Assessment of fertility potential for the soils of Northern Brahmaputra valley zone using Principal Component Analysis

An attempt is made to model relationships of soil physical-chemical-hydraulic parameters of 50 rice-growing soils for fertility potential classification under 6 physiographic units of Northern Brahmaputra Valley Zone (NBVZ) of Assam. The physiographic units studied were Old Flood Plain (OFP), Lower Alluvial Plain (LAP), Upper Alluvial Plain (UAP) Lower Piedmont Plain (LPP), Upper Piedmont Plain (UPP) and Structural Hill (SH) soils. Relationships of 27 soil parameters were established using Principal Component Analysis (PCA). The PCs identified are (i) Inherent Potentiality; (ii) Soil Loss; (iii) Nitrozinc; (iv) Cation Exchange; (v) Acidity; (vi) Copper; and (vii) Anionic factors which could explain 81% variability in soil parameters. Based on eigen vectors of PCs, component scores were determined for ranking soils and physiographic units. Dhullie (No. 32) soil ranked first for soil fertility, while OFP soils were most fertile. The ranking of soils was in agreement with analytical values of soil physical-chemical-hydraulic parameters. UPP soils had maximum values for CEC, acidity and anionic factors, compared to LPP soils for copper. The values were maximum for UAP for nitrozinc factor; LAP for soil loss factor; and SH for inherent potentiality. Among 27 soil parameters studied, silt, organic matter, CEC, manganese, field capacity, AWC and clay were found significant and contributed to the total variability. The soil classification would be useful for development of strategies for efficient management of crops under Northern Brahmaputra Valley Zone of Assam.