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With increasing costs of energy and threatened shortages of water, farmers recognize the need to schedule irrigation more efficiently. The first requirements in scientific scheduling are to estimate how much water can be stored in the soil profile and how much can be extracted without significantly reducing crop yield. Shakewich and Zwarich (1968) described field capacity and permanent wilting point in terms of silt, clay, fine sand, very fine sand, and organic matter contents. However, few soil analytical laboratories separate the sand fraction or determine organic matter content to an adequate depth. Determination of soil moisture retention characteristics within the rooting zone has become commonplace for technicians and professionals involved in irrigation scheduling. The laboratory data obtained from pressure plates are frequently used as a first estimate of field moisture retention characteristics. The objective of this paper is to develop some general relationships between texture, depth, and moisture held at various tensions. This may reduce the need for laboratory determination of soil moisture retention curves and permit easy determination of the irrigation point, i.e. that soil moisture at which irrigation water should be applied to prevent reduced crop yield. Soil texture data are readily available for most soils or can be determined very simply if required.
empirical relations between laboratory determinations of soil texture and moisture retention
Oosterveld, M. and C. Chang 1980. EMPIRICAL RELATIONS BETWEEN LABORATORY DETERMINATIONS OF SOIL TEXTURE AND MOISTURE RETENTION. Canadian Agricultural Engineering 22(2):149-152.
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