Too little, too imbalanced: Nutrient supply in smallholder oil palm fields in Indonesia

CONTEXT: Smallholders account for ca. 40% of oil palm area in Indonesia but average yield remains low. Despite higher overall fertilizer use in Indonesia compared with other Southeast Asian countries, poor plant nutrition has been identified as a major factor explaining yield gaps in smallholder oil palm fields and little is known about the underlying management drivers. OBJECTIVE: To assess nutrient management in smallholder fields and identify entry points to narrow the existing yield gap via improved plant nutrition. METHODS: We assessed nutrient balances and gaps for nitrogen (N), phosphorous (P), potassium (K), and magnesium (Mg) and inter-relationships between fertilizer use, leaf nutrient concentration, and yield, using data collected from 977 smallholder fields in Indonesia over two years. RESULTS AND CONCLUSIONS: There was a positive relationship between yield and nutrient rates, especially for potassium (K). Only half of the fields received fertilizer and average nutrient rates in fertilized fields represented 45% (N), 83% (P), 28% (K), and 25% (Mg) of the associated removal with harvested yield. Applied fertilizer was generally rich in N and P, but poor in K and Mg, leading to nutrient imbalances. Additionally, farmers did not follow appropriate practices on fertilizer placement and splits. Improving current fertilizer supply and management is needed to increase smallholder yields and profit. SIGNIFICANCE: Current agricultural and research programs will benefit from re-orienting efforts to improve nutrient management in oil palm as a pathway to narrow yield gaps in smallholder fields, which, in turn, requires strengthening extension services to fill in knowledge gaps and tune subsidy programs to facilitate farmer access to fertilizer sources more suited to the crop.