Érika Andressa da Silva

Plant-available soil water capacity: estimation methods and implications

A capacidade de agua disponivel no solo para as plantas e definida como o conteudo de agua entre a capacidade de campo e o ponto de murcha permanente e tem vasta aplicacao pratica no planejamento do uso da terra. Em um perfil de Latossolo representativo da regiao do Cerrado, objetivaram-se estudar e comparar metodos de estimativa para o ponto de murcha permanente, empregando os aparelhos de psicrometro WP4-T e a câmara de Richards, utilizando amostras com e sem preservacao da estrutura, bem como para a capacidade de campo, estimando-a pela umidade do solo submetido as tensoes 6, 10 e 33 kPa, e pelo ponto de inflexao da curva de retencao de agua calculado nos modelos de van Genuchten e polinomial cubico. Verificou-se que para o Latossolo em estudo a capacidade de campo determinada no ponto de inflexao apresenta maior valor de umidade em comparacao aos demais metodos e que mesmo nesse ponto sao encontradas diferencas na estimativa em razao do modelo utilizado. Pelo psicrometro WP4-T, valores significativamente menores de umidade foram encontrados para a estimativa do ponto de murcha permanente. Concluiu-se que a capacidade de agua disponivel foi influenciada marcantemente pelo metodo utilizado na estimativa da capacidade de campo e do ponto de murcha permanente, o que precisa ser considerado em virtude da importância pratica desse parâmetro.

Ultrasonic Aggregate Breakdown of an Oxisol as Affected by Cavitation Intensity

ABSTRACT In the soil aggregate stability analysis using ultrasound, the absorbed energy by soil–water suspension is expressed in J mL−1 or J g−1. However, the same energy (J) can be obtained from different combinations of sonication time and power. We evaluated the effect of four different amplitudes (12, 18, 24, and 30 µm) by varying the sonication time in order to obtain the same total ultrasonic energy applied. Aggregates 4–8 mm size from a Brazilian Acrudox were sonicated using a sonicator probe-type. After each sonication, the soil aggregates were wet-sieved and obtained the oven-dried mass of aggregates (8–2 mm; 2–1 mm; 1–0.5 mm; 0.5–0.25 mm; and <0.25 mm). Different responses on soil aggregate breakdown were observed by varying the amplitude, although the amount of applied energy was the same. This work reinforces the need of description of all experimental conditions for suitable comparison of different results.

Aggregate stability by the "high energy moisture characteristic" method in an oxisol under differentiated management

Studies testing the High Energy Moisture Characteristic (HEMC) technique in tropical soils are still incipient. By this method, the effects of different management systems can be evaluated. This study investigated the aggregation state of an Oxisol under coffee with Brachiaria between crop rows and surface-applied gypsum rates using HEMC. Soil in an experimental area in the Upper Sao Francisco region, Minas Gerais, was studied at depths of 0.05 and 0.20 m in coffee rows. The treatments consisted of 0, 7, and 28 Mg ha-1 of agricultural gypsum rates distributed on the soil surface of the coffee rows, between which Brachiaria was grown and periodically cut, and compared with a treatment without Brachiaria between coffee rows and no gypsum application. To determine the aggregation state using the HEMC method, soil aggregates were placed in a Buchner funnel (500 mL) and wetted using a peristaltic pump with a volumetric syringe. The wetting was applied increasingly at two pre-set speeds: slow (2 mm h-1) and fast (100 mm h-1). Once saturated, the aggregates were exposed to a gradually increasing tension by the displacement of a water column (varying from 0 to 30 cm) to obtain the moisture retention curve [M = f (Ψ) ], underlying the calculation of the stability parameters: modal suction, volume of drainable pores (VDP), stability index (slow and fast), VDP ratio, and stability ratio. The HEMC method conferred sensitivity in quantifying the aggregate stability parameters, and independent of whether gypsum was used, the soil managed with Brachiaria between the coffee rows, with regular cuts discharged in the crop row direction, exhibited a decreased susceptibility to disaggregation.