Soil organic matter and nitrogen contents of veld and cultivated soils in the central orange free state

Summary

The organic matter and nitrogen contents of soils from cultivated lands were compared with those from adjacent veld sites at 0–30, 30–60, and 60–90 cm depths.

At 0–30 cm depth the veld and adjacent cultivated soils did not differ much in organic matter and nitrogen contents. The largest differences were found at 60–90 cm depth, where the soils under cultivated lands contained considerably less organic matter and nitrogen than the veld soils. This was particularly evident in two sites at the Glen College of Agriculture and to a lesser degree in two sites in the Theunissen district where the soil was more sandy.

The soil from the cultivated lands showed a marked decrease in organic matter and nitrogen contents and a distinct narrowing of the C : N ratio with increasing depth whereas the C- and N-contents and the C : N ratios of veld soils differed much less between depths.

These results were explained by the soil moisture conditions prevailing under veld and cultivated lands during the course of the year.

Judging from the decreases in organic matter and nitrogen contents since cultivation commenced, Central Orange Free State soils may vay considerably in the amounts of mineral nitrogen liberated following cultivation.