Zinc fractions and nutrition of maize (Zea mays L.) as affected by Olsen-P levels in soil

Zinc (Zn) deficiency with large phosphorus (P) application for plant nutrition is commonly an investigated antagonistic interaction. However, required P fertilization for optimum grain yield with desirable grain Zn content is a major constraint owing to poor understanding of relationships between P application rates, residual P accumulated in the soil after surplus fertilizer P applications, and soil Zn transformations together with plant Zn uptake. Results showed that the effect of added P fertilizer was more pronounced with decreasing availability of water-soluble and exchangeable (WS), specifically adsorbed (SPAD), Mn-Oxide bound (MnOX), amorphous Fe-oxides (FeOX), and organically bound (OM) zinc fractions in 'high' P (22.5-50 kg ha(-1)) soils than 'medium' (12.5-22.5 kg ha(-1)) and 'low' P (< 12.5 kg ha(-1)) soils. Further, the addition of farmyard manure (FYM) significantly improved the availability of all the soil Zn fractions. Plant Zn uptake decreases with P additions of 39 and 52 kg P ha(-1) by 20 and 26% in 'high' P soils, 15 and 26% in 'medium' P soils, and 6 and 12% in low P soils respectively, indicating higher Olsen-P levels restricts the translocation of Zn from roots to above-ground parts of the plant. Maximum grain Zn content averaging 30 mg kg(-1) over three years was observed at Olsen-P level of 21.5 mg kg(-1). Path analysis highlighted that extractable OM and MnOX fractions in 'high' P soils, WS and FeOX fractions in 'medium' P, and WS fractions in low P soils were the most prevalent fractions that contribute towards Zn uptake of maize plants.