Crop root system response to irrigation

Abstract

In the field, root systems develop in response to both endogenous plant design and soil environment. Downward penetration of root systems results primarily from the growth of monocot axes or of dicot taproots; root proliferation at a given depth results from the growth of laterals at that depth. Root length densities generally decline exponentially with depth under well-watered conditions. Root growth rates are partially controlled by soil conditions. Under irrigation, the most critical soil properties for root growth are oxygen diffusion rate, water content and soil strength and all of these properties are interrelated. Under excess irrigation, especially in heavy soils, root growth may be limited by oxygen diffusion rate. Under limited irrigation, root growth may be limited by lack of water or high soil strength. When irrigation maintains wet surface soils, most of the root system is found in the upper part of the profile where the majority of the water is also taken up.Root systems are dynamic. They develop according to biologically-determined patterns. However, the quantity of roots produced at any point in the soil results from an interaction between these biological patterns and other factors including general plant vigor and local soil conditions.Roots have a definite life-span and this life-span varies with root type, being very long for taproot or axis components and shorter for most laterals. Thus developmental information is also important for assessing how root length populations available for the uptake of water and minerals at various soil depths vary with time.Because developmental concepts play an important role in our ability to understand both growth and function of roots, this review will center discussion on the developmental and growth patterns of roots and on interactions between these developmental patterns and irrigation. Root system designCrop root systems are comprised of two types of roots: 1) downward-growing main roots and 2) lateral roots and their branches produced along the length of the main roots (Klepper 1990). The downward-growing roots are taproots in dicot species and axes in monocots (e.g., cereals). For those dicot species which develop a fibrous root system, several of the laterals take over the downwardgrowing habit; the same feature is observed when a taproot or axis tip is killed in a species that normally has a dominant taproot. This division of the root system into two types allows us to simplify root system development into 1) the increase in rooting depth, brought about by taproots and axes, and 2) the increase at any given depth in root length density above that caused by the presence of axes, brought about by the production of laterals and their branches.These two types of roots are also functionally different. For the most part, the vertical main roots serve as conduits for water collected by branches. This does not mean to say that the main axes aren't absorptive over at least some of their life; their absorptive properties are quantitatively very important earl...

Effects of Soil Rhizosphere Aeration on the Root Growth and Water Absorption of Tomato

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