Overcoming Iron Deficiency Chlorosis in Citrus through Intercropping with Perennial Grass Species

The objective of this experiment was to investigate the influence of intercropping with three different perennial grass species (Festuca ovina L., Festuca rubra subsp. tricophylla L. and Poa nemoralis L.) on the Fe nutritional status of citrumelo ‘Swingle’ (Citrus paradisi Macf. x Poncirus trifoliata), a highly Fe chlorosis susceptible citrus rootstock. One-year old citrumelo plants were grown in pots on calcareous soil-sand mixture under greenhouse conditions and treated as follows: 1) citrumelo plants grown in a monoculture system (without a companion crop); 2) citrumelo plants fertilized with 18.6 mg Fe per plant in form of FeEDDHA; 3) citrumelo plants separately intercropped with the three perennial grass species. These grasses were sown at a rate of 3 seeds cm-2, mowed only one time and allowed to re-grow. The experiment lasted five months. Chlorophyll measurements were performed on the youngest fully expanded leaves in terms of SPAD index and at the end of the experiment leaf chlorophyll content (µg cm-2), leaf length and width and dry weight of young shoots were determined. Intercropping citrumelo plants with F. rubra was effective almost as FeEDDHA in preventing the development of leaf chlorosis and improving their growth compared to the control plants, while those intercropped with F. ovina overcame Fe deficiency symptoms only after mowing/clipping this grass species. The Poa nemoralis did not demonstrate any potential to prevent leaf chlorosis or improve the growth of citrumelo plants. These results indicate that only Fe-efficient perennial grass species can be utilized as an effective ecological orchard floor management practice to improve the Fe nutrition of fruit trees grown on calcareous soils.