Spatial Variability of P/Zn Ratios on Calcareous Soil Under the Wheat Plants (Triticum aestivum)

Abstract

One of the main reasons of available Zn deficiency of the soils is excessive application of phosphorus (P) fertilizers. However, the ratio of P/Zn in the field soil is essential for optimal Zn use by the crops; there is little information concerning this ratio depending on varied soil and plant conditions. In this study, topsoil (0-20 cm), subsoil (20-40 cm) and plant samples were collected from the plots based on a 25 x 25 m grid under the wheat plants. The coefficient of variance (C.V.), kurtosis and skewness values revealed that a great spatial variability occurred in available P, Zn and P/Zn ratio for topsoil. Contour map of site-specific Zn contents indicated that the experimental topsoil had mainly sufficient amounts of available Zn (average 0.85 mg kg^-1), whereas, three dimensional map of Zn concentrations of wheat plants indicated that about 98% of the plants on these soils had a low level of Zn (11-20 mg kg^-1). Significant correlation, r = 0.48 and P < 0.0 I, was also found between the sitespecific P/Zn ratios in the topsoils and P/Zn ratios in the wheat plants. The findings clearly show that the site-specific P/Zn ratio in the field soil was an important factor for maximum Zn utilization by the wheat plants. Hence, fertilization programme based on site specific P and Zn demands of the wheats will increase Zn use efficiency of the plants with proper P/Zn ratios. Contour maps based on proper site-specific samplings will provide more accurate information for balancing P/Zn ratios.