Effect of Zinc and Organic Matter Application on Various Zinc Fractions under Direct-seeded Rice in Vertisols

Abstract

A field experiment was conducted to assess the effect of zinc (Zn) with and without organic manure on Zn uptake by direct seeded rice and various Zn fractions in a Vertisol. The field experiment was carried out in two factor randomized block design with three manures i.e. 10 t farmyard manure (FYM), 5 t poultry manure (PM) and 5 t piggery manure (PiM) ha-1 as first factor and four levels of Zn i.e. 0, 1.25, 2.5 and 5 kg ha-1 as ZnSO4 as second factor. Total Zn uptake by rice and its content in grain increased significantly with the increasing levels of Zn as well as application of organic manures. Various fractions of Zn in surface soil increased significantly with the increasing levels of Zn. The Zn content in various fraction varied in the order of water soluble (WS) < exchangeable < complexed < organically bound < occluded and residual. The maximum Zn content was left in residual fraction. The Zn content in fractions like water soluble, exchangeable, complexed and organically bound were comparatively low (below 1 mg kg-1). Various fractions, like WS, exchangeable, complexed, organically bound and occluded Zn together contributed only 3.7% to the total Zn, whereas the rest 96.3% was left in the residual fraction. The available Zn status in soil increased significantly with the levels of Zn and organic manures in the order of PM > FYM > PiM. Increasing levels of Zn and organic manure application increased Zn content in various pools. Occluded and residual fractions of Zn remained unaffected due to the application of either Zn or organic manures. The Zn content in various pools correlated significantly with the yield and total uptake. The use efficiency of Zn increased due to combined application of Zn with organic manures in the order of Zn + PM> Zn + PiM > Zn + FYM > Zn alone while on increasing the dose of Zn, the use efficiency decreased. Zinc use efficiency of rice increased when Zn levels were raised from 1.25 to 2.5 kg Zn ha-1 applied alone or in combination with 10 t FYM but increasing the Zn level to 5 kg Zn ha-1 decreased the Zn use efficiency.