Marcelo Rocha dos Santos

INFLUÊNCIA DO TIPO DE AMOSTRAGEM NA CONSTANTE DIELÉTRICA DO SOLO E NA CALIBRAÇÃO DE SONDAS DE TDR

The technique of TDR (time-domain reflectometry) is an important tool for the study of soil water content. For a correct use of this technique, models that relate the volumetric water content in soil with the soil dielectric constant must be calibrated, considering the characteristics of each soil. The purpose of this study was to evaluate the influence of soil type and sampling form (disturbed and undisturbed samples) on the dielectric constant (Ka) of the soil and the performance of models to estimate the volumetric water content in soil (θ) by TDR. The soils were a Haplic Cambisol, an Oxisol and a Typic Quartzipsamment, with different textures. Disturbed and undisturbed Haplic Cambisol and Oxisol samples were collected, but only disturbed Typic Quartzipsamment samples, due to its low aggregation. Calibration was performed with probes consisting of three rods (effective length 0.10 m and resin length 0.05 m), spaced 0.017 apart and without resistor on the center rod, connected to a TDR 100 (Campbell Scientific) equipment. The Ka values, for a same e value, were affected by variation of the soil type, but not influenced by the type of soil sampling (disturbed or undisturbed). For the models tested to estimate e as a function of Ka, the cubic polynomial model fit the θ data determined by gravimetry best for the Typic Quartzipsamment and Haplic Cambisol, whereas for the Oxisol a linear model fit better.

Efeito da aplicação sucessiva de precipitações pluviais com diferentes perfis na taxa de infiltração de água no solo

O processo de infiltracao e influenciado pelas condicoes da superficie do solo e pela precipitacao pluvial. O objetivo deste trabalho foi avaliar a influencia de aplicacoes sucessivas de precipitacoes pluviais com diferentes perfis na formacao do encrostamento superficial e, consequentemente, na taxa de infiltracao de agua em solo sem cobertura e com cobertura. Foram aplicadas tres precipitacoes pluviais sucessivas para cada perfil de precipitacao pluvial, em intervalos de 24 h, sendo usados os perfis de precipitacao pluvial constante, exponencial decrescente, duplo exponencial adiantado e atrasado, com uma lâmina media de 55 mm por aplicacao. Buscou-se ajustar um fator de decaimento da taxa de infiltracao (Ti) em funcao da energia cinetica acumulada da chuva, denominado de fator f, dado pela razao entre a taxa de infiltracao estavel (Tie) com efeito da chuva e a Tie sem o efeito da chuva. Foram avaliadas duas condicoes de cobertura do solo, solo sem cobertura e solo coberto com palhada, sendo os ensaios de infiltracao realizados com um simulador de chuvas, em parcelas experimentais de dimensoes de 1,0 x 0,7 m. Os resultados foram avaliados por meio de analises graficas, analise de variância e teste de media. Verificou-se que os diferentes perfis de precipitacao pluvial nao influenciaram a infiltracao de agua no solo, tanto para o solo sem cobertura como para o solo com cobertura, sendo esta influenciada somente pelas aplicacoes sucessivas, com menores valores da taxa de infiltracao obtidos na segunda e terceira aplicacoes. O decrescimo na Ti em solo sem cobertura foi devido a formacao de encrostamento superficial, o que ocorreu logo na primeira aplicacao. A Tie em solo sem cobertura teve decrescimo de 75 % se comparada a Tie em solo com cobertura. A lâmina infiltrada nao foi influenciado pelos quatro perfis de precipitacao pluvial. O fator f foi descrito com uso de uma equacao do tipo exponencial.

Modelagem da infiltração em solos com encrostamento superficial. Parte II: condutividade hidráulica variando no tempo

ABSTRACT The soil crust affects significantly the soil water infiltration rate. Thus, the infiltration simulation models must somehow consider the effect of crust layer to obtain good results.The objective of this work was to evaluate the performance of the Green-Ampt-Mein-Larson (GAML) model to simulate the soil water infiltration for crusting soils. The trials were carried out in a Podzol Tb distrophic Haplic Cambisol, using a rain simulator, on a bare soil. The GAML model parameters were determined , being proposed for the hydraulic conductivity of transmission zone (Kt) value the use of Kt*, which is equal to Tie x f, where Tie is stable infiltration rate and f is a decrease factor of the Tie as a function of cumulative kinetic energy of rainfall (Ec), i.e., Kt value varying over time. The GAML model with constant Kt value over time did not provide good performance, overestimating the values of infiltration rate (Ti) in most cases, where as the use of Kt* the GAML model showed good performance, being the best results obtained by combination of Kt* with matric potential (jf) values calculated by Cecilio et al. (2007) equation. The GAML model with the hydraulic conductivity in the transmission zone (Kt) value varying over time showed good results in simulation of the infiltration process in soils subjected to crusting.

Modelagem da infiltração em solos com encrostamento superficial. Parte I: modelo GAML para solos estratificados

A B ST R A C T The aim of this study was to evaluate the Green-Ampt-Mein-Larson (GAML) model and GAML model modified by Moore (1981) for layered soils, in the simulation of water infiltration process in crusting soil. The infiltration tests were performed on a Cambisol without coverage, and three successive precipitations at intervals of 24 h. For the inclusion of the soil crust layer in the input parameters of the GAML model, the value of hydraulic conductivity in the transmission zone (Kt) was equal to stable infiltration rate (Tie) obtained in bare soil, and in the GAML model for layered soils, a surface layer (crust) were proposed with a thickness of 5 mm and soil crust saturated hydraulic conductivity (Kc) determined from experimental data, and equal to 10 and 25% of the saturated hydraulic conductivity (K 0 ). In the second and third rainfall, the combinations without consideration of crust did not achieve good results and overestimated infiltration rate over time. For the model of GAML, the best results were obtained using Kt = Tie determined in bare soil, while in Model GAML for layered soils, were obtained with a value of Kc = 10 and 25% of K 0 .

DISTRIBUIÇÃO DE RAÍZES E EXTRAÇÃO DE ÁGUA DA BANANEIRA ‘BRS PRINCESA’ SOB DIFERENTES CONFIGURAÇÕES DE IRRIGAÇÃO

The aim of this study was to evaluate root distribution and water uptake patterns of the ‘BRS Princesa’ banana under different irrigation strategies in the semiarid region of northern Minas Gerais. To conduct the experiment, fve irrigation strategies were adopted: 50% of water depth reduction (WD), with a 7 day alternation frequency (AF) for the irrigated side of the plant; 50% of WD and AF of 14 days; 50% of WD 21 days; 50% of fxed irrigation WD (one lateral line on only one side of the plant); and full irrigation (two lateral lines with the valve open) throughout the cycle, with samples being collected in four different distances from the pseudostem (0.25, 0.50, 0.75 and 1.0 m) and in fve different soil depths (0.05 to 0.15; 0.15 to 0.25; 0.35 to 0.45; 0.55 to 0.65 and 0.75 to 0.85 m). The experiment was arranged in a completely randomized 5 x 4 x 5 factorial design, with three replicates. Average root length density (RLD) was similar among treatments; however, when the banana was subjected to irrigation with partial water defcit, the plant exhibited greater root development; there is a reduction of RLD with the soil depth and maintenance of distribution of the roots with distance from the pseudostem; very thin to small roots are concentrated in a depth of 40 cm in the soil profle and 70 - 90% of these roots are located up to 75 cm from the pseudostem; a shorter interval of alternation of the irrigated side in PRD enables extraction of water in deeper layers.

DEFICIT IRRIGATION IN CONSECUTIVE CYCLES ON YIELD AND WATER USE EFFICIENCY IN ‘TOMMY ATKINS’ MANGO TREES

We aimed to understand two strategies of deficit irrigation and their effects on yield and water-use efficiency (WUE) in ‘Tommy Atkins’ mango trees, for three consecutive cycles. In the experiment with Regulated Deficit Irrigation (RDI), the treatments were: T1, full irrigation at every fruit development stage, 100% of ETc; T2, 100% of Etc at stages II and III and 50% of Etc at stage I; T3, 100% of ETc at stages I and III and 50% of ETc at stage II; T4, 100% ETc at stages I and II and 50% of ETc at stage III; T5, 100% of ETc at stages II and III and 75% of ETc at stage I; T6, 100% ETc at stages I and III and 75% of ETc at stage II and T7, 100% ETc at stages I and II and 75% of ETc at stage III. In the experiment with Partial Rootzone Drying (PRD) for the three crop stages: T1, 100% of ETc, conventional dripping irrigation; T2, 100%; T3, 80% of ETc; T4, 60% of ETc and T5, 40% of ETc. As for the treatments T2, T3, T4 and T5, the side to be irrigated was alternated every 15 days. At the end of 3 production cycles, we observed a reduction in productivity when RDI was applied at SI. The water-use efficiency was higher in the first cycle in relation to the third cycle under RDI. The PRD with 80% of ETc maintains the productivity and with 40% of ETc, increases WUE.

Uso da reflectometria no domínio do tempo para avaliar a distribuição de fósforo em colunas de solos fertirrigados

EnglishStudies to monitor soil solute dynamics in fertigated areas are of great importance, because they allow the adoption of measures of fertigation management, making the nutrients available in the places of greatest root density. The objective of this study was to evaluate, using the TDR technique, the phosphorus distribution in Neosol Quartizarenic (RQ) and Red Latossol (LV) soil columns fertigated with MAP. The MAP fertigations were performed in the columns; the soil water content (8) and soil bulk electric conductivity (CEs) were obtained using (with) TDR probes installed at various depths, and the nutrient concentration was estimated using mathematical models. In both soils the phosphorus was adsorbed in surface layer, not reaching 12 cm depth, regardless of the moment of the fertigation was started portuguesEstudos direcionados para o monitoramento da dinâmica de solutos no solo, sob areas fertirrigadas, sao de fundamental importância, pois permitem adotar medidas de manejo da fertirrigacao possibilitando disponibilizar o nutriente nos locais de maior densidade radicular. Objetivou-se com esse trabalho avaliar, usando a tecnica da TDR, a distribuicao de fosforo em colunas de Neossolo Quartzarenico (RQ) e Latossolo Vermelho (LV) fertirrigadas com MAP. Foram realizadas fertirrigacoes com MAP nas colunas e determinados os teores de agua (8) e condutividades eletricas do solo (CEs) com uso de sondas de TDR instaladas em varias profundidades, sendo a concentracao do nutriente estimada som uso de modelos matematicos. Em ambos os solos o fosforo ficou adsorvido a camada superficial, nao alcancado os 12 cm de profundidade, independentemente do momento da fertirrigacao