^–1, providing not only substrate for additional denitrification following rainfall, but also a mobile N source for both offsite transport by surface and groundwater and assimilation by plants. Both N₂O and N₂ production from denitrification were unresponsive to changes in soil moisture until field capacity was approached or exceeded. Temperature coefficients (Q₁₀) for DEA varied from 1.6 to 2.8 between 7 and 30 °C, depending on the temperature interval, while high DEA between 20 and 40 °C pointed to a denitrifying community well-adapted to regional summer soil temperatures. Glucose-C or NO₃^––N amendments proved equally stimulatory to DEA in homogenized soils relative to water-only controls. However, addition of the combined substrates gave the best response, indicating that these chemical factors were equally important controls on potential denitrification in these soils once anaerobic conditions had become established.     

Ameliorating effects of phosphorus,lime and animal manure on wheat yield and root cation exchange capacity in degraded alfisols of north-west himalayas

A field experiment over the two years was conducted to study the ameliorating effects of P, lime and animal manure on wheat (cv s-308) yield, root CEC and on economic doses of P. Phosphorus was applied as single superphosphate at the rate of 0, 13, 26, 39, 52, 65 and 78 kg P per ha; lime as CaCO₃ at 0 and 1 t/ha, and well cured animal manure at 0 and 8 t/ha. The application of P, to the extent of 65 kg/ha, increased the root CEC of wheat up to bloom stage only whereas nutrient concentration, uptake and; grain and straw yield were found to increase up to maturity. Similarly, addition of 8t/ha of animal manure resulted in a significant increase in root CEC up to bloom, nutrient concentration and uptake, vis-a-vis grain and straw yield of wheat were found to enhance up to maturity. However, the application of lime, though, increased the root CEC and nutrition of crop during both years, it did so in cases of wheat yield only during the first year of the experiment. Root CEC, particularly, at early growth stages, was very well correlated with N, P, K, Ca and Mg concentrations and uptake, and wheat yield at maturity. The economic dose of P for wheat in association with 8 t/ha of animal manure under the present conditions was found to be 39.4kg p/ha.     

Microbial nitrogen dynamics in south central Chilean agricultural and forest ecosystems located on an Andisol

The natural soil N supply in volcanic soils (Andisols) can be a significant source of plant-available N for agro-ecosystems. Nevertheless, intensive farming systems in south Chile apply high fertilization rates, which lead to high production costs and involve a risk for adverse ecosystem effects. In order to achieve sustainable land management, a better understanding of the processes that govern soil N availability and loss, and their external drivers, is required. In this study, we selected a winter-cropland, a summer crop-winter fallow rotation, and a forest, used as a reference ecosystem. Gross N transformations (¹⁵N isotope dilution) and microbial community structure (phospho-lipid fatty acid analysis) in the topsoil were determined. Gross N mineralization was about ten times lower in the agro-ecosystems than in the forest, while gross nitrification was low in all sites. Gross N immobilization equalized or exceeded the gross inorganic N production in all sites. Microbial biomass was 3–5 times more abundant in the forest than in the agro-ecosystems. A positive relationship between the ratio fungi/bacteria and total microbial biomass was observed in these Andisols. We suggest that the reduction in fungal biomass induced a lower extracellular enzyme production and limited soil organic matter depolymerisation in the agro-ecosystems. We conclude that soil N cycling was unable to provide a significant N input for the croplands, but also the risk for ecosystem N losses was low, even under fallow soil conditions. Current fertilization practices appropriately anticipated the soil N cycling processes, but further research should indicate the potential of alternative land management to reduce fertilizer cost.