Syväkastelun ja olkikatteen vaikutuksesta maaveden jännitykseen aitosaven pohjamaassa

Abstract

The author gives a preliminary report of a more extensive investigation concerning the moisture and temperature conditions in orchard soil profiles (6). This report concerns the studies made at Koivula orchard in South-west Finland. The variation of subsoil moisture contents during the growing season in 1956 were measured by tensiometers (5. 4. 1. 3). Fig. 1 indicates the effect of surface mulching with straw as compared to the effect of a plain surface on the moisture tension at 70—80 cm. depth. The corresponding values in soils irrigated with a combined subsoil fertilizing and irrigation apparatus (8,9.) are given in Fig. 2 (plain soil) and in Fig. 3 (straw mulched soil). On the basis of the moisture contents of garden subsoils given in this paper it can be concluded that, in the relatively dry conditions of South-west Finland, four irrigation treatments (each corresponding to about 40 mm. of precipitation) are required for preventing the subsoil moisture tension from rising up to 700 mm. Hg in unmulched heavy clay soil (Fig. 2). The first treatment should be made during the latter part of June and the others at two-week intervals. Using straw mulcing, the corresponding moisture content of orchard subsoil can be preserved if two treatments (at the beginning and at the end of June) are used (Fig. 3). Straw mulching without irrigation (Fig. 1) prolonged the period of suitable moisture content of subsoil in spring for about two weeks and thus the dry period under straw cover continued for only about six weeks. On the contrary, the dry period under the plain surface commenced at the beginning of July and was still continuing at the beginning of October. Because of the climatic conditions on Finland the growing season is very short, thus limiting the growth of plants. In addition, the plants usually suffer from droght during the warmest part of the growing season. Thus in our conditions the soils should not be drained too intensively in the spring, but conservation and increase of the soil moisture content during the summer months seems to be beneficial, especially in orchard soils. Because of the varying climatic conditions during different growing seasons systematical studies concerning moisture conditions in orchard soils should be planned.