Study of Soil Fertility and Plant Nutrition of Proteas Cultivated under Subtropical Conditions.

摘要

A study of soil physicochemical characteristics and mineral nutrition of four cultivars of Leucospermum cordifolium ('Scarlett Ribbon,' 'High Gold,' 'Veldifre,' 'Sunrise') and Leucospermum patersonii species was carried out along 2 years in commercial protea plantations, distributed throughout a subtropical region (La Palma Island, Canarian Archipelago). Soils presented a slightly acid pH range, whereas organic matter showed suitable values. Generally, available soil phosphorus (P) contents were less than 25 mg kg-1, with high available potassium (K) and calcium (Ca) levels, though the ratio of Ca of the sum of available cations was usually appropriate. Despite the high electrical conductivity (EC) levels (4.31-8.87 dS m-1) determined in some soils, no salinity symptoms were ever detected. Distribution and behavior of foliar nutrients nitrogen (N), P, K, Ca, magnesium (Mg), and sodium (Na) along time showed that nutritional needs varied in some cases among cultivars and species. L. patersonii presented the least N concentration, whereas 'High Gold' and 'Veldfire' had the greatest levels. Data denoted that P requirements were larger in younger plants, during the recovery after pruning, and while new buds developed. 'Sunrise' cultivar stood out for its large foliar levels of P, whereas 'Scarlett Ribbon' and 'Veldfire' had the least K contents. As a general pattern, K decreased in winter samplings. L. patersonii species and the cultivar 'Sunrise' exhibited the highest Ca values, and the same was true for Mg only in the species. A special need for Na appeared in all the cultivars and species studied. L. patersonii and the cultivar 'Sunrise' showed the greatest Na levels. A general stabilization of nutrient concentrations was observed in the fourth, fifth, and/or sixth samplings, so that November is recommended for taking samples for current foliar analysis. In this context, foliar ranges for the studied nutrients are suggested.