A field experiment was conducted at the Coconut Research Institute in Sri Lanka to examine the biological nitrogen fixation potential of three Gliricidia sepium provenances (OFI 14/84, 17/84, 12/86) and a local landrace (designated LL), using the 15N isotope dilution method. There was marked variation in dry matter, total N, nodulation and 15N enrichment among the Gliricidia genotypes (= 0.001), and the dry matter yield of Cassia siamea (syn. Senna siamea), the non-N2 fixing reference plant was higher than for G. sepium. In all cases, highest biomass and total N were aboveground, with roots on average accounting for < 20 % of total dry matter or the total N in plants. Atom % 15N excess was highest in C. siamea, and lowest in OFI 14/84. Although atom % 15N excess was lower in Gliricidia leaves than in the other organs (all of which had similar 15N enrichments), values of % N derived from atmospheric N2 fixation ( % Ndfa) calculated for any individual organ or for the whole plant were similar. This was because the relative distribution of 15N in the different parts of the fixing plant followed the same trend as in the reference plant. There were significant differences (p = 0. 01) in N2 fixation between the Gliricidia genotypes.The values ranged from 17.8 g N tree -I (equivalent to 86 kg N ha -l at 5000 trees ha -1) in OFI 12/86 to 61.7g N tree -~ (equivalent to 309 kg N ha -1) in OFI 14/84. Although most of this variability was due to differences in both % Ndfa and total N in plant, amount of N fixed was more correlated with total N in plant (r = 0.935) than with % Ndfa (r = 0.707). On average, % Ndfa in all three G. sepium provenances and LL was about 55 % or 34.6 g N tree-l (equivalent to some 166 kg N ha-l) in the 9 months within which N2 fixation was measured. This represents a substantial contribution of N into the soil-plant system. SamplingPlants were separated into roots, stem, branches and leaves, which were chopped into 1-5 cm pieces, and then weighed fresh. A 300 g sub-sample was taken for drying at 70°C to constant weight in a forced-draft

Coconut is a major commercial crop of Sri Lanka. Growing a number of other crops in association with coconuts is a widespread practice in all coconut-growing areas of the country. The rationale for the practice is that other crops can profitably be grown between or under the coconuts during the different growth stages of the palms and thus the overall productivity of the land under this long-duration crop can substantially be increased.The paper gives a concise account of the practice in Sri Lanka indicating the crops most commonly grown as intercrops, arrangement of different crops and early research results on the productivity of the intercrops and their effect on coconuts. Adequate supplies of water and labour are the two major inputs needed for the success of the system. Drought, lack of funds, price instability, lack of technical know-how on intercrop management and problems of timely availability of inputs are the major constraints experienced by farmers in expanding intercropping. Research on both biological and socio-economic aspects is needed to overcome these constrainsts and extend this potentially attractive system.

In recent years much attention has been focussed on the importance of moisture conservation practices in coconut lands, particularly in drier parts of the Coconut triangle. Experiments were conducted in mature coconut plantations, to study the effect of various methods of application of coconut husk and coir dust, in lateritic and sandly soils, on the yield of palms. The results revealed that the use of both husks and coir dust was beneficial to coconut production. This was partly attributed to their ability ot retain moisture in the soil and regeneration of more roots per unit area. In terms of copra yield per palm coir dust appeared to be more effective than husk in lateritic soil. Of the different placement methods, husk in pits caused significant improvent in nut and copra yield per palm, while coir dust placed in trenches had the least effect. Furthermore, placing husk or coir dust in pits between two palms appeared to be more effective and economical than in circular trenches round each palm. Based on these results, use of coir dust in pits is recommended as an effective alternative to husk pits, for moisture conservation and in reducing the adverse effects on the palm during the dry period.

No abstract

Coconut is a major commercial crop of Sri Lanka. Growing a number of other crops in association with coconuts is a widespread practice in all coconut-growing areas of the country. The rationale for the practice is that other crops can profitably be grown between or under the coconuts during the different growth stages of the palms and thus the overall productivity of the land under this long-duration crop can substantially be increased. The paper gives a concise account of the practice in Sri Lanka indicating the crops most commonly grown as intercrops, arrangement of different crops and early research results on the productivity of the intercrops and their effect on coconuts. Adequate supplies of water and labour are the two major inputs needed for the success of the system. Drought, lack of funds, price instability, lack of technical know-how on intercrop management and problems of timely availability of inputs are the major constraints experienced by farmers in expanding intercropping. Research on both biological and socioeconomic aspects is needed to overcome these constraints and extend this potentially attractive system.