PCA and fuzzy clustering-based delineation of soil nutrient (S, B, Zn, Mn, Fe, and Cu) management zones of sub-tropical Northeastern India for precision nutrient management.

Understanding the spatial distribution of plant available soil nutrients and influencing soil properties and delineation soil nutrient management zones (MZs) are important for implementing precision nutrient management options (PNMO) in an area to achieve maintainable crop production. We assessed spatial distribution pattern of plant available sulphur (S) (PAS), boron (B) (PAB), zinc (PAZn), manganese (PAMn), iron (PAFe), and copper (PACu), and soil organic carbon (SOC), pH, and electrical conductivity (EC) to delineate soil nutrients MZs in northeastern region of India. A total of 17,471 representative surface (0-15 cm depth) soil samples were collected from the region, processed, and analysed for above-mentioned soil parameters. The values of PAS (0.22-99.2 mg kg-1), PAB (0.01-6.45 mg kg-1), PAZn (0.05-13.9 mg kg-1), PAMn (0.08-158 mg kg-1), PAFe (0.50-472 mg kg-1), PACu (0.01-19.2 mg kg-1), SOC (0.01-5.80%), pH (3.19-7.56) and EC (0.01-1.66 dS m-1) varied widely with coefficient of variation of 15.5-108%. The semivariogram analysis highlighted exponential, Gaussian and stable best fitted models for soil parameters with weak (PACu), moderate (PAB, PAZn, PAFe, SOC, pH, and EC) and strong (PAS, and PAMn) spatial dependence. The ordinary kriging interpolation revealed different distribution patterns of soil parameters. About 14.8, 27.5, and 3.40% area of the region had PAS of ≤15.0 mg kg-1, PAB of ≤0.50 mg kg-1, and PAZn of had ≤0.90 mg kg-1, respectively. About 67.5, and 32.5% area had SOC content >1.00 and < 1.00%, respectively. Soil pH was ≤5.50, and >5.50 to ≤6.50 in 41.7 and 40.3% area of the region, respectively. The techniques of principal component analysis and fuzzy c-mean algorithm clustering produced 6 MZs of the region with different areas and values of soil parameters. The MZs had different levels of deficiency pertaining to PAS, PAB, and PAZn. The produced MZ maps could be used for managing PAS, PAB, PAZn, SOC and soil pH in order to implement PNMO. The study highlighted the usefulness of MZ delineation technique for implementation of PNMO in different cultivated areas for sustainable crop production.

Assessment of heavy metal status and identification of source in soils under intensive vegetable growing areas of Brahmaputra valley, North East India.

This study investigated the content of Cd, Pb, Cr, and Ni in the soils of intensive vegetable growing areas of the Brahmaputra valley, North East India, to assess their status and detect any buildup of metals due to long-term and continuous application of agrochemicals and organic manures. The content of heavy metals was determined in eighty composite surface soil samples (0-20 cm) collected from eight different locations of the valley having a history of more than forty years of vegetable production. This finding is novel as no comprehensive investigation has been done till date in respect of the content of heavy metals in the intensive vegetable growing areas of Brahmaputra valley. The locations are considered free from any pollution caused by industrial effluent or urbanization processes. The investigational data showed that the content of Cd, Pb, Cr, and Ni in the soils ranged from 0.43 to 3.24, 6.00 to 22.90, 3.00 to 15.24, and 3.30 to 14.30 mg kg-1, respectively. The overall mean values of the heavy metals showed a decreasing order of Pb (14.79 mg kg-1) > Cr (8.87 mg kg-1) > Ni (8.37 mg kg-1) > Cd (1.43 mg kg-1). The findings of the study indicated significant enrichment of the metals in the surface soils over the local background values of the elements measured in the C horizon. Though the concentrations of Pb, Cr, and Ni of the soils were well below the reference levels used in different countries, Cd showed distinctly higher value with maximum enrichment level. The soils were categorized as slightly to moderately polluted based on different pollution indices. Based on the ecological risk index, soils were in the low-risk category, but in respect of Cd, most of the soils fell under the moderately risky category. Multivariate analysis suggested the predominance of lithogenic influence on the content of Pb, Ni, and Cr while Cd content bears a distinct signature of the anthropogenic source. The buildup of Cd in the studied soils is a matter of critical concern and needs proper monitoring and management strategies to avoid any potential detrimental effect on soil, crop, and human health.