Paulo Ivonir Gubiani

Método alternativo para a determinação da densidade de partículas do solo: exatidão, precisão e tempo de processamento

Soil particle density (Dp) has been mainly determined using methods which measure solids volume by liquid displacement and its volumetric quantification. The volumetric measurement shows low precision, requires time for complete liquid drainage and is the longer lasting step. The objective of this paper was to substitute the volume displacement measurement step by weighing the volume displaced and to present an alternative method to measure the Dp. The Dp of 60 soil samples varying in texture and organic matter was determined by volumetric flask and modified volumetric flask, estimating exactness, precision and processing time. The Dp averages for both methods were similar, with the modified flask method presenting greater precision and smaller processing time.

Indicadores hídrico-mecânicos de compactação do solo e crescimento de plantas

The effect of soil compaction on plant growth is widely used as orientation for soil management. Although the limiting water range (LLWR) underlies the systematization of the relationship between compaction and physical factors directly related to plant growth, its efficiency to predict biological responses, especially of grain yield, has not yet been proven. Results of research at the cellular level indicate that the water and mechanical stress levels that occur in the roots during soil drying are partially represented by the LLWR. Consequently, the expected response in crop growth and production cannot be achieved in most cases. In addition to refining the boundaries of the LLWR, new indexes need to be developed, capable of integrating the variation of the physical factors of soil along the growth cycle of plants determined by meteorological factors. Indicators of frequency of the period of absence and of accumulation of water and mechanical stress were suggested. Without advances, the ability to predict the risk of reduced crop yields due to soil compaction will be marginal and insufficient to support actions of soil management.

Qualidade físico-hídrica e rendimento de soja (Glycine max L.) e feijão (Phaseolus vulgaris L.) de um Argissolo Vermelho distrófico sob diferentes sistemas de manejo

The physical-hidric quality has been affected by the compaction process that soils are being undergone in different agricultural systems. The objective of this study was to evaluate the physical-hydric quality of a Rhodic Paleudalf undergone to different tillages. One experiment with soybean and two with black bean were installed using a completely randomized experimental design. Seven compaction levels were tested in the agricultural year of 2004/2005: NT= no tillage since 1989; NTPLOW1 = no tillage that received a chisel plough in december of 2004; NTPLOW2 = no tillage that received a chisel plough in december of 2002 and february of 2004; NTCOMP1 = no tillage with four passes of a buck loader of 10Mg in december of the 2001/2002; NTCOMP2 = no tillage with four passes of a buck loader of 10Mg in december of 2002/2003; NTCOMP3 = no tillage with four passes of a buck loader of 10Mg in december of the agricultural year 2001/2002 and 2002/2003 and CT = conventional tillage. The largest changes in the physical-hidric quality were observed in the conventional and no tillage that received additional compaction in two agricultural years (NTCOMP3). No tillage (NT) presented the best physical-hidric conditions of soil and stayed longer within the volumetric moisture range considered ideal for crop development. The hydraulic conductivity of saturated soil did not differ among the treatments. Soybean yield was not affected by the treatments, whereas the chisel plough (NTPLOW1) was favorable to the black bean yield.

CRESCIMENTO E PRODUÇÃO DE MILHO ASSOCIADOS COM O INTERVALO HÍDRICO ÓTIMO

O Intervalo hidrico otimo (IHO) e muito utilizado como indicador agronomico de qualidade fisica do solo, contudo pouquissimas pesquisas relacionaram o IHO com crescimento e producao de plantas. Os escassos resultados sao insuficientes para confirmar ou negar a eficiencia do IHO, porem apontam para a discordância entre IHO e producao das culturas. O objetivo deste estudo foi analisar a correlacao do IHO com as variaveis de crescimento e com a producao de graos da cultura de milho (Zea mays L.) de oito cultivos (quarto na safra 2010/11 e quatro na safra 2011/12) em Latossolo Vermelho distroferrico tipico, com diferentes estados de compactacao. Os tratamentos consistiram de plantio direto, que recebeu escarificacao e compactacao adicional. Foram medidos a altura de plantas (Ap), o indice de area foliar (IAF), a profundidade efetiva de raizes (Ze), o rendimento de graos e o peso de 1000 graos nos oito cultivos de milho. O IHO foi determinado para seis combinacoes de resistencia do solo a penetracao e potencial matricial (RP:Ψ), usadas nos limites inferiores: (2:-0,8), (3:-0,8), (4:-0,8), (2:-1,5), (3:-1,5) e (4:-1,5), expressos em MPa. O IHO esteve fracamente associado com Ap, IAF e Ze. Os coeficientes de correlacao variaram entre -0,20 e 0,36 e a maioria das correlacoes nao foi significativa. Alem disso, a melhor relacao linear explicou apenas 17 % da variacao da altura das plantas em funcao da variacao do IHO. Nao houve correlacao entre IHO e producao de graos de milho. Esses resultados indicaram que, embora o IHO seja sensivel a compactacao do solo, ele nao e um indice agronomico robusto para orientar o manejo da compactacao para culturas, cujo objetivo principal e a producao de graos.

ALTERAÇÕES ESTRUTURAIS E MECÂNICAS DE SOLO DE VÁRZEA CULTIVADO COM ARROZ IRRIGADO POR INUNDAÇÃO

A conversao de area natural para area de uso agricola pode degradar a estrutura do solo, favorecendo a ocorrencia de compactacao. Este trabalho teve por objetivo avaliar as alteracoes nas propriedades fisico-hidricas e mecânicas de um Gleissolo Haplico provocadas pela conversao de um campo natural antropizado para area de cultivo de arroz irrigado. Propriedades fisico-hidricas (densidade, porosidade total, macro e microporosidade, indice de vazios e retencao de agua) e mecânicas (pressao de preconsolidacao, indice de compressao, coeficiente de descompressao e indice de recuperacao) foram avaliadas nos horizontes A1 (0,0-0,25 m), A2 (0,25-0,51 m), Cg1 (0,51-0,92 m) e Cg2 (0,92-1,20+ m) em solo sob campo antropizado sem uso agricola e nos horizontes Ap (0,0-0,17 m), A (0,17-0,40 m), Cg1 (0,40-0,70 m) e Cg2 (0,70-1,00+ m), em solo cultivado com arroz irrigado. Oito anos de cultivo de arroz sob preparo convencional e irrigacao por inundacao nao alteraram significativamente as propriedades fisico-hidricas e mecânicas, de acordo com a analise de agrupamentos. Porem, o cultivo de arroz aumentou a densidade do solo e reduziu o indice de vazios, a porosidade total e a macroporosidade. A relacao da elasticidade com a densidade do solo, a porosidade total e o indice de vazios foi influenciada pelo tipo de estrutura, pois maiores compressoes e descompressoes ocorreram nos horizontes de estrutura prismatica, em comparacao aos horizontes de estrutura macica.

Interação entre disponibilidade de água e compactação do solo no crescimento e na produção de feijoeiro

Soil physical properties, plant growth, and water availability in the soil are factors that interact in response to changes in soil structure. Knowing how these factors interact in field conditions is of great importance for management of soil compaction for crop yield. In this paper, three levels of soil compaction, with and without irrigation, were assessed in regard to growth and yield of common bean (Phaseolus vulgaris L.). The probability of interaction between soil compaction and irrigation was 88 % for leaf area index (LAI) and 86 % for yield. However, water availability led to distinct responses between growth and grain yield at different levels of soil compaction. From the lowest to the highest level of soil compaction, the increase in soil water availability due to irrigation (120 mm) resulted in decreasing gains in LAI (1.8, 0.8, and 0.3) and increasing gains in grain yield (695, 1042, and 1198 kg ha-1). Thus, with the increase in soil compaction, the soil water content exhibits decreasing control on plant growth, but the yield remains more elastic than growth. Thus, the compensation in common bean growth through the increase in water content declined as the state of compaction increased, but compensation in grain yield was greater than in growth. Consequently, the use of different plant characteristic provides different critical levels to physical indicators of soil compaction. Thus, the choice of irrigating and/or chiseling depends on knowing how the harvested part of a plant responds to compaction and soil water availability in combination.

Duração das alterações em propriedades físico-hídricas de Latossolo argiloso decorrentes da escarificação mecânica

The objective of this work was to determine the duration of the effects of soil decompaction, by mechanical chiseling, through physical and hydraulic indicators of a clayey Oxisol under no-tillage (NT). The treatments consisted of months (0, 6, 12, 18, 24, 30, and 36) after chiseling under NT and of a control treatment without chiseling under NT during 27 years. The following variables were evaluated: penetration resistance, infiltration rate, bulk density and relative density, pore size distribution, and saturated hydraulic conductivity. The duration of the effects of mechanical chiseling varied according to the evaluated soil property, lasting six months for bulk density and relative density, total porosity, and macroporosity; 18 months for penetration resistance; and 24 months for hydraulic conductivity and infiltration rate. Soil properties related to water transport, such as hydraulic conductivity and steady infiltration rate, maintain the effect of mechanical chiseling for a longer time and, therefore, are more suitable to measure the duration of mechanical decompaction.

Valores críticos de densidade do solo avaliados por condições de contorno

The irregular association between crop production and soil bulk density (ρ) weakens the application of ρ for diagnosis and management of soil compaction. With the aim of evaluating this problem, this study introduce a mathematical procedure to simulate limits of ρ for water demand and soil penetration resistance (R) dynamic as a function of the time (t) of water extraction by crop evapotranspiration (E) of the soil layer explored by plant roots (L). Parameters of both penetration resistance and water retention curves of an Oxisol were used in the simulations of ρ and R for different conditions of E, t and L. The ρ varied inversely proportional to E and t and directly proportional to L. The equation of ρ also allows calculating the critical bulk density (ρc) calculated with the least limit water range (LLWR). Simulations done for up to six days of water extraction (t=6) in soil layers L with ρc from the LLWR for the Oxisol (1340kg m-3) indicate that the maximum R may increase from 2 to 8MPa, depending upon the E (0.002 to 0.006m d-1 ) and L (0.2 to 0.6m) conditions. Low values of R obtained when the E is small and L is large characterize conditions for normal crops production even the ρ is equal to the ρc.

Implications of the variability in soil penetration resistance for statistical analysis

A resistencia do solo a penetracao e uma medida da sua compactacao relacionada com o crescimento das plantas, mas sua variabilidade dificulta a analise estatistica. Os objetivos deste trabalho foram analisar a variabilidade da resistencia do solo a penetracao sobre a eficiencia de testes parametricos e nao parametricos na discriminacao do efeito de niveis de compactacao e classificar os coeficientes de variacao da resistencia do solo a penetracao nas classes baixa, media, alta e muito alta. A resistencia do solo a penetracao foi medida em diferentes datas, em Argissolo Vermelho Distrofico tipico sob semeadura direta por 16 anos, em tres condicoes: (i) sem aplicacao de trafego adicional e escarificacao, (ii) com aplicacao de compactacao adicional e (iii) com escarificacao. Em cada data, 19 medidas de RP (feitas de 0 a 28,5 cm, a cada 1,5 cm) foram agrupadas para formar varias camadas com diferentes espessuras. Em cada camada, os efeitos de tratamentos foram avaliados pela analise de variância (ANOVA) e por Kruskal-Wallis, num delineamento inteiramente casualizado, sendo os coeficientes de variacao de todas as analises classificados como baixo, medio, alto e muito alto. A ANOVA discriminou melhor os efeitos dos niveis de compactacao, porem a taxa de rejeicao da hipotese nula decresceu de 100 para 80 % quando o coeficiente de variacao aumentou de 15 para 26 %. Os valores de 15 e 26 % definiram, respectivamente, os limites de separacao das classes baixa/media e alta/muito alta para coeficientes de variacao de RP do Argissolo estudado.

Tensão e extração de água em mesa de tensão e coluna de areia, em dois solos com elevada densidade

The determination of moisture content in soils under tension follows the assumption that the water matric potential is at equilibrium with an applied tension. The time the soil water tension reaches the equilibrium under the 6kPa tension was determined in Hapludalf and Hapludox clay soils. In the Hapludalf, the equilibrium between the applied tension and water matric potential, in most of the samples, was obtained between 72 and 96h, while in Hapludox, equilibrium was not reached until the 168h. The water tension in the samples had no significant correlation with bulk density and did not reach the tension applied on the suction table and sand suction column. Nevertheless, more than 97% of the soil water was extracted at 48h both in Hapludalf and Hapludox, suggesting that this time is sufficient to estimate the soil moisture at 6kPa tension, independently of clay content.