Diagnosis of macronutrient deficiency in Erythrophleum fordii, a nitrogen-fixing rosewood species

Erythrophleum fordii (Caesalpiniaceae; nitrogen fixing species) is one of traditional rosewood species indigenous to Southeast Asia and southern China. Slow growth and symptoms such as leaf discoloration, curling and defoliation were usually observed in the nursery and its young plantations due perhaps to deficiencies of specific nutrients. Here sand culture experiment was conducted for its seedlings to assess their visual foliar symptoms, growth performance and nutrient interaction in response to six macronutrient deficiencies. Leaves of E. fordii seedlings discolored in all treatments of nutrient deficiency, and sizes of both old and young leaves became small under nitrogen (N) deficiency, while only young leaves grew small  under deficiencies of calcium (Ca) and sulphur (S). Seedling growth was inhibited significantly under deficiencies of N, potassium (K) and phosphorus (P) except that P deficiency increased diameter at root collar. The difference of seedling N concentration between –N and control was normally much smaller than those for other nutrient elements because -N seedling could acquire N by nitrogen fixation of nodules under N deficiency. In spite of this, N was still major limiting factor for plant growth under N deficiency. Besides in P deficiency, P was also the major limiting factor under deficiencies of magnesium (Mg), Ca and S, which indicated that P play an important role in nutrient demand and balance for E. fordii. Antagonism or synergism occurred widely between six macronutrients, especially for P, K and Ca, their concentrations increased or decreased in all six deficiency treatments in comparison with the control. The implications of these findings were also discussed with a case study on nutritional diagnosis for a young plantation of this species.