Phosphorus Acquisition and Utilization Efficiency in Thomson Navel Orange Grafted on Three Rootstocks in Two Different Soils from Mazandaran Province

The objectives of this study were to evaluate P acquisition efficiency (PAE) and internal phosphorus (P) utilization efficiency (PUE) in Thomson Navel Orange (Citrus sinensis L. Osbeck.) grafted on three rootstocks in two soils. For this purpose, a pot experiment was conducted in a completely randomized design using factorial arrangement in three replications. Treatments consisted of two levels of P (0, 100 mg/kg) and three rootstocks of citrus (sour orange, Swingle citrumelo, and Troyer citrange) and two soil types with different percentage of CaCO3. (CaCO3% in soil “1” and “2” were 16% and 2.3 %, respectively). Eighteen months after planting seedlings in pots, plants were harvested and plant indices including dry weight and P uptake were measured. In addition, PAE and PUE were determined. The results of this study showed that shoot dry weight of Thomson Navel Orange on sour orange, citrumelo and citrange was significantly increased in the two studied soils following P application (p < 0.05). After application of P fertilizer, the highest dry weight of shoots was found for Thomson Navel Orange on sour orange (74%) in soil “1”; and on citrumelo rootstock (49%) in soil “2”. When P supply was deficient, Thomson Navel Orange on sour orange rootstock in the soil “1”, and on citrange and sour orange rootstocks in the soil “2” were more efficient in P acquisition than other rootstocks. With an adequate P supply and based on PUE, Thomson Navel Orange on sour orange rootstock in the soil “1”, and Thomson Navel Orange on citrange and on sour orange rootstocks in the soil “2” were more efficient in internal P utilization than other rootstocks. The results showed that the choice of an efficient rootstock in P uptake depends on the soil condition and is site-specific. In order to improve the performance of citrus seedlings in the studied areas, it is recommended either to use a P- efficient rootstock in these areas or, if it is not possible to use an efficient rootstock due to soil and climatic constraints, use P fertilizer based on the soil available phosphorus.