Studies on soil organic matter: Part I. The chemical nature of soil organic nitrogen

Abstract

1. The acid hydrolysis of six soils with nitrogen contents ranging from 0·1 to 2·38% has been studied by determining the amounts of ammonia-, humin- and α-amino-N present in the soil hydrolysates after various periods of hydrolysis.2. Under the conditions of hydrolysis employed (3 ml. of 6N-HCl/g. soil) the period required for maximum liberation of amino-acids from the soils was about 12 hr. 24·2–37·1% of the total-nitrogen of the soils examined was liberated as α-amino-N in this period. Further hydrolysis led to destruction of amino-acids. Similar amounts of α-amino-N were liberated by hydrolysis of the soils with alkali (5N-NaOH).3. From 69 to 87% of the total-nitrogen of the soils was brought into solution by acid hydrolysis; the amount dissolved by hydrolysing with alkali or with alkali under reducing conditions (alkalistannite) was not significantly different. It is concluded that most of the insoluble-nitrogen found after acid hydrolysis is not derived from protein material, and it is suggested that some of this nitrogen is in the form of heterocyclic nitrogen compounds.