Soil moisture deficit

Runoff sensitivity, particularly in arid and semi-arid climates, is largely a result of sensitivity in soil moisture response. If rainfall amount and frequency decrease, more soil moisture is lost to evapotranspiration, creating a soil moisture deficit that must be replaced before surface runoff or significant ground-water flow returns. The converse also tends to... 

Rawson, H.M., Bagga, A.K. Bremner, P.M. (1977). Aspects of adaptation by wheat and barley to soil moisture deficits. Australian Journal of Plant Physiology, 4, 389-401. 

When the rainfall is well distributed, crops are less likely to suffer than in wet periods followed by long diy periods. During such dry periods the crops have to survive on the available water held in the soil (see Section 3.3. 4, Water in the soil, page 45). The difference between the actual amount of water in the soil and the amount held at field capacity is known as the soil moisture deficit (SMD). It is one of the main factors in determining the need for irrigation. 

The crop is sensitive to soil moisture deficit and higher yields are obtained from irrigating at early flowering and pod fill. 

Seed Germination. Across the American cotton belt, cotton germinates under environmental stresses such as low soil temperature, moisture deficit or excess, oxygen deficits, and mineral extremes. Seed treatments to increase tolerance to early season stresses would be very beneficial. When large scale replanting depletes the best seed, lower quality seed must be used. So any treatment which would improve the performance of such seed, even under favorable environmental conditions, would be valuable. In the future, plant breeders may select breeding lines for... 

Calcic horizons develop in soils where there is a net moisture deficit, such that carbonate produced in a drier season is not leached away during a wetter season. Most present-day calcretes form in areas with warm to hot climates (mean annual temperature of 16-20°C) and low, seasonal rainfall (100-500mm Goudie, 1983). The upper boundary more likely spans the range 600-1000 mm (Mack and James, 1994). Royer (1999) has pointed out that from a large dataset of 1481 studies, carbonate-bearing soils correlate with a mean annual precipitation of <760 mm. Most of the dataset came from western USA and, as Retallack (2000) warns, there is great variability in the rainfall levels associated with the boundary between calcareous and non-calcareous soils in different parts of the world, or even as Birkeland (1999, p. 291) points out, there are marked local variations within the western USA. 

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