Management of nutrients for efficient use in small holder oil palm plantations

In the Ophir nucleus estate smallholder scheme in West Sumatra, smallholders have produced larger yields than the nucleus estate since harvest began due to the use of more intensive management techniques which were extended to farmers through a co-operative management system. Although smallholders work under very different management constraints and opportunities compared to large scale estates, very little work has been done to adapt agronomic techniques developed by the estate sector for use in intensively managed oil palm smallholder plantations. Mineral fertilizers represent the largest production cost in mature oil palms but a large proportion of total nutrient uptake may be cycled in crop residues. In the Ophir project, fertilizers were applied over weeded circles which represent 20 % of the soil surface and pruned fronds were stacked in heaps along alternate inter-rows covering 12 % of the soil surface. A further 8% of the soil surface was occupied by harvesting paths used for the transport of fruit bunches and no fertilizer or mulch was applied to the remaining 60 % of the soil surface. The effective rate of nutrient application in both palm circles and the frond stack was large. Soil analysis showed that whilst the concentration of exchangeable K and Mg was increased in soil in the circle zone, the application of urea resulted in reduced soil pH and large losses of Ca due to leaching. The concentration of exchangeable K and Mg was maintained in soil beneath the frond stack where the application of pruned fronds resulted in a marked increase in the concentration of exchangeable Ca and reduced P adsorption. Soil bulk density and soil resistance was increased in the unamended path soil where the concentration of soil exchangeable K was reduced. The rate of water infiltration into the soil was reduced in the path and circle zones but increased in the frond stack compared with untreated soil, The results from a pot experiment in which Pueraria phaseoloides was grown in soils from the palm circle, frond stack and path zones showed that differences in soil chemical properties found by soil analysis were large enough to produce differences in plant growth and nutrient uptake. The root length density of tertiary and quaternary roots was found to be larger in amended soil in the circle and frond stack zones and smaller in the unamended soil in the path zone, where soil had been disturbed by the frequent traffic of harvesters and laden wheelbarrows. Results suggest more efficient nutrient use could be achieved by extending the ameliorative effect of pruned fronds from 20 % to 75 % of the soil surface and, in subsequent years, mineral fertilizer broadcast over the entire soil area.