Long-term effect of organic/inorganic input on the distribution of zinc and copper in soil fractions under a rice – wheat cropping system

Abstract

A long-term experiment under a rice – wheat system was used to investigate the effect of organic and inorganic fertilizer application on the zinc (Zn) and copper (Cu) in various soil fractions. Levels of Zn and Cu in the different fractions were comparable to the initial levels after 7 years of continuous cropping without any fertilization. However, addition of organic manures in the absence of inorganically applied Zn or Cu increased the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions of Zn and Cu over their initial levels. Application of N₁₅₀P₇₅K₇₅Zn₂₅ + farmyard manure (FYM) or N₇₅P_37.5K_37.5Zn₂₅ + green manure lowered the Zn content in the carbonate and crystalline iron oxide fractions, with a concomitant increase in Zn associated with the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions compared to the N₁₅₀P₇₅K₇₅Zn₂₅ treatment alone. Levels of Cu in the water-soluble plus exchangeable, organic fraction and the manganese oxide and amorphous iron oxide fractions were significantly higher in the N₁₅₀P₇₅K₇₅Zn₂₅ + FYM, N₁₅₀ + press mud and N₇₅P_37.5K_37.5Zn₂₅ + green manure treatments than in the N₁₅₀P₇₅K₇₅Zn₂₅ treatment alone. A maximum increase in Cu of 1.4 – 1.5-fold was observed in the organic fraction. The residual fraction, and amorphous and crystalline iron oxide fractions constituted the major proportion of total Zn and Cu in soil.

Keywords:

• Long-term
• rice – wheat
• organic manures
• zinc
• copper
• chemical fractions