Peltojen salaojituksesta

In Finland the underdrainage of fields has been of small importance, although the need of draining the soil is great. The weightiest reason for this are the high costs of underdrainage which for ex. in 1950 made on an average 60.000 mks per hectare. The costs depend principally on the lenght of drains per hectare, which in Finland is principally considered to be dependent on the kind of soil. Table No. 1 shows the costs of drainage and the number of drains per hectare, in different soils. Besides the costs also technical restrictions have been an impediment to the advance of drainage in our country. Among other things the production of tile-pipes is quite insufficient. The costs of drainage in heavy clay are divided according to table No. 2. Examinations as to the possibilities of reducing in some respect the said costs have resulted in the conclusion that these possibilities are very small at the most expensive point, viz. the tile- pipes 45%. The greatest saving possibilities are to be found in the digging costs. Big digging machines may not have a decisive influence on the question in Finland, this fact being due to the high rate of interest and the scarcity of capital. It would be desirable to develop inexpensive digging machines for underdrainage, because in Finland the season suitable for drainage is very short. A great obstacle in this respect is, however, the fact that the demands for depth of the drains now in force in Finland are so great —in South-Finland the digging depth is 125 and in North Finland 145 cm. In the article the possibilities of reducing the depth of the drains are examined, and according to the experiences and researches made in Sweden, such possibilities could be imagined. In order to further a rapid advance of underdrainage in Finland cheaper methods of drainage than the tile and the board drainage now in use ought to be adopted. Also the possibilities offered by the hills as well as the old plot-trenches ought to be observed and made use of. The author presents a new method which he has tested in mineral soils. A small channel filled with sifted gravel or macadam is made at the bottom of old plot-trenches. The ability of such a channel to conduct water can be exactly estimated (picture No. 13) and so the quantity of gravel or macadam and the grain size can be made dependent on the quantity of water to be conducted. Across such trenches will be made tile-drains at a distance of 50—100 m from each other. By this method the costs can be reduced to about 50 % of the present costs. The gravel or the macadam will be safeguarded against silting up by peat or moss. In peat soil the author has experimented with the arch-drain shown in picture No. 16, which is also made at the bottom of an old trench. Special shovels have been developed for the preparation of this kind of drains. Although the duration of such drains is shorter than the duration of the woodpipe drains, they are to be recommended, at least in certain kinds of peat soil, on account of their cheapness. Besides, although the conducting material would be resistant, the sinking of the peatlands (see picture No. 17) will set a limit to the duration of the wood pipe drainage, because the deep-dug drains will, at the beginning, reduce the crops. Finally the article contains economical comparisons between the expensive and the cheap method