Osvaldo Salazar

Evaluation of soil fertility and fertilisation practices for irrigated maize (Zea mays L.) under Mediterranean conditions in Central Chile

The main aim of this study was to carry out an evaluation of soil fertility and fertilisation practices for irrigated maize (Zea mays L.) under Mediterranean conditions in central Chile. Soil samples were collected from 31 maize fields for macro- and micronutrient analysis; additionally a crop management survey was carried out in each field. These data were used to identify the range of critical soil-test concentrations of nutrients and the relationships among these soil fertility parameters; to assess the relationship between maize yields and nutrient status of soils; to evaluate the current fertiliser practices of farmers comparing them with nitrogen (N), phosphorus (P) and potassium (K) fertiliser model calculations; and to analyse whether The results showed that there was a dominance of neutral-alkaline soils with low organic matter and N levels, and high P, cations and micronutrient levels. Regression analysis explained at least 59% of the variation in maize yields, when soil pH and available zinc (Zn) content were identified as the most important variables controlling maize yield. Results suggest that in neutral-alkaline soils cultivated with maize and high inputs of N-P-K, there may be a maize yield response to Zn applications. It was found that most farmers over-fertilised with N (from 60 to 360 kg N ha-1) and P (from10 to 120 kg P2O5 ha-1), converting maize fields in an important non-point source of pollution of water bodies in Central Chile.

IDENTIFICATION OF HYDROLOGICAL FACTORS CONTROLLING PHOSPHORUS CONCENTRATION IN DRAINAGE WATER IN SANDY SOILS

ABSTRACT The relationship between total phosphorus (TP) and molybdate-reactive phosphorus (MRP) concentrations in subsurface drainage waters in the hydrological conditions prevailing during autumn and spring flow events was statistically analysed using multiple linear regression analysis. Data on hydrological conditions in three drainage experimental plots in a loamy sand in south-east Sweden complemented with DRAINMOD-predicted data were used as independent variables. Regression models explained at least 80% of the variation in TP and MRP concentrations in drain outflow, based on adjusted coefficient of determination ( R 2adj ) calculations. DRAINMOD-predicted cumulative infiltration ( INFIL cum ) was identified as the most important hydrological condition controlling TP and MRP concentrations in drain outflow in three autumn events and in two out of three spring events. This suggests that the first infiltrating water found more soluble P forms available for transport, after which TP and MRP concentration in drainage outflows gradually decreased during the flow events.

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.

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.

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.

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).

Human-Induced Soil Degradation in Chile

Recent statistics for Chile show that around 37 million ha (49 % of national territory) display diverse levels of erosion, with Regions IV, V and VI containing the highest eroded area, although human-induced soil erosion is concentrated principally from Region IV to Region X. Because the losses of soil quality (non-erosive processes) are not usually obvious they often receive less attention, but it is clear that they can cause a serious long-term economic decline by directly affecting agricultural productivity. Therefore, this chapter aims to describe the relevant human-induced processes (erosive and non-erosive) in Chile considering available information on assessment methods used by various researchers. It is clear that the only thing that can save the country from accelerated soil degradation is a step forward in the ethical thought of man with respect to natural resources.

Management of Soil Properties in Chile

The various types of soil found in Chile differ widely in their biological, chemical and physical characteristics, responding to diverse combinations of factors and processes of soil formation. Environmentally speaking, soil physical, chemical and biological properties are strongly related, being critical in controlling water and/or plant nutrient availability, the fate of many pollutants and preserving soil biodiversity, with ecosystem consequences. This chapter summarises the results of many years of research work carried out throughout Chilean territory, with the focus on suitable integrated management of these soil characteristics and on the agricultural production perspective. There is no doubt that gaining a full and solid understanding of the soils in Chile is one of the greatest challenges to coming generations, given the limited land availability and the many pressures this natural resource has experienced and will continue to experience.

General Chile Overview

Chile, described as the skinniest country in the world, has great forestry, livestock, and agricultural potential, thanks to a diverse range of soil types and climate conditions, as well as to the presence of strong natural barriers against pests and diseases offered by a harsh desert to the north (the Atacama Desert), the Andes Mountains to the east, the Pacific Ocean to the west and the Antarctic territory to the south. Chile provides the most varied natural sceneries in the world and their mountains and Pacific littoral are a true laboratory of geomorphology, with a total length of 35,000 km when all of the inlets and islands are considered. Therefore, this chapter is oriented to describe in general the geology and geomorphology, climate, vegetation and land use aspects of this tricontinental country (American, Oceanic and Antarctic territory) of startling contrasts.