Positive ions that are available in soils absorb on grain surfaces. The total sum of cations that can be absorbed bij a soil/sediment at a certain PH is defined by the cation-exchange capacity (CEC, in meq g-1: mol equivalents per gram). The uptake of cations is an important parameter in agriculture and the larger the CEC, the more cations can be absorbed to the soil. The CEC depends highly on the pH of soil and sediments, where the CEC decreases with decreasing PH (increasing acidity). The exchange of ions on sediments occurs commonly fast on geological time scales, but the kinetics of adsorption in natural environments is still poorly understood. The strength of the bonding between the cations and the sediments varies from weak Van der Waals bondings (physical adsorption) to strong chemical bonds. The CEC is widely used for agricultural assessment because it is a measure of general soil fertility as well as an indicator of structural stability because CED is capabel of enhancing development of shrinkage cracks. The list below shows the CEC for different types of minerals. The data indicate that the CEC can vary over 2 orders of magnitude for various types of , minerals and can vary one order of magnitude within one soil type. Cation exchange capacity for different types of sediment (Eisma, 1992; Locher and de Bakker, 1990):

Cation exchange capacity.

The literature on atmospheric particulate maffer (PM), or atmospheric aerosol, has increased enormously over the last 2 decades and amounts now to some 1500—2000 papers per year in the refereed literature. This is in part due to the enormous advances in measurement technologies, which have allowed for an increasingly accurate understanding of the chemical composition and of the physical properties of atmospheric particles and of their processes in the atmosphere. The growing scientific interest in atmospheric aerosol particles is due to their high importance for environmental policy. In fact, particulate maffer constitutes one of the most challenging problems both for air quality and for climate change policies. In this context, this paper reviews the most recent results within the atmospheric aerosol sciences and thepoticy needs, which have driven much ofthe increase in monitoring and mechanistic research over the last 2 decades. The synthesis reveals many new processes and developments in the science underpinning climate—aerosol interactions and effects of PM on human health and the environment. However, while airborne particulate matter is responsible for globally important influences on premature human mortality, we stijl do not know the relative importance of the different chemical components of PM for these effects. Likewise, the magnitude of the overall effects of PM on climate remains highly uncertain. Despite the uncertainty there are many things that could be done to mitigate local and global problems of atmospheric PM. Recent analyses have shown that reducing black carbon (BC) emissions, using known control measures, would reduce global wanning and delay the time when anthropogenic effects on global temperature would exceed 2°C. Likewise, cost-effective control measures on ammonia, an important agricultural precursor gas for secondary inorganic aerosols (SlA), would reduce regional eutrophication and PM concentrations in large areas of Europe, China and the USA. Thus, there is much that could be done to reduce the effects of atmospheric PM on the climate and the health of the environment and the human population. A prioritized list of actions to mitigate the full range of effects ofPM is currently undeliverable due to shortcomings in the knowledge of aerosol science; among the shortcomings, the roles of PM in global climate and the relative roles of different PM precursor sources and their response to climate and land use change over the remaining decades of this century are prominent. In any case, the evidence from this paper strongly advocates for an integrated approach to air quality and climate policies.

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Particulate matter, air quality and climate: Lessons learned and future needs

Site-specific management promotes the identification and management of areas within the field, which represent subfield regions with homogeneous characteristics (management zones). However, determination of subfield areas is difficult because of the complex combination of factors which could affect crop yield. One possibility to capture yield variability is the use of soil physical properties to define the management zones as they are related to plant available water. With the aim of characterizing the spatial variability of the main soil physical variables and using this information to determine potential management zones, soil samples were taken from 70 locations in a 33-ha field in Badajoz, southwestern Spain. Firstly, accurate spatial distribution maps of the soil attributes were generated by using regression kriging as the most suitable algorithm in which exhaustive secondary information on soil apparent electrical conductivity (ECa) was incorporated. ECa measurements were carried out with a Veris 3100 operating in both shallow (0–30 cm), ECs, and deep (0–90 cm), ECd, mode. Clay, coarse sand and fine sand were the soil physical properties which exhibited higher correlation with ECa (positively correlated with the finer texture component, clay, and negatively correlated with the coarser ones, coarse and fine sands), particularly with ECs. Thus, this was the secondary variable used to obtain the kriged maps. Later, principal component analysis and fuzzy cluster classification were performed to delineate management zones, resulting in two subfields to be managed separately. This number of subfields was determined using the fuzzy performance index and normalized classification entropy as the way to optimize the classification algorithm.

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Delineation of management zones using mobile measurements of soil apparent electrical conductivity and multivariate geostatistical techniques

Delineation of site specific nutrient management zones for a paddy cultivated area based on soil fertility using fuzzy clustering

Sustainable soil nutrient management with proper understanding of spatial variability of soil properties helps in enhancement of crop productivity and avoiding soil degradation. It has more importance in oil palm plantations, since the area under oil palm cultivation is on rise globally. Moreover, the crop is a nutrient-requiring one and effective nutrient management contributes about 50% of fresh fruit bunch (FFB) production. Therefore, the present study was carried out to assess spatial distribution of soil properties and to delineate soil management zones (MZs) in oil palm plantations of a hot and humid tropical region of India for efficient soil nutrient management. A total of 180 geo-referenced representative soil samples (from 0 to 0.20 m depth) were collected from oil palm plantations of Pedavegi and Denduluru mandals of west Godavari district of Andhra Pradesh, India. Collected soil samples were processed and analysed for soil properties like pH, electrical conductivity (EC), soil organic carbon (SOC), available phosphorus (P), available potassium (K), exchangeable calcium (Ca), exchangeable magnesium (Mg), available sulphur (S) and available boron (B). The values of soil properties varied widely with low (7.7%) to moderate (29.0 to 77.4%) coefficient of variations. Semivariogram analysis and ordinary kriging revealed varied spatial distribution pattern with moderate to strong spatial dependence for most of the soil properties. Development of the MZs was carried out by principal component (PC) analysis and fuzzy c-means clustering. Three PCs with eigen values >1 and accounting 60.31% of total variance were used for further analysis. On the basis of fuzzy performance index and normalized classification entropy, three MZs were identified. The MZs differed significantly with respect to studied soil properties. Thus, the study emphasized that the methodology for delineating MZs could be effectively used for site-specific soil nutrient management in oil palm plantations and other crops for maximizing crop production in the study area.

Spatial variability of soil properties and delineation of soil management zones of oil palm plantations grown in a hot and humid tropical region of southern India

Determination of management zones for a tobacco field based on soil fertility

Spatial variability in soil properties has long been observed within uniformly managed fields. Understanding the spatial characteristics of soil properties would be helpful in the development of site-specific management. Uniform management results in overapplication in areas with high nutrient levels and underapplication in areas with low nutrient levels. The objective of this study was to quantify the degree of spatial variability of soil properties. This is important to tobacco quality across flue-cured tobacco (Nicotiana tabacum) plantation fields. Fourteen soil properties were analyzed by geostatistical techniques. Soil organic matter (OM) had significantly positive correlations with active soil OM, total N (TN), available N, available phosphorus, available potassium, Cu, Fe, and Mn. Soil TN, Zn, cation exchange capacity, and silt showed strong spatial dependence, with nugget-sill ratios ranging from 3.39% to 23.43%. Other soil properties showed moderate dependence, with nugget-sill ratios of 30.87% to 49.99%. Spatial dependence ranged from 34.3 m (Zn) to 376.3 m (Mn). The OM contour map showed highest similarity with that of TN. Variography and kriging are useful tools for soil-sampling strategies and variable-rate application in site-specific farming.

Spatial variability of soil properties in a long-term tobacco plantation in Central China.

Changes in photosynthetic characteristics,and chlorophyll content were studied in the developmenting process of tobacco leaves,and the chloroplast microstructure was observed simultaneously.The results showed that:the photosynthetic rate showed a downward trend after the first rise during the developmenting process.Stomatal conductance(Cs) and transpiration rate(Tr) were significantly correlated with photosynthetice rate,intercellular CO2 concertration(Ci) and photosynthetic rate (Pn) were significantly negatively correlated.Chlorophyll changed in the same trend with Pn.Combined with the results of chloroplast ultrastructure,it could be concluded that the changes in Pn were closely related to the development of chloroplast ultrastructure and chlorophyll content.Gradual improvement of chloroplast ultrastructure and chlorophyll content were the main reason for the incresse of Pn,chloroplast microstructure was disintegrated gradually during the descending process of Pn.It was non-stomatal limitation that caused the decrease of Pn.

Li YanTao

Papers

Determination of management zones for a tobacco field based on soil fertility

Spatial variability of soil properties in a long-term tobacco plantation in Central China.

Changes in photosynthetic characteristics and chloroplast ultrastructure during the development of tobacco leaf.

Spatial variability of soil texture in tobacco field: Spatial variability of soil texture in tobacco field