Kalkituksen vaikutuksista maaperän orgaaniseen ja helppoliukoiseen fosforiin

Abstract

The purpose of the investigation is to elucidate which part of the phosphorus of soil is changed to easily soluble and root-soluble by liming and how fertilizing effects on the organic phosphorus of soil. For test material samples were selected to represent as far as possible the types of soil in which 1 the total phosphorus consists to a great extent of organic phosphorus and to a smallest possible extent of ferric and aluminium phosphates (heavy clay 5) and 2. the total phosphorus consists to a great extent of ferric and aluminium phosphates and to a small extent of organic phosphorus (muddy clay 4). Besides, in some samples phosphorus is present both in organic form and as ferric and aluminium phosphates (muddy clay 3), and the content of both being low (heavy clay 6). In addition, samples have been obtained from many years’ fertilizer experiment fields. Soil samples have been preserved limed and moistened in different ways for 9 months (Table 1) and for 6 months (Table 2). After incubation lime the organic phosphorus of samples was determined by treating with 0.25 N NaOH and easily soluble phosphorus with lactate method (Table 1). The samples preserved for a shorter period were analyzed according to Neubauer test whereby 3 successive harvests were made (Table 2). Due to liming organic phosphorus was decreased and the lactate-soluble phosphorus increased in samples containing amply organic phoshorus (Table 1). The Neubauer test gave similar results as the lactate method (Table 2). It can be concluded from the data that the increase of lactate-soluble and root-soluble phosphorus caused by liming is to a large extent ascribable to mobilization of organic phosphorus since it is greatest in soils where the percentage of organic phosphorus is highest. A part of the increase of easily soluble phosphorus is due to hydrolyzation of ferric and aluminium phosphates, since also in samples, containing little organic phosphorus but plenty of ferric and aluminium phosphates (muddy clay 4), increase of easily soluble phosphorus has occurred. In soil containing very little phosphorus both in organic form and as ferric and aluminium phosphates no increase of easily soluble phosphorus has been noted, on the contrary, a distinct reduction has been observed. Fertilizing has no effect on the percentage of organic phosphorus (Table 1). It seems that the amount of organic phosphorus depends more on the type of soil than on fertilizing.