Root depths

The plant cover should have potential rooting depth greater than the thickness of the soil cover. Many native species have potential rooting depths of 2 m or more.14... 

Several plant parameters are important to the design of ET landfill covers. Among the most important are parameters describing rooting depth, leaf-area-index (LAI), temperature requirements, time to maturity, and water requirements. Models that are suitable for use in design of ET covers will utilize these parameters. The quality of the plant model controls the quality of AET estimates. 

SOL Z (mm) Depth from soil surface to the bottom of a layer. Since all the subcatchments were conceptualized as single layer units, SOL Z is equal to SOLZMX (mm), the maximum rooting depth of soil profile. 

There are many types of roots, including thick fibrous, deep tap, shallow, and tubers, all in one plant community. Some roots explore the soil to significant depth (i.e., as much as 250 cm deep), while others are shallow (i.e., only 25 cm deep). Different rooting depths are found in all plant types grasses, legumes, shrubs, and trees. Each root type will contribute its own unique exudates and characteristics to its unique volume of soil and the associated soil solution. 

Finally, certain triazine herbicides can be used selectively in orchards and in some horticultural crops. In this case, selectivity is not based only on physiological differences between species, but on physical selectivity associated with the location of the herbicide and the roots of the crop and weed species in the soil. Triazine herbicides such as simazine, which has very low solubility in water, remain close to the soil surface in most mineral soils. Careful application of simazine in horticultural or fruit crops can result in the herbicide being available to control shallow-rooted weed species without harming the deeper-rooted perennial species. The success of this use is dependent not only on the relative rooting depths of the tolerant and susceptible species, but also on soil conditions and other factors that may affect herbicide fate and movement. 

From Worked example 5.1, there are 2500 t ha in the top 20 cm, which approximates to rooting depth. 

Mobilization of water from the soil is closely related to root depth and root density in each layer of soil. Fine roots of active B. brizantha pastures, established in deeply weathered clayey soils in eastern Amazonia, reach depths of 8 m or more (Nepstad et al. 1994). In abandoned pastures (50% B. humidicola and P. maximum cover and 50% invading shrubs and small trees), fine roots ( < 1 mm in diameter) were found at depths of 12 m (Nepstad et al. 1994). Fine-root biomass in the superficial soil layers of an active pasture in Paragominas, eastern Amazonia, was 3 times higher than that found in an adjacent primary forest area. Fine root biomass in the active pasture decreased by a factor of 100 between the surface and 6 m depth. In an abandoned pasture area, the distribution pattern of fine-root biomass was similar to that observed in the deeper soil layers of the forest ecosystem. This pattern is associated with the fine roots of the existing dicotyledonous invading species. 

Figure 9 Early Paleozoic changes in (a) soil differentiation as indicated by clay content (volume percent) and alumina/bases (molar ratio) of the most weathered horizon of calcareous red paleosols (b) soil bioturbation as indicated by proportion of transect in paleosols occupied by roots or burrows (percent) and by measured rooting depth (m) (c) atmospheric CO2 levels (PAL) calculated from a sedimentary mass balance model (d) maximum coal seam thickness and average thickness of at least 10 consecutive seams (m) (e) diameter of fossil plant stems and roots (m) (f) diversity of fossil land plants (number of species) (g) diversity of soil animals (number of families) (Retallack, 1997c) (reproduced from Dinofest, 1997, pp. 345-359).

Figure 5.20. Movement of Ca in the form of CaCOj, CaCb, and CaS04 by water leaching through an oxisol. The Ca was initially added to the soil surface. (Adapted from K. D. Ritchey et al. 1980. Calcium leaching to increase rooting depth in a Brazilian savannah oxisol. Agron. I. 72 40-44.)...

Unsaturated soil to root depth Evaporation Leaching Root Uptake 0 Surface- Subsurface application Washoff Transport Degradation (chemical/biological) Soil Retention Root uptake Transport. ... 

Unsaturated soil zone below root depth (vadose zone) Movement Upward A Lateral Downward Transport % Degradation (chemical/biological) Soil Retention Transport. 

Bailie, 1. C., and Mamit, J. D. (1983). Observations on rooting depth in mixed dipterocarp forest. Malayan Forester 46, 369-374. 

If soils are to be cultivated for crop production, other conditions must be present that are conducive to plant growth, i.e., a favorable climate, adequate water and rooting depth, absence of excessive flooding or seawater intrusions, favorable terrain, and sufficient cultivat-able area. AraUe or cultivatable land, therefore, consists of only about 24% of the earth s land surface. Another 27% is suitable only for grazing, and 47% of the earth s land surface will not support any agricultural activity [3],... 

Compaction of the soil. Compaction reduces the ntrmber arrd size of the pores. It can also aifect rooting depth arrd hence the amormt of available water. 

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