Effect of organic manures, their biochars and arbuscular mycorrhizae fungi on distribution of zinc chemical fractions in a calcareous soil

Zinc (Zn) is an essential micronutrient that the higher plants require it for normal growth and quality and quantity development. High soil pH, low amount of soil organic matter and high calcium carbonate content are the most important factors that led to a decrease of Zn bioavailability in soil. The aim of this research was to investigate the effects of arbuscular mycorrhizae fungi inoculation and application of two types of organic manures and their derived biochars on distribution of Zn chemical forms in a calcareous soil after corn cultivation using a sequential extraction procedure.
To do this research, appropriate amount of soil from the surface layer (0-30 cm) of a calcareous soil was collected, air dried and passed through 2mm sieve. A factorial experiment as a completely randomized design was performed with three replications under greenhouse conditions. The first factor including organic manure at five levels (without organic manure (C), sheep manure (SM), poultry manure (PM), sheep manure biochar (SMB) and poultry manure biochar (PMB) each at 2 % w/w) and the second factor was fungal inoculation at three levels (non-inoculation (NG), inoculation with Funneliformis mosseae (FM) and Glomus versiform (GV)). Biochars were produced using the pyrolysis of organic manures (500 0C during 4 h) in the limited oxygen conditions. After applying treatments to the soil, corn seeds (Zea mays L.) were planted in plastic pots and held for 10 weeks. Sequential extraction procedure of sing et al. was used to determine the zinc chemical forms in the soil after corn cultivation. This procedure separate the soil Zn into 7 different fractions including: soluble笗Ⅺ砞榹 (WsEx-Zn), carbonatic (Car-Zn), Organic (OM-Zn), Manganese oxide (MnOx-Zn), Amorphous iron oxides (AFeOx-Zn), Crystalline iron oxides (CFeOx-Zn) and Residual (Res-Zn).
The concentration of WsEx and OM fractions of Zn were significantly increased and Zn concentration in AFeOx and CFeOx forms were significantly decreased compared to control by application of fungi treatments. The greatest increase of Zn concentration in WsEx (31.9 %) and OM (12.9 %) forms were observed in the GV treatment. The sequence of effect of various organic treatments application on enhancement of Zn concentration in each chemical forms were different however, the effect of PMB treatment on increasing the concentration of most Zn chemical forms (Car-Zn (81.1 %), OM-Zn (42 %), MnOx-Zn (15 %) and AFeOx-Zn (14.1 %)) was more than the other organic treatments. Distribution of native Zn chemical fractions were as follows: Res >> CFeOx > AFeOx > Car > MnOx > OM > WsEx whereas the distribution of Zn chemical fractions as influenced by application of GV, PM and SMB treatments were changes in this way: Res >> CFeOx > AFeOx > Car > MnOx > WsEx > OM. There were positive and significant correlations between WsEx-Zn, Car-Zn, AFeOx-Zn and CFeOx-Zn fractions with DTPA extractable Zn, which is indicating the effective role of these fractions in the supply of required Zn plant. The results of interaction effects of treatments showed that the effect of simultaneous application of fungi and organic manure on the concentration of each Zn chemical fractions was different and depended on type of organic manure and mycorrhizae fungi applied.
Application of both species of arbuscular mycorrhizae fungi caused the conversion of Zn from less available forms to fractions with more bioavailability in the soil and the effect of the GV species was considerably more than the FM species. Also, Zn added to the soil as affected by application of organic manures, concentrated in fractions with more bioavailability and the effect of the PMB treatment was more obvious than the other treatments.