Extractable Phosphorus Content Research Articles

High-resolution assessment of riverbank erosion and stabilization techniques with associated water quality implications

ABSTRACT Agriculture is a key contributor to poor water quality, but the sources of sediment and nutrient losses from agricultural catchments – including from riverbank erosion – are highly variable. Riverbank erosion is particularly difficult to quantify and control. Here, we developed a quick assessment approach to quantify riverbank erosion rates and associated sediment and nutrient loading rates into waterways using airborne LiDAR combined with field-collected data. We applied this approach and explored its relationships to water quality at four sites within the Blackwater catchment in Northern Ireland for two analysis periods. GIS LiDAR image differencing revealed that volume changes in riverbank elevation equated to average erosion rates which indicated spatial and temporal variability in erosion rates. Combining the erosion rates with in-situ riverbank bulk density and total extractable phosphorus content provided sediment and phosphorus loading rates. The relative differences between estimated erosion at the different sites corresponded well with in-stream suspended sediment variations, but patterns for total phosphorus concentrations were more complex. We conclude that the use of LiDAR combined with field data is an innovative means for riverbank erosion quantification. Furthermore, by using LiDAR-to-LiDAR analyses, the reductions in erosion, sediment, and phosphorus loading rates following riverbank stabilization techniques can be determined.

Landscape scale ecology of Tetracladium spp. fungal root endophytes

BackgroundThe genus Tetracladium De Wild. (Ascomycota) has been traditionally regarded as a group of Ingoldian fungi or aquatic hyphomycetes—a polyphyletic group of phylogenetically diverse fungi which grow on decaying leaves and plant litter in streams. Recent sequencing evidence has shown that Tetracladium spp. may also exist as root endophytes in terrestrial environments, and furthermore may have beneficial effects on the health and growth of their host. However, the diversity of Tetracladium spp. communities in terrestrial systems and the factors which shape their distribution are largely unknown.ResultsUsing a fungal community internal transcribed spacer amplicon dataset from 37 UK Brassica napus fields we found that soils contained diverse Tetracladium spp., most of which represent previously uncharacterised clades. The two most abundant operational taxonomic units (OTUs), related to previously described aquatic T. furcatum and T. maxilliforme, were enriched in roots relative to bulk and rhizosphere soil. For both taxa, relative abundance in roots, but not rhizosphere or bulk soil was correlated with B. napus yield. The relative abundance of T. furcatum and T. maxilliforme OTUs across compartments showed very similar responses with respect to agricultural management practices and soil characteristics. The factors shaping the relative abundance of OTUs homologous to T. furcatum and T. maxilliforme OTUs in roots were assessed using linear regression and structural equation modelling. Relative abundance of T. maxilliforme and T. furcatum in roots increased with pH, concentrations of phosphorus, and increased rotation frequency of oilseed rape. It decreased with increased soil water content, concentrations of extractable phosphorus, chromium, and iron.ConclusionsThe genus Tetracladium as a root colonising endophyte is a diverse and widely distributed part of the oilseed rape microbiome that positively correlates to crop yield. The main drivers of its community composition are crop management practices and soil nutrients.

Glyphosate and AMPA concentrations in the respirable dust emitted experimentally by soil aggregates, shortly after herbicide application

The objective of this study was to analyze glyphosate- and aminomethylphosphonic acid (AMPA) concentrations in the respirable dust (RD) emitted by different soil aggregates, shortly after herbicide application in a field approach. The relationships of both glyphosate and AMPA in the aggregates with organic matter- (OM), total iron- (Fe), and extractable phosphorus contents (P) as well as with pHCaCl2 values were analyzed. An Kastanozem haplic of the Semiarid Pampas (Argentina) was analyzed 7 days after glyphosate application. The RD (particulate matter <10 mm in diameter, PM10) was generated and collected for the following aggregate-size fractions: <0.42 mm, 0.42 to 0.84 mm, 0.84 to 2 mm, 2 to 6.4 mm, 6.4 to 19.2 mm, and >19.2 mm. OM, P, Fe and pHCaCl2 were analyzed in the aggregate fractions, and glyphosate- and AMPA contents were measured both in RD and in the aggregate fractions. Glyphosate concentration varied between 16 mg kg−1 (aggregates <0.42 mm) and 4.7 mg kg−1 (aggregates >19.2 mm) and increased with decreasing size of the aggregates. Glyphosate concentration in RD varied between 48.5 mg kg−1 (aggregates <0.42 mm) and 17.8 mg kg−1 (aggregates >19.2 mm). Finest aggregates emitted RD with higher glyphosate concentrations. A positive relationship was determined between glyphosate in aggregates and glyphosate in RD (p < 0.05), indicating that aggregates with higher glyphosate concentration emitted a more glyphosate-enriched RD. Glyphosate in the aggregate fractions was not related to Fe, OM or pH of aggregates. Glyphosate- and P concentrations in aggregates were positively correlated. This is explained because both substances share a phosphonic acid functional group and they have similar reactivities in the soil. AMPA concentration varied between 130 mg kg−1 (aggregates >19.2 mm) and 307 mg kg−1 (aggregates <0.42 mm) in aggregates and between 527 ug kg−1 and 746 ug kg−1 in RD. AMPA concentrations in RD were not related to AMPA concentrations in aggregates. The contents of AMPA were higher than those of glyphosate in both, RD and aggregates, due to the longer persistence of AMPA in relation to glyphosate. In all cases, glyphosate- and AMPA concentrations were higher in RD than in the aggregates. Our results suggest that the RD emitted by agricultural soils has higher glyphosate- and AMPA concentrations than the bulk soil. These results encourage future investigations to elucidate if other pesticides (and the surfactants used in their formulations) are present in the RD emitted by agricultural soils. This information is necessary in order to evaluate the effects of the particulate matter emitted by agricultural soils on the whole ecosystem and the human health.

Effect of Land Cultivation on Soil Nutrient Sedimentation in Water at Southern China

Soil erosion associated with land cultivation exerts a great impact on ecological environment. Such an impact is specific of land, crop, tillage, management and so on. This study aimed to investigate the effects of crop cultivation on water quality by comparing nutrient distribution in the sediment at Southern China. Two sedimentation sites adjacent to the uncultivated (S1) and cultivated upland (S2) were selected and samples were analyzed. Results showed that soil pH decreased with the increasing depth above 20 cm and then kept relatively stable of the both sediments. Soil organic matter, nitrogen and phosphorus contents decreased with the increasing depth. There was no significant difference between two sediments in organic matter and nitrogen contents, but the total phosphorus and extractable phosphorus contents in S2 were much higher than that in S1. The data indicated that soil eroded from S2 could possess much high potential to deteriorate water quality. Nutrient sedimentation can reflect the history of soil erosion and provide useful information for sustainable soil management and water conservation through improving cultivation and tillage measures.

Delimitación del área probable de entierros del sitio RSCII (Santo Tomé, Santa Fe) mediante el análisis químico del suelo

El fósforo (P) es uno de los principales constituyentes de los tejidos orgánicos, así como de los desechos fisiológicos de los vertebrados. Es, además, uno de los elementos más estables en el perfil de suelo, por lo que se lo considera un marcador químico de actividad humana confiable en la escala local o de sitio. En el caso particular de las áreas utilizadas en forma recurrente a través del tiempo para el entierro de cadáveres, los niveles de P del suelo suelen verse notoriamente incrementados como consecuencia del aporte de fosfatos por los procesos de descomposición de los cuerpos. Por ello, sus valores de concentración permiten identificar áreas de entierros aun cuando los huesos no están presentes, así como también estimar su extensión probable en caso de excavaciones parciales. Por ello, sus valores de concentración permiten identificar áreas de entierros aun en los casos en los que los huesos están parcial o totalmente ausentes, así como estimar su extensión probable. En este contexto, el objetivo del presente trabajo es estimar, a partir de la medición de la concentración de fósforo extraíble (Pe) y del modelado espacial con técnicas de interpolación, la extensión probable del área de entierro detectada en el sitio Río Salado-Coronda II (RSCII), localizado en la ciudad de Santo Tomé, en el centro-este de la provincia de Santa Fe.

Soil Extractable Phosphorus Contents as Affected by Phosphatic Fertilizer Sources Applied with Different Levels of Humic Acid

Soil Extractable Phosphorus Contents as Affected by Phosphatic Fertilizer Sources Applied with Different Levels of Humic Acid

Assessment of Physicochemical Parameters of Soils from Selected Abattoirs in Port Harcourt, Rivers State, Nigeria

Pollution arising from anthropogenic activities is a common phenomenon. Soil samples collected from three abattoirs in Port Harcourt (Agip, Iwofe, and Mile III) between the months of January to July. The samples were analyzed for physicochemical parameters after following laboratory procedures, using the appropriate probes. It was observed that the pH of the soils was acidic, ranging from 4.59 ± 0.03–4.99 ± 0.14, electrical conductivity ranged from 208.00 ± 11.21- 404.34 ± 7.18 μS/cm, temperature from 33.14 ± 1.29 -35.04 ± 0.96°C while salinity had a range of 27.531.91-58.65 ± 2.25. The textural class was sandy-clay-loam, implying that the soil contains sand in a higher proportion. Total moisture content was within the range of 16.66 ± 1.73 -21.07 ± 2.05 %, chloride content ranged from 17.10 ± 1.61-31.75 ± 2.00 % whereas total nitrogen and nitrogen based parameters were generally very low in concentration in the soil. Extractable phosphorus content in the soil ranged from 0.66 ± 0.03-1.34 ± 0.33 %, total organic carbon ranged from 12.81 ± 0.15- 16.41 ± 0.49 %, and total organic matter ranged from 22.33 ± 0.86-29.58 ± 0.72 mg/Kg. Total hydrocarbon content ranged between 11.85 ± 0.48 and 27.12 ± 0.48 mg/Kg. The observed result indicated that human activities within the abattoir have influenced the physicochemical speciation of the abattoirs. The high content of the organic components of the abattoir can serve as useful manure for cultivation of plants. However, constant check on the activities at the abattoirs should be put in place to avoid pollution of the environment.

Soil physicochemical properties impact more strongly on bacteria and fungi than conversion of grassland to oil palm

The conversion of grassland to oil palm is expected to increase throughout tropical regions where oil palm grows. Given the extent of land use change, there are concerns associated with impacts on ecosystem function and nutrient cycling. For this work, soil samples were collected in Papua New Guinea from 15 sites with oil palm (planted on grassland) and adjacent remnant grassland. Using DNA-based approaches, bacterial and fungal community composition was assessed in each sample, along with abundance of genes involved in key nitrogen cycling steps: nitrification (bacterial and archaeal amoA genes), nitrite reduction (nirS gene), and nitrous oxide reduction (nosZ gene). Across all microbial properties measured, variation among sites was greater than variation due to land use change. This was driven by among-site variation in soil physicochemical properties, particularly total soil organic carbon content and δ13C, electrical conductivity, exchangeable calcium, potassium and magnesium content, and extractable phosphorus content. The results suggest that in this environment, routinely measured soil properties such as soil pH, organic carbon, and exchangeable cation contents may serve as indicators for the effects of land use and management on soil microbial community composition and functioning.

Stable carbon isotope signatures of ancient Maize agriculture at El Kinel, Guatemala

Abstract Stable C isotope studies of the soil organic matter (SOM) have delineated areas with histories of vegetation change from C3 forest to C4 maize (Zea mays L.) agriculture and back to the contemporary C3 forest. The objectives of this study were to: (1) determine if land around El Kinel, Guatemala possessed a vegetative history of shifts from C3 forest to C4 maize agriculture in the past, (2) determine if 10 years of contemporary maize production is sufficient time to deposit an isotopic signature of C4 plants in the root zone (top 40 cm), and (3) to examine the extractable phosphorus concentrations and δ13C in soils of important archaeological features that included a midden, a burial, and two ancient reservoirs (aguadas). The lack of a shift in δ13C greater than 3.5‰ in the top 40 cm of the contemporary maize field suggested that continual maize cultivation of more than ten years is required to create an isotopic signature for maize agriculture. Carbon isotopic evidence was found in soil profiles ...

Extractable Phosphorus Contents of Some Soils of Bangladesh and Their Correlation with Phosphorus Concentration in Rice Leaves

To observe the availability of phosphorus by different extraction methods in some cultivated soils of Hathazari Upazilla of Chittagong District, this study was carried out with 36 surface soil samples (0 - 15 cm) belonging to six soil series, namely Bijipur, Pahartali, Mirsarai, Manu, Raojan and Noapara. Physical and chemical characteristics of the soils were also determined with an objective of identifying the soil factor(s) regulating P extractability. Three P extraction methods, namely Olsen (0.5 M NaHCO3, pH 8.5), Mehlich-3 (0.2 N CH3COOH + 0.013 N HNO3 + 0.015 N NH4F + 0.25 N NH4 NO3 + 0.001 M EDTA) and Bray & Kurtz-1 (0.03 N NH4F + 0.025 N HCl) were used. There was a wide variation in the extractability of P ranging from low to high categories. Olsen method extracted the largest amount of P (2.07 - 45.36 mg·kg-1) while Bray & Kurtz-1 extracted the smallest amount (1.02 - 21.79 mg·kg-1). The mean extractable P in soils was found to be in the order of Olsen > Mehlich-3 > Bray & Kurtz-1. Soil pH was the most dominant factor in determining P extractability. Available P was negatively correlated with percentage of clay, organic carbon and CEC and positively correlated with pH. Although the three methods extracted different amounts of P from soil, values of P extracted by the different methods were strongly correlated among themselves and with the leaf phosphorus concentration of rice growing in these soils.

Life-history traits explain rapid colonization of young post-agricultural forests by understory herbs

Large areas of agricultural land in Europe have been planted with broadleaved trees during the past decades. The aims of this study were to determine stand-scale colonization rates of European forest herbs in young (14–18years old) post-agricultural broadleaved forest plantations, to analyze whether colonization rates were related to life-history traits and site characteristics, and to compare the results with studies in older post-agricultural forests. The colonization of herbaceous forest species was mapped in 16 young broadleaved forests and compared with their distribution in adjacent older forests in southern Sweden. Stand characteristics were analyzed in 32 paired sample plots. Colonization rates (myear−1) were calculated for 43 forest plant species. For 30 forest plant species we also compared current colonization rates with results from 30 to 75year old stands. Colonization rates increased with maximum plant height and the potential dispersal distance, but were negatively related to diaspore mass and clonal spread. Soil, canopy and vegetation conditions in young forests were not significantly related to colonization rates. Nevertheless, young forests had higher soil pH and extractable phosphorus concentrations while soil organic matter content, basal area and canopy cover of the trees were higher in the adjacent older forests. Higher resource availability in young forests may favor competitive tall herbs over low-growing ancient forest plants. The comparison with colonization rates into older post-agricultural plantations revealed that while approximately half of the species had similar or lower rates, the other half had on average ca. ten times higher colonization rates in the present study, ranging from 3.0 to 11.5myear−1 indicating the potential for relatively fast colonization by some forest plants. We conclude that planted post-agricultural forests can start to contribute to restoration of forest plant diversity shortly after canopy closure when located adjacent to older forests. However, many small forest plants, including those species which form extensive flower carpets characteristic of ancient forests, colonize young forests very slowly. Further research should focus on the development of restoration measures which facilitate the colonization process of ancient forest herbs.

Metal immobilization and phosphorus leaching after stabilization of pyrite ash contaminated soil by phosphate amendments

In this study we would like to show the importance of a holistic approach to evaluation of chemical stabilization using phosphate amendments. An extensive evaluation of metal stabilization in contaminated soil and an evaluation of the leaching of phosphorus induced after treatment were performed. The soil was highly contaminated with Cu (2894 mg kg(-1)), Zn (3884 mg kg(-1)), As (247 mg kg(-1)), Cd (12.6 mg kg(-1)) and Pb (3154 mg kg(-1)). To immobilize the metals, mixtures of soil with phosphate (from H(3)PO(4) and hydroxyapatite (HA) with varying ratios) were prepared with a constant Pb : P molar ratio of 1: 10. The acetic acid extractable concentration of Pb in the mixture with the highest amount of added phosphoric acid (n(H(3)PO(4)) : n(HA) = 3 : 1) was reduced to 1.9% (0.62 mg L(-1)) of the extractable Pb concentration in the untreated soil, but the content of water extractable phosphorus in the samples increased from 0.04 mg L(-1) in the untreated soil sample up to 14.3 mg L(-1) in the same n(H(3)PO(4)) : n(HA) = 3 : 1 mixture. The high increase in arsenic mobility was also observed after phosphate addition. The PBET test showed phosphate induced reduction in Pb bioavailability. In attempting to stabilize Pb in the soil with the minimum treatment-induced leaching of phosphorus, it was found that a mixture of soil with phosphate addition in the molar ratio of H(3)PO(4) : HA of 0.75 : 1 showed the most promising results, with an acetic acid extractable Pb concentration of 1.35 mg L(-1) and a water extractable phosphorus concentration of 1.76 mg L(-1). The time-dependent leaching characteristics of metals and phosphorus for this mixture were evaluated by a column experiment, where irrigation of the soil mixture with the average annual amount of precipitation in Slovenia (1000 mm) was simulated. The phosphorus concentration in the leachates decreased from 2.60 mg L(-1) at the beginning of irrigation to 1.00 mg L(-1) at the end.

Oxidation of a PAH polluted soil using modified Fenton reaction in unsaturated condition affects biological and physico-chemical properties

A batch experiment was conducted to assess the impact of chemical oxidation using modified Fenton reaction on PAH content and on physico-chemical and biological parameters of an industrial PAH contaminated soil in unsaturated condition. Two levels of oxidant (H 2O 2, 6 and 65 g kg −1) and FeSO 4 were applied. Agronomic parameters, bacterial and fungal density, microbial activity, seed germination and ryegrass growth were assessed. Partial removal of PAHs (14% and 22%) was obtained with the addition of oxidant. The impact of chemical oxidation on PAH removal and soil physico-chemical and biological parameters differed depending on the level of reagent. The treatment with the highest concentration of oxidant decreased soil pH, cation exchange capacity and extractable phosphorus content. Bacterial, fungal, and PAH degrading bacteria densities were also lower in oxidized soil. However a rebound of microbial populations and an increased microbial activity in oxidized soil were measured after 5 weeks of incubation. Plant growth on soil treated by the highest level of oxidant was negatively affected.

Effects of Long-term Organic Material Amendments on Soil Properties and Corn Yield in Rainfed Area of Thailand

A long-term field experiment on organic material application has been conducted since 1980 at Phraphuttabat Technical Service Center, Lop Buri Province, Thailand, to clarify the effectiveness of organic materials on chemical and physical properties of soil and yield of corn. Mimosa was the most effective crop for increasing organic matter content of soil. Total and Bray II extractable phosphorus content markedly increased in city compost plots. Rice straw showed significant effect on increasing total and exchangeable potassium in soils. Total Ca, Mg, Cu, Zn, extractable Cu, Zn and exchangeable Ca contents distinctively increased in city compost plots. Extractable Fe content significantly increased in the mimosa plot. Average yield of corn with and without fertilizer from 2000 to 2005 showed that the use of crotalaria, mimosa, rice bean and city compost was beneficial to increase the production of corn yield for one, two, four and three years out of a six year experimental duration, respectively. The 5-year moving average of corn yield for 26 years showed the following trends. Corn yield in the mimosa plot without fertilizer increased but the increase was relatively low. The corn yields in the rice bean plot were relatively high during 1982-1986 and 1999-2003 in both fertilizer plots. The yield of corn in crotalaria plots with and without fertilizer was at a relatively low level from 1980 to 1988, and increased from 1989 to 2005. This long-term experiment suggests that application of green manure improved soil properties. Competition of green manure with corn resulted in a relatively low yield of corn and on the contrary, without the competition of green manure corn yields were relatively high. Rice straw mulch with fertilizer was effective in maintaining corn yield under critical rainfall years, while rice straw mulch without fertilizer did not increase the corn yield like that of the fertilizer plot under critical rainfall conditions. Although city compost application was effective in increasing corn yield, precautions against heavy metal contamination should be taken into consideration.

Artificial recharge of groundwater through sprinkling infiltration: Impacts on forest soil and the nutrient status and growth of Scots pine

We studied the chemical changes in forest soil and the effects on Scots pine trees caused by continuous sprinkling infiltration over a period of two years, followed by a recovery period of two years. Infiltration increased the water input onto the forest soil by a factor of approximately 1000. After one year of infiltration, the pH of the organic layer had risen from about 4.0 to 6.7. The NH 4-N concentration in the organic layer increased, most probably due to the NH 4 ions in the infiltration water, as the net N mineralization rate did not increase. Sprinkling infiltration initiated nitrification in the mineral soil. Macronutrient concentrations generally increased in the organic layer and mineral soil. An exception, however, was the concentration of extractable phosphorus, which decreased strongly during the infiltration period and did not show a recovery within two years. The NO 3-N and K concentrations had reverted back to their initial level during the two-year recovery period, while the concentrations of Ca, Mg and NH 4-N were still elevated. Nutrient concentrations in the pine needles increased on the infiltrated plots. However, the needle P concentration increased, despite the decrease in plant-available P in the soil. Despite the increase in the nutrient status, there were some visible signs of chlorosis in the current-year needles after two years of infiltration. The radial growth of the pines more than doubled on the infiltrated plots, which suggests that the very large increase in the water input onto the forest floor had no adverse effect on the functioning of the trees. However, a monitoring period of four years is not sufficient for detecting potential long term detrimental effects on forest trees.

Effect of Poultry Litter to Water Ratios on Extractable Phosphorus Content and its Relation to Runoff Phosphorus Concentrations

Source factors with regard to phosphorus (P) loss in runoff waters are often soil test P and P content of fertilisers applied. More recently, water extractable P (WEP) fractions in fertilisers and animal manure have been the focus of many field and plot-scale studies. This study evaluated changes in the WEP content of six poultry litters by varying the extraction ratio from 1:10 (20 g fresh poultry litter to 200 ml water) to 1:200 (1 g fresh poultry litter to 200 ml water), and also the relation between WEP content determined at these different ratios and P concentrations in runoff water collected during rainfall simulations. Six different poultry litters were surface-applied at equivalent total P (TP) application rates (∼67 kg [TP] ha−1) to 1·52 by 6·10 m grass plots on a 5% slope which received artificial rainfall at 5 cm h−1 until 30 min of continuous runoff was observed. Four plots were used per treatment including four control plots (no poultry litter application). Water-extractable P content of the various poultry litters increased with a decrease in the amount of poultry litter used in the extraction, i.e. from an extraction ratio of 1:10 to 1:200. However, these results also suggest that the 1:10 extraction ratio may extract different fractions of WEP compared to the 1:200 extraction ratio, and that some variability in dry weight extraction ratios existed when using fresh poultry litter. Water-extractable P application rates were positively correlated to P concentrations in runoff waters from the small plots. This study reaffirmed the importance of WEP content of poultry litter when determining the potential for P loss in surface runoff but demonstrated differences in the relation between runoff soluble reactive P (SRP) concentrations and WEP application rates related to the runoff to rainfall ratio.

An Alum‐Based Water Treatment Residual Can Reduce Extractable Phosphorus Concentrations in Three Phosphorus‐Enriched Coastal Plain Soils

The accumulation of excess soil phosphorus (P) in watersheds under intensive animal production has been linked to increases in dissolved P concentrations in rivers and streams draining these watersheds. Reductions in water dissolved P concentrations through very strong P sorption reactions may be obtainable after land application of alum-based drinking water treatment residuals (WTRs). Our objectives were to (i) evaluate the ability of an alum-based WTR to reduce Mehlich-3 phosphorus (M3P) and water-soluble phosphorus (WSP) concentrations in three P-enriched Coastal Plain soils, (ii) estimate WTR application rates necessary to lower soil M3P levels to a target 150 mg kg(-1) soil M3P concentration threshold level, and (iii) determine the effects on soil pH and electrical conductivity (EC). Three soils containing elevated M3P (145-371 mg kg(-1)) and WSP (12.3-23.5 mg kg(-1)) concentrations were laboratory incubated with between 0 and 6% WTR (w w(-1)) for 84 d. Incorporation of WTR into the three soils caused a near linear and significant reduction in soil M3P and WSP concentrations. In two soils, 6% WTR application caused a soil M3P concentration decrease to below the soil P threshold level. An additional incubation on the third soil using higher WTR to soil treatments (10-15%) was required to reduce the mean soil M3P concentration to 178 mg kg(-1). After incubation, most treatments had less than a half pH unit decline and a slight increase in soil EC values suggesting a minimal impact on soil quality properties. The results showed that WTR incorporation into soils with high P concentrations caused larger relative reductions in extractable WSP than M3P concentrations. The larger relative reductions in the extractable WSP fraction suggest that WTR can be more effective at reducing potential runoff P losses than usage as an amendment to lower M3P concentrations.

The relationship between pasture degradation and soil properties in the Brazilian amazon: a case study

Abstract Pasture degradation is one of the greatest problems related to land use in the Amazon region, forcing farmers to open new forest areas. Many studies have identified the causes and the factors involved in this degradation process, in an attempt to reverse the situation. The purpose of this study was to examine the relationship between pasture degradation and some soil properties, to try to identify the most significant soil features in the degradation process. A cattle raising farm in the eastern Amazon region, with pastures of different ages and degrees of degradation, was used as the site for this study: a primary forest area, PN; three Guinea grass (Panicum maximum Jacq.) pastures in an increasingly degraded sequence—P1, P2 and P3; one Gamba grass (Andropogon gayanus Kunth) pasture following an extremely degraded Guinea grass pasture, P4. Aboveground phytomass data showed differences between the pastures, reflecting initially observed degradation levels. Grass biomass decreased sharply from P1 to P2 and disappeared at P3. Pasture recovery with Gamba grass at P4 was very successful, with grass biomass higher than P1 and weed biomass smaller than P2 and P3. Root biomass also decreased with pasture degradation. Soil bulk density increased with pasture decrease at the topsoil layer. Results from the soil chemical analysis showed that there were no signs of decrease in organic carbon and total nitrogen after the forest was transformed into pasture. In all pastures, degraded or not, the soil pH, the sum of bases and the saturation degree were higher than in the forest soil. The extractable phosphorus content, lower in forest soil, remained quite stable in pasture soils, but it could become a limiting factor for the maintenance of Guinea grass. Results indicated that pasture degradation does not seem to be directly related to the modification of the chemical features of soils.

Analytical approaches to the determination of phosphorus partitioning patterns in sediments.

Three methods for phosphorus fractionation in sediments based on chemical extractions have been applied to fourteen aquatic sediment samples of different origin and characteristics. Two of the methods used different approaches to obtain the inorganic fractions. The Hieltjes and Lijklema procedure (HL) uses strong acids or bases, whereas the Golterman procedure (G) uses chelating reagents. The third one, the Standards, Measurements and Testing (SMT) protocol, was proposed in the frame of the SMT Programme (European Commission) which aimed to provide harmonisation and the validation of such methodologies. This harmonised procedure was also used for the certification of the extractable phosphorus contents in a sediment certified reference material (CRM BCR 684). Principal component analysis (PCA) was used to group sediments according to their composition and the three extraction methods were applied to the samples including CRM BCR 684. The data obtained show that there is some correlation between the results from the three methods when considering the organic and the residual fractions together. The SMT and the HL methods are the most comparable, whereas the G method, using a different type of reagent, yields different distribution patterns depending on sample composition. In relation to the inorganic phosphorus, the three methods give similar information, although the distribution between non-apatite and apatite fractions can be different.

Influence of scattered paddock trees on surface soil properties: A study of the Northern Tablelands of NSW

Summary Surface soil conditions were assessed under three tree species on a property near Armidale on the Northern Tablelands of NSW. In both a stocked and adjacent destocked paddock, five trees each of three eucalypt species: Eucalyptus melliodora, Eucalyptus blakelyi and Eucalyptus nova‐anglica, were selected. Soil samples were collected (depth 0–10 cm) along transects 20 m in length running from beneath the tree canopy progressively outwards into the open paddock. Six additional transects were also sampled outside the influence of the trees. Soil properties at a distance from the trees differed little between the stocked and destocked paddock with only a slight acidification in the stocked paddock. However, soil properties around the scattered trees showed considerable variation between stocked and destocked equivalents and most notably in a systematic pattern with distance from the trees themselves. For example, bulk density increased significantly, whereas soil pH, carbon, nitrogen and extractable phosphorus contents all decreased significantly with distance from the trees. However, stocking and camping had modified some of these soil properties. In the stocked paddock, the systematic change in nitrogen and phosphorus with distance from the trees was less clear and the degree of dispersion of the data was largest at the most heavily camped site. In this paddock, bulk density was also generally higher whereas pH, carbon and nitrogen contents were lower compared with the destocked equivalent. Extractable phosphorus content was also higher around the trees in the stocked paddock especially where camping activity was most intense. It is concluded that, although animal camping can modify their effects, scattered trees have a beneficial effect on soil properties and in this respect they have value in the grazing system from a soil conservation perspective.