Strategy to reduce fertilizer application in volcanic paddy soils: Nutrient reserves approach from parent materials

• High K-bearing minerals present in soils from acid but were absent in soils from basic materials.
• Soils derived from acid materials contain high available K2O implying omission of KCl fertilizer.
• Soils derived from basic materials contain high available P2O5 implying omission of SP-36 fertilizer.
• Omission of KCl and SP-36 fertilizers in paddy soil based parent material properties promoted environmental quality.
• Knowledge on weatherable minerals present in paddy soils leads strategic management of inorganic fertilizers.

Volcanic paddy soils are widespread across Asia and their natural fertility is different, depending on parent material properties associated with nutrient reserves. This implies there is an opportunity to reduce fertilizer application and environmental pollution. The objective of the study was to compare easily weatherable minerals, available Si and nutrient reserves of paddy soils derived from acid, intermediate and basic volcanic materials. Soils deriving from acid, intermediate and basic volcanic materials were sampled from Sumatera, Sulawesi and Java Islands, respectively for mineralogical and chemical analyses. Water was sampled from irrigation canals and pit profiles for analyses of cations and anions. Results showed minerals rapidly releasing their elemental constituents into soil during weathering processes (referred to as easily weatherable minerals) increased from 27 to 94% in the following order of soils derived from basic > intermediate > acid volcanic materials. In soils developing from acid materials, the available K-derived parent materials was more than enough while P was insufficient to meet rice requirement. On the other hand in soils derived from basic materials, the P availability was sufficient while K insufficient for rice crops. Those findings indicate a strategic fertilizer management in rice cultivation by omitting KCl and SP-36 (superphosphate with 36% P2O5) applications to soils developed from acid and basic materials, respectively. For soils developed from intermediate materials, both KCl and SP-36 are needed. The available Si varied widely from 66 to 583 mg kg−1. Using the critical level of 300 mg SiO2 kg−1, the paddy soils derived from intermediate and basic materials have sufficient Si, while soils from acid materials have insufficient Si for rice crops. Dissolved Al was only observed in irrigation water and solution of soil profile derived from acid volcanic materials. Findings in this study may be used as a baseline to manage nutrients of paddy soils derived from a specific volcanic material.