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Smectitic soils of the tropics are medium- to fine-textured alluvial soils containing moderate to large amounts (20% or more) of smectite, a shrinking and swelling clay mineral, in the clay fraction. Small to moderate amounts of other layer silicate minerals, such as illite, chlorite, vermiculite, and kaolinite, are also present in the clay fraction. Smectitic soils have moderate to high values of CEC (10-50 cmol/kg of soil), high base saturation, and high water-retention capacity. These soils are usually developed on alluvial materials rich in basic cations, especially Mg. Smectitic soils commonly occur on alluvial plains in river valleys and deltas as well as in inland depressions. In the wetter tropics, large areas of smectitic soils are found in tropical Asia, especially Vietnam, Thailand, and Myanmar (Burma). These young alluvial soils are rich in nutrient-bearing weatherable minerals, such as micas, feldspars, and hornblende. Smectitic soils on the alluvial plains and inland valleys have a shallow groundwater table, and some soils are flooded during the rainy season. Thus, they are best suited for rice cultivation. For example, in the flood plains along the Mekong and Chao Phraya rivers of the Indo- China peninsula, mineral-rich deposits from annual flooding are able to maintain relatively high rice yields with little or no additional nutrient inputs. Smectitic soils occurring in seasonally flooded coastal mangrove swamps are known as acid sulfate soils. These soils are used for cultivation of swamp rice and floating rice during the rainy season, depending upon the depth of flooding by fresh water. In drier regions, clayey smectitic soils (mainly Vertisols) often exhibit large cracks during the dry season and become very sticky and difficult to work with during the rainy season. In the drier tropics, large areas of clayey smectitic soils are found in central India, central Sudan, southern Ghana, and in the Lake Chad region of central Africa. Clayey smectitic soils are usually found in the inland depressions scattered throughout the drier regions of West, East and Central Africa. Because of their high chemical fertility, these soils are important soils for cropping and grazing in the drier tropics.

This chapter looks at the ecosystem of the forest floor. The forest floor consists chiefly of soil. One of the most distinctive soils is podsol, the typical soil in conifer forests. This soil is easily recognizable if you expose it by digging a hole, or even more easily by seeing it exposed in an eroding stream bank. It has a thin, dark top layer of packed needle-leaf litter gradually decaying into humus (newly decomposed material with organic ingredients only). Immediately below that is a layer, often thick, of almost pure white sand. The soil is cold, acidic, and sometimes wet. The most common flowers on the coniferous forest floor belong to three families: one, of plants that prefer acid soil; a second, of epiparasitic plants; and a third, of ancestors of the epiparasites. The remainder of the chapter discusses the floor of the boreal forest; the value of dead wood and debris; and animals found in the evergreen forest—beavers, birds, and ducks.

In reality, there can be no generic definition of an “ideal soil” because a soil’s performance is influenced by the local climate, landscape characteristics, grape variety, and cultural practices and is judged in the context of a winegrower’s objectives for style of wine to be made, market potential, and profitability of the enterprise. This realization essentially acknowledges the long-established French concept of terroir: that the distinctiveness or typicity of wines produced in individual locations depends on a complex interaction of biophysical and human cultural factors, interpreted by many as meaning a wine’s sense of place. As discussed in “Soil Variability and the Concept of Terroir” in chapter 1, because of this interaction of factors that determine a particular terroir, it is not surprising that no specific relationships between one or more soil properties and wine typicity have been unequivocally demonstrated. While acknowledging this conclusion, it is still worthwhile to examine how variations in several single or combined soil properties can influence vine performance and fruit character. These properties are: • Soil depth • Soil structure and water supply • Soil strength • Soil chemistry and nutrient supply • Soil organisms Provided there are no subsoil constraints, the natural tendency of long-lived Vitis vinifera, on own roots or rootstocks, to root deeply and extensively gives it access to a potentially large store of water and nutrients. In sandy and gravely soils that are naturally low in nutrients, such as in the Médoc region of France, the Margaret River region in Western Australia, and the Wairau River plain, Marlborough region, New Zealand, the deeper the soil the better. A similar situation pertains on the deep sandy soils on granite in the Cauquenas region, Chile. However, such depth may be a disadvantage where soils are naturally fertile and rain is plentiful, as in parts of the Mornington Peninsula, King and Yarra Valley regions, Victoria, Australia, and the Willamette Valley region in Oregon (see figure 1.11, chapter 1), because vine growth is too vigorous and not in balance.