Micronutrients in Soils Suitable for Proteas in Tenerife (Canary Islands)

Abstract

The cultivation of Proteas is proving to be an excellent alternative in the middle and high zones (from an altitude of 300 to 400 meters upward) of the island of Tenerife (Canary Islands). Until now, this area has been devoted to production for the domestic market, and represents more than 70% of arable land. Symptoms of micronutrient deficiency have been observed in crops in these zones and adequate information on micronutrient requirements of the Proteaceae family is lacking. This work was undertaken to verify the soil availability of Cu, Fe, Mn, and Zn in order to assess the micronutrient status of the Proteaceae.

Cu concentration in most samples (86.5%) ranged from 1-10 mg L-1 Cu, which are normal values in agricultural soils; 22.1% of soils could be considered marginal for some crop types, and almost 6% had contents below 1 mg L-1, a concentration that is critical for this micronutrient. The frequency distributions diagram for available Zn levels indicated that 6.4% of the soils presented Zn deficiency conditions (< 0.5 mg L-1) for most crop plants, and also for Leucadendron, while 16.8% of the soils were potentially deficient or were included in a marginal zone (0.5 to 1.0 mg L-1). Values higher than 10 mg L-1, considered to be excessive in available Zn, appeared in 19.9% of our soils. Only a 10.6% of samples had Fe contents below 30 mg L-1, a level considered critical by FAO. The majority of soils (84.3%) showed available Mn levels acceptable for plants (between 5 and 140 mg L-1); only 0.3% of the soils had Mn levels below 2 mg L-1 and 2.5% of the soils ranged from 2 to 5 mg L-1, levels that are deficient to marginal. Marked differences in Cu, Zn, Fe and Mn contents between the north and south zones were found. The northern zone had considerably higher levels of these micronutrients than the southern zone. Various correlations between some soil parameters and the micronutrients were tabulated.