Subsurface ways of irrigation by waste waters consist in balanced water supply into the root zone of cultivated crops. Irrigation equipment is used for distribution of water and consists of the perforated line and drains made of plastic materials, microporous tubes, equipment of point and trickle irrigations. The type of irrigation equipment and its arrangement is chosen by the degree of purification of waste water. Water flowing out from the irrigation line forms in soil the zone of capillary suspended water which supplies water and nutrients released from waste waters to cultivated crops. Advantage of the suggested way of irrigation consists in elimination of close contact of a worker and cultivated crop with waste water. Finding the course of purifying effect of soil in subsurface irrigation, protection of groundwaters against contamination and finding the extent of binding essential plant nutrients in soil medium and the potential of its utilization have not been solved sufficiently till now. The research studies concentrated on purifying effect of soil in subsurface irrigation have been carried out in the first phase on two types of laboratory models, the second phase will continue directly in the field. Irrigation doses were deliberately three times higher. Hence, it simulated the effect of eventual overloading or the consequence of precipitation following the irrigation straightaway. An arrangement of large-capacity model is presented in Fig. 1. The results of research of subsurface irrigation by sewage waste waters on sandy and loamy soils show a good purifying effect in different indicators of contamination. In sandy soils (Tab. 1) the value of purifying effect in the starting phase of filtration range from 92.2 to 96.9% in CHSK, 97.3 to 99.8% in BSK5, 95.6 to 99.1% in ammonia, 94.6 to 95.9% in phosphates. Outwash occurs in calcium, magnesium and nitrates. Purifying effect of soil on loamy soils (Tab. II) is: 96.6 to 98.8% in BSK5, 86.0 to 89.2% in CHSK, 99.0 to 99.1% in ammonia, 96.7 to 98.4% in phosphates. Outwash occurs with calcium, magnesium and nitrates. The leakage of nitrates can be prevented by the uptake by vegetation. Detailed information are reported by Salek (1992), Salek, Elazizy (1993). The research of subsurface irrigation by sewage waste waters confirmed that in exceptional short-time overloading with sewage waste waters the soil can purify waste water on a high level. Nutrients gradually released from waste water are in the form well-available by plants. Generally, in view of agriculture and hygiene the subsurface irrigation by waste waters is an acceptable way of solution of specified irrigation, it has a lot of advantages for which we recommend to use it.
