Análise da variabilidade espacial do rendimento de culturas e de propriedades do solo em pequenas parcelas agrícolas

[Abstract] The objective of this study was to assess spatial variability of soil properties and crop yield under no tillage as a function of time, in two soil/climate conditions in São Paulo State, Brazil. The two sites measured approximately one hectare each and were cultivated with crop sequences which included corn, soybean, cotton, oats, black oats, wheat, rye, rice and green manure. Soil fertility, soil physical properties and crop yield were measured in a 10-m grid. The soils were a Dusky Red Latossol (Oxisol) and a Red Yellow Latossol (Ultisol). Soil sampling was performed in each field every two years after harvesting of the summer crop. Crop yield was measured at the end of each crop cycle, in 2 x 2.5 m sub plots. Data were analysed using semivariogram analysis and kriging interpolation for contour map generation. Yield maps were constructed in order to visually compare the variability of yields, the variability of the yield components and related soil properties. The results show that the factors affecting the variability of crop yield varies from one crop to another. The changes in yield from one year to another suggest that the causes of variability may change with time. The changes with time for the cross semivariogram between phosphorus in leaves and soybean yield is another evidence of this result

Evolución del microrrelieve de la superficie del suelo medido a diferentes escalas

Se denomina microrrelieve de la superficie del suelo, o sencillamente rugosidad, a la configuración de la superficie, a su microtopografía, desde la escala milimétrica hasta la métrica. La rugosidad de la superficie influye considerablemente en el reparto de agua de lluvia entre infiltración y escorrentía. El almacenamiento temporal de agua en las pequeñas depresiones que se forman entre agregados y terrones es un parámetro importante para la modelización de procesos erosivos. En este trabajo se revisan las técnicas disponibles para caracterizar la microtopografía del suelo, poniendo particular énfasis en las diferencias entre métodos destructivos o de contacto y telemétricos, que también presentan distinta la resolución de medida y destacando la indudable ventaja de los segundos para analizar la evolución de la superficie del suelo. En un caso, se estudió el efecto del contenido hídrico inicial sobre la evolución de la microtopografía de un lecho de siembra bajo la acción de lluvia simulada, tras caracterización mediante rugosímetro laser. Para ello, se establecieron dos condiciones iniciales diferentes, suelo seco y húmedo, lo que permitió evaluar la importancia relativa de dos de los principales mecanismos de desagregación, estallido por aire ocluido e impacto de la gota de lluvia, sobre el desmoronamiento del microrrelieve de la superficie original. Se pudo comprobar la mayor velocidad de evolución de la superficie inicial seca, como consecuencia de la acción del aire atrapado. En otro caso se estudió el efecto del laboreo en la evolución de la rugosidad bajo la acción del agua de lluvia natural, en condiciones climáticas tropicales. Se partió de superficies creadas por arado y arado + niveladora. La caracterización del microrrelieve se efectuó mediante un rugosímetro de agujas y se pudo comprobar que la superficie inicial originada por laboreo primario evolucionaba más rápidamente. En los dos casos estudiados la evolución degradativa se expresó cuantitativamente tanto en términos de disminución de la rugosidad aleatoria como de reducción del agua de lluvia almacenada en las depresiones de la superficie / Soil surface microrelief, or singly roughness, is refered to as the the milimeter scale configuration or microtopography variations of the soil surface within a meter scale area. Roughness considerably influences rainfall repartition between infiltration and runoff. Soil surface temporal storage of water in the small depression formed by clods and individual aggregates is tought to be an important parameter for modelling erosive processes. Current available techniques for characterizing soil surface microtopography were reviewed in this paper, so that particular emphasis has been placed on the differences between contact or destructive methods and non-contact methods. Because both types of methods are also characterized by a different scale resolution, noncontact devices are considered most adequates for soil surface evolution studies. The first case study assessed the effect of initial soil water content on the microrelief evolution of an artificial seedbed. Measurements were made before and after simulated rainfall using a noncontact laser profile meter. Two different soil initial conditions were studied, moist and dry, which allowed to assess the relative importance of the most important desagregation mechanisms which are responsible for decay of the original soil surface microrelief, namely rupture induced by trapped air action and impact of rainfall drops. As expected, a faster evolution of the dry surface was observed, which was explained by occluded air effects. The second case study was devoted to tillage effects on soil roughness. Field experiences were made under natural rainfall in subtropical climate. Initial surfaces were created by mouldboard plow and mouldboard plow + .disked. Soil surface microrelief was characterized by means of a pinmeter. A faster evolution of the soil surface resulting from primary tillage was observed. In the two study cases microrelief decay could we quantitatively assessed both, using the random roughness and the surface water storage parametersGalicia. Consellería de Economía e Industria; PGIDT01 AGR10302 PRMinisterio de Ciencia y Tecnología; REN2000-04445-C02-01-H

Soil water storage and bulk density under three conditions of soil surface in a Cambisol of Lugo, Spain

[Resumo] Objetivou-se, com o presente trabalho, investigar as variações de armazenamento de água e da densidade do solo de um Cambissol gleico, em Lugo, Espanha, sob três condições de superfície. A avaliação do teor de água e da densidade do solo no campo foi acompanhada com leituras durante 16 meses, usando-se uma sonda de nêutrons gama. Três condições de superfícies foram estudadas: pastagem ( Lolium perenne) com 4 anos; pastagem com 2 anos e solo descoberto. As avaliações foram realizadas nas profundidades de 0,20, 0,30, 0,60 e 1,20 m. Com base nos resultados, concluiu-se que: as condições de superfície proporcionaram diferenças no armazenamento de água, até a profundidade de 0,60 m; as variações de armazenamento de água influenciaram a avaliação da densidade do solo; a superfície com o solo descoberto apresentou menor variação no conteúdo de água armazenada enquanto a superfície com a pastagem de 4 anos mostrou maior variação

Surface initial characteristics and rainfall influence on fractal dimension of soil microrelief

[Abstract] The complex behavior of soil surface microrelief and its evolution is difficult to quantify. Several empirical roughness indices and geostatistical procedures currently used have been found to be sensitive to describe roughness differences between surfaces and changes within a surface due to rainfall. Such indices are simple, quantitative and synthetic descriptors of the complex soil surface organization, thought spatial indices provide some information about the association of main elements (biggest clods and aggregates) determining microrelief variations. Fractals are mathematical objects that show the same structure when examined at all possibles scales. Fractal dimension, the basic parameter characterizing a fractal object, is a potential index to quantify soil micorelief characteristics and changes induced by rainfall energy. A high resolution non-contact laser profile meter was used to measure microtopography on two artificial soil surfaces, before and after simulated rainfall. The experimental surfaces were reconstructed from aggregates of a plough layer and were thought to simulate two types of natural seedbeds, rough and fine. The calculation of the fractal dimension was performed through a variational method, by a numerical algorithm based on the roughness around the local root mean square (RMS), which develops a straight line roughnes (SLR). Plotting SLR values versus distance along a profile in a log-log scale results in a straight trend line over a limited range of distance, the slope of which is designed as Hurst exponent, related to the fractal dimension. Thus, the spatial organisation of the soil surface can be considered as a fractal structure over a finite range of scales. Mean values of the surface fractal dimension were 2.51 for the rough surface and the 2.72 for the fine one. The slow decrease of microrelief caused by surface sealing under rainfall was also described by the fractal index. This study showed that fractal analysis provides a relevant quantification of seedbed type and an assessment of microrelief changes in relation to rainfall amount

Medida del microrrelieve del suelo y estimación de la retención hídrica en depresiones de la superficie

[Resumen] Los objetivos de este trabajo son analizar el efecto de la precipitación sobre el microrrelieve de la superficie del suelo y calcular la retención en microdepresiones a partir de una red de datos de altura. Mediante un rugosímetro láser se midieron perfiles en un recipiente con suelo procedente del horizonte de laboreo de un Cambisol crómico, antes y después de lluvia artificial. La superficie inicial intenta reproducir un lecho de siembra. Las superficies sucesivas se describieron mediante modelos de elevación digital con celdillas de 2 mm y resolución en altura de 0,25 mm. Índices de rugosidad como la desviación estándard de la altura o los propuestos por Linden y Van Doren (1986) permiten seguir la evolución del microrrelieve. La retención máxima en microdepresiones para el estado inicial es de 1mm, cifra que se reduce substancialmente por acción de la precipitación.[Abstract] The main objectives of this study were to investigate how rainfall energy affects soil surface microrelief and to calculate depressional surface storage from grid elevation data. A non-contact laser profile meter was used to measure hight profiles of boxes filled with soil from the plough layer of a Chromic cambisol before and after simulated rain. The studied surface was thought to simulate a seedbed. Digital elevation models of the soil surfaces were developed with a resolution in hight of 0.25 mm and a grid spacing of 2 mm. Roughness indices, such as the standard deviation of hights, and the limiting slope and limiting difference, according to Linden and Van Doren (1986) were found to be sensitive to surface microrelief variations. Maximum microdepression storage was 1 mm for a horizontal initial surface, but was substantially reduced by subsequent rainfall

Organic matter content influence on soil phy-sical properties

[Abstract] Soil physical characteristics of agricultural soils with a range of texture and organic matter content, i. e., dry and wet pore space organisation, were investigated. In order to study the specific effect of organic matter for each soil, frequently both grassland and cultivated adjacent land were sampled. Because of the complexity of the soil particle structure, measurements were performed at the textural level on 2-3 mm aggregates. The compactness of grassland horizons was found to be lower than that of its cultivated counterparts. Mercury intrusion porosimetry showed that lacunar pores prevailed, whose volume increased as organic carbon content increased. The volume of clay-fabric pores was very small and did not appear to depend on the variation in organic matter content. Water content near saturation increased with increasing organic matter content and for potentials of about 1,500 kPa water retention curves tended to converge. Pore size distribution patterns as measured mercury intrusion porosimetry and derivedfrom water retention characteristics were compared. The low shrinkage potential of moderately coarse and medium textured soils was also verified. A lack of potential for regeneration of good soil structure by fragmentation was deduced from the shrinkage curves

Lime amendment effects on physico-chemical and chemical fluctuations of flooded soils

Rice growth in wetlands or paddy soils is economically important in Latin America.Lime amendment is becoming a conventional practice for rice production in this area. A field study was conducted to compare changes induced by liming paddy soils in Corrientes (Argentina). Three different treatments were considered: a control plot, with no lime addition, and two amended plots with 625 kg/ha and 1250 kg/ha rates of dolomite application. Before flooding and at two week intervals during ten weeks after flooding, the following soil physico-chemical and chemical parameters were measured in each of the treatments: Eh, pH, NH 4+-N, extractable Mn and Fe and P. In all the three treatments two weeks after flooding a sharply Eh fall and simultaneously a sharply pH rise was observed. Lime addition showed a clear trend to lower Eh values, all over the waterlogging study period. However, the initial differences in pH between the control plot and plots amended with dolomite vanished at the end of the ten weeks experience. Before flooding, high NH4+-N differences between treatments were also observed. In the control plot, the trend during anaerobiosis was to increase the low initial NH 4+- N level, whereas the high NH4+-N content at the beginning of the experience in the amended plots was somewhat reduced. Extractable Mn and Fe increased as a function of flooding duration and lime addition increased the extractability of these two elements, so that at the end of the experience Mn and Fe levels were much higher in dolomite amended plots than in control. Olsen- extractable P was also initially higher in the amended plots than in the control plot and after flooding no unique fluctuation trend was observed