Variability Of Soil Chemical Properties Research Articles

Small relief shape variations influence spatial variability of soil chemical attributes

Soils with small variations in relief and under the same management system present differentiated spatial variabilities of their attributes. This variability is a function of soil position in the landscape, even if the relief has little expression. The aim of this work was to investigate the effects of relief shape and depth on spatial variability of soil chemical attributes in a Typic Hapludox cultivated with sugar cane at two landscape compartments. Soil samples were collected in the intercrossing points of a grid, in the traffic line, at 0-0.2 m and 0.6-0.8 m depths, comprising a set of 100 georeferenced points. The spatial variabilities of pH, P, K, Ca, Mg, cation exchange capacity and base saturation were quantified. Small relief shape variations lead to differentiated variability in soil chemical attributes as indicated by the dependence on pedoform found for chemical attributes at both 0-0.2 m and 0.6-0.8 m depths. Because of the higher variability, it is advisable to collect large number of samples in areas with concave and convex shapes. Combining relief shapes and geostatistics allows the determination of areas with different spatial variability for soil chemical attributes.

Spatial Variation of Soil Properties Relating to Vegetation Changes

Bekele and Hudnall provide an interesting perspective on the spatial variation of soil chemical properties in a natural area undergoing transition from prairie to forest. Their focus is on the unique calcareous prairie ecosystem of Louisiana where prairie remnants are being encroached upon by the forest, primarily eastern red cedar (Juniperus virginiana L.). Bekele and Hudnall were especially interested in investigating any differences in spatial variability among similar sites and in documenting the scale at which the variability occurs. Geostatistical methods have been used to describe and model spatial patterns in soil data for more than 20 years. The accessibility of user-friendly geostatistical software packages has increased the use of spatial analysis of soil’s data but carries the risk that these tools are used without due consideration of the underlying theory, especially in the field of semivariogram modeling or recommended good practices. The feedback between plant community composition and species distribution and soil properties in natural systems has promise to provide enhanced insight into the short- and long-term relationships between plants and soil properties. This is an intriguing area of research that couples plant ecology and soil science and should provide valuable information on the interaction of soils with the processes of plant succession and competition. Researchers in this area are urged to be cautious in verifying the assumptions behind popular geostatistical methods and explicit in describing the important steps such as trend analysis, which can reveal critical interpretive information.

Spatial Variability of Soil Chemical Properties of a Prairie–Forest Transition in Louisiana

Woody plant expansion, particularly eastern red cedar (Juniperus virginiana L.), has been a major threat to Louisiana calcareous prairies. Previous studies have shown that woody plant expansion into grasslands is associated with an increase in soil heterogeneity. We studied the within site spatial variability and among site differences of surface (0–15 cm depth) soil pH, electrical conductivity (EC), and Mehlich III extractable Ca, Mg, K, Fe and Mn from three remnant prairie-forest associations in Winn Parish, Louisiana. The prairie soil was consistently basic (pH > 7.0) and the forest soil was acidic (pH < 7.0) while the transition soil was neutral (pH = 7.0). A nonparametric statistical test for the equality of medians among sites showed the median values of the soil attributes differed (α = 0.05) except for soil Ca and Fe. The similarity in Ca concentration among sites was attributed to the calcareous parent material common to the three sites. Geostatistical analysis showed that spatial dependence was expressed over a range of 20–30 m for most of the soil attributes considered. Semivariogram shapes were similar among sites, suggesting the greater control of soil parent material on the observed spatial soil pattern. Shorter range of variation emerged only for soil pH when soil data from the forest and transition were deleted, indicating the scaling characteristics of soil pH and its susceptibility to plant induced changes. It is concluded that soil pH can be used as an index to determine prairie-forest boundary, and to access the impact of eastern red cedar on these and similar sites derived from calcareous parent material. Further, results from this study can be used for designing future ecological studies within the prairie by taking the soil spatial variability into account.

Variabilidade espacial de atributos do solo para adoção do sistema de agricultura de precisão na cultura de cana-de-açúcar

O objetivo do presente trabalho foi avaliar a variabilidade espacial de atributos de Latossolos sob cultivo de cana-de-açúcar na região de Jaboticabal (SP). Foram feitas amostragens do solo a intervalos regulares de 50 m, em uma área de 90 ha, nas profundidades de 0,00-0,20 e 0,60-0,80 m para determinação de pH, CTC, V % e teores de matéria orgânica, P, K+, Ca2+, Mg2+, H + Al e argila. Os dados foram submetidos às análises: estatística descritiva, geoestatística e interpolação por krigagem. Os alcances de dependência espacial para os atributos químicos do solo e teores de argila na camada de 0,60-0,80 m de profundidade foram menores, quando comparados àqueles referentes à camada de 0,00-0,20 m. Estes resultados demonstraram maior descontinuidade na distribuição espacial dos atributos do solo na camada de 0,60-0,80 m de profundidade dos Latossolos, indicando que essa classe de solos não apresentou homogeneidade de seus atributos como conceituadamente a ela foi atribuída. O manejo no solo alterou a dependência espacial dos atributos do solo na camada superficial de forma a diminuir a variabilidade espacial dos atributos químicos do solo em relação à camada mais profunda. A investigação da variabilidade espacial de atributos químicos e do teor de argila da camada superficial e subsuperficial dos solos proporcionou condições para a definição de zonas homogêneas de manejo, o que permite a adoção do sistema de agricultura de precisão.

First-year soybean growth and production as affected by soil properties following land leveling

In severely disturbed soils, such as those that have been recently land leveled, the interactions among soil properties are accentuated because of the disruption of pre-leveling equilibrium, and manifest their controlling influence on growth and production of sensitive crops, such as soybean [Glycine max (L.) Merr.]. The objective of this study was to identify pre-plant soil properties that influence first-year soybean growth and production following shallow land leveling in an alluvial soil commonly used for rice and soybean production in the Mississippi Delta region in eastern Arkansas, USA. Soil physical (i.e., bulk density and particle-size fractions), chemical (i.e., organic matter, pH, electrical conductivity, and extractable soil nutrients) and biological (i.e., bacterial and fungal biomass) properties were evaluated in the top 10 cm of soil following land leveling. Soybean leaf area index at the R5-6 growth stage, plant population, above-ground dry matter, seed yield and harvest index were also measured at 50 grid points spaced evenly within a 0.36-ha study area. Post-leveling soil properties were significantly correlated with first-year soybean growth and production parameters. Variations in soil chemical properties, particularly extractable soil nutrient contents, organic matter concentrations and biological properties (i.e., microbial activities) accounted for the largest percentage of the variability in first-year soybean growth and production parameters. Results from this study indicate that factors other than those measured in this study, such prolonged soil moisture conditions and poor internal drainage, may contribute to the resulting variability of first-year soybean growth and productivity following land leveling.

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision-agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil-sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal-component analysis of landscape attributes and unsupervised classification of principal-component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest- and lowest-yielding MZ in three of five seasons, receiving average precipitation, less-pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Appropriateness of Management Zones for Characterizing Spatial Variability of Soil Properties and Irrigated Corn Yields across Years

Recent precision‐agriculture research has focused on use of management zones (MZ) as a method for variable application of inputs like N. The objectives of this study were to determine (i) if landscape attributes could be aggregated into MZ that characterize spatial variation in soil chemical properties and corn yields and (ii) if temporal variability affects expression of yield spatial variability. This work was conducted on an irrigated cornfield near Gibbon, NE. Five landscape attributes, including a soil brightness image (red, green, and blue bands), elevation, and apparent electrical conductivity, were acquired for the field. A georeferenced soil‐sampling scheme was used to determine soil chemical properties (soil pH, electrical conductivity, P, and organic matter). Georeferenced yield monitor data were collected for five (1997–2001) seasons. The five landscape attributes were aggregated into four MZ using principal‐component analysis of landscape attributes and unsupervised classification of principal‐component scores. All of the soil chemical properties differed among the four MZ. While yields were observed to differ by up to 25% between the highest‐ and lowest‐yielding MZ in three of five seasons, receiving average precipitation, less‐pronounced (≤5%) differences were noted among the same MZ in the driest and wettest seasons. This illustrates the significant role temporal variability plays in altering yield spatial variability, even under irrigation. Use of MZ for variable application of inputs like N would only have been appropriate for this field in three out of the five seasons, seriously restricting the use of this approach under variable environmental conditions.

Seasonal variation in the soil respiration rate in coniferous forest soils

In order to evaluate the seasonal variation in the soil respiration rate, we established three study plots in three different forest site types. Soil samples were taken weekly from the study plots during one growing season. Seasonal variation in soil chemical properties was small, the only clear trends being in the NH 4–N and NO 3–N concentrations. The soil respiration rates decreased during spring and summer, the minimum values occurring at the end of August. The soil respiration rates again increased during the autumn, but did not reach values close to those in the spring. Adjusting the moisture content of the samples to 60% of water holding capacity (WHC), reduced the variation in the soil respiration rate. When the soil respiration rate was measured at a constant temperature (14 °C), the respiration rate was regulated by moisture and pH. When the moisture content was kept constant (WHC 60%), the respiration rate was mainly controlled by the amount of organic matter (N and C org) and pH. When the respiration rate was calculated on the basis of the N concentration, the variation was mainly explained by pH. The possible effects of environmental pollution, e.g. anthropogenic soil acidification, on the respiration rate can be identified by keeping the moisture content and temperature constant, and calculating the results on an organic matter basis (N and C org).

Exploring the spatial relations between cereal yield and soil chemical properties and the implications for sampling

Abstract. In general, agricultural management has focused on differences between fields or on the gross differences within them. Recent developments in agricultural technology, yield mapping, Global Positioning Systems and variable rate applications, have made it possible to consider managing the considerable variation in soil and other properties within fields. This system is known as precision agriculture. More precise management of fields depends on a better understanding of the factors that affect crop input decisions. This paper examines the spatial variation in crop yield, soil nutrient status and soil pH within two agricultural fields using geostatistics. The observed properties vary considerably within each field. The relation between yield and the measured soil properties appears to be weak in general. However, the range of spatial correlation for yield, shown by the variogram, is similar to that of the soil chemical properties. In addition the latter changed little over two years. This suggests that information on the scale of variation of soil chemical properties can be derived from yield maps, which can also be used as a guide to a suitable sampling interval for soil properties.

Seasonal variation of soil chemical properties and CO 2 and CH 4 fluxes in unfertilized and P-fertilized pastures in an Ultisol of the Brazilian Amazon

Conversion of the tropical forest to pasture results in changes in the quality and quantity of the soil organic matter (SOM) and other physical and chemical soil properties. Most studies concerning the carbon (C) cycle have focused on soil C stocks. However, little information is available on tropical soil respiration rates. The objectives of this paper are, firstly, to determine how conversion of a natural forest to a pasture and P fertilization affect (1) some soil properties and carbon and nutrient content, and (2) CO 2 and CH 4 exchanges at the soil–atmosphere interface. For such purposes, a forest-to-pasture chronosequence (pasture established in 1983, 1987, and 1994) was selected at the Fazenda Nova Vida in Rondonia. Soil sampling was done during the dry season (July 1996) and 6 months later during the rainy season (January 1997). Results show increased pH levels, exchangeable cations, and carbon stocks with the pasture installation. On the contrary, the level of available phosphorus decreased with the increasing age of the pastures, justifying the phosphorus fertilization practice. Regarding the CO 2 and CH 4 fluxes, we found that the forest and pasture soils had greater respiration (CO 2 release) rates during the wet season than during the dry season but no specific and significant relationships between the emission and the pasture age was found. Forest soil CH 4 consumption rates were three times lower during the wet season, whereas pasture soils showed a net emission of CH 4 even during the dry season.

Geostatistical analysis of soil chemical properties and rice yield in a paddy field and application to the analysis of yield-determining factors

To obtain basic information for rational site-specific soil management for rice production, spatial variability of soil chemical properties and grain yield of rice was evaluated in a 50 m × 100 m paddy field. One hundred surface soil samples were collected from each of the 5 m × 10 m plots before puddling to investigate the spatial variability of their chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of mineralizable N, inorganic N, available P, exchangeable Ca, Mg, K, and Na. Grain yield was also measured at harvest for the corresponding 100 plots. Geostatistical analysis was carried out to examine their within-field spatial variability using semivariograms, and multivariate analysis was also carried out to evaluate yield-determining factors. Geostatistical analysis of the soil properties indicated a high to moderate spatial dependence for all the properties except for the inorganic N content. The ranges of spatial dependence were about 20–30 m for the pH, EC, total C content, total N content, content of exchangeable Na, about 40 m for the contents of available P, mineralizable N, exchangeable Ca and Mg, and about 50–60 m for the C/N ratio and content of exchangeable K. Grain yield showed a moderate spatial dependence with a range of about 50 m. The results of spatial dependence enabled to prepare kriged maps of the soil properties and yield to compare their spatial distribution in the field. Multivariate analysis further showed, in combination with geostatistics, that the soil chemical properties contributed significantly to the yield as yield-determining factors and explained as much as 65% of the spatially structured or non-random variation of the yield. In conclusion, the possible benefit of site-specific soil management or precision agriculture was demonstrated even in an almost flat paddy field.

Spatial variability of soil chemical properties in a paddy field

To obtain basic information for site-specific soil management to improve nutrient use efficiency by plants, spatial variability of soil properties was evaluated in a 50 m × 100 m paddy field. Ninety-one surface soil samples were collected after harvest to investigate the spatial variability of their chemical properties: pH, EC, total C content, total N content, C/N ratio, contents of available P, exchangeable Ca, Mg, K, and Na. Fifty samples were also collected after transplanting to investigate that of nitrogen-related properties: total C content, total N content, C/N ratio, and contents of mineralizable N and inorganic N. Geostatistical analysis was carried out to examine within-field spatial variability using semivariograms and kriged maps as well as descriptive statistics. Descriptive statistics showed that the coefficient of variation for the EC, total C content, total N content, contents of available P, exchangeable K, Na, mineralizable N, and inorganic N exceeded 10%, suggesting a relatively high variability. Geostatistical analysis indicated a high spatial dependence for all the properties except for the pH and inorganic N content. The ranges of spatial dependence were about 20 m for EC, total C content, total N content, C/N ratio, contents of exchangeable Ca, Mg, Na, and mineralizable N, and about 40–50 m for the contents of available P and exchangeable K. Based on the results of spatial dependence, kriged maps were prepared for the properties to analyze their spatial distribution in the field. The results reflected the history of soil management of the field in addition to the characteristics of the inherent soil properties. In conclusion, rational sampling interval was evaluated at 20–50 m depending on the soil properties, and the need for site-specific soil management and possibility of precision agriculture were demonstrated even in an almost flat paddy field.

Variabilidade horizontal de atributos de fertilidade e amostragem do solo no sistema plantio direto

As adubações, a lanço, quando desuniformes, ou as em linhas, no sistema plantio direto, aumentam a variabilidade dos atributos químicos do solo. Nestas condições, há necessidade de se saber qual a melhor forma e o número de subamostras por coletar para uma boa representatividade da fertilidade da área a ser cultivada. O objetivo deste estudo foi quantificar a variabilidade horizontal de atributos de fertilidade do solo no sistema plantio direto com diferentes modos de adubação e tempos de cultivo, com vistas em definir o número de subamostras necessárias para formar uma amostra representativa da fertilidade do solo de uma área. Foram coletadas, em novembro de 1997, 36 amostras simples, com pá de corte, na camada de 0-10 cm, de forma diferenciada nas adubações a lanço (5 e 10 cm, espessura da fatia e largura) e em linhas (5 cm de espessura da fatia pela largura das entrelinhas de semeadura da última cultura), em oito lavouras comerciais na região noroeste do Rio Grande do Sul. O número mínimo de subamostras para estimar com boa representatividade (α = 0,05 e erro em relação à média de 10%) o pH, o índice SMP e o teor de matéria orgânica foi baixo (menor do que 8) e alto (maior do que 40) para fósforo e potássio (Mehlich-1). O número de subamostras indicado para o sistema convencional (20) pode ser usado no sistema plantio direto, desde que seja admitido um erro de 20% em relação à média.

Spatial Variability of Soil Chemical Properties in a Paddy Field

Spatial Variability of Soil Chemical Properties in a Paddy Field

PLANT REMOVALS IN PERENNIAL GRASSLAND: VEGETATION DYNAMICS, DECOMPOSERS, SOIL BIODIVERSITY, AND ECOSYSTEM PROPERTIES

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced diversity; there were negative correlations between plant and arthropod diversity, presumably because of negative influences of C4 species in the most diverse treatments. There was evidence of lag relationships between diversity of plants and that of the three decomposer groups, indicating multitrophic effects of altering plant diversity. Relatively small effects of plant removal on the decomposer food web were also apparent in soil processes regulated by this food web. Decomposition rates of substrates added to soils showed no relationship with treatment, and rates of CO2 evolution from the soil were only adversely affected when all plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusion of plant species from the species pool can have important consequences for overall vegetation composition in addition to the direct effects of vegetation removal, and various potential effects on both the above- and belowground subsystems. The nature of many of these effects is driven by which plant species are lost from the system, which depends on the various attributes or traits of these species.

Plant Removals in Perennial Grassland: Vegetation Dynamics, Decomposers, Soil Biodiversity, and Ecosystem Properties

The consequences of permanent loss of species or species groups from plant communities are poorly understood, although there is increasing evidence that individual species effects are important in modifying ecosystem properties. We conducted a field experiment in a New Zealand perennial grassland ecosystem, creating artificial vegetation gaps and imposing manipulation treatments on the reestablishing vegetation. Treatments consisted of continual removal of different subsets or “functional groups” of the flora. We monitored vegetation and soil biotic and chemical properties over a 3-yr period. Plant competitive effects were clear: removal of the C3 grass Lolium perenne L. enhanced vegetative cover, biomass, and species richness of both the C4 grass and dicotyledonous weed functional groups and had either positive or negative effects on the legume Trifolium repens L., depending on season. Treatments significantly affected total plant cover and biomass; in particular, C4 grass removal reduced total plant biomass in summer, because no other species had appropriate phenology. Removal of C3 grasses reduced total root biomass and drastically enhanced overall shoot-to-root biomass ratios. Aboveground net primary productivity (NPP) was not strongly affected by any treatment, indicating strong compensatory effects between different functional components of the flora. Removing all plants often negatively affected three further trophic levels of the decomposer functional food web: microflora, microbe-feeding nematodes, and predaceous nematodes. However, as long as plants were present, we did not find strong effects of removal treatments, NPP, or plant biomass on these trophic groupings, which instead were most closely related to spatial variation in soil chemical properties across all trophic levels, soil N in particular. Larger decomposer organisms, i.e., Collembola and earthworms, were unresponsive to any factor other than removal of all plants, which reduced their populations. We also considered five functional components of the soil biota at finer taxonomic levels: three decomposer components (microflora, microbe-feeding nematodes, predaceous nematodes) and two herbivore groups (nematodes and arthropods). Taxa within these five groups responded to removal treatments, indicating that plant community composition has multitrophic effects at higher levels of taxonomic resolution. The principal ordination axes summarizing community-level data for different trophic groups in the soil food web were related to each other in several instances, but the plant ordination axes were only significantly related to those of the soil microfloral community. There were time lag effects, with ordination axes of soil-associated herbivorous arthropods and microbial-feeding nematodes being related to ordination axes representing plant community structure at earlier measurement dates. Taxonomic diversity of some soil organism groups was linked to plant removals or to plant diversity. For herbivorous arthropods, removal of C4 grasses enhanced diversity; there were negative correlations between plant and arthropod diversity, presumably because of negative influences of C4 species in the most diverse treatments. There was evidence of lag relationships between diversity of plants and that of the three decomposer groups, indicating multitrophic effects of altering plant diversity. Relatively small effects of plant removal on the decomposer food web were also apparent in soil processes regulated by this food web. Decomposition rates of substrates added to soils showed no relationship with treatment, and rates of CO2 evolution from the soil were only adversely affected when all plants were removed. Few plant functional-group effects on soil nutrient dynamics were identified. Although some treatments affected temporal variability (and thus stability) of soil biotic properties (particularly CO2 release) throughout the experiment, there was no evidence of destabilizing effects of plant removals. Our data provide evidence that permanent exclusion of plant species from the species pool can have important consequences for overall vegetation composition in addition to the direct effects of vegetation removal, and various potential effects on both the above- and belowground subsystems. The nature of many of these effects is driven by which plant species are lost from the system, which depends on the various attributes or traits of these species.

Sorghum growth in acid soils of West Africa: Variations in soil chemical properties

Three field experiments were conducted to alleviate soil chemical properties associated with poor early growth of sorghum [Sorghum bicolor (L) Moench] in selected Grossarenic and Plinthic Paleustalfs or Eutric Nitosols of subhumid West Africa. These experiments were implemented for two growing seasons on the same plots. Soil amendments used (lime, manure, Tilemsi phosphate rock, and water‐soluble P source) significantly increased soil pH (5.1–7.8), decreased exchangeable Al3+ (0.48–0 cmolckg−1), and increased Bray‐1 P content (7.1–48.5 mg kg−1), organic C content (0.19–0.51), and ECEC (1.30–3.10 cmolc kg−1). The net effects of such improvements were excellent sorghum growth and yield in the first growing season. However, most sorghum seedlings failed to grow in the second growing season. Affected sorghum seedlings had deficient contents of P (<2 g kg−1) and Al contents higher (more than twofold) than the toxic level of 500 mg Al kg−1. These suggest that P deficiency and Al toxicity may be associated with reduced sorghum growth in these soils. The short‐term sorghum response to amendments and fertilizers suggests that the simple technology of liming may be an inadequate prescription for managing these acid soils.

Large area spatial variability of soil chemical properties in central Brazil

Understanding the spatial distribution pattern of soil properties is important to determine soil constraints to plant nutrition and appropriate management of soil resources in recently cultivated areas. This study addresses spatial variability of exchangeable potassium (K e) and sum of bases ( S B) in Mato Grosso State, Brazil. Geostatistical methods described the spatial variability and predicted along four transects crossing different soil mapping units and land use types. Ordinary kriging appropriately estimates values in unsampled areas. It identifies places where more intensive sampling is required. This study shows that land use affected spatial variability of K e and S B in well-defined structural patterns. In particular, K e exhibits a strong spatial dependence and anisotropy in two horizons. Traditional surveys of soil fertility, together with data from soil survey maps, can be used in combination with geostatistics by decision-makers to support management planning and to predict indicators related to soil quality as a measure of sustainability. As it turns out, K e and S B need to be sampled at different densities, and soil survey information can be used to advantage to reduce the sampling efforts of S B by 96%.

Sources of soil variation in an acid Ultisol of the Philippines

Field-scale variation in soil fertility can be a major source of uneven crop growth on acid soils of the humid tropics, but this has not received much research attention. We used factorial kriging (FKA) to analyze processes causing spatial variation in soil chemical properties (pH, P, K, Na, Ca, Mg, Al) measured at two depths within a single field on an acid Ultisol in the Philippines. A linear model of coregionalization comprising (i) a nugget effect, (ii) a spherical structure with a range of 20 m, and (iii) a linear structure was fitted to the experimental auto- and cross-variograms of the topsoil properties. Variograms for subsoil variables were modeled using a nugget effect plus a linear structure. Regionalized factors associated with short- and long-range variation were then mapped and formed the basis for a conceptual model of soil formation and soil variation at the study site. Patchy inputs of nutrients from buffalo excrement have led to pronounced short-range variation in P, Ca, Mg, and K concentrations in the topsoil. The effects of these are superimposed on long-range processes operating along the topographic slope. The latter include vertical and lateral water flow causing translocation of basic and acidic cations. Leaching of acidity along the major directions of the field slope seems to be a process of general importance in sloping lands of the humid tropics. Amelioration of soil acidity as well as design of field experiments have to account for this kind of slope-dependent systematic soil variation. Combining pedological expert knowledge with techniques such as FKA helps to explore complex processes in a quantitative way.

Spatial Variability of Soil Chemical Properties in Grazed Pastures

AbstractExcretal deposition concentrates nutrients in animal watering and resting areas of pastures, and including these areas in soil sampling may bias fertilizer recommendations. Our objective was to determine the magnitude and extent of nutrient enhancement near a water source in each of two experimental tall fescue (Festuca arundinacea Schreb.) pastures. The rectangular 0.44‐ha pastures were in southcentral Iowa and included three soils: a fine, montmorillonitic, mesic Typic Argiaquoll, a fine‐loamy, mixed, mesic Typic Argiudoll, and a fine, montmorillonitic, mesic Aquic Argiudoll; pH 6.8 to 7.0. Before grazing began in 1976, extractable P (Bray and Kurtz P‐1) and exchangeable K ranged from 3 to 9 and 87 to 156 mg kg−1, respectively, at 0 to 75 mm. After 5 yr of grazing by cattle, soil was sampled at 0 to 75 and 75 to 150 mm on a grid pattern starting at the water source and analyzed for extractable P and exchangeable K, total N, and organic C. Chemical values between the grid points were interpolated by kriging, and contour plots were constructed for each variable. Extractable P and exchangeable K exhibited large accumulations near the water source, with many P and K measurements exceeding 100 and 1000 mg kg−1, respectively. The zone of enhanced P and K levels extended to approximately 10 to 20 m from the water source. Total N declined from 4.2 to 2.1 g kg−1 with progressive distances from the water; however, the range of values was proportionately less than for P and K. Organic C concentrations showed less distinct trends in relation to distance from the water source. The results showed a distinct zone of nutrient enhancement within 20 m of the water source that should be either avoided or sampled separately when sampling pastures for fertilizer recommendations.