Nitrogen Budget in a Pineapple Crop Growing in the Orinoco Lowlands

Abstract

Field measurements showed the nitrogen (N) inputs and output of a fertilized pineapple crop [Ananas comosus (L.) Merr. c.v. Red Spanish] growing in the Orinoco llanos during consecutive seasonal courses. The process rate changed with growth life‐cycle stages and seasonal conditions. The N accumulated by pineapple over the growing period was 226 kg N ha−1. It depended on the available N in the soil and the timing of split application of N fertilizer. Detailed monitoring of plant N‐accumulation rate showed a maximum rate (3.20 kg N ha−1 d−1) at the harvesting time. The N‐harvested ratio and N‐use efficiency were 0.27 and 138 g g−1, respectively. The calculated N‐mineralization rate of the soil was 167 kg N ha−1 over the life cycle. The fate of fertilizer N applied to pineapple was determined in microplots using urea labelled with 9.634% atom excess 15N. Fertilizer N recovery accounted for 48% of the applied 15N. The corresponding fractions of 15N recovered in the soil were 0.16 for the 0.0‐ to 0.3‐m depth and 0.01 for the 0.3‐ to 0.7‐m depth. The unrecovered fertilizer N in this study (34%) was largely due to volatilization (20% of the fertilizer) and denitrification (1.2%). Volatilization was shown to be greatly influenced by the seasonal conditions, namely the volumetric soil water content. In the pineapple field, monitored N input exceeded N output by 134 kg N ha−1, which is likely to lead to maintenance of soil N. Furthermore, utilization of N from crop residues input (164 kg N ha−1) has repercussions for the sustainable use of the Savanna Oligotrophic soils.