Vízügyi Közlemények, 1962 (44. évfolyam)

4. füzet - IX. Könyvismertetés

(14)* cumstances the magnitude of the crop is proportionate to the length of the fruit bearing branches, i. e. to growth. On this basis the approximate value of the transpiration coefficient a> and the likely crop yield can be estimated: As to be seen from diagram a in Fig. 10, the optimum practicable quantity of soil moisture to be consumed is identical with the abscissa at the tangent point P of the curve, this abscissa being 64 per cent of the final value and 88 per cent of the ordinate. No more than 75 per cent of the maximum soil moisture should preferably be taken into consideration, since the reduction in crop yield due to the remaining '25 per cent does hardly attain 2 per cent, which is negligibly small in relation to the water quantity becoming available, and which can be utilized with high efficiency elsewhere. Diagram b represents the geometrical loci of the numerical values of the transpiration coefficient and may be regarded as the efficiency curve of irrigation water. As shown by this diagram, the practically preferable maximum of soil moisture is between 50 and 100 per cent on the abscissa. In order to attain the highest possible crop yield storage irrigations are suggested in autumn, at the end-autumn time, besides the applications of irrigation water in the growing season. It is demonstrated that the soil layer above which moisture storage is aimless, and even necessarily connected with certain hazards, lies at a depth of 2,0 to 2,5 m. Storage is performed by gradually increasing charges in a manner, that there should remain, for reasons of safety, sufficient absorbing capacity within the soil for a water volume equalling three times the average precipitation, in the period between the last storage irrigation in end-winter and the commencement of appreciable moisture consumption by vegetation (from the 15th March to the 30th April). Referring to observations made in connection with an instance of natural subsoil irrigation, it is established that the probable maximum of total moisture quantity, i. е., of precipitation + irrigation water that can be introduced into the soil, is about twice as high as that due to precipitation alone. This is considered as an informative value only. The existence of critical irrigation periods, respectively times is investigated for winter apple trees. As a result of these investigations it is concluded that the critical period largely coincides with that of rapid growth. Within this period the most significant irrigation for yield is the one preceding the exhaustion of the soil moisture storage. This irrigation should be performed for winter apple trees around the 20th July. Irrigation may become necessary even beyond this time, i. е., outside the irrigation season, if the weather is dry for extended periods. For such applications smaller quantities should be used at more frequent intervals in order not to disturb the process of ripening of the fruit. The irrigation of orchards is continuous if the tree grows together with the years' crop the so-called crop-buds ensuring the crop in the subsequent year, e.g. the winter apple tree (Fig. 11 ). Irrigation is, however, divided if these two phenomena take place in different periods, e.g. the mulberry tree (Fig. 12). Summarizing the investigations relating to the growth curve it can be stated that growth is essentially identical, regardless whether a fruit tree having a long, or a short growing period is considered. Thus e. g. in absolute value the 200 day long growing period of the winter apple tree is identical with the 93 day long period of the mulberry tree. The method described above was developed on the basis of experiments and observation, and was tested by the author for two decades in orchard irrigations. Yet it is regarded as a practical starting basis only. The application of the method is illustrated by a practical example in which the time of irrigation, the quantity of irrigation water and the anticipated crop yield are estimated and planned. The execution of the plan is also described, as shown partly in Fig. 13. (Translated by Z. Szitvássy struct, eng.) soil moisture (litre) 1 kg dry plant material