Oscar Seguel

Morphophysical pedotransfer functions for groundwater pollution by nitrate leaching in Central Chile

Nitrate leaching (NL) is a major concern in agriculture due to its impact on human health and ecosystems. Solute movement through soil is governed by various hydraulic and physical properties that determine water flow. To study such relationships, a pedotransfer function of groundwater pollution was developed in two alluvial irrigated soils under long-term pig slurry applications. Two basins of central Chile, San Pedro (Typic Xerochrepts) and Pichidegua (Mollic Xerofluvents) were selected, where maize (Zea mays L.) was grown in spring-summer, while during autumn-winter period a ryegrass-barley-oat mixed crop was established in San Pedro and a fallow management applied in Pichidegua. Soils in cultivated and control sites were characterized in physical and hydraulic terms. Nitrogen and water budgets were determined measuring periodically (biweekly) N concentration (N-NO3- and N-NH4+) and monitoring water contents in soil profiles, respectively. Dye tracer tests were performed with brilliant blue (BB) dye and the staining patterns analyzed. To contrast the effect of slurry additions over soil physical properties and over NL, t-Student tests were performed. Some accurate pollution groundwater NL pedotransfer functions were obtained calculated through least square fit models and artificial neural networks. Textural porosity, mean diameter variation, slow drainage porosity, air conductivity at 33 kPa water tension and N-NO3- concentrations were directly related to NL. In terms of preferential flow analysis, stained path width > 200 mm was inversely associated to NL. Finally, dye tracer tests provided a better understanding of the characteristics and pattern of water/solute movement through soil to groundwater.

Conservation tillage and water availability for wheat in the dryland of central Chile

The dryland areas of Central Chile are associated to Mediterranean climate. Under these conditions, water availability during crop growth is a crucial factor for crop productivity. Conservation tillage systems play an important role in this area, increasing soil water availability; however, crop yield responses can be variable. Soil management should be aimed at reducing water loss and promoting water use by crops. The aim of this review is to analyze and discuss the factors affecting water availability in the Mediterranean drylands of Central Chile, as well as to study the effect of tillage systems on the water use efficiency of wheat.

Preferential flow paths in two alluvial soils with long-term additions of pig slurry in the Mediterranean zone of Chile

Spatial variability of soil hydraulic properties helps to understand the complexity and dynamic patterns of solute distributions in soils. This study assessed the effects of slurry additions and soil physical properties on preferential flow and nitrate concentrations in two Mediterranean soils of central Chile under conventional agriculture management with long-term slurry additions. Two alluvial basins continuously cropped with maize (Zea mays) were selected, Pichidegua (Mollic Xerofluvent) and San Pedro (Fluventic Humixerept). Soils that had been amended with pig slurry were compared with unamended controls. Soil texture, bulk density, particle density, organic matter, porosity and hydraulic conductivity (Ks) were measured. Soil nitrate concentrations at different depths were determined every 2 weeks during the study, and a dye tracer test using Brilliant Blue FCF was conducted on each soil. Digital picture analysis was then performed to classify flow types in the soil profiles through the distribution of stained path width. Stained path width allowed classification of soil flow types. Preferential flow showed no evidence of being affected by pig slurry; the stained patterns were mainly explained by tillage and soil physical properties, such as texture and Ks. Matrix flow-types in the first horizon grading to macropore flow-types at depth characterised all profiles, except San Pedro amended soil, where homogeneous matrix flow dominated through the entire profile. Concentrations of nitrate showed temporal variation during the measurement season, mainly due to the mineralisation–immobilisation budget and leaching, both triggered by Mediterranean climate conditions. Physical properties helped to explain nitrate distribution in the studied soils.

Shear strength of aggregates compared with bulk soil of two haploxerolls from Chile

Shear strength of aggregates and the bulk soil matrix in two Haploxeroll of central Chile was assessed in order to determine: (1) the effect of previous tillage on shear parameters between aggregates and in the soil matrix and (2) the effects of structure development on differences between dry-wet mechanical parameters. Undisturbed soil cylinders and single aggregates (0-10 cm layer) were collected from untilled and conventionally tilled sites in the Santiago (STG) and Mapocho Soil Series (MPC). General soil properties and shear parameters were determined. The shear tests were conducted on confined and free-draining aggregates and on soil cores, equilibrated at field capacity and air-dried, to obtain data on cohesion and angle of internal friction in the samples. Dry aggregates from the tilled sites showed 40 and 70% greater cohesion compared to untilled sites in STG and MPC soils, respectively, associated with a decrease in coarse porosity in the STG soil and a decrease in organic matter in the MPC soil, thus reducing its friability. In air-dried condition, aggregates from untilled sites developed 6-7 fold strength compared with soil matrix and the difference increased (9-13 fold) in samples from tilled sites. Undisturbed soil cores showed higher friction values when air-dried (68° in average, compared with 43° in individual aggregates), but at -33kPa water tension the tendency was reversed. The results of this study confirm that smaller differences between wet and dry behaviour are associated with better structural development and lower tillage intensity.

Pesticide Risk Management Using Indicators for Vineyards in the Central Valley of Chile

Abstract The Apalta catchment is a wine-producing area of 1300 ha, lying south of Santiago, located in the Colchagua Valley, near Santa Cruz in the VI Region of Chile. The vineyards are planted on slopes of up to 22°, the rows being aligned mainly down the slope. This cropping system and its management lead to a potential contamination of natural resources. To assess the risk of environmental contamination due to the application of pesticides in different pest control strategies, indicators at a field level were derived according to a step-by-step procedure. Using these indicators, runoff was found to be the main process of impact. The different pest control strategies in this catchment caused different potential risks, though these in general were low.

Direct measurement and prediction of bulk density on alluvial soils of central Chile

The significance of soil bulk density ( rb) as a key indicator of soil quality was examined in this study. Bulk density values obtained by direct methods (clod, cylinder, and excavation) with three sample sizes (small, medium, and large) were compared with those obtained by 10 published pedotransfer functions (PTFs) for two alluvial soils (a massive fine-textured Fluventic Haploxeroll and an aggregated, coarse-textured Fluventic Haploxerept) of central Chile. With the exception of small cylinders in fine-textured soil, there were nonsignificant differences between the methods and sample sizes assessed. On the coarse-textured soil, there were nonsignificant differences between the excavation and clod methods, but mediumsized cylinders differed from other cylinder sizes. In general, the clod technique tended to give higher values than the other methods. Using basic information (texture and organic matter/C content) from the existing PTFs for both sites, a better fit for coarse-textured than fine-textured soils was obtained. This indicates that it is necessary to define a set of locally calibrated PTFs that address the complexity of the soil resource throughout Chile.

Long-term monitoring of soil fertility for agroforestry combined with water harvesting in Central Chile

Agroforestry associated with water harvesting was evaluated in field experiments conducted in central Chile, 1996–2008. Soil fertility parameters, such as soil organic matter (SOM), soil reaction (pH), total nitrogen (NT), total phosphorus (PT) and total potassium (KT) contents were measured for five different treatments: control (C), agroforestry (A), agroforestry with water harvesting (AR), woody perennial (W) and woody perennial with water harvesting (WR). Acacia saligna was used as the woody perennial component. Treatments, including Acacia saligna (A, AR, W and WR) increased SOM and NT stocks over time compared with the control, probably due to higher SOM and N inputs from the litter and root turnover. The treatments with water harvesting (AR and WR) showed the highest SOM and NT contents by 2008, suggesting that this practice had positive effects on water infiltration rates and soil water content in the soil, important parameters in the process of root turnover. However, there were no significant differences in other soil parameters, such as pH, PT and KT, perhaps due to the short study time, and soil spatial and temporal variability between treatments.

Structural characterization of a compacted alfisol under different tillage systems

Conservation tillage is a management system used to mitigate and rehabilitate the dryland areas of southern-central Chile in severely compacted soils. The objective of this study was to evaluate the soil physical properties in the root zone under an oat-wheat crop rotation after three years of the establishment of three tillage systems: conventional tillage (CT), zero tillage (ZT) and zero tillage with subsoiling (ZTS). Soil bulk density, porosity, water retention curve, stability of macro- and microaggregates, airflow at field capacity, rest coefficient, and number of roots were evaluated. The results showed that the soil had low water holding capacity in the profile due to the low water retention at the permanent wilting point (matric water potential lower than -1.500 kPa), associated with a high bulk density and clay content. The conservation tillage systems (ZT and ZTS), were similar in the parameters of fast drainage pores (FDP), aggregate stability index, airflow, and rest coefficient compared with CT. However, the volume of pores with diameters between 10-50 μm was higher in ZTS in a 24% and 13%, compared with ZT and CT, respectively. In addition, the root development increased significantly in ZTS. In conclusion, the physical condition of the compacted soil was improved by the zero tillage system with subsoiling, which promoted a better root system in the first horizons in highly compacted soils.

Physical properties of a fine textured haplocambid after three years of organic matter amendments management

AbstractIn Copiapo Valley, the 3 th Region of Chile, a three-year study (2007-2009) was conducted to evaluate the effect of organic amendments and cover crops on soil physical properties (Typic Haplocambid) in a table grape ( Vitis vinifera ) orchard. Four treatments were established during three seasons: control without organic amendments (T1), broad bean-corn-rape rotation (T2), goat manure addition (15 t ha -1 ) (T3) and corn-broad bean-barley rotation (T4). Soils measurements, bulk density, pore size distribution, aggregate stability, water repellence and air conductivity were conducted on soil samples collected at three soil depths (0-10, 10-30 and 30-50 cm). Saturated hydraulic conductivity and mechanical strength were also evaluated. On grape plant measurements, root development, pruning weight and harvested grape production were evaluated. Soil bulk density was reduced with goat manure addition in comparison with any other treatment, which resulted in lower mechanical strength in the top soils. None of the treatments had negative effects on water repellency. The crop treatments enhanced the coarse porosity throughout the soil profile, improving the continuity of porous system with their root development and inducing high air conductivity. Other hand, the control soil and manure application showed a pore discontinuity in a pre-existing plow pan. Aggregate stability and saturated hydraulic conductivity were greater in goat manure application, but the treatments which included crop rotation did not show significant differences compared with the control. Because of the short duration of the study, it is assumed that the soil improvements were not detected as expected in grape production yet. Keywords: Compaction, cover crops, aggregate stability, soil porosity

Main Features of Chilean Soils

The geographical position in South America, the great length from north to south, the enormous fluctuation in altitude, recent volcanic activity, glacial activity, climate diversity and other factors are responsible for the variety of Chilean soils. Soil parent materials are varied including mainly very old rocks, volcanic ashes, fluvial and/or glacial deposits and colluvial and/or alluvial deposits. Residual and colluvial soils are distributed along more rugged landscapes that coexist with soils derived from volcanic ash, but all have a dominant forestry potential. Alluvial, glacial and fluvio-glacial soils are distributed principally along the discontinuous Longitudinal Central Valley and southern Patagonian plains, where agricultural activities are mainly developed. Around 65 % of Chilean territory has been covered by detailed and semi-detailed soil cartography, described and classified mainly according to the Soil Taxonomy system (USDA).