Assessment of Soil Fertility Index on Various Soil Types in Rice Fields Using Principal Component Analysis in Tikung District, Indonesia

Background: Soil fertility is key determinant of sustainable and productive rice cultivation and may vary according to soil type and irrigation systems. This study aimed to assess the Soil Fertility Index (SFI) of paddy fields under different soil types and irrigation systems in Tikung District, Lamongan Regency, Indonesia. Methodology: A survey using purposive sampling was conducted at 32 observation points representing four soil types: Typic Endoaquerts, Haplustalfs, Haplustepts, and Haplusterts, under technical and semi-technical irrigation systems. Soil samples were collected from depths of 0–30 and 30–60 cm, resulting in 64 samples. Soil pH, Cation exchange capacity, Aase saturation, Available phosphorus, Exchangeable potassium, and Soil organic carbon were analyzed. Principal Component Analysis was used to determine the contribution of soil properties and derive weighting factors for SFI calculation. Findings: SFI values ranged 0.53 to 0.90, classified into moderate and high fertility categories. Typic Endoaquerts and Haplustalfs exhibited the highest fertility status, whereas Typic Haplustepts showed the lowest. Paddy fields under technical irrigation generally had higher SFI values than those under semi-technical irrigation. Spatial analysis showed that 861.48 ha (19.7%) had high fertility, while 3,507.52 ha (80.28%) was classified as moderate fertility. Soil organic carbon was identified as the primary limiting factor across most locations. Contribution: The findings demonstrate that soil type and irrigation systems are associated with variation in soil fertility status and provide field-based information for developing site-specific soil fertility management strategies and particularly highlight the importance of improving soil organic carbon management to support sustainable rice production.