Do silicon levels in the matrix influence the mineral nutrition of Pennisetum clandestinum (Hochst. ex Chiov)?

Abstract

Pennisetum clandestinum (Kikuyu grass, Graminae) is an active Si accumulator growing in altitude in Kenya. To verify the influence of Si on mineral uptake, P. clandestinum was cultivated in two different substrata both with low silicon levels. P. clandestinum growing in organic-rich soils (43.3% organic matter) contained much more Cu, Mn and Zn but less Si in the whole plant and Fe in the roots than species growing in a sandy matrix, indicating that Si does not interfere with the uptake of such nutrients. In 90% of the cases, roots have the highest average values regardless of the type of culture considered. Plants in sand substrates (82.2% sand) exhibited much more Si (particularly roots) than plants in organic-rich soils, despite the high carbonate content of both matrices and the acid pH used in the nutrient solution. The more Si is present in shoots and roots, the less P is detected. N/P ratios of shoots of sand culture confirm a nutrient limitation of P. Shoot biomass in organic-rich soils was approximately two times higher than in sand. Conversely, root biomass in sand was almost twice the average value in organic-rich soils.

Keywords:

• Organic-rich soil cultures
• sand cultures
• micronutrients
• silicon
• biomass
• Pennisetum clandestinum

Acknowledgements

The authors are grateful to Prof. Dr J. Pais, Prof. Dr J. F. S. Oliveira and Eng° Joaquim Simão (F.C.T.), for facilities in the use of laboratories and unconditional support and to Dra. Fátima Figueiredo for revising the manuscript.