Coconut-growing soils of Kerala: 1. Characteristics and classification

Coconut plantations are the major land use systems in Kerala state. The tropical hot humid climate and soils of the state are considered suitable for the palm, with the exception of highlands occurring 600 m above MSL. However, the productivity of coconut is abysmally low in the state with an average productivity of around 40 nuts per year per palm. To find out whether the highly weathered and leached low activity clay soils developed in tropical hot humid climate is responsible for the low yield, an assessment of soil qualities in the coconut-growing soils of the state was made. Six distinct regions of coconut cultivation in the state were identified and delineated based on the variability of agro-climate and soils, viz., Central and Eastern Palakkad, Northern Kerala, Central Kerala, Southern Kerala, Onattukara sandy plains and coastal sandy plains. Soil profiles were studied at representative sites in each region. Investigated morphological features and sampled horizon-wise for the analysis of physical and chemical properties of the soil. Coconut-growing soils of Kerala state are in general deep and well drained, clayey or sandy having good structure permitting rapid transmission of water. The soils of Palakkad, Southern Kerala and Coastal Sandy Plains have near neutral reaction whereas the extensive areas of laterite soils of Northern and Central Kerala and sandy soils of Onattukara were strongly acid and had high levels of KCl extractable aluminium. The acid soils also analysed for low levels of basic cations, potassium, calcium and magnesium. Soils from all regions except Palakkad have low CEC. Surface and sub-soils base status were extremely low for soils of Northern and Central Kerala and Onattukara sandy plain. The soils of Central and Eastern Palakkad were classified as Typic Haplustalfs, Northern Kerala as Plinthic Humults, Central Kerala as Typic Plinthustults, Southern Kerala as Rhodic Kandiustults and the soils of sandy plains as Ustipsamments, according to soil taxonomy.