Page 29 - Ilmu Tanah Book

16 The Chemistry and Fertility of Soils under Tropical Weeds

relationship between the existence of weeds on soil properties is described
conceptually in Fig. 1.11. In general, weeds may affect the soil pH and soil
enzymatic activities, which may then affect the processes of soil mineral
weathering and organic matter decomposition. This processes may affect the
status of soil base cations (Ca, Mg, K, Na) and acid cations (Al, H) as well as soil
solution anions (P, S, N) and also heavy metal nutrient elements (Fe, Mn, Cu, Zn,
Mo) and heavy metal non-nutrient elements (Pb, Cd, Hg). The soil negative
charges, soil CEC, and base saturation may also change due to the changes in soil
pH. The decrease in soil pH may of course lower the amount of soil negative
charges, CEC, and base saturation.

Weeds Enzymes

Organic C Soil Mineral Soil Organic
Total N Matters Matters

Soil pH
Base Cations
(Ca Mg K Na)

Acid Cations
Soil
(Al, H)
Negative
Charges P, S, N
(CEC) Anions

Heavy Metal
Cations
(Fe Mn Cu Zn
Soil E Pb Cd Hg etc)

Fig. 1.11. The direct and indirect effects of weeds on the chemistry of soils.

Abdul Kadir Salam and Nanik Sriyani – 2019