|Title||Kwantitatieve aspecten van humusopbouw en humusafbraak|
|Source||University. Promotor(en): A.C. Schuffelen. - Wageningen : Pudoc - ISBN 9789022000854 - 109|
|Publication type||Dissertation, internally prepared|
|Keyword(s)||humus - humushorizonten - strooisel - bodemchemie - humus horizons - litter (plant) - soil chemistry|
|Categories||Soil Fertility / Soil Chemistry|
|Abstract||Some common expressions on humus were current that were not based on exact or quantitatively analysed data.
To achieve a desirable humus content, it was necessary to know the relation between supply of humus and humus content, here studied, and the relation between humus content and productivity.
A field trial begun in 1911 to compare complete fallow with normal exploitation indicated two axioms: from a supply of crude organic matter a certain constant part became humus each year; from humus in soils a certain constant part was mineralized each year.
If supply was equal each year it was possible to derive the following formula for the rise or fall in humus content: y = y m - (y m - y 0 ) (1 - K 2 ) t, where y = humus content, y m = humus content at ultimate equilibrium,y 0 = initial humus content, K 2 = rate of mineralization (see axiom 2), and t = time in years. Further y m = K 1 /K 2 x, where K 1 = rate of humification (see axiom 1), and x = supply with raw organic material.
These formulae were tested in the few available experiments, suitable for the purpose (which did not include the classical Rothamsted fields). K 1 was 0.4; thus 40 % of the supply becomes humus each year. K 2 had values between 0.015 and 0.02; from this it followed that 2 % of the humus was yearly mineralized. No difference was yet found in the value of either coefficients for different organic materials and in different soils.