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The study was carried out to evaluate the soil water content under four species of nitrogen fixing trees (NFTs) interplanted with coconuts (Cocos nucifera L.) in gravelly soils in Sri Lanka. The NFTs (viz., Calliandra calothyrsus, Leucaena leucocephala, Acacia auriculiformis and Gliricidia sepium) were planted when the coconut palms were 38 years old. Seven years after planting NFTs, the soil water content was monitored weekly during the dry period extending from the base of the coconut palm towards the NFT species, using a neutron moisture meter. Results showed that NFT-interplanted plots had higher water content than the sole stand of coconuts, with the gliricidia- and acacia plots having higher water content than leucaena- and calliandra plots. Water loss from the topsoil (0 to 20 cm depth) in the NFT-interplanted plots was significantly lower than from the bare soil. The NFT species extracted soil water mainly from the 20 to 100 cm layer. Calliandra extracted a significantly higher amount of water from the top soil, leucaena extracted more water from beyond 100-cm depth. Among the NFT-interplanted plots, the acacia and gliricidia plots conserved more water in the soil. |
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