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The Chemistry and Fertility of Soils under Tropical Weeds 123
groups like OH and COOH. Organic acids like citric acid and oxalic acid may form
+
2+
dissolved complexes with Mg and K . This process may greatly enhance the soil
+
mineral weathering because it may decrease the solution K .
Salam (2019) shows that the release of K from soils minerals of Oxisols from
West Java Indonesia and Mollisols from Wisconsin the United States of America
significantly increased with the decrease in soil pH (Fig 7.4). This pattern is also
shown by several soils from West Java Indonesia and Wisconsin the United States
of America used in a series of experiment by Salam (1989). This data show the
+
effectiveness of H as an attacking agent in soil chemical weathering.
120
100
Released K (mg kg -1 ) 80
60
40
20
0
4 5 6 7
Oxisols Mollisols
Fig. 7.4. The released K from soils under different pH.
7.4 The Effects of Weeds on Soil Potassium Release
To cope with problem of K deficiency in tropical regions, several break-
throughs are being developed (Salam, 1989; Salam and Corey, 1993). The use of
indigenous K by some methods is promising (Salam and Corey, 1993; Jalali and
Abdul Kadir Salam and Nanik Sriyani – 2019
