Bicarbonate-extractable Phosphorus Research Articles

Adsorption and immobilization of phosphorus from water and sediments using a lanthanum-modified natural zeolite: Performance, mechanism and effect

The challenge of effectively controlling endogenous pollution and achieving phosphate recovery remains a hotspot worldwide. The development of a passivator with high adsorption capacity and superior passivating effect is crucial for effective implementation in controlling endogenous pollution. In this study, a lanthanum-modified natural zeolite (LZ) and a lanthanum-modified magnetic zeolite (LMZ) were synthesized using precipitation and hydrothermal methods. Additionally, characterization and incubation experiments were conducted to assess the adsorption and passivation effects of the material. The results showed that the LZ and LMZ had excellent phosphorus (P) adsorption and passivation capabilities. LZ and LMZ exhibited remarkable adsorption capacities of 122.7 and 109.17 mg/g, respectively, surpassing those of most lanthanum-modified materials. The characterization showed that inner sphere complexation and electrostatic attraction served as the primary mechanisms facilitating phosphate adsorption. Moreover, LZ and LMZ were also used as sediment passivators to immobilize P within sediments. The addition of LZ and LMZ could not only control the release of P in overlying water but also transform unstable iron-bound phosphorus (BD-P) and organoclastic phosphorus (Org-P) into stable aluminum-bound phosphorus (OH-P) and calcium-bound phosphorus (H-P). The application of both LZ and LMZ could effectively reduce various forms of Bio-P in the sediment, including algal-available phosphorus (Al-P), sodium bicarbonate extractable phosphorus (Olsen-P), water-soluble phosphorus (WA-P), and iron oxide extractable phosphorus (Fe-P). The amount of LZ and LMZ needed for fixed Fe-P in sediments could be quantitatively calculated within a certain range. Since LMZ could be recovered from water under the action of an applied magnetic field and had better effects on the potential active phosphorus (Mob-P) and Bio-P in the sediments, LMZ could have high potential for use as a passivator for internal pollution control.

The Brigalow Catchment Study: V*. Clearing and burning brigalow (Acacia harpophylla) in Queensland, Australia, temporarily increases surface soil fertility prior to nutrient decline under cropping or grazing

In the Brigalow Belt bioregion of Australia, clearing of brigalow (Acacia harpophylla) scrub vegetation for agriculture has altered nutrient cycling over millions of hectares. In order to quantify the effect of this vegetation clearing and land use change on soil fertility, the Brigalow Catchment Study commenced in 1965. Initial clearing and burning of brigalow scrub resulted in a temporary increase of mineral nitrogen, total and available phosphorus, total and exchangeable potassium and total sulfur in the surface soil (0–0.1 m) as a result of soil heating and the ash bed effect. Soil pH also increased, but did not peak immediately after burning. Soil fertility declined significantly over the subsequent 32 years. Under cropping, organic carbon declined by 46%, total nitrogen by 55%, total phosphorus by 29%, bicarbonate-extractable phosphorus by 54%, acid-extractable phosphorus by 59%, total sulfur by 49%, total potassium by 9% and exchangeable potassium by 63% from post-burn, pre-cropping concentrations. Fertility also declined under grazing but in a different pattern to that observed under cropping. Organic carbon showed clear fluctuation but it was not until the natural variation in soil fertility over time was separated from the anthropogenic effects of land use change that a significant decline was observed. Total nitrogen declined by 22%. Total phosphorus declined by 14%, equating to only half of the decline under cropping. Bicarbonate-extractable phosphorus declined by 64% and acid-extractable phosphorus by 66%; both greater than the decline observed under cropping. Total sulfur declined by 23%; less than half of the decline under cropping. A similar decline in total potassium was observed under both land uses, with a 10% decline under grazing. Exchangeable potassium declined by 59%. The primary mechanism of nutrient loss depended on the specific land use and nutrient in question.

Survey of long-term productivity and nutritional status of Leucaena leucocephala-grass pastures in subtropical Queensland

A survey of the productivity and nutritional status of leucaena (Leucaena leucocephala subsp. glabrata) pastures of different ages was conducted in subtropical Queensland from 2006 to 2008. Four leucaena stands (aged 8, 20, 31 and 38 years) growing on the same Vertosol soil type at Brian Pastures Research Station were surveyed. In the higher rainfall season of 2007–2008, leucaena yields and rainfall-use efficiency were highest in 8-year-old stands [2128 kg total dry matter (DM)/ha or 4.0 kg DM/ha.mm] and lowest in 38-year-old stands (978 kg total DM/ha or 1.9 kg DM/ha.mm). The reduced productivity in the 38-year-old leucaena pasture was associated with a decline in stem number/plant and leucaena plant density due to observed plant mortality. The reduced yield and vigour of aging leucaena was associated with nitrogen deficiency related to declining phosphorus and sulfur availability for adequate symbiotic N2 fixation and leucaena plant growth. Nutrient deficiencies of phosphorus and sulfur in leaf tissue were related to low to medium initial soil fertility (7–27 mg/kg of bicarbonate extractable phosphorus in the top 20 cm), coupled with inherent subsoil constraints (shallow soils, sodicity and high pH), and exacerbated by both long-term removal of nutrients by grazing animals and a reduction in soil phosphorus and sulfur availability over time. To maintain the productivity of leucaena pastures, plant nutritional status needs to be monitored in order to determine strategic fertiliser application.

Soil sampling protocol reliably estimates preplant NO3−in SDI tomatoes

Subsurface drip irrigation (SDI), because it can precisely deliver nutrients close to plant roots, could lead to carefully determined applications of fertilizer to meet crop needs and less risk of nitrate (NO3-) leaching to groundwater. Appropriate fertilizer applications, however, depend on an accurate assessment of the spatial distribution of the main plant macronutrients (N, P and K) in the soil profile before planting. To develop nutrient sampling guidelines, we determined the spatial distributions of preplant nitrate (NO3-), bicarbonate extractable phosphorus (Olsen-P) and exchangeable potassium (K) in the top 20 inches (50 centimeters) of subsurface drip irrigated processing tomato fields in three of the main growing regions in the Central Valley of California. Nutrient distribution varied with depth (P and K), distance from the center of the bed (NO3-) and growing region (NO3- and K). No depletion of NO3-, Olsen-P or K in the root feeding areas close to the drip tape was detected. Preplant NO3- ranged considerably, from 45 to 438 pounds N per acre (50 to 491 kilograms/hectare), the higher levels in fields with consecutive crops of tomatoes. A sampling protocol that growers could use, developed from analysis of the distribution results, provided reliable estimates of preplant NO3- as well as P and K in all surveyed fields.

Switchgrass Biochar Effects on Plant Biomass and Microbial Dynamics in Two Soils from Different Regions

Biochar amendments to soils may alter soil function and fertility in various ways, including through induced changes in the microbial community. We assessed microbial activity and community composition of two distinct clayey soil types, an Aridisol from Colorado (CO) in the U.S. Central Great Plains, and an Alfisol from Virginia (VA) in the southeastern USA following the application of switchgrass (Panicum virgatum) biochar. The switchgrass biochar was applied at four levels, 0%, 2.5%, 5%, and 10%, approximately equivalent to biochar additions of 0, 25, 50, and 100 t ha−1, respectively, to the soils grown with wheat (Triticum aestivum) in an eight-week growth chamber experiment. We measured wheat shoot biomass and nitrogen (N) content and soil nutrient availability and N mineralization rates, and characterized the microbial fatty acid methyl ester (FAME) profiles of the soils. Net N mineralization rates decreased in both soils in proportion to an increase in biochar levels, but the effect was more marked in the VA soil, where net N mineralization decreased from −2.1 to −38.4 mg kg−1. The 10% biochar addition increased soil pH, electrical conductivity, Mehlich- and bicarbonate-extractable phosphorus (P), and extractable potassium (K) in both soil types. The wheat shoot biomass decreased from 17.7 to 9.1 g with incremental additions of biochar in the CO soil, but no difference was noted in plants grown in the VA soil. The FAME recovery assay indicated that the switchgrass biochar addition could introduce artifacts in analysis, so the results needed to be interpreted with caution. Non-corrected total FAME concentrations indicated a decline by 45% and 34% with 10% biochar addition in the CO and VA soils, respectively, though these differences became nonsignificant when the extraction efficiency correction factor was applied. A significant decline in the fungi:bacteria ratio was still evident upon correction in the CO soil with biochar. Switchgrass biochar had the potential to cause short-term negative impacts on plant biomass and alter soil microbial community structure unless measures were taken to add supplemental N and labile carbon (C).

Does a Trend in Declining Stem Density of Lepidium latifolium Indicate a Phosphorus Limitation? A Case Study

AbstractLepidium latifolium (perennial pepperweed) is a weedy alien crucifer that has invaded wetlands throughout the western United States. We monitored L. latifolium invasion of an Elytrigia elongata (tall wheatgrass) community at the Honey Lake Wildlife Refuge in northeastern California. In 1993, a 40-m2 plot was delineated, at which time only two single plants of L. latifolium were present. Beginning in 1994, L. latifolium stem density was measured yearly until 2011. From 1994 through 2000, the density of L. latifolium increased to greater than 120 stems m−2. At its height of stem density and stature between 1998 and 2000, it appeared that E. elongata had been extirpated. From 2001 through 2006, stem density and plant stature of L. latifolium declined, but there were still areas of the plot where stem density exceeded 60 stems m−2. From 2007 through 2009, stem density decreased considerably and averaged less than 30 stems m−2 and a healthy recovery of E. elongata occurred. In the years 2010 and especially 2011, stem density increased, but individual plants were small in stature. Soil bicarbonate-extractable phosphorus data suggest that phosphorus availability may be crucial to the invasiveness of L. latifolium. Long-term biogeochemical cycling by L. latifolium may reduce soil phosphorus availability in deeper soil horizons and enrich availability in the soil surface, which alters the competitive relationship between L. latifolium and E. elongata.

Changes in Organic Carbon and Selected Soil Fertility Parameters in Agricultural Soils in Tasmania, Australia

Twenty-four sites in northern Tasmania on Ferrosols formed on Tertiary basalt were sampled in 1997, 2005, and 2010. The farming systems at the sites during this period were either (a) continuous pasture, (b) continuous cropping of vegetable, cereal, and other cash crops in rotation, or (c) a mix of pasture and cropping (intermittent cropping). Average organic carbon (OC) concentrations across all sites and both sample depths (0–150 mm and 150–300 mm) decreased from 4.0% in 1997 to 3.5% in 2005 and 3.3% in 2010 (P < 0.001). Average OC was greater at 0–150 mm (4.1%) than at 150–300 mm (3.1%) (P < 0.001). Average total soil nitrogen (N) in 2010 (0.42%) at 0–150 mm was not significantly different (P = 0.07) from the average in 1997 (0.38%). Soil pH in water (pHw) showed the opposite trend to OC, increasing with time from 6.0 in 1997 to 6.2 in 2010. This reflects the consistent use of calcite and dolomite in Tasmanian farming because the natural pHw of these soils is less than 5.5. Exchangeable calcium and magnesium were also greater in 2010 compared with 1997. Bicarbonate-extractable phosphorus (P) averaged across both depths increased (P < 0.001) steadily from 77 mg kg−1 in 1997 to 95 mg kg−1 in 2005 to 126 mg kg−1 in 2010. At the five sites that remained under continuous cropping throughout the study, average 2010 OC in the topsoil was 3.2%, a decrease of 0.5% since 1997; pHw was unchanged at 6.4; and bicarbonate-extractable P increased by an average of 73 mg kg−1 to 211 mg kg−1. For the three sites that remained in pasture the corresponding topsoil changes were 0.3% less OC to an average of 4.8%; pHw 0.4 units greater at 6.0; and 41 mg kg−1 more bicarbonate-extractable P to an average of 99 mg kg−1. At the six sites converted from continuous pasture to intermittent cropping the average 2010 topsoil OC was 4.5%, a loss of 1.3%; pHw increased by 0.5 units to 6.1; and bicarbonate-extractable P increased by 35 mg kg−1 to 97 mg kg−1. There was a highly significant (R2 = 0.82) exponential relationship between topsoil OC in 2010 and the number of years each site had been cropped during the 38 years 1972–2010, for which reliable records were available (OC = 4.933e−0.018years), which suggested an equilibrium topsoil OC concentration of about 2.5% under continuous cropping on these soils. These results indicate that Tasmanian farmers on Ferrosols continue to increase the pHw and P fertility of their soils and that increasing cropping intensity on these soils comes at the expense of soil carbon.

Soil fungi influence the distribution of microbial functional groups that mediate forest greenhouse gas emissions

The distribution of microbial functional groups in soil may be governed by the interaction between the soil environment and the presence of other microbial competitors or facilitators. In forest soils, one of the most important groups of organisms are fungi, which are vital to many ecosystem processes such as nutrient cycling and decomposition, and can form direct connections to primary producers. Nevertheless, the overall effect of soil fungi on the structure and distribution of the other soil microbial functional groups has not been thoroughly investigated. We hypothesized that by altering the soil environment, fungi create favorable conditions for Archaea, methane oxidizing bacteria (MOB) and denitrifying bacteria (DNB), thereby potentially influencing the ability of forest soils to produce or consume greenhouse gases. To test these hypotheses, we studied the distribution of microbial functional groups and fungi in forest soil using molecular methods and related that distribution to soil environment and extracellular enzyme activity as a measure of microbial activity and metabolic effort. Non-metric multidimensional scaling of terminal restriction fragment length (TRFLP) profiles found that DNB and MOB largely separated within ordination space, suggesting little overlap of these bacteria in soil cores. In addition, DNB were significantly positively correlated with fungal biomass and with chitinase activity while MOB were negatively correlated with both. Most archaeal TRFs were also negatively correlated with fungal biomass, suggesting that forest Archaea and MOB have similar relationships to fungal biomass. Soil chemistry including soil carbon (C), nitrogen (N) and bicarbonate extractable phosphorus (P) were not significantly correlated with DNB, MOB or Archaea. Our results suggest that soil fungi might influence the spatial distribution of important prokaryotic groups in forests, including some groups that mediate the production and consumption of important greenhouse gases.

Ash from the thermal gasification of pig manure—effects on ryegrass yield, element uptake, and soil properties

Effects of thermally gasified pig manure ash (GA) and lime-free gasified ash (LF-GA) on properties of an acidic soil (pH 4.5) and the growth and elemental uptake of ryegrass (Lolium rigidum Gaudin) were investigated. The GA was an effective liming agent (2% addition raised soil pH from 4.5 to 7.9); both GA and LF-GA increased soil electrical conductivity and bicarbonate-extractable phosphorus (P). Soil fertilised with LF-GA supported slightly higher plant dry matter (DM) yield than GA (1.5–1.7 v. 1.2–1.5 g DM/kg soil) for the first harvest, due to greater initial P availability at pH &lt;5 than at pH &gt;6. However, plant yields for the subsequent two harvests were similar, as soil acidity dissolved lime in untreated ash (GA) over time. Maximum yields for ash-treated soil and soil treated with mono-calcium phosphate (MCP) were similar. Relative agronomic effectiveness of P sources for three harvests, based on plant P content compared with values for MCP, were 6, 11, and 12% for GA and 19, 10, and 33% for LF-GA. Internal efficiency of P utilisation was similar for all three P sources for each harvest, indicating that differences in yield were mostly a consequence of differences in P supply. Heavy metal concentrations in plants fertilised with ash were minor and within regulatory limits. In general, application of ash did not systematically affect the concentrations of elements (Al, B, Cd, Mg, Mn, Fe, Pb, S, Se) in plants.

Phosphorus Status in Soils of Great Groups in Qena Governorate

The present investigation was carried out to study the phosphorus status of different soil great – groups present in Qena Governorate .The soil in Qena Governorate is belonged to the following great – groups :Vtt, Eftt, Epqt and Eott. One hundred and five location samples distributed all over the entire area representing the soils of each great group in each territory of Qena Governorate were prepared. The P status of the soils of each great –group was assessed using a variety of chemical extraction methods. A pot experiment was also carried out to study the supplying power of P using Reygrass plants. The obtained results shows that:- The bicarbonate extractable inorganic P (NaHCO3-Pi) in the studied soil samples of different great – groups showed a wide variations that cooped with different chemical of these soils . The amount of Pi in the surface layers of the soils of all great-groups were noticeably higher than that of sub-surface ones. The bicarbonate extractable organic P ( NaCO3-Po) contents in the studied soils were different between soils of –great groups and among the soils of each great – groups. The values of total bicarbonate extractable phosphorus (NaHCO3-Pt) showed a considerable variation in Pt among various samples. The data also indicated that Pt in soil generally decreased as the soils became coarse in texture, low in organic content and in total CaCO3 content. P uptake by Raygrass was positively and significantly (P<0.05) correlated with both bicarbonate extractable P forms Pi and Po as well as the total bicarbonate extractable phosphorus Pt .The pearson simple correlation coefficients for the P uptake against Pi, Po and Pt were 0.7817**,0.7823**and 0.8215**, respectively.

Existing Versus Added Soil Organic Matter in Relation to Phosphorus Availability on Lateritic Soils

Lateritic soils (Ultisols and Oxisols) are commonly characterised by high phosphate sorbing capacity due to the type of clay and present high content of aluminium (Al) and iron (Fe) oxides. Addition of fresh organic matter (OM) may contribute to management of these soils by releasing more bicarbonate-extractable phosphorus (BP) through organic phosphorus (OP) transformation, or by the soluble component of OM additions desorbing phosphate by ligand exchange. It is not known, however, whether BP results solely from addition of new OM (by either mineralisation or desorption) or from transformation of inherent or pre-existing in soil. We considered that removing the existing soil OM and replacing it with an equivalent amount of new OM may help to resolve this issue, especially with respect to P transformation after OM additions. Three lateritic soils of Western Australia (including a deep regolith material with very low inherent soil OM (SOM)) were used, and sub-samples of the three soils were combusted (450° C) to obtain soils effectively free from existing OM. A further sub-sample of the soils was not combusted. Both soil groups, receiving the same amount of organic carbon (OC, from 80 ton ha-1 biomass + soil OM or biomass equal to soil OM) from peat, wheat straw (Triticum aestivum L.) and lucerne hay (Medicago sativa L.), were incubated for nine months. Soil bicarbonate-extractable P as well as non-extractable P (NP, measured as Total-P (TP)-BP) increased due to new OM application in the order lucerne hay&gt;peat&gt;wheat straw. The correlation between BP with soil organic carbon (SOC) became more positive over time. Microbial biomass phosphorus (MBP) was not well correlated with the increase of NP content and phosphatase was not related to the increase in BP. Overall, freshly applied (new) OM not only contributed to the increased level of P compared with the existing OM treatment.

Chickpea and white lupin rhizosphere carboxylates vary with soil properties and enhance phosphorus uptake

Chickpea and white lupin roots are able to exude large amounts of carboxylates, but the resulting concentrations in the rhizosphere vary widely. We grew chickpea in pots in eleven different Western Australian soils, all with low phosphorus concentrations. While final plant mass varied more than two-fold and phosphorus content almost five-fold, there were only minor changes in root morphological traits that potentially enhance phosphorus uptake (e.g., the proportion of plant mass allocated to roots, or the length of roots per unit root mass). In contrast, the concentration of carboxylates (mainly malonate, citrate and malate, extracted using a 0.2 mM CaCl2 solution) varied ten-fold (averaging 2.3 µmol g −1 dry rhizosphere soil, approximately equivalent to a soil solution concentration of 23 mM). Plant phosphorus uptake was positively correlated with the concentration of carboxylates in the rhizosphere, and it was consistently higher in soils with a smaller capacity to sorb phosphorus. Phosphorus content was not correlated with bicarbonate-extractable phosphorus or any other single soil trait. These results suggest that exuded carboxylates increased the availability of phosphorus to the plant, however, the factors that affected root exudation rates are not known. When grown in the same six soils, three commonly used Western Australian chickpea cultivars had very similar rhizosphere carboxylate concentrations (extracted using a 0.2 mM CaCl2 solution), suggesting that there is little genetic variation for this trait in chickpea. Variation in the concentration of carboxylates in the rhizosphere of white lupin did not parallel that of chickpea across the six soils. However, in both species the proportion of citrate decreased and that of malate increased at lower soil pH. We conclude that patterns of variation in root exudates need to be understood to optimise the use of this trait in enhancing crop phosphorus uptake.

Effect of soil amendment with bauxite Bayer process residue (red mud) on the availability of phosphorus in very sandy soils

The chemical properties of red mud, a by-product of Bayer process refining of bauxite to alumina, make disposal of the material problematic. It is very alkaline (pH &gt;11), contains a large amount of sesquioxides, and thus has a very high P retention capacity. These characteristics have encouraged its use as a soil amendment to enhance P retention of soils so as to reduce leaching of P. To investigate the effect of added red mud on the availability of existing P in sandy soils an incubation experiment was conducted using 3 types of red mud (untreated red mud, red mud amended with 5% gypsum, and red mud leached with dilute acid to remove all soluble salts) mixed with 12 podsol topsoils at rates of 0, 2.5, 5, 10, 20, and 40�t/ha. The mixtures were incubated wet for 28 days in the dark at 20°C, both with and without a microbial inhibitor. The decrease in 0.5 M sodium bicarbonate extractable phosphorus (bic-P) was 40–60% of initial bic-P at 40 t/ha of all 3 red muds after wet incubation without microbial suppressant. This decreased to 20–40% after drying or with addition of the microbial suppressant. The decrease in bic-P was not due to the increase in pH due to red mud application and appears to involve both chemical and microbial actions. The increase in soil pH of up to 3 units would be beneficial for pasture production at most rates of red mud application and the associated increase in electrical conductivity is not sufficient to affect plant growth.

Changes in bicarbonate-extractable phosphorus over time when P fertiliser was withheld or reapplied to pasture soils

Field studies were established on 9 different soil types used for pasture production in the high rainfall zones of southern Victoria. Sites were selected to represent a range of phosphorus (P) buffering capacities (PBC) and were analysed for a series of chemical and physical properties before receiving P fertiliser treatments. A single application of P fertiliser in the form of triple superphosphate (TSP), single superphosphate (SSP), or TSP and lime (5 t/ha) was applied at amounts ranging from 0 to 280 kg P/ha at the start of the experiment, whilst treatments of 35 and 70 kg P/ha were reapplied at 6-monthly intervals. Soils were analysed for bicarbonate-extractable P concentration, using both the Olsen P and Colwell P methods, 6, 12, 18, 24, and 30 months after P fertiliser was applied. A strong positive linear relationship existed at all sites and time periods between the amounts of P applied as a single application and both the Olsen P and Colwell P concentrations. The slopes of these relationships measured the change in extractable P concentration per unit of P applied (ΔEP) and the rate of decline in ΔEP values represented the decline in the effectiveness of the P fertiliser with increasing time from application. The decline in these ΔEP values varied with soil type. The ΔEP values of some low to moderate P buffered soils remained 2–3 times higher compared with the most highly buffered soils, after 30 months. Despite this, the decline in ΔEP values between 6 and 30 months was difficult to predict using a single soil property. Multiple linear regressions involving a measure of PBC and either organic carbon or exchangeable hydrogen were useful methods of predicting the decline in ΔEP values across the 9 field sites examined in this study. In general, the reapplication of P fertiliser every 6 months resulted in significantly higher extractable P concentrations compared with the same rates applied in a single application, across all sites and rates of P applied. The application of SSP, TSP, and TSP and lime had little impact on ΔEP values 18–30 months after treatments were applied.

Temporal dynamics of gradients of phosphorus, ammonium, pH, and electrical conductivity between a di-ammonium phosphate band and wheat roots

Our previous studies have demonstrated that di-ammonium phosphate (DAP) banded into soil led to a rise in pH and EC, and concentrations of NH4+ and bicarbonate-extractable phosphorus around the band. When these chemical gradients develop too close to plant roots, they may cause toxicity and stop root growth. However, the temporal dynamics of gradient development and effects on plants are not known. In this study, wheat was grown in specially constructed pots, with DAP banded 2.5 cm below the seed and either 1 or 2.5 cm horizontally from seed. Plants were harvested at different growth stages to establish the temporal variation in soil chemical gradients between the fertiliser band and the plant roots. Visual toxicity symptoms and decreased root and shoot dry weight and root length in the plants growing with DAP banded 1 cm horizontally away from seed were obvious 14 days after sowing, but disappeared after 6 weeks. Plants in that treatment had a significantly lower number of heads than control plants, implying that there was a harmful effect on reproductive growth and yield with DAP banded too close to wheat seed. The pH increased by one unit and EC increased 2-fold in the soil section containing a DAP band 14 days after sowing. By Day 63, the pH peak disappeared and the EC peak in the 1-cm horizontal distance banding treatment shifted toward soil sections containing the highest root density (4 cm away from the seed on the side opposite to where fertiliser was banded). In the 2.5-cm banding treatment, the EC peak disappeared 42 days after sowing. The ammonium peak was measured in the soil section containing the fertiliser band in the 1-cm banding treatment on Day 14, but the peak shifted to the section with the highest root density by Day 42, and disappeared completely by Day 63. The 2.5-cm banding treatment resulted in a lower ammonium peak compared with the 1-cm treatment after 14 and 42 days, and the highest concentration was found in the section with the highest root density by Day 63. Phosphorus concentration gradients were similar to those of ammonium, except that less depletion and movement of P occurred during the 63-day experiment. In conclusion, the chemical gradients around the fertiliser band show strong temporal and spatial dynamics. However, toxicity caused by close banding and hence high concentrations of ammonium in the initial growth stage results in a decreased wheat yield potential.

Phosphate transport by communities of arbuscular mycorrhizal fungi in intact soil cores.

• Variation in phosphate uptake capacity is reported here for natural communities of arbuscular mycorrhizal fungi associated with annual pasture plants. • Tests were made of methodology for quantifying phosphate uptake by hyphae associated with clover in soil cores from pastures containing different morphotypes of the fungi. This provided a direct measure of the phosphate uptake capacity of hyphae from 32 P-labelled soil in a root-free mesh bag inserted into the centre of intact soil cores. • Bicarbonate-extractable phosphorus in the soils ranged from very deficient to close to adequate for plant growth. Uptake of 32 P was related to an estimate of the length of hyphae formed in four of the five soils, but not to either the length or the proportion of roots colonized. In the fifth soil type, phosphate uptake by hyphae was negligible. • Phosphate uptake by natural communities of arbuscular mycorrhizal fungi in intact soil cores can be assessed directly, and is shown to be highly variable. The experimental approach could be applied widely for field investigations of phosphate uptake by hyphal networks.

Quantitative phosphorus measurement: A field test procedure for archaeological site analysis at Piedras Negras, Guatemala

Currently there is a wide interest in the use of chemical analyses for the evaluation of anthropogenically altered soils and other archaeological deposits. Because soil phosphorus levels increase in areas of human habitation, and leave a permanent signature that can only be removed by erosion of the soil itself, phosphorus mapping has become a popular field procedure to indicate areas of habitation where overt evidence of ancient occupance is absent. We have developed a methodology to obtain accurate acid-extractable phosphorus concentrations (mg/kg) in calcareous soils under the primitive field conditions of Piedras Negras, Guatemala. Predicated on Mehlich-II acid extractant and colorimetric methods, this procedure processed 36 samples per hour at very low cost per sample. Based on eight replicate measurements of a group of samples, the coefficient of variation of the procedure was 8.3%. Subsequent analysis of 35 soil samples in a controlled laboratory revealed a moderate correlation of 0.44 between the Mehlich-extractable phosphorus and total phosphorus. The correlation was 0.91 between the Mehlich procedure and Olsen bicarbonate extractable phosphorus, indicating that Mehlich-based results are similar to those obtainable using a traditional extractable phosphorus method on soils of neutral to alkaline pH. There was a moderate correlation between Mehlich P and ring-test rating (r = 0.42). The wider dynamic range of the Mehlich extraction, coupled with the use of a battery-operated colorimeter, facilitated the finding of a refuse midden within an area of phosphate enriched soils. Further tests indicated that phosphorus concentrations measured in the field deviated by only 7% from those made under controlled laboratory conditions. © 2000 John Wiley & Sons, Inc.

Response to phosphorus application of second rotation radiata pine on podsolised sands from planting to first thinning: implications for management

Summary Phosphorus fertiliser, applied at planting to two second rotation radiata pine (Pinus radiata D. Don) sites at rates up to 60 kg P ha−1 increased the concentration of extractable phosphorus in the top metre of soil, particularly the top 0.15 m, for at least 2 years. There was a significant response in basal area growth 3 years after phosphorus application at one site, but no effect on height growth. At the other site, there was no effect of phosphorus application at planting in terms of either height or basal area growth to age 3 years. Phosphorus (60 kg p ha−1) was re-applied at age 3 years, and this increased extractable phosphorus concentrations in the top 0.15 m of soil, and foliar phosphorus concentrations measured over a 9 month period. A third application of 60 kg P ha −1 at age 4 years further increased the range of foliar phosphorus concentrations. Despite the increase in foliar phosphorus concentrations to 0.14%, well above the concentration of 0.08 % in the unfertilised control, there was little positive effect on any aspect of growth by age 8 years at either site. Application of 50 and 100 kg P ha −1 at one site when the stand was 10 years old resulted in increased levels of bicarbonate extractable phosphorus in the top 0.4 m for the following 2 years. Both the concentration and the total amount of phosphorus in the profile decreased with time. Foliar phosphorus concentrations also increased in phosphorus fertilised treatments. These changes were accompanied by increased basal area growth in the 7 years following phosphorus reapplication. Results from this study, along with other results on the response to phosphorus by stands at the same stage of development on sandy soils in the region, highlight differences in response to phosphorus fertiliser even on similar soils. The chance of obtaining a growth response to phosphorus applied at planting on second rotation sites is unreliable, especially under current silvicultural practices that retain slash on site between rotations. Growth responses may be more assured at a later stage in plantation development. This behaviour seems to parallel the experience with nitrogen applications described in other studies.

Yield and phosphorus nutrition of potatoes (Solanum tuberosum L.) cv. ‘Delaware’ grown on a yellow Karrakatta sand containing freshly- and previously-applied Alkaloam - gypsum

Summary. Potatoes (Solanum tuberosum L.) cv. ‘Delaware’ were grown over winter on a yellow Karrakatta sand amended with Alkaloam–gypsum (AG; previously referred to as red mud–gypsum) at up to 240 t/ha, both freshly-applied (2 experiments) and applied 2.5 years earlier (1 experiment). Several levels of phosphorus fertiliser (0–600 kg P/ha) were applied to the freshly-applied AG and a single level (600 kg P/ha) was applied to the previously-applied AG. Amendment of the soil with 60 t AG/ha (freshly-applied) doubled the amount of fertiliser phosphorus retained in the top 30 cm of soil when 100 kg P/ha was applied. On freshly-applied AG, bicarbonate-extractable phosphorus showed an upward trend with level of AG, being 16 mg/kg (0–15 cm) at 0 t AG/ha and 34 mg/kg at 90 t AG/ha. This will decrease phosphorus fertiliser requirements in the following potato crop by 49% relative to unamended soil based on previously published soil test standards. Amendment with freshly-applied AG increased the level of applied phosphorus required for 99% of maximum petiole phosphorus concentration by 46 and 139% in the 2 experiments compared with unamended soil. Maximum yield was significantly reduced by 7–10% at 60 t/ha of freshly-applied AG compared with unamended soil while on residual AG it was only reduced at 240 t/ha (12%) (trend only). Yield reductions were not correlated with a reduced availability of phosphorus, however, they may have been due to a reduced availability of potassium. The concentrations in the tubers of antimony, arsenic, cadmium, chromium, cobalt, lead, mercury and nickel did not exceed legal limits on soil amended with AG.

Changes in bicarbonate-extractable phosphorus of a basalt-derived duplex soil associated with applications of superphosphate to pasture grazed by sheep

The effect of 3 successive yearly applications of single superphosphate (SSP) to pastures on bicarbonate- extractable soil phosphorus (Olsen P) was measured. The soil was a duplex derived from basalt and the pastures, based on perennial ryegrass and subterranean clover, were continuously stocked with sheep. Six levels of SSP were compared at 3 stocking rates. The amount of P applied annually varied from 0 to 100 kg/ha. These data were used to create an empirical model which used the current value for Olsen P (Olsen Pn), the amount of P applied as fertiliser that year (fert Pn), and a lower limit for Olsen P for basalt-derived duplex soils (Olsen Plow) to predict the Olsen P for the following year (Olsen Pn+1). The model had the form: Olsen Pn+1 = Olsen P low + afert Pn + b(Olsen Pn – Olsen Plow). Olsen P low was fixed at 3 mg P/kg soil, and the coefficients a and b were 0.0995 and 0.8020. The model accounted for 96.6% of the variance in Olsen Pn+1. This model was tested at the same site at 2 other periods: when fertiliser was withheld for 3 years and again after applications of SSP were resumed. The model was also tested against data from another experiment conducted on a similar soil. The model can estimate the amount of fertiliser required to maintain the P status of the soil and predicts that to increase Olsen P by 1 unit in the following year it is necessary to apply 10 kg P/ha in excess of soil maintenance requirement.