Crop evapotranspiration

The water that is available in the soil is depleted by the consumption of plants (perspiration), by surface evaporation and by drainage.

The sum of perspiration and evaporation is known as evapotranspiration (Etc). This varies depending on the climate, the characteristics of the crop, the management practices and the means of development, therefore the precise knowledge of the Etc It is a fundamental tool that contributes to the adequate management of water resources and the improvement of crop productivity.

The measurement of the evapotranspiration of a crop can be determined directly through the methods of mass transfer, of an energy balance, from the measurement of the components of the water balance in the soil on cultivated land or through the use of lysimeters. These methods generally require precision in measurements, require specialized equipment and long periods of measurement, in general they are expensive, hence their use is limited to determinations for some crops of interest and research level.

Therefore for most crops, the Etc It is estimated from the crop coefficient approach (Kc), as the product of an evapotranspiration of the reference culture (ET) and the crop coefficient.

Etc Kc x ET


Etc = Evapotranspiration of the crop (mm day-1)
Kc = Crop coefficient (dimensionless)
ET = Evapotranspiration of the reference culture (mm day)-1).

La ET it is calculated from mathematical functions based on climatic data, for example the FAO Penman-Monteith equation, from the measurement of water that evaporates daily on a free water surface such as the Class A evaporimeter tank, or by using specific devices such as the Cenirrometer.

The Kc are determined experimentally by measuring some components of the water balance in a volume of cultivated soil, in lysimeters whether drainage, hydraulic or weighing. These devices allow to quantify the evaporation, transpiration and drainage processes with high precision in a given volume of soil, although they present some disadvantages such as: the alteration of the soil for its filling, relatively small sizes, high cost per labor requirement and construction devices

Once the values ​​of Kc for the different stages of growth and development of the crop, these are multiplied by the ET calculated by one of the mentioned methods and you get the Etc to be applied in the water balance. Cenicaña initiated an investigation that seeks to determine the Kc values ​​for the new varieties of sugarcane using weighing lysimeters under our local conditions and during the different stages of crop development both in staff and in soca.

The weighing lysimeters used consist of plastic tanks, externally reinforced with a metal structure in the shape of a cage that surrounds them, these are installed in the field, filled with soil and cultivated with cane, with normal crop management. Humidity and tension sensors are placed inside the lysimeter. The tank rests on a rigid platform, which in turn is supported by four load cells, a drainage system with a counter is installed at the base. The data of both the load cells and the humidity, voltage and meter meters are recorded continuously in a data logger and transmitted via a wireless network system to a central computer, so that the researcher You can continuously verify the information.

The results of these investigations will allow to obtain information to have greater precision in the water balance in order to improve the management of irrigation in the cultivation of sugarcane in the Cauca river valley.

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