Macro-nutrient uptake by cocoa seedlings (Theobroma cacao L.) as influenced by clone and soil-applied nitrogen levels

Clonal cocoa (Theobroma cacao) seedlings are used in national rejuvenation programs for cocoa farmers in Indonesia. However, the effects of nitrogen fertilization in clonal cocoa are poorly understood. Therefore, we evaluated the effect of clones and nitrogen addition to the soil on macro-nutrient concentration and uptake by young seedlings. Ten different clonal cocoa seedlings were grown for five months in pots and arranged in a nursery of the Indonesian Coffee and Cocoa Research Institute (ICCRI), Jember, Indonesia. Each clone received two N treatments (0 and 2.3 g N applied at the beginning of the experiment). A factorial randomized block design was used with four replications. Plant tissue macro-nutrient concentration and uptake were investigated. We found a significant (P<0.05) clonal effect on P, K, and Mg concentration in the shoots. Clones also significantly (P<0.05) affected root P and Mg uptake as well as shoot Mg uptake. N treatments resulted in a significant (P<0.001) increase in N and Ca concentrations in both roots and shoots. However, the N treatment significantly (P<0.001) reduced root P, shoot P and shoot Mg levels. Overall, root uptake of N, Mg and Ca significantly (P<0.001) increased as a result of the N treatment. Similarly, shoot uptake of N, P, K, Mg, and Ca were significantly higher (P<0.001) in plants that had received N compared to those that had not. However, root P uptake was significantly (P<0.05) lower in plants with N compared to plants without N. The significant clone effects in P, K and Mg uptake in this study suggests a genotypic variability in macro-nutrient uptake by cocoa seedlings. N fertilization has significant effects on the macro-nutrient uptake of cocoa seedlings.