Article acquaints readers with a tenziometrichesky method of definition of terms and norms of watering and the device tenziometr, allowing to operate waterings of vegetable cultures.
The modern technology of cultivation of vegetable cultures provides use for watering of system of a drop irrigation. One of important questions at its introduction – operative control of humidity of the soil with a view of timely carrying out waterings. Considering specifics of consumption by vegetable cultures of water, in particular at the drop irrigation, one of the simplest and exact methods of definition of terms and norms of watering should consider tenziometricheskiya. By researches of Institute of hydraulic engineering and UAAN land improvement (Kiev and its center to Simferopol), some other scientific institutions it is established that use tenziometrov for control of humidity of a korneobitayemy layer of earth provides necessary accuracy and efficiency in comparison with other methods (termostatno-weight, a neutron vlagometriya, with use of balansomer, evaporators, diagnostics of waterings on concentration of cellular juice).
Tenziometr – the device intended for determination of capillary potential of soil moisture (Kp) which characterizes water-retaining forces of the soil and causes availability of moisture to plants. Tenziometr of the simplest design produced in lots by KNITs IGIM UAAN (Simferopol), consists of a porous ceramic probe (sensor), the water chamber and the vacuum gage connected tightly among themselves. If a probe filled with diaerirovanny (boiled) water to place to the soil, water and the substances dissolved in it through its porous walls will move to the soil or on the contrary – from the soil in a probe. This process lasts up to achievement of balance between pressure of moisture in the soil and waters in a probe. Pressure of water in tenziometre, after the accounting of an altitude correction of the water chamber, also will characterize size of capillary potential of soil moisture (Kp).
Between humidity of the soil and Kp there is the functional dependence named the main hydrophysical characteristic (OGH). This dependence established experimentally, use for determination of humidity of the soil on indicators tenziometrov. Kp it can be used also for definition of terms of waterings – without preliminary determination of humidity of the soil.
The operational information about humidity of the soil can be used both for direct definition of terms of watering, and in different automated control systems for an irrigation.
The preirrigation size of Kp depends on a view of the soil, its granulometric structure, a type of plants and phases of their development. That is, for the same culture it will be different – on sandy, for example, and heavy and loamy soils. Essential influence on preirrigation size (threshold) of Kp renders intensity of meteoconditions. Influence on value of preirrigation size of capillary potential of soil moisture of Kp of granulometric structure of the soil is shown in table 1.
Table 1. Interrelation of potential of soil moisture (KPA) with humidity of the soil
Average values of preirrigation humidity of the soil, irrigation norms in a year from 75 % are given by security with a precipitation in table 2.
Table 2. Average values of preirrigation humidity of the soil, irrigation norms for vegetable cultures in a year from 75 % security with a precipitation
When using tenziometrov for diagnostics of waterings the importance is taken by depth and a place of their installation. For the vegetable cultures which root system is concentrated in a layer of 0-50 cm, tenziometry it is possible to establish in initial phases of development on depth of 15-20 cm, and after penetration of roots into deeper layers installation additional tenziometra for control of humidity of the soil on depth 30-40 is required see. An optimum installation site – at distance of 10-15 cm from an axis of the irrigation pipeline between drop water releases. Tenziometra it is necessary to establish on each irrigation module. Recommended depth of moistening of a korneobitayemy layer of earth under vegetable cultures is given in table 3.
Table 3. Depth of moistening of a korneobitayemy layer of earth under the vegetable
cultures in different phases of their development
Size of irrigation norm count as a difference of stocks of the moisture corresponding to the smallest moisture capacity (NV) and 70-90 % for NV, taking into account factor of local moistening of the soil at a drop irrigation.
Tenziometra are simple on the technical device, are convenient in operation, rather inexpensive, and the principle of their work substantially corresponds to "work" of a root of a plant. Thanks to these useful properties tenziometry found very wide application both in scientific researches, and in practice of agricultural industry – for determination of humidity of the soil and diagnosing of terms of watering of crops.
The IGIM UAAN Crimean research center offers services in installation of sensors of humidity of the soil.
V. Storchous, candidate of agricultural sciences, IGIM UAAN Crimean research center.
G. Tsyplyak, leading expert of department of plant growing, director general of Association of vegetable growers of the Crimea.