Clonal differences in nitrogen use efficiency and macro-nutrient uptake in young clonal cocoa (Theobroma cacao L.) seedlings from Indonesia

Abstract

Nitrogen (N) is one of the most required nutrients in cocoa production. Unlike in many other crops, there is limited knowledge on genotypic variation in nitrogen use efficiency (NUE) in clonal cocoa. We therefore evaluated the effect of nitrogen application on cocoa NUE in 10 clonal cocoa scions that were top-grafted on 4-month old rootstock seedlings of cocoa clone MCC 02. Grafted seedlings received either 0 or 2.3 g/plant of N at the beginning of the experiment, which lasted for five months and was arranged in a nursery of the Indonesian Coffee and Cocoa Research Institute (ICCRI) in Jember, Indonesia. A factorial randomized block design was used with four replications. We found that clones significantly affected rootstock stem diameter and dry biomass both in roots and shoots. Nitrogen application decreased rootstock stem diameter and root biomass but increased shoot-root ratio. Following the N application, we observed significantly higher N concentration and uptake both in roots and shoots. This higher N concentration and uptake contributed to significantly lower NUE in both roots and shoots. We did not observe clonal differences in N concentration, uptake, NUE in either roots or shoots and ANR (Apparent Nitrogen Recovery). Nitrogen application influenced P, K, Mg, and Ca uptake in both roots and shoots. There was a clonal effect on P, K and Mg uptake and on P and Mg use efficiency in both roots and shoots. This implies that the studied clones vary in their P and Mg nutrient use efficiency but not in NUE.