Page 28 - Ilmu Tanah

The Chemistry and Fertility of Soils under Tropical Weeds 15

Weed Plant-Roots
+
[H ] Increases -->
Excreting H , acids, and pH Decreases
+
enzymes, and
(Enzymes) Increase
Releasing Respired CO 2

Soil Minerals + OM Released K +
+
+ H + Enzymes from
Releasing K + Soil Minerals/OM

K + K+
Adsorption by Soil Colloids Absorption by Weed Plant
(Exch. K) Roots
Increased K Release Increased K Release

+
Fig. 1.10. Conceptual relationship between excreted H and organic acids and respired CO 2
+
by plant roots, released K from soil minerals and organic matters, and improvement of
plant growth (Salam et al, 2019).

The soluble nutrient elements released from soil mineral and organic matters
may encounter different fates like those happening for free Fe (Fig. 1.2). Part of
the released K and other nutrient elements may be absorbed by weed and plant
roots. Some other parts may be adsorbed by soil colloids increasing the soil
exchangeable nutrient elements like exchangeable K, exchangeable Ca, etc. or
leached through the soil body by water percolation. Some parts may also
precipitate forming secondary minerals or absorbed by microorganisms.
The effects of weeds are not limited to those mentioned above. In addition to
intensifying the weathering of soil mineral matters and the decomposition of soil
organic matters, weeds may also increase the total organic C and total N through
the excretion of organic acids and their dead parts (Sembodo et al., 2017). The
Abdul Kadir Salam and Nanik Sriyani – 2019