Effects of Sludge Dressing in Dry Field Soils on Soil Physical Conditions and Plant Growth

Abstract

Feasibility of sludge dressing on dry fields has been investigated for a management of sludge which does not contain harmful objects. Sludge used was obtained from the bottom of Lake Kasumigaura, was mixed into volcanic ash soil named Kanto Loam and sandy soil from the sand dunes of Kashi ma. Experiments were made in Wagner pots with mixing ratio of sludge and soils varied in several grades, and in the field to be compared with the results of the pot test. The sludge mixed with Kanto Loam changed into clods, which did not break down easily in a short period. Because of these clods the available moisture of Kanto Loam decreased and the crop sprouting was obstructed. These clods seemed to be gradually destroyed by cultivation and by repetition of drying and wetting, but it was thought that the mixing work should be improved to diminish the obstruction which will last for several years. The experimental result of Chinese cabbage vegetation showed that the sludge dressing in Kanto Loam which has great phosphate-adsorption coefficient had a merit of supplying the phosphate to a certain extent. In the case of dressing the sludge in sandy soil, the available moisture increased and vegetation went well generally. When the mixing ratio was increased, crusts took place at the soil surface making a barrier against germination. It should be noted that the soil liquefied suddenly while sludge was being mixed into sandy soil when the pores of the soil were just filled up with sludge. The merit or the demerit of sludge dressing on dry fields is to be evaluated in consideration of the conditions involved.