Comparative study of a Zn-enriched post-methanation bio-sludge and Zn sulfate as Zn sources for a rice–wheat crop rotation

Abstract

A field experiment was carried out during 2005–2007 to compare the efficacy of Zn-enriched post-methanation bio-sludge (ZEMB, 4.4% Zn) and ZnSO4 (ZSH, 22% Zn) as Zn source to rice (Oryza sativa L.)—wheat (Triticum aestivum L.) rotation. A new Zn source (ZEMB) contained most of the Zn (98.4% of total Zn) in citrate-soluble form as compared to ZSH which had all Zn in water-soluble form. Chemical speciation of Zn in the aqueous solution of both fertilizers revealed that 85.8% of water-soluble Zn present in ZEMB existed as complexes of dissolved organic matter. In the field experiment, application of ZEMB at 5 kg Zn ha−1 to I-year rice increased the grain yields of rice and wheat in both years significantly over the control while application of ZSH at 5 kg Zn ha−1 to I-year rice increased only grain yields of I- and II-year rice (first year and second year, respectively). The magnitude of increase in grain yields was also higher with ZEMB than with ZSH. Application of ZEMB at 5 kg Zn ha−1 to I-year rice maintained significantly higher concentrations of Zn in the flag leaves of rice and wheat in both years, in the grains of I- and II-year rice, and also in the straw of I-year rice than ZSH applied at an equivalent dose. Total Zn uptake values for I-year rice and wheat and II-year rice, apparent recovery of applied Zn and also DTPA-extractable Zn in soil were significantly higher with ZEMB at 5 kg Zn ha−1 than with ZSH at an equivalent dose.