The Root-System of Agave Sisalana in Certain East African Soils

Abstract

The results of root investigations of Agave sisalana in various soils are given. Excavation was carried out by the water method since this was the most suitable for use with only African assistants. A triangular prism with apex at the base of the plant and base about 18 in. wide at 10 or more feet away was excavated mainly by washing and it was found that such a section gave an accurate picture of the root system. The size of the root system of the average 5-year-old sisal plant was shown to be larger in the soils examined than might have been expected from the scanty literature consisting in the main of a few generalizations. The plants examined had many roots over 5 ft. in length, with a maximum radial spread of bearers (i.e. main suberized roots carrying feeders) to at least 10 ft. from the base. The main concentration is usually in the top 24 in. but roots have been found at 6 ft. down, the water-retaining properties of the soil largely influencing the depth of distribution. There is thus considerable root competition, especially in dry soils, under the spacing used in East African planting (8 x31/2 ft.) which is intensified when weeds are allowed to grow. Surface clean weeding only is advocated since deep cultivation injures the sisal roots. Roots grow well on soils with a pH 9.15 to at least pH 4.75. A high concentration of alkali is shown to upset the plant nutrient balance. A badly drained soil is fatal and in certain soils the presence of a water table has caused the death of roots even when a height of 12-18 inches above it.