Impact of Continuous Fertilization on Heavy Metals Content in Soil and Food Grains under 25 Years of Long-Term Fertilizer Experiment

ABSTRACT

In the present investigation, an attempt was made to determine the direct effects of fertilizers on various soil properties like acidification, organic matter content, the content of essential and toxic trace metals in soils and food grains under long term (>25 years) fertilizer experiment. Soil and plant samples were collected from Bengaluru center of All India Coordinated Research Project on Long-Term Fertilizer Experimental site in the sub-regions AESR 8.1 of India, with the treatments e.g. control, 100% N, 100% NP, 100% NPK, 150% NPK, 100% NPK + Lime, 100% NPK+ farmyard manure (FYM) at 0 to 60 cm depth with an interval of 15 cm. Laboratory analysis was conducted to know the vertical distribution of heavy metals and micronutrient cations in soil and plant produce by following the standard method. The DTPA soil Zn remained unchanged with the higher rates of N application, i.e. 100% N. There was very little effect of N, NP, and NPK application on the buildup of DTPA-able Zn, Fe, Mn, and Cu content in both the soils. However, the application of NPK + FYM showed a buildup in comparison to control for Fe 10 mg kg⁻¹, Mn 18 mg kg⁻¹, Zn 1.23 mg kg⁻¹, and Cu 0.84 mg kg⁻¹ in soil. Continuous fertilizer application contributed a meager amount accumulation of Cd, Pb, Ni, Co, and Cr in the soil under the finger millet – maize cropping sequence. The estimation of heavy metals in food grains, supposed to come from fertilizers, lime materials applied in soil was also of our concern. All the cited heavy metals were present in the maize and finger-millet grains. Risk assessment to human health (Hazard Quotient, HQ) for the intake of heavy metals through consumption of contaminated food grains was computed and observed that the values of ‘HQ’ for all the crops were far less than unity (<1) and safe for the consumers.

KEYWORDS:

• Heavy metals
• soil
• fertilizer
• food grains
• hazard quotient
• long-term fertilizer experiment

Acknowledgments

The authors express their gratitude to the Ministry of Forest and Environment, New Delhi, for financial support.

Additional information

Funding

This work was supported by the Ministry of Forest and Environment, New Delhi.