Eva Vidal Vázquez

Assessing the Spatial Uncertainty of Mapping Trace Elements in Cultivated Fields

Abstract Many of the cultivated soils in Galicia (NW Spain) consist of grassland areas and, subsequently, cattle density is also considerable. As a result, dispersion of heavy metals into the rural environment associated with manure and slurry applications has been reported. Mapping the spatial distribution of heavy metals in soils is important for soil management; currently, geostatistical methods are used to generate maps of fertilizer and heavy metal contents and also to assess the uncertainty of the predicted concentrations of these elements. The main objective of this study was to assess the spatial variability of trace elements in a small catchment (10.7 ha), where slurry application was intense. Moreover, the use of geostatistical tools for the description and modeling of metal distribution is illustrated. Fifty‐five soil samples were digested by nitric acid in a microwave (U.S.E PA‐SW‐846 3051) method to assess Mn, Zn, Cu, Ni, Pb, and Cd contents by ICP/AES. The pattern of spatial distribution of total metal contents was analyzed by means of different geostatistical techniques and by the inverse distance method. When a pattern of spatial dependence was found, kriging was used to construct contour maps after semivariogram analysis. High statistical variability was observed for the metals studied. Mean Cu content was 28.5 mg kg−1 and that of Zn was 64.7 mg kg−1, the differences between maximum and minimum being 62.3 mg kg−1 and 122.1 mg kg−1 for Cu and Zn, respectively. Also, some hot spots with high levels of Cd (>l3 mg kg−1) with respect to background values were recorded. The spatial distributions of total Zn and Cu contents were characterized using spherical semivariograms with no nugget effect. Ordinary kriging estimates were compared with results obtained by indicator kriging. Sequential simulation was also applied to analyze the spatial distribution of the metals studied. This study reveals that these methods are useful to determine spatial distribution and uncertainty of trace metal contents in cultivated fields and thus to characterize the heavy metal status at the scale studied. In contrast, EDTA‐ and CaCl2‐extractable Zn and Cu contents did not show spatial structure at all; hence, nongeostatistical techniques were used to attempt to interpolate these metal fractions.

Perdas de água e solo por erosão hídrica em duas direções de semeadura de aveia e ervilhaca

The sowing direction influences soil surface roughness, which, combined with rainfall and other variables, e.g., canopy cover, affects soil water erosion. Using a rotating-boom rainfall simulator, five tests of simulated rainfall were applied to black oat (Avena strigosa), and vetch (Vicia sativa), at a constant intensity of 64 mm h-1, between August and November 2006, to assess water and soil loss in the following treatment: mechanized seeding of oats in downslope rows; mechanized seeding of oats along contour lines; mechanized seeding of vetch in downslope rows, and mechanized seeding of vetch along contour lines. The experiment was conducted in two replications on an Inceptisol, with a mean slope of 0.119 m m-1. The canopy cover was greater in oat than vetch until rainfall test 2 and higher in vetch in the tests 3 and 4, with no variation due to the sowing direction of the crops and increasing from the beginning to the end of the growth period. The time until the water started to run off was longer in the treatments with seeding along contour lines than downslope, in both crops; the maximum runoff rate along the contour lines was lower and the time until maximum runoff rate longer. The sediment concentration in runoff decreased over the rainfall tests; it was lower in oat than vetch, and 52 % lower in contour than downslope sowing. Soil loss decreased over the rainfall tests; these losses were 12 % lower in oat and 56 % lower in vetch contour than downslope sowing; the water loss had the same performance as soil loss, although with lower magnitudes. The accumulated soil losses increased with accumulated rain volume (VR) and rain erosivity (EI30), between the first and fourth test, according to the equations: SL = 0.859 (1-e-0.0059VR) (R2 = 0.99) and SL = 0.832 (1-e-0.0004EI30) (R2 = 0.99).

Crop Residue Effects on Organic Carbon, Nitrogen, and Phosphorus Concentrations and Loads in Runoff Water

Degraded soil surface conditions favor surface runoff, thus enhancing sediment and nutrient losses. This study examined the effect of crop residues on carbon (C), nitrogen (N), total phosphorus (TP), and total dissolved P (TDP) losses by surface runoff in an agricultural loamy soil with degraded structure. Runoff and sediment yield were made over 1‐m2 plots using a rainfall simulator with constant 65 mmh−1 intensity. Four successive rainfall applications were performed, the first three ones 25 mm each and the last one 65 mm. Added corn straw varied between 0 and 4 tha−1 in the five studied treatments. Organic C, N, and TP concentrations in runoff showed a trend to decrease because of the effect of corn straw on soil losses. However, TDP concentration increased with increasing crop residue in the lower two rainfall events. Sedimentary P constituted the major proportion of P in runoff. After 140 mm of cumulative rainfall, nutrient losses were as follows: organic C from 137.7 to 792.7 kgha−1, N from 16.65 to 88.82 kgha−1, TP from 1.72 to 7.87 kgha−1, and TDP 57 to 87 gha−1. Total losses of the studied nutrients were correlated with soil losses.

Influence of Biosolids Rate on Chemical Properties of an Oxisol in São Paulo, Brazil

Abstract Organic residues may cause major health and environmental problems. This is the case in our study area, where more than 10 billion L per year of residential and industrial waste are produced. Land application of biosolids can be an economical solution by recycling waste and can provide valuable fertilizer if used correctly. The aim of this work was to study the effect of biosolids on the chemical properties of an Oxisol. The experiment was located at Ilha Solteira northwest of São Paulo State, Brazil. The soil was cropped to Sorghum bicolor. The field experimental design consisted of random blocks with six treatments and four replications of each treatment. Biosolids were surface applied to four treatments at rates of 5, 10, 20, and 40 Mg ha−1 on a dry matter basis; in addition, a treatment with mineral fertilizer and a control were included. One year after biosolids application, soil samples were taken at 0–10, 10–20, and 20–40 cm. Organic matter content (Walkley–Black) and pH (CaCl2) were routinely determined. Cation exchange capacity, exchangeable bases (Ca, Mg, K), and P were determined by exchange resin extraction. No significant differences in any of the analyzed properties were found below the 20‐cm depth. Extractable phosphorus (P) and potassium (K) increased with increasing biosolids rate in the top 20 cm, whereas calcium (Ca) and (Ma) magnesium content were not significantly influenced by biosolids. Soil pH decreased with increasing biosolids application. The sewage sludge application did not influence the sorghum production in the first year of culture, under unfavorable soil moisture conditions, but it influenced the dry matter.

Fractal dimension and geostatistical parameters for soil microrelief as a function of cumulative precipitation

A rugosidade da superficie pode ser influenciada pelo tipo e pela intensidade do preparo do solo entre outros fatores. A vantagem de se usar indices fractais em estudos de microrrelevo e que eles permitem a particao das caracteristicas da rugosidade em propriedades ou que dependem exclusivamente da escala ou que independem totalmente dela. Por outro lado, a geoestatistica prove algumas ferramentas que podem ser uteis no estudo da dinâmica da variabilidade da superficie do solo, diferentes daquelas avaliadas pela dimensao fractal. Verificou-se se e possivel aplicar geoestatistica na analise da variacao do microrrelevo de um Latossolo sob seis tratamentos de preparo do solo, a saber: grade de discos, arado de discos, escarificador, grade de discos+grade niveladora, arado de discos+grade niveladora e escarificador+grade niveladora. As medidas foram feitas logo apos o preparo do solo e subsequentemente apos cumulativos eventos de chuva natural. Medicoes duplicadas foram feitas em cada tratamento para cada data, produzindo um total de 48 superficies. Um rugosimetro de agulhas foi utilizado para as medidas da rugosidade da superficie. A area de cada parcela era 1,35 m por 1,35 m e as medidas espacadas de 0,25 m, produzindo um total de 3025 pontos por parcela. Tendencia devido a inclinacao do terreno e causadas pelo preparo do solo foi removida dos dados experimentais. Foram ajustados modelos aos semivariogramas de cada superficie e os parâmetros desses modelos analisados e relacionados aos parâmetros de dimensao fractal. Foi encontrada relacao entre a dimensao fractal, D, e os parâmetros dos modelos dos semivariogramas. O parâmetro de auto-afinidade, l, nao mostrou relacao forte com parâmetros dos modelos dos semivariogramas apesar de ter tido uma relacao de potencia entre D e l.

Phosphorus Contents and Loads at the Outlet of an Agroforestry Catchment in Northwestern Spain

Phosphorus (P) export in watershed runoff can accelerate the eutrophication of fresh waters. Intensification of crops and animal farming in many areas has created regional imbalances in P inputs and P outputs in farm practice. The aim of this study was to assess the temporal changes in concentration and losses of total P (TP), total sedimentary P (TSP), and total dissolved P (TDP) at the outlet of an agroforestry catchment 36.3 km2 in size located at northwestern Spain. The study data sets range from January 1999 to December 2005. Phosphorus load of surface water sampled at the catchment outlet was strongly affected by agricultural practices. Most particulate SP was exported during storm flow events. The TSP contents ranged up to 1063 µg/L, and TDP contents ranged up to 259 µg/L. However, in most of the study events particulate P was less than 300 µg/L and during base flow less than 50 µg/L. Total and particulate P showed a very close relationship, but there was no consistent relationship between water discharge and total P or dissolved P. A few events of intensive precipitation are responsible for the transport of suspended sediments and particles, mobilizing sediments from different source areas. The mean yearly TP export was 0.80 kg/ha and annual dissolved TDP export was approximately 0.30 kg/ha.

Escoamento superficial em diferentes sistemas de manejo em um Nitossolo Háplico típico

Soil tillage influences soil management and damages structure, reduces the porosity and water infiltration and increases surface runoff. A rotating-boom rainfall simulator was used to investigate the treatments: conventional tillage (CT), no-tillage in burn residue (NB), no-tillage in desiccated residue (ND), and traditional no-tillage in desiccated residue (NT), both cropped, as well as conventional tillage without crop (bare soil - BS), and native pasture treatment (NP), in a Typic Hapludox soil, in the Southern Plateau of Santa Catarina State, Brazil, from March, 2001 to February, 2004, with the objective of quantifying surface runoff. Three simulated rainfall tests were applied in maize and bean crops and five in soybean crop. The surface runoff initial time (IT) and surface runoff peak time (PT), the surface runoff constant rate (RR) and surface runoff volume (RV), and C coefficient of the Rational Equation were quantified. The IT, PT, RR, RV and C coefficient changed with soil tillage treatments and with soil cultivation. The IT and PT were smaller in the CT and BS treatments, while the RR, RV and RC were smaller in ND and NT treatments. The RR changed from 18 mm h-1 in NT to 44 mm h-1 in BS treatments, while the RC changed from 0.29 in NT to 0.71 in BS treatments. The VE varied from 106 m3 ha-1 in ND to 434 m3 ha-1 in BS treatments.

Phosphorus Determination after Mehlich 3 Extraction and Anion Exchange Resin in an Agricultural Soil of Northwestern Spain

Differences in soil phosphorus (P) contents measured by various techniques may have implications for agronomic and environmental testing. Reduced-tillage systems combined with surface manure application increase the potential risk of nutrient losses by surface runoff. A field trial was conducted to evaluate the effect of livestock slurry on nutrient accumulation at the surface layer of an acidic soil rich in organic matter with excess P levels and loamy texture. Two reduced-tillage systems, no tillage (NT) and minimum tillage (MT), and four different fertilizer treatments were assessed. The amounts of P extracted by anion-exchange resin (AER) and by Mehlich 3 (M3) were compared; in addition, differences between two determination methods of P contents extracted by Mehlich 3, namely molybdic acid colorimetric standard procedure (M3-COL) and inductively coupled plasma–mass spectroscopy (M3-ICP), were evaluated. Ninety-six soil samples were taken from the 0- to 5-cm surface layer in three successive dates after increasing manure addition. Colorimetric Mehlich 3 P ranged from 49 to 431 mg dm–3. The ranks of mean extractable soil P concentrations were AER < M3-COL < M3-ICP. The linear correlation coefficient between M3-COL and M3-ICP was highly significant (R2 = 0.89; P < 0.01), but a two-straight-lines model or a quadratic relationship were more adequate for describing the dependence between the two determination procedures after M3 extraction. Relative and absolute differences between M3-COL and M3-ICP showed a tendency to increase as organic carbon content increased. Phosphorus content extracted by AER and M3-COL or M3-ICP reported a significant but much less predictable relationship with R2 values of 0.27 and 0.21 (n = 96), respectively. The P in the surface layer accumulated more under NT than under MT.

Variabilidade espacial da rugosidade superficial do solo medida com rugosímetros de agulhas e laser

ABSTRACT SPATIAL VARIABILITY OF SOIL SURFACE ROUGHNESS MEASURED BY PIN ANDLASER RELIEFMETERSThe spatial variability of the soil surface roughness was analysed by instruments of differentprecision degrees in a grid of data points. For measuring the roughness it was used a laser reliefmeterbefore and after application of different amounts of rain (0 mm, 10 mm, 55 mm, 85 mm) in thelaboratory. At field conditions (pasture and ploughed surface) a pin reliefmeter was used at fourdifferent dates. The results showed a great spatial dependence of soil surface roughness in bothmethods and for all treatments. The great variation of semivariogram parameters obtained with pinreliefmeter data for all different dates was due to the distribution and size of soil aggregates. Thisindicates how difficult it is to obtain a representative tridimensional microrelief model at fieldconditions. All other semivariograms obtained with laser reliefmeter data (simulated surface) weresimilar among themselves, indicating that despite the alterations in the soil surface roughness, thespatial dependence pattern did not change with different amounts of rain.

Heavy‐Metal Losses from an Agroforestry Catchment

Abstract Long‐term agricultural sustainability and water quality are impacted by different chemicals, including heavy metals. Heavy‐metal losses at the catchment scale depend largely on land‐management practices. Water‐quality indicators are required near soil‐quality indicators for different regions and farming systems. The purpose of this work is to analyze the heavy‐metal losses from a mixed agroforestry catchment. Iron (Fe), Magnesium (Mn), Zinc (Zn), and Copper (Cu) were measured in the drainage water of a 36.3 km2 catchment located at the Valiñas River (Coruña, northwest Spain), and a total of 193 samples were collected during the course of 2003. The sampling strategy was a stratified point sampling involving more frequent sampling when flow was high. Water metal content was analyzed by inductively coupled plasma (ICP‐AES). The content ranges of dissolved heavy metals were as follows: Fe between 10 and 267 µg/L, Mn 0.2 and 77 µg/L, Zn 0.62 and 53.7 µg/L, and Cu 0.20 and 9.26 µg/L. Heavy metal content strongly varied along the study time, depending on storm flow but also on timing of animal‐waste applications.