The effects of increased phosphorus application on shoot dry matter, shoot P and Zn concentrations in wheat (Triticum durum L.) and maize (Zea mays L.) grown in a calcareous soil

Zinc (Zn) deficiency is a worldwide nutritional problem resulting in significant reduction in crop yields. It is often observed in calcareous soils and also after heavy doses of phosphorus (P) fertiliser applications, the latter being termed P-induced Zn deficiency. For management purposes, it is important to understand how crops with different root architecture would respond to P-induced Zn deficiency. This glasshouse study was aimed at determining the effects of increased P application on shoot dry matter, shoot P and Zn concentration in wheat and maize grown in a calcareous soil supplied with five rates of P (0, 30, 60, 90 and 120 mg kg(-1) soil). Compared to the control treatment, increasing soil P supply increased shoot P concentration (2.7 - 3.0 fold), while decreased shoot dry matter (10 and 23%) and shoot Zn concentration (75 and 82%) (wheat and maize, respectively). In wheat, the reduction in shoot dry matter was associated with Zn concentrations below the critical level indicating P-induced Zn deficiency as being the main cause of reduced shoot growth. In maize, the reduction in shoot dry matter was accompanied by higher than adequate shoot P concentrations and lower than adequate shoot Zn concentrations suggesting P toxicity and Zn deficiency as the main contributing factors for reduced shoot growth. The results suggest that heavy applications of P fertilizers can induce not only Zn deficiency but also P toxicity depending on the crops thus P application rates should be chosen carefully.