Submitted to: Journal of Plant Nutrition
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2007
Publication Date: 1/20/2008
Citation: Ribero, M.A., Silva, J.O., Aitken, W.M., Machado, R.C., Baligar, V.C. 2008. Nitrogen Use Efficiency in Cacao Genotypes. Journal of Plant Nutrition. 31:239-249. Interpretive Summary: Nitrogen (N) is one of the most yield limiting nutrients for cacao in many tropical soils. Application of nitrogen fertilizer is essential to achieve reasonable cocoa bean yields, however these result in increased input costs. Planting cacao varieties that are better at utilizing the available nitrogen might help to reduce N fertilizer input costs, but we don’t have enough information to identify which varieties are best. A green house experiment was conducted to evaluate growth response and N use efficiency of two cacao varieties. They responded differently to applied nitrogen, which shows that differences in their ability to use nitrogen do exist. Findings of this research will be useful in cacao breeding programs and could be helpful to design better fertilizer management programs for cacao. Ultimately, such findings will help poor cacao farmers adapt management practices that reduce poduction costs.
Technical Abstract: Cacao (Theobroma cacao L) is mostly grown on soils with low natural fertility. On such soils nitrogen (N) is one of the most yield limiting nutrients for cacao. Information is lacking on N use efficiency in cacao. A greenhouse experiment was conducted to evaluate growth response and N use efficiency by two cacao genotypes. The genotypes used were TSH- 565 and ICS -9 and N rates adapted were 0, 120, 240, 360 and 480 mg N /pot. In both genotypes, increasing levels of applied N improved growth (stem girth, dry wt of shoot and roots and shoot/root ratio), and concentration and uptake of N. Genotypes were differing significantly for stem girth and ICS -9 produced greater stem girth compared with TSH -565. Nitrogen uptake had a linear relationship with root dry weight of two the genotypes. In both genotypes, increasing levels of applied N overall increased N-uptake efficiency (NEFF =N concentration in shoot x shoot/root) but decreased N-use efficiency by shoot and roots (NUE = g dry matter of shoot or root/mg N) and N- use efficiency of carbohydrate (NUEC= mg of total carbohydrates in shoot/ mg of N in shoot). Both genotypes responded differently to applied N despite the existence of low genetic diversity between them. Method used here appears to be a suitable method for identification of cacao genotypes that are efficient in uptake and utilization of N.