Soil structure and plant growth: Impact of bulk density and biopores

Abstract

Compacted soils are not uniformly hard; they usually contain structural cracks and biopores, the continuous large pores that are formed by soil fauna and by roots of previous crops. Roots growing in compacted soils can traverse otherwise impenetrable soil by using biopores and cracks and thus gain access to a larger reservoir of water and nutrients. Experiments were conducted in a growth chamber to determine the plant response to a range of uniform soil densities, and the effect of artificial and naturally-formed biopores. Barley plants grew best at an intermediate bulk density, which presumably represented a compromise between soil which was soft enough to allow good root development but sufficiently compact to give good root-soil contact. Artificial 3.2 mm diameter biopores made in hard soil gave roots access to the full depth of the pot and were occupied by roots more frequently than expected by chance alone. This resulted in increased ~plant growth in experiments where the soil was allowed to dry. Our experiments suggest that large biopores were ~ not a favourable environment for roots in wet soil; barley plants grew better in pots containing a network of narrov~ biopores made by lucerne and ryegrass roots, responded positively to biopores being filled with peat, and some pea radicles died in biopores. A theoretical analysis of water uptake gave little support to the hypothesis that water supply to the leaves was limiting in either very hard or very soft soil. The net effect of biopores to the plant would be the benefits of securing extra water and nutrients from depth, offset by problems related to poor root-soil contact in the biopore and impeded laterals in the compacted biopore walls.

Management of crop water under drought: a review

“…water transmission and storage pores. Stirzaker et al (1996) reported improved barley root penetration through a compacted soil layer via biopore channels created weather artificially or by ryegrass and lucerne. Nuttall et al (2008) considered that primer plants with a highly branched root systems, e.g.…”

“…Perkons et al (2014) measured higher root length density of main crops such as wheat, barley and rapeseed in deep soil following a taproot species compared to a fibrous rooted pre-crop and related this to enhanced largesized biopores. Stirzaker et al (1996) mentioned the problem of root-soil contact for roots growing in large biopores. White and Kirkegaard (2010) studied this problem in detail, showing that wheat roots growing in biopores interacted with surrounding soil by root hairs, while roots growing in cracks had reduced root hair formation.…”

Resistência à penetração em latossolos: valor limitante à produtividade de arroz de sequeiro

“…Entretanto, no menor conteúdo de água, os componentes de produtividade demonstram que a compactação foi prejudicial ao desenvolvimento da cultura, nos dois solos. STIRZAKER et al (1996) obtiveram resultados semelhantes em cevada cultivada em casa-devegetação. Estes autores verificaram que, em maiores conteúdos de água, a densidade do solo intermediária proporcionou maior desenvolvimento de cevada e que, em solos mais secos, a menor densidade do solo foi mais favorável ao desenvolvimento da cultura.…”

“…Este autor afirma que a absorção de água pelas raízes ocorre em um raio médio de 0,02m. Em casa-de-vegetação foi observado maior desenvolvimento de cevada no menor valor de densidade do solo, em condição de menor conteúdo de água (STIRZAKER et al, 1996). Neste sentido, DEXTER (1987) afirma que o crescimento pode ser inibido na resistência à penetração de 1MPa em solo seco, no entanto, em solo úmido, pode haver crescimento em valores de resistência à penetração superiores a 4MPa.…”

“…Neste sentido, STIRZAKER et al (1996) verificaram, em casa-devegetação, que a densidade do solo intermediária proporcionou maior crescimento de cevada e que, em condições de menor conteúdo de água do solo, menores valores de densidade foram mais propícios ao crescimento da cultura.…”