Submitted to: Soil Science and Plant Nutrition (SSPN)
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2005
Publication Date: 11/1/2005
Citation: Baligar, V.C., Fageria, N.K. 2005. Aluminum influence on growth and uptake of micronutrients by cacao.. Soil Science and Plant Nutrition (SSPN). 151:7009-7013. Interpretive Summary: In tropical regions cacao is grown on a wide range of soil types, and most of these soils are leached, acidic and infertile. On such soils aluminum toxicity and deficiencies of micronutrients are major yield limiting factors for cacao. Information is limited concerning the influence of soil aluminum on growth and uptake and utilization of micronutrients by cacao. The results obtained showed that higher soil aluminum levels might reduce cacao growth significantly. Reduction of soil acidity constraints with addition of lime, and application of micronutrients appears to be key factors in improving yield potential of cacao growth on degraded leached tropical soils. These findings are helpful to tropical farmers managing sustainable cacao production on degraded acid soils of the cacao grwoing region of South America.
Technical Abstract: Cacao (Theobroma cacao L) productivity in tropical soils is largely determined by aluminum toxicity and inadequate supply of essential available nutrient. However, information on micronutrient requirements by cacao in acid soils is scarce. A growth chamber experiment was conducted to evaluate soil Al saturation (0.2, 19 and 26 % of CEC) effects on root and shoot growth and micronutrient uptake parameters (concentration, uptake efficiency ratios, influx and transport) by cacao. Root and shoot growth were significantly reduced by higher soil Al saturations, however, root growth was more sensitive to Al toxicity than shoot growth. Critical soil Al saturation (soil Al saturation at which 10% reduction of optimal growth is achieved) for root growth was 2% and for shoot growth it was 15%. Uptake of Cu, Fe, Mn and Zn decreased quadratically with increasing soil Al saturation in the range of 0.2 to 26% but uptake for B increased with increasing soil Al saturation. Among the micronutrients, maximum uptake was for Mn and minimum uptake was for Cu. Micronutrient use efficiency ratio (ER, mg shoot dry wt produced/mg of element in shoot) was in the order of Cu >B > Zn > Fe > Mn. The ER for B, Mn, and Zn increased quadratically and significantly with increasing soil Al saturation. Positive quadratic relations were observed for soil Al saturation and influx of micronutrients with the exception of Fe. The transport of Cu, Fe, Mn and Zn to shoots decreased quadratically with increasing soil Al saturation. Applications of micronutrients are generally required for improving yield potential of cacao in highly weathered tropical soils.