Stamatis Stamatiadis

Impacts of agricultural practices on soil and water quality in the Mediterranean region and proposed assessment methodology

In countries around the Mediterranean basin, the degradation of soil and water resources is a serious threat for the human welfare and the natural environment as a result of the unique climate, topography, soil characteristics, and peculiarities of agriculture. The detrimental effects of agricultural practices on soil quality include, erosion, desertification, salinization, compaction, and pollution. The resultant impacts on water resources include pollution due to nutrient and pesticide leaching and intrusion of seawater into aquifers. In order to select the appropriate sustainable strategies for preventing those impacts, research should focus on development of an accurate soil quality monitoring system at multiple scales based on a functional evaluation of soils. The objectives of this work are: (a) to point out the peculiarities of the Mediterranean region; (b) to underline the most important impacts of agricultural practices on soil and water quality, in respect to the above peculiarities; and (c) to propose a simple and cost effective methodology for the assessment of soil quality at a watershed scale, based on zones of specific functional interest. The proposed assessment methodology would provide information about the status of the soil resources, correlate soil quality with management and aid with the development of sustainable management practices.

Field and laboratory evaluation of soil quality changes resulting from injection of liquid sewage sludge

Soil quality changes resulting from repeated or single injection of liquid municipal sewage sludge were evaluated in terraced cropland in eastern Nebraska, USA. Differences in soil properties among sampling locations were explained primarily by two factors, landscape position and sludge injection. Selected chemical properties (pH, EC, NO3‐N) did not generally differ between landscape positions, but soil organic matter (organic C and N) and microbial activity indices (soil respiration, biomass N, available N, mineralization and nitrification rates) were more sensitive indicators of change. Values of these indicators generally increased down-slope from the upper terrace to the grassed waterway on a west facing slope. A probable similar pattern on the east slope was obscured by repeated application of sludge. Single or repeated (long-term) sludge injection increased the readily decomposable organic matter, ammonium- and available-N in soil (0‐30.5 cm depth). These changes stimulated soil microbial activity as evidenced by increased basal respiration, net mineralization and nitrification rates. Consequently, nitrification of ammonium-N was reflected in soil chemical properties as increased soil nitrate-N (to levels that were more than two times higher than sufficiency levels for corn) and EC and by decreased pH. In-field measurements detected changes in physical properties such as a decrease of infiltration rate caused by sludge injection and soil compaction as a result of traffic operations. Differences between the sites of single and repeated sludge injection were found in soil pH, ammonium-N, organic matter and microbial activity. Recent sludge injection resulted in higher ammonium-N concentration and higher microbial activity in soil, and repeated sludge injection resulted in lower pH and in greater organic matter content. Regardless of these differences in soil properties between the sites of single and repeated sludge application, the overall changes that were caused by sludge injection had both positive and negative effects on soil quality and the sustainability of this management practice. Increase of organic matter content and biological activity improved soil fertility, but excessive amounts of ammonium salts contained in liquid sludge resulted in soil nitrification, excessive nitrate formation and acidification. These processes reduce soil productivity, increase the risk of ground- and surface-water contamination and pose a threat to plant and animal health. # 1999 Elsevier Science B.V. All rights reserved.

Land-Use Effect on Selected Soil Quality Parameters

Land use is a key factor that affects soil quality. The purpose of the present study was to investigate changes of selected soil chemical properties related to soil function under different land uses. Five experimental sites arranged in a complete randomized blocks located within the Kalloni watershed (Lesvos Island, Greece) corresponding to different land uses (Pinus brutia forest, brushwood pasture, rain-fed olive grove, wheat, and maize) were compared for soil pH, electrical conductivity (EC), total nitrogen (N), nitrate N (NO3-N), Olsen phosphorus (P), and organic matter. Soil nitrate and P concentration were in the order corn > wheat > olive > pasture > forest. Soil EC and NO3-N showed significant within-year variability only in the corn and wheat systems. Corn and wheat had the lowest soil organic-matter content followed the order forest > pasture > olive grove = wheat = corn. However, total N did not significantly differ among land uses.

Natural Abundance of Foliar 15N as an Early Indicator of Nitrogen Deficiency in Fertilized Cotton

ABSTRACT Information on the contribution of various soil nitrogen (N) sources to plant N uptake is often needed for the implementation of sustainable or site-specific management practices in agriculture. Considering the limitations of traditional methods in meeting these needs, this study investigated the potential of leaf δ15N as an early indicator of nutrient deficiency in cotton. The spatial and temporal natural abundance of 15N was measured in the soil and leaves of a fertilized cotton field located near the village of Moschochori (Larissa, Greece). The isotopic signal of the leaves was interpreted in the context of the relative contribution of fertilizer to cotton N uptake,as has been demonstrated in the past for other agricultural crops such as wheat (Triticum aestivam L.) and corn (Zea mays). Spatial variability of leaf δ15N was high early in the growing season (June), reflecting differences in fertilizer N availability and uptake between the east and west side of the field, as well as differences resulting from soil denitrification in depressions. The west side of the field appears to have lost significant amounts of fertilizer N, due to leaching during the rainy period in May, that accumulated in depressions near the waterway. In the subsequent months, the isotopic signal of the leaves was consistently high and indicated reduced fertilizer N uptake on the west side that resulted in deficiencies of N as well as of phosphorus (P) and potassium (K). The significant correlations of mid-square leaf δ15N with late-season nutrient content and soil elelctrical conductivity(EC) provided evidence that the natural abundance of 15N was a sensitive indicator of soil and plant nutrient status in this fertilized cotton field.

Investigation of Soil Property Changes and Olive Tree Stress as Caused by Excessive Sewage‐Sludge Application

This study was undertaken to assess the impact of a single excessive sludge application (300 Mg ha−1) on the soil surface of an olive orchard several years after the event. Selected soil properties were compared in two soil profiles, one in the sludge‐amended field and another in an adjacent unamended field of naturally growing trees. Leaf analysis included macronutrients [nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg)], trace elements [copper (Cu), zinc (Zn), manganese (Mn), iron (Fe), nickel (Ni), boron (B)], and isotopic composition (δ 15N and δ 13C). Soil pH and other chemical properties were increased in the surface soil and the root zone of the sludge‐treated profile in comparison to those of the untreated control. The multifold increase of Bray P and nitrates indicated a serious risk for dissolved phosphates in runoff and nitrate contamination of groundwater. Trace‐element content also increased, but not greater than the critical soil concentration. Olive trees responded to excessive sludge application by increased N uptake as evidenced by increased leaf N content and elevated 15N signal. The increased leaf δ 13C signal of the leaves further indicated tree stress in the sludge‐amended field during the summer growing season in comparison to the naturally growing control trees. Isotopic composition, leaf nutrient, and trace element concentration did not reveal the causes of leaf tip burning in half of the trees of the sludge‐amended field.

Satellite Visible–Near Infrared Reflectance Correlates to Soil Nitrogen and Carbon Content in Three Fields of the Thessaly Plain (Greece)

Surface visible–near infrared (NIR) reflectance of bare soil by remote sensing devices has been used to infer topsoil properties such as organic matter, soil texture, water content, salinity, and crop residue cover. Spectral mapping of soil properties can be ultimately used as a tool for the implementation of site-specific management practices at the field scale or for soil–landscape modeling at a regional scale. The accuracy of prediction of soil properties with satellite imagery is affected by conditions and properties of the soil surface, by radiometric and atmospheric effects, and by spatial and spectral resolutions. In this study, a high-resolution World View 2 image was used to map soil reflectance in three 10-ha fields of differing soil types and textures that were located in different sections of the east Thessaly Plain. Radiance data from four visible-NIR channels were extracted from the same coordinates that soil samples were taken at two soil depths within each field. Point radiance values were correlated to soil organic matter, total carbon (C) and nitrogen (N) contents, their isotopic composition, carbonate content, nitrate content, pH, electrical conductivity, and soil texture that were analyzed in the laboratory. Strong correlation coefficients emerged between green/NIR image reflectance and total soil N, organic matter, and carbonate content across the three fields in both soil depths. The greatest negative correlation coefficient (R2 = 0.77) was obtained between satellite NIR reflectance and soil N content. More data are needed to verify these relationships, but the results indicated the potential of high-resolution satellite imagery to quantify within-field and regional-scale variability of soil N and C in the Thessaly Plain.

Irrigation and Nitrogen Fertilization Effects on Soil Chemical Properties and Cotton Yield

A 2-year field experiment was conducted in central Greece (Platykampos, Larissa) to investigate productivity parameters of cotton under conditions of water stress. A Latin square split-plot design with three replications was used to evaluate the effect of three irrigation levels (250, 350, and 450 mm) and three fertilization rates (60, 110, and 160 kg N ha–1), where irrigation level was the whole-plot factor and the fertilizer was the split-plot factor. The results showed that irrigation level had no significant effect on soil chemical properties, but these only changed with fertilizer application. Concentration of soil nitrates increased in proportion to the amount of applied fertilizer in early July. The associated rise in electrical conductivity (EC) was not sufficiently high as to adversely affect salt-tolerant cotton. The soil acidity produced during formation of nitrate was evident by a soil pH decrease of 0.2 units in the high fertilizer application. A great decline of nitrate N and EC and a rise of pH in all treatments in early August indicated rapid N uptake by the crop during the late stage of vegetative growth. In contrast, cotton yield was not affected by the rate of fertilizer application but by the level of irrigation. This is the reason that correlations between soil properties and yield were insignificant in early July and August. It appears that there was sufficient N available to the crop from sources other than fertilizer N (soil-derived N and irrigation N). Preplant soil nitrates were greater than residual nitrates in the second growing season and indicated depletion of soil mineral N pools of the order of 36 kg N ha–1 in the 0- to 25-cm depth. Significant negative correlations between soil properties and cotton yield appeared only at the end of the season and indicated that depletion of soil mineral N increased with increasing crop N requirement or irrigation level.