Jesús H. Camacho-Tamayo

Variabilidad espacial de atributos físicos de un Typic Haplustox de los Llanos Orientales de Colômbia

The objective of the present work was to determine the behavior of the spatial variability of the penetration resistance (RP), bulk density, soil density, total porosity and the sand, lime and clays contents, as well as the relation between these properties. The present study was conduced in Puerto Lopez (Meta-Colombia). Soil samples were collected in a regular grid, comprising 42 points, spaced at separation distances of 25 m between points, for two depths (0,00 - 0,10 and 0,10 - 0,20 m). The RP was analyzed up to the depth of 0,42 m. The RP did not correlate with any property in the first depth. Between 0.10 - 0.20 m depth, the RP were correlated with the lime and sand contents. The RP semivariograms indicates no spatial correlation in both depths, possibly due to soil tillage practices, which modifies the superficial spatial structure, gradually inducing to soil homogeneity. The properties adjusted mainly to exponential and spherical semivariograms models. For 0,10 - 0,20 m depth, the properties presented nugget effect, without spatial correlation, except for the bulk density.The objective of the present work was to determine the behavior of the spatial variability of the penetration resistance (RP), bulk density, soil density, total porosity and the sand, lime and clays contents, as well as the relation between these properties. The present study was conduced in Puerto Lopez (Meta-Colombia). Soil samples were collected in a regular grid, comprising 42 points, spaced at separation distances of 25 m between points, for two depths (0,00 - 0,10 and 0,10 - 0,20 m). The RP was analyzed up to the depth of 0,42 m. The RP did not correlate with any property in the first depth. Between 0.10 - 0.20 m depth, the RP were correlated with the lime and sand contents. The RP semivariograms indicates no spatial correlation in both depths, possibly due to soil tillage practices, which modifies the superficial spatial structure, gradually inducing to soil homogeneity. The properties adjusted mainly to exponential and spherical semivariograms models. For 0,10 - 0,20 m depth, the properties presented nugget effect, without spatial correlation, except for the bulk density.

Análise espacial de atributos físicos e carbono orgânico em argissolo vermelho-amarelo cultivado com cana-de-açúcar

A agricultura convencional utiliza o solo intensivamente, modificando os seus atributos. Neste estudo, objetivou-se avaliar a variabilidade espacial de alguns atributos fisicos e carbono orgânico do solo em um Argissolo Vermelho-Amarelo cultivado com cana-de-acucar, usando geoestatistica. O trabalho foi realizado em Maracanau - CE, em uma area de producao de cana-de-acucar, manejado mediante preparo conservacionista sobre uma cobertura de palhada de cana-de-acucar. As amostras de solo foram retiradas de uma profundidade de 0,00 - 0,20 m, em uma malha, com intervalo regular de 10 m, totalizando 100 pontos. Em cada amostra, foi analisado densidade de particulas, densidade do solo, carbono orgânico, porosidade total, macroposidade e microposidade. O coeficiente de variacao indicou variabilidade baixa para densidade de particulas, densidade do solo e porosidade total e media para as variaveis macroporosidade, microporosidade e carbono orgânico. As variaveis analisadas mostraram dependencia espacial, a qual foi observada nos mapas de krigagem. A distribuicao de poros por tamanho e a porosidade total indicam condicoes fisicas razoavelmente boas, embora com valores de densidade do solo ligeiramente acima do nivel considerado adequado para a classe textural do solo.

IDENTIFICATION OF AGRONOMIC MANAGEMENT UNITS BASED ON PHYSICAL ATTRIBUTES OF SOIL

Oil palm (Elaeis guineensis Jacq) is an alternative for the development of productive systems in the tropics. By determining the spatial variability of physical characteristics of soil, specific recommendations for certain areas within a zone can be made. Geostatistical analysis can determine the existence and characteristics of the spatial distribution and is an appropriate tool for analyzing the spatial variability of soil properties. The aim of this study was to determine areas with homogeneous physical characteristics in order to establish agricultural management units, using geostatistical techniques. For this study, 62 samples were collected in 10.6 ha in the municipality of El Reten (Magdalena, Colombia). The properties analyzed were: content of sand, silt and clay, particle density, bulk density, total porosity, gravimetric and volumetric water content, hydraulic conductivity and infiltration rate. All properties showed spatial correlation, with adjustments to semivariograms theoretical models, mostly to the spherical model, with ranges between 84.87 and 218.60 m and moderate to strong spatial dependence. The contour maps obtained through ordinary kriging, allowed for the identification of the relationship between the different physical properties of the soil and subsequent classification to determine the Agronomic Management Units (AMU).

Effect of Agricultural Intervention on the Spatial Variability of some Soils Chemical Properties in the Eastern Plains of Colombia

A B S T R A C T Growing demand for food exerts pressure on natural resources and may lead to the expansion of agricultural frontiers in developing countries. Most of this pressure appears in tropical zones, in native savannahs, with naturally infertile soils prone to degradation. Crop management in these regions is based on generalized estimates, leaving aside the inherent soil variability, leading to low production efficiency and high risk of environmental damage. This study aims at determining the spatial variability of some chemical properties, including organic carbon, pH, exchangeable acidity, exchangeable aluminum, P, Ca, Mg, K and Na for two Oxisols with different levels of agricultural intervention, in Puerto Lopez, Colombia, in order to identify guidelines for site-specific management. A forty-two point grid (25 · 25 m) was established for samplings at two depths: 0-100 and 100-200 mm. Descriptive statistics and geostatistics were used to analyze soil properties spatial dependence. Variogram models were obtained and from them maps of properties were drawn using ordinary punctual kriging. The results showed that spatial variability of the soil chemical properties depends upon the use of amendments, fertilizing methods, tillage and the inherent characteristics of each variable analyzed. A greater influence of the agricultural intervention on spatial variability was evident in the upper 100 mm of soil. Spatial dependence was found for most of the studied soil properties. However, K and Na presented variograms with pure nugget effects and/or very short ranges. The information generated is a base to derive guidelines for site-specific agriculture.

Estudio de algunas propiedades físicas y fisiológicas precosecha de la pera variedad Triunfo de Viena

The objective of the present work was to determine some physical and physiological properties of pear development cv. Triunfo de Viena, produced under the equatorial cold at the Colombian Andes. The fruit growth was evaluated at 30 days intervals starting at its full bloom. The studied properties were fruit weight, size, flesh firmness, soluble solids concentration, pH, titratable acids (% malic acid) and respiratory rate. The soluble solids concentration and pH are not sensible properties to determine the appropriate harvest time, presenting constant values and low dispersion. The fruit presents spherical form and its superficial area is a direct function of the fruit weight. The flesh firmness, titratable acids (TA) and respiratory rate, decrease when the pear grows, presenting harvest values of 67,82 N for flesh firmness, titratable acidity of 0,24% and respiratory rate of 29,60 mg CO 2 kg -1 h -1 . The soluble solids concentration (SS), and the relation SS/TA increase at the fruit ripening. At harvest time the fruits present SS about 12,0oBrix, relation SS/TA of 49,36 and pH 3,94.

Spatial variability of an Alfisol cultivated with sugarcane

La variabilidad del suelo ocurre debido a factores que actuan en varias escalas espaciales y temporales, naturales o antropicas. El objetivo del presente estudio fue evaluar la variabilidad espacial y la relacion de algunos atributos quimicos, mediante diferentes tecnicas estadisticas. El trabajo fue realizado en el municipio de Maracanau (CE, Brasil), en area comercial de cana de azucar, en un Typic Hapludalfs. Se tomaron muestras de suelo cada 10 m, en una malla regular de 100 m x 100 m, en una capa entre 0 y 0,20 m, para la determinacion de acidez intercambiable, pH (KCl), Ca, Na, K, Mg, P, N, suma de bases, capacidad de intercambio cationica, saturacion de bases y materia organica. Los datos fueron analizados mediante estadistica descriptiva, multivariada y, geoestadistica e interpolacion por kriging ordinario. Los atributos presentaron variabilidad baja o media, donde el pH fue el unico atributo que no presento dependencia espacial. Las diferentes tecnicas estadisticas ayudaron a caracterizar la variabilidad espacial del suelo y la identificacion de las diferentes relaciones entre atributos, cuyos resultados permiten una mejor planeacion y control en la produccion agricola, especialmente en la realizacion de practicas de manejo localizado de insumos agricolas.

Spatial Analysis of Infiltration in an Oxisol of the Eastern Plains of Colombia

Estudios que involucran la variabilidad de los atributos del suelo, ayudan al analisis del comportamiento de las variables hidrofisicas en el espacio, para apoyar la toma de decisiones bajo la concepcion de agricultura de precision. El objetivo del presente trabajo fue caracterizar la variabilidad espacial de la infiltracion superficial y su relacion con algunos atributos fisicos del suelo. El muestreo se realizo en una malla rectangular de 64 puntos, con distancias perpendiculares de 52 m x 45 m entre puntos de muestreo. Los atributos estudiados fueron densidad aparente, contenidos de arena, limo y arcilla, humedad del suelo, infiltracion acumulada, infiltracion basica, sortividad y conductividad hidraulica saturada (Ks). Los datos se analizaron mediante estadistica descriptiva y geoestadistica, identificando la relacion entre los atributos, mediante la correlacion de Pearson y agrupamiento jerarquico. Los resultados sugieren un comportamiento de los parametros cercano a la normalidad, donde los atributos relacionados con el movimiento del agua en el suelo presentaron mayor variabilidad, con valores bajos de infiltracion basica (1,46 cm h-1) y Ks (0,80 cm h-1), que junto con los altos valores de densidad aparente (1,87 g cm-3), muestran limitaciones por compactacion. La infiltracion acumulada y Ks fueron los unicos atributos que no se ajustaron a modelos de distribucion espacial, encontrandose alcances superiores de 150 m para los otros atributos, distancia que permite optimizar muestreos futuros para el estudio de la variabilidad espacial. La correlacion de Pearson y el analisis cluster permitieron establecer las relaciones entre los atributos del suelo, relaciones que fueron corroboradas espacialmente en los mapas de contorno, donde se observo la influencia de los contenidos de arcilla y arena en el comportamiento de la densidad aparente, y de estos atributos en los procesos de infiltracion de agua en el suelo.

Variabilidad espacial de los modelos de infiltración de Philip y Kostiakov en un suelo Ândico

To know the infiltration behavior is very important due to its application in the agricultural production, since it allows to define the operation of irrigation systems and to study the effects of different practices of soil use. The objective of present study was to determinate the spatial variability of the infiltration model parameters of Philip and Kostiakov, as well as its relation with the bulk density, soil particles density and the sand, lime and clay contents. The infiltration tests were made using double ting infiltrometers, in a rectangular grid of 5 x 8 points of sampling, spaced at separation distance of 20 m, among two moisture soil conditions. It was found that soil spatial variability and mainly the clay contents affect the spatial variability of the infiltration, showing that the parameters of Philip and Kostiakov model, not always adjusted to theoretical semivariogramas models. The model that fitted for all sampling points in the two moisture soil conditions was Kostiakov. The test presented limiting for the Philip model, when the soil water content is high, indicating that this model is not adequate in this andic soil.

Operational characteristics of four metering systems for agricultural fertilizers and amendments

The use of fertilizers and solid amendments in agriculture generates special interest for their effect on crop productivity, as well as for their environmental impact. The efficient use of these products demands knowing their physical and mechanical properties, the storing conditions effect and the operational characteristics of the metering systems used in the fertilizing equipment. In this context, the present study was developed with the purpose of evaluating the operational characteristics of different fertilizing metering systems and to determine the adequate metering system-product operational parameters, using powder lime, powder gypsum, granular 10-30-10 (N-P-K), and granular urea. Operational differences were established among four types of commercial fertilizer metering systems, including wire auger, star-shaped feed wheel, feed screw and ridged traction wheel. The study found that the unloading rate depends directly on the fertilizer metering systems rotating speed and is affected by particle size, repose angle, bulk density and moisture content of the applied product. The wire auger and star-shaped feed wheel metering systems were adequate for the distribution of powder products and the feed screw for granulated fertilizers. Furthermore, theoretical and experimental characteristic equations were established, defining curves for calibration and handling of the products plus the rotating speed range in which a better distributing behavior was achieved.

Application of organic and inorganic materials and phosphorus adsorption in an Oxisol

The Oxisols present high fixation of phosphorus (P) caused by oxides and hydroxides of iron and aluminum in the clays. The application of mixtures of organic and inorganic materials can help to decrease this fixation. Two organic materials were used (chicken manure and compost) and two inorganic materials (lime and triple superphosphate). A total of thirteen treatments were established in randomized blocks and composed of different combinations of mineral and organic fertilizers. The adsorption of P was determined by means of the Langmuir isotherms, at the moment of the crop establishment and ten weeks later. All the treatments showed that when the concentration of P was increased, the curves of adsorption presented an asymptotic tendency and they were delimited at a level of maximum adsorption, which indicates the existence of chemisorption. When chicken manure was added in concentrations smaller than 25 mg L-1 of P, the adsorption of P decreased, and when the concentrations were greater than 75 mg L-1 the retention of P increased. The combined application of organic materials with chemical fertilizers presented the smallest fixation in P, nevertheless it has to be made periodically, because after 10 weeks the P adsorption increased again.