Zinc Deficiency in Rainfed Wheat in Pakistan: Magnitude, Spatial Variability, Management, and Plant Analysis Diagnostic Norms

Abstract

Zinc (Zn) deficiency is a widespread micronutrient disorder in crops grown in calcareous soils; therefore, we conducted a nutrient indexing of farmer-grown rainfed wheat ( Triticum aestivum , cv. Pak-81) in 1.82 Mha Potohar plateau of Pakistan by sampling up to 30 cm tall whole shoots and associated soils. The crop was Zn deficient in more than 80% of the sampled fields, and a good agreement existed between plant Zn concentration and surface soil AB-DTPA Zn content ( r =0.52; p <= 0.01). Contour maps of the sampled areas, prepared by geostatistical analysis techniques and computer graphics, delineated areas of Zn deficiency and, thus, would help focus future research and development. In two field experiments on rainfed wheat grown in alkaline Zn-deficient Typic Haplustalfs (AB-DTPA Zn, 0.49-0.52 mg kg(-1)), soil-applied Zn increased grain yield up to 12% over control. Fertilizer requirement for near-maximum wheat grain yield was 2.0 kg Zn ha(-1) , with a VCR of 4:1. Zinc content in mature grain was a good indicator of soil Zn availability status, and plant tissue critical Zn concentration ranges appear to be 16-20 mg kg(-1) in young whole shoots, 12-16 mg kg(-1) in flag leaves, and 20-24 mg Zn kg(-1) in mature grains.