FIELD DRAINAGE.

New Zealand Herald, Volume LXVII, Issue 20595, 20 June 1930, Page 18

FIELD DRAINAGE.

A NEW EXCAVATOR. An attempt to assist the farmer to carry out field drainage moro economically received recognition at tho British Royal Agricultural Society's Show at Newport by tho award of a silver medal to a simple form of excavator. This implement is cabledrawn and works to a depth of about 22in, in two cuts, effecting a great saving in the cost of trench-digging. An cxhaustivo study of tho cost of tile drainago has been made over somo 14 years in Minnesota. Though the actual costs incurred during a period (1908-21), marked by widely varying economic conditions, cannot bo taken as a definite basis for final conclusions, they are useful for making comparisons and working ouC percentages. Tho percentages of costs are as follows:—Engineering and supervision, 8.3; tiles (including freight and haulage), 46.2; trenching and laying and refilling trenches, 43.6; miscellaneous, 1.9. These figures, though applicable to American conditions, are enough to show what a largo proportion of the total cost centres round tho tiles. It is calculated that with a small horse drawn excavator one ma-chine-hour is equal to 4.4 man-hours, wbilo one machine-hour of a motor-driven excavator is equivalent to 8.4 man-hours. Useful tables and graphs are given, showing tho hours required to dig trenches of various depths for varying diameters of tile under varying conditions of soil. Thus, to dig ft trench 3ft. deep for a tile 4-6 in. in diameter will tako per 100 ft. in easy ground 6.27' hours, in average ground 7.32 hours, and in hard ground 10.21 hours

Rainwater, it is stated, penetrates tho soil manly when tho soil is cultivated and the differences in temperature between the

soil and the air arc of tho greatest importance in soil moisture movement. Vertical movement occurs only to tho depths to which daily variations of temperature tako effect. This depth, under the conditions of tho test, was found to be about 3ft,