Applicability of the morgan test for determining available soil phosphate

Abstract

An examination of the bforgan ' quick ' test showed that the amount of phosphate extracted from. soils increascd with the widening of the ratio, soil/extractant. and with the period of extraction; the maximum extraction was obtained in most soils by shaking the soil with the extractant for I hr. Of the likely phosphorus-bearing constituents of soil Morgan's reagent dissolves mainly calcium (and probably magnesium) phosphates : organic forms of phosphorus dissolve only to a small extent. In the soil examined. Morgan's tcst failed to distinguish the effect of I 7 successive annual applications of supcrphosphate at the rate of I O O Ib. per acre. However, it did detect, decisively, corresponding applications a t the rates of 200 and 400 lb. pcr acre.The 3Iorgan test further demonstrated the depression of phosphate a\railabilitv by rcpeatetl application of ammonium sulphate, the opposite effect of liming, the very substantial increase in availability after the application of dung, the absence of any effect of treatments with potassium sulphate and a n apparent seasonal variation in phospliatr status in the soil examined.