The Earth’s crust is composed of enormous sections of rock called tectonic plates. Tectonic plates resemble puzzle pieces which move constantly against each other. Volcanoes often form in the areas where tectonic plates make contact. The friction created between two plates by the constant movement melts the Earth’s crust, causing the rock underneath the crust to turn into magma due to the great temperatures created by friction.
The now molten hot rock or magma creates great pressure, and over time, it finds its way through the fractures in the plates. Once magma reaches the surface of the Earth, it is called lava. Approximately 1500 volcanoes around the world are considered active, and from these, nearly 90% lie in the Ring of Fire, which is a ring of oceanic volcanoes circling the Pacific Ocean.
Most divergent plate boundaries lie in the bottom of the oceans. That is why most volcanic activity occurs in the oceans. Volcanoes may be formed at subduction zones. A subduction zone is a place where two plates, one oceanic plate and one continental plate, collide. At a subduction zone, an oceanic plate submerges under a continental plate. The friction creates magma. When magma reaches the surface, then, a volcano is formed. A typical example of this type of volcano is Mount Etna on the east coast of Italy.
<span>C. Mountains and ice
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Yara Crop Nutrition
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Agronomic Principles
Crop Characteristics
Potatoes produce a fibrous root system. These roots are at best no more than 24in long. Thus potatoes are shallow rooted compared to cereals for example, which can root to at least 47in depth. As a result, potatoes are often unable to exploit nutrients and soil moisture at depth within a soil profile.
While root growth occurs when soil temperatures are between 50 to 95˚F (10 to 35˚C), best, most active root development is at soil temperatures of between 59 and 68˚F (15 and 20˚C).
Leaf (haulm) growth occurs at temperatures of between 44.6 to 86˚F (7 to 30˚C) , but optimal growth is at around 68 to 77˚F (20 to 25˚C). Optimum temperatures for stolon growth are similar.
effects of soil temperature on root development
The potato tuber is an enlarged portion of the stolon. The initiation of this tuber is triggered by short day lengths (photoperiods), and involves growth hormones. The colder the soil temperature, the more rapid the initiation of tubers and the greater the number of tubers formed. The optimum soil temperature for tuber initiation is 59 to 68˚F (15 to 20˚C).
Under these conditions, the potato plant will have short stolons and shoots. Longer day lengths delay tuber initiation and favor the growth of the stolon and shoot. High temperatures also reduce tuber formation. Late varieties seem to be more sensitive to long day lengths or high temperature conditions.
Low nitrogen and high sucrose levels in the plant favor the formation of more tubers.
Once formed, tubers grow rapidly, reaching a maximum rate of up to 1,249 lb/ac/day in temperate climates. See figure below:
potato tuber growth rate, germany
Physiological Aging
By planting sprouted seed, crop growth can be advanced. The magnitude of this response and its effect on increasing crop yield is related to the physiological age of the seed at planting.
A because radon and neon are colorless and calcium is silvery-white.
