Nutrient dynamic in cocoa leaves under different nitrogen sources: a reference tool for foliar analysis

Abstract Cocoa is a crop in increasing demand and cultivated worldwide. However, basic information concerning the movement of nutrients in leaves over time is still unknown, and methods to find an optimal time to collect a sample are still ambigu-ous. The present work focused on describing the movement of foliar nutrients (N, P, K, Ca and Mg) in productive 5-year-old cocoa clone CCN51 plants at the same dose of 114.8 kg ha-1 under different sources of nitrogen fertilization (Urea, calcium ni-trate, ammonium sulfate and a control without application). Samples were taken from the time the leaf reached 70% of its total expansion until 10 months of age. The results indicated that the contents of N, Ca and Mg increased as the leaf grew, remained stable between 116 and 158 days of shoot emergence (DSE) and then decreased at the beginning of the leaf senescence period. While the K and P con-tents decrease from the beginning of the trial until 158 DSE where they are stable until the final stage of leaf life. Around 110 to 120 DSE, the leaves of cocoa CCN51 show a more stable nutritional content, a period in which samples can be collected for leaf analysis.摘要 可可作为需求持续攀升的作物，在全球范围内广泛种植。然而，有关叶片养分随时间迁移的基础信息仍未明确，且确定最优采样时机的方法仍存在模糊性。本研究聚焦于阐明在施氮剂量统一为114.8 kg·ha⁻¹、不同氮源（尿素、硝酸钙、硫酸铵及无氮空白对照）处理下，5年生丰产可可CCN51无性系植株的叶片养分（氮（N）、磷（P）、钾（K）、钙（Ca）、镁（Mg））迁移规律。采样时段覆盖叶片达到总展开度70%时至叶片生长至10月龄的全过程。结果显示：氮、钙、镁的含量随叶片发育逐渐升高，在枝条萌发后116至158天（Days After Shoot Emergence，DSE）期间保持稳定，随后在叶片衰老初期出现下降；而钾与磷的含量自试验启动至枝条萌发后158天（DSE）持续降低，此后直至叶片生命周期末期维持稳定。在枝条萌发后110至120天（DSE）左右，可可CCN51的叶片养分含量更为稳定，此阶段可采集叶片样品用于养分分析。