Abstract
Palm oil is currently the most important vegetable oil in the world, and Indonesia is the world’s largest producer. Oil palm plantations are an important source of revenue, but rapid expansion has led to deforestation and loss of biodiversity. Forty per cent of the plantation area in Indonesia is owned by smallholders, whose yields are relatively poor. The objective of this thesis was to investigate the yield gaps and agronomic practices in Indonesian smallholder oil palm plantations, with a focus on fertiliser application, and to propose and test better management practices that can contribute to sustainable intensification. The research consisted of an in-depth literature review, several surveys, the collection of samples in smallholder plantations, and a three-year experiment with 14 smallholder farmers.
In yield gap analysis, three yield levels are recognised: potential, limited, and actual yield. The potential yield in a plantation is determined by radiation, CO2 concentration, temperature, planting material, culling, planting density, pruning, pollination, and crop recovery (harvesting). The yield-limiting factors are rainfall, irrigation, soil, waterlogging, topography, slope, and nutrition. The yield-reducing factors are weeds, pests, and diseases. In smallholder plantations, the yield gap is mostly explained by poor planting material, poor drainage, sub-optimal planting density, poor culling (leading to large variability and the presence of unproductive palms), infrequent harvesting, soil erosion, poor nutrient management, and rat damage, but the effects of these factors on yield vary depending on local conditions.
The survey data showed clear evidence of insufficient and unbalanced fertiliser applications, and visual nutrient deficiency symptoms were observed in many plantations. Leaf sample results showed that 57, 61 and 80% of the plantations in Jambi and Sintang were deficient in N, P and K, respectively. In Riau, 95, 67 and 75% of the plantations were deficient in N, P and K. The implementation of better management practices (including harvesting, weeding, pruning, and nutrient application) in 14 smallholder fields for three years resulted in palms with significantly larger leaves and heavier bunches compared with palms under farmer management, but improvements in yield were small and not statistically significant, and financial returns on better practices were negative. Possible causes of the small yield response were good starting yields, increased inter-palm competition for sunlight, and environmental constraints (particularly the 2015 El Niño event and waterlogging in Jambi).
On the basis of our findings on yield gaps, nutrient limitations and better practices, we discuss how Indonesian smallholders may be supported to achieve sustainable intensification at a larger scale, and we reflect on the broader implications of our findings for a future supply of truly sustainable palm oil.