Roots in irrigated clay soils: Measurement techniques and responses to rootzone conditions

Abstract

This paper reviews research carried out at the Griffith Laboratory in Australia over the last decade on techniques for, and results of, observations of roots in irrigated clay soils. Our results emphasise the adaptability of root systems to rootzone conditions. Experiences with techniques for observing roots non-destructively in the field and both non-destructively and destructively in lysimeters are described. We concluded that the minirhizotron technique, applied in the field, was unreliable under our conditions. Horizontal root observation tubes were used in lysimeters to measure root length density (RLD) and to assess whether roots were clumped together or randomly distributed. Destructive sampling and measurement of RLD was used to establish a theoretical relationship between root intercept counts along the tubes and RLD. The application of image analysis to both destructive and non-destructive sampling in the lysimeters is outlined. The non-destructive lysimeter studies showed that roots were significantly clumped. Analysis of root intercept and root hole counts on the faces of sample cubes taken from the lysimeters showed root distribution was anisotropic over the whole soil profile for both safflower and wheat. There were many more roots and root holes present in the sampled soil cubes than was indicated by independent sampling for washed out RLD. Safflower appeared to have a faster turnover of roots than did wheat or maize. Lysimeters, equipped with horizontal root observation tubes, enabled studies to be made of many factors affecting root growth. Soils affect where and how fast roots grow, although there is also a strong species interaction. For example, soybean roots proliferated above a fresh water table in one soil but not in another; wheat had little tendency to proliferate above the water table in either soil. In wet soils, roots cease to grow once soil oxygen levels decrease below 10 mg 02 ls~i] 9 This level should form the basis for soil drainage criteria. In drying soils, roots will grow successively into soil regions containing soil water: the level of adaptation being determined by soil conditions, crop growth stage and level of Offprint requests to: W. S. Meyer evaporative demand. The methods of root observation used in our studies have given quantitative assessment of root distribution. However, further research is needed to link horizontal and vertical root distribution and root adaptation more strongly to crop development and soil conditions.

Root growth, water uptake, and sap flow of winter wheat in response to different soil water conditions

“…This might on the one hand be due to a great amount of water stored at those depths in the silty soil but probably also due to nutrient distribution in the soil profile at this site, which might have promoted root development in deeper soil layers (Thorup-Kristensen et al, 2009;Yang et al, 2003). On the other hand, some studies indicated that root length densities estimated from rhizotubes may underestimate the root densities in surface soil layers due to temperature effects (Fitter et al, 1998) or roots growing parallel to the horizontal plane not intersecting the tube surface (Meyer and Barrs, 1991). We obtained root lengths ranging from 1.5 to 7.0 km m −2 , which is within the range of the results from White et al (2015) who investigated root development of 11 winter wheat varieties in 4 different soils (from clay to sandy loam) in the UK.…”

Intervalo Ótimo De Potencial Da Água No Solo: Um Conceito Para Avaliação Da Qualidade Física Do Solo E Manejo Da Água Na Agricultura Irrigada

“…Um valor do IOP foi calculado para cada amostra, onde o valor da densidade do solo é conhecido. Para o solo estudado, os valores críticos para o crescimento das culturas, associados ao potencial matricial, à resistência do solo e porosidade de aeração foram, respectivamente, a capacidade de campo (CC) ou o potencial de 0,008 MPa (Libardi & Saad, 1994;Marciano et al, 1998), o ponto de murcha permanente (PMP) ou o potencial de 1,5 MPa (Savage et al, 1996), a resistência do solo à penetração (RP) de 2,0 MPa (Taylor et al, 1966) e a porosidade de aeração (Par) de 10% (Meyer & Barrs, 1991 …”

Vertical root distribution in single‐crop and intercropping agricultural systems in Central Kenya

“…Therefore, to cope with shortage of water supply, the depth of the most densely rooted soil layer was more important to the water supply of this species than the maximum rooting depth (Yu et al, 2007). Most probably, the capability of maize to efficiently deplete the water resources of the soil is related to the generally higher root length per unit soil volume of monocotyledonous crops compared to dicotyledonous ones (Meyer and Barrs, 1991). This kind of spatial complementarity among crop species in the use of resources also pertains to nutrients: in a study conducted in Sumatra, the woody intercrop Peltophorum dasyrrachis was shown to take up relatively more N from deeper soil layers compared to maize, due to a greater proportion of Peltophorum roots in deeper soil horizons (Rowe et al, 2001).…”