Columbia subject headings:
Harvard subject headings:
Humus--Tropics--Congresses.
Soil dynamics--Tropics--Congresses.
Soil ecology--Tropics--Congresses.
Soil management--Tropics--Congresses.
Princeton subject headings:
Humus--Tropics--Congresses.
Soil dynamics--Tropics--Congresses.
Soil ecology--Tropics--Congresses.
Soil management--Tropics--Congresses.