Some physiological bases of agricultural and gardening practice. A sunlight and photosynthesis

you are: Some physiological bases of agricultural and gardening practice

The Quantity fotosinteticheski the active sunlight, received by sheet, depends on its position in a sheet cover. With increase in light exposure of separate horizontal sheet intensity of photosynthesis increases to a certain maximum which is reached at light exposure considerably smaller, than on full solar to light (fig. 14.5). Surplus of light over this sating intensity is spent in vain, at least for the given sheet. As the top leaves receive a full sunlight, they should use it economically. These leaves from above are usually focused to a falling sunlight not under direct, and a slanting corner.

At such coal the given quantity of light is distributed on the big general sheet surface than if leaves settled down at right angle to it (fig. 4.6). Therefore light exposure of a surface of sheet decreases, but it does not reduce photosynthesis, as force of light still superoptimum. If leaves are located naklonno bolshee their number can be in the uppermost layer of foliage and the big sheet surface can function with optimum efficiency; therefore it turns out photosynthetic production more than if all top leaves have been located horizontally.

In a direction to the bottom circles intensity of light quickly decreases. Usually leaves cover each other not completely so beams of a full sunlight can still get through small ruptures in the top weight of foliage and reach the bottom layers. The sunlight should pass in other places through one or several leaves. The quantity of light absorbed by sheet, variously depending on the maintenance in it of a chlorophyll, but usually makes about 90% from falling radiation. Thus, the second circle of leaves receives 10% from a full sunlight, and the third - 10% from 10%, i.e. Only 1%. If the uppermost leaves is better use a full sunlight at their arrangement at an acute angle to beams, the bottom leaves function at low intensity of light falling at right angle is better; thus unit of a sheet surface catches light greatest quantity (fig. 14.7). Thus, at an ideal plant the bottom leaves are located horizontally, and the inclination of leaves increases in each overlying circle, reaching a maximum (almost vertical position) at the uppermost leaves. Selectors often aspire to deduce such plants.

Even if the lowermost leaves effectively absorb all falling energy, they, possibly, will work in a mode close to a point of indemnification. If the sheet receives not enough light even for achievement of this point (fig. 14.5) he will breathe more, than fotosintezirovat see, and it will appear, thus, excessive burden for a plant. Such leaves usually grow old, turn yellow and fall down.

Quantity of leaves in crops express an index of a sheet surface (JLP) - the relation of a total surface of leaves to the area of the soil covered with plants. For example, if ILP it is equal 4, it means that over each square metre of soil is 4 м2 a sheet surface. Using this indicator, it is possible to estimate efficiency of culture concerning solid accumulation - an end result of photosynthetic activity. At culture with horizontal leaves, for example a clover, optimum ILP (quantity of leaves at which the lowermost leaves are almost in indemnification point) less, than at culture with mainly vertical leaves, for example, wheat as vertical leaves shade underlaying area, than horizontal less. Therefore optimum ILP for a clover it can be equal 4, and for wheat - nearby 7. Using this data, it is possible to pick up appropriate tactics for cultivation of grasses.

If to allow plants to generate it is too much leaves, productivity will decrease, as the lowermost leaves will function below a point-indemnification. On the other hand, intensive stravlivanie will lead to such loss of leaves that light will reach the soil, not used completely for photosynthesis. Therefore the best - to support ILP, near optimal. It it is possible to reach, every time pitting or mowing down a grass as soon as ILP starts to exceed an optimum so that ILP became a little below optimum. Such way it is possible to support optimum speed of accumulation of a solid.

The Purpose of regulation of a sheet surface consists in maintenance of its optimum size at given solar radiation. It is obvious that this size varies depending on intensity of light and, means, from a season. Vegetative planting can require in bolshej a sheet surface for optimum growth rate in the middle of summer, than the beginning or the end of the vegetative period when the sunlight is less intensive. This fact becomes important at a choice of terms of crops. In moderate zones cold weather limits early-spring crops of cultures in the spring. Often the culture develops only very small sheet surface to the middle of summer so the sunlight is used badly; meanwhile the culture continues to grow, and the area of leaves above optimum (fig. 14.9) becomes closer by the autumn. The ideal culture - that which can be sowed early and which quickly develops a sheet surface so solar radiation is better is used in the middle of summer, i.e. When it is most intensive. Deducing holodostojkih grades for early-spring crops allows to hope for increase in crops.