Moisture content and bulk density largely characterize physical and mechanical soil status and behaviour. A nondestructive determination of these soil properties is essential. Time domain reflectometry (TDR), although widely accepted for determination of volumetric water content, 8, has its limitations, and recently a frequency domain (FD) sensor has been developed and tested. An equation relating relative permittivity, E', to gravimetric water content, w , and bulk density, p, was established for three soil types (sand, sandy loam and clay). If E' and w are known, our model can be used to calculate bulk density and associated volumetric water content, 8, keeping in mind that 8 = pw. Utilization is found in long-term monitoring of moisture fluctuations or short-term detection of traffic-induced soil compaction.
Aggregates were collected from the arable layer at eight sites in the IJsselmeer polders. The compositions of the soils were determined, and measurements were made of porosities, tensile strengths and water stabilities of undisturbed aggregates. Porosity was negatively correlated with the age of the soils since reclamation. Tensile strength of dry aggregates and water stability were both positively correlated with the clay content. The soils had extremely high values of friability. Tensile strength was negatively correlated with porosity. Porosity had no clear influence on water stability. (Abstract retrieved from CAB Abstracts by CABI’s permission)
A new approach in defining the range of soil structure for optimal maize production is proposed. The effect of different degrees of compaction of ploughed sandy soils on soil aeration and mechanical impedance and on root and shoot growth of maize was tested in 5 model field experiments in the eastern Netherlands. In this first paper the effects on soil aeration and penetration resistance are described. The narrower the range of matric water potentials which allow unimpeded root growth, the greater the potential risks for plant growth and the greater the need for a controlled supply of water. Soil structures which substantially impede root growth even at the most favourable water potential are classified as dangerous. (Abstract retrieved from CAB Abstracts by CABI’s permission)
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