Critical levels and sufficiency ranges for leaf nutrient diagnosis in cowpea grown in the Northeast region of Brazil

ABSTRACT Proposing sufficiency ranges and critical levels is an important technique for correct evaluation of leaf nutrient diagnosis. In this study, the objective was to propose critical levels and sufficiency ranges of macro- and micronutrients for the diagnostic leaf of cowpea, collected at flowering, with the results of macro- and micronutrients and productivity in the Northeast of Brazil. The critical level was calculated by the reduced normal distribution and by the boundary line method, which was also used to generate sufficiency ranges. For the critical level by reduced normal distribution, the relationship of the nutrients with 90% of maximum productivity was adopted. For the boundary line, the relationship of the nutrients that are in the upper line of a dispersion diagram was considered. The critical levels by reduced normal distribution for nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), copper (Cu), iron (Fe), manganese (Mn) and zinc (Zn) are: 35.3 g kg-1, 1.8 g kg-1, 20.5 g kg-1, 11.1 g kg-1, 2.6 g kg-1, 3.2 mg kg-1, 105 mg kg-1, 89 mg kg-1and 22 mg kg-1, respectively. However, the critical levels generated by the boundary line for N, P, K, Ca, Mg, Cu, Fe, Mn and Zn are 39.5 g kg-1, 2.3 g kg-1, 21.2 g kg-1, 11.3 g kg-1, 2.9 g kg-1, 4.2mg kg-1, 142 mg kg-1, 143mg kg-1 and 24 mg kg-1, respectively. The sufficiency ranges by the boundary line method, to achieve 95% of maximum productivity, are equivalent to 34.4-44.7g kg-1, 1.7-2.9 g kg-1,18.6-23.6 g kg-1,8.8-13.7 g kg-1,2.3-3.5 g kg-1,3.1-5.4 mg kg-1,73-210 mg kg-1,104-181 mg kg-1 and 22-27 mg kg-1 for N, P, K, Ca, Mg, Cu, Fe, Mn and Zn, respectively.

摘要 确定养分适宜范围与临界值，是精准开展叶片营养诊断评估的核心技术手段。本研究以巴西东北部地区豇豆开花期采集的诊断叶片为研究材料，结合其大量元素、微量元素含量及产量数据，旨在明确该作物叶片大量与微量元素的临界值及适宜范围。本研究分别采用减正态分布法与边界线法计算养分临界值，其中边界线法同时用于生成养分适宜范围。采用减正态分布法时，以养分含量与90%最高产量的对应关系作为判定依据；采用边界线法时，则以散点图上边界线对应的养分含量关系为判定标准。通过减正态分布法得到的氮（N）、磷（P）、钾（K）、钙（Ca）、镁（Mg）、铜（Cu）、铁（Fe）、锰（Mn）及锌（Zn）临界值依次为：35.3 g·kg⁻¹、1.8 g·kg⁻¹、20.5 g·kg⁻¹、11.1 g·kg⁻¹、2.6 g·kg⁻¹、3.2 mg·kg⁻¹、105 mg·kg⁻¹、89 mg·kg⁻¹及22 mg·kg⁻¹。然而，通过边界线法得到的上述各养分临界值依次为：39.5 g·kg⁻¹、2.3 g·kg⁻¹、21.2 g·kg⁻¹、11.3 g·kg⁻¹、2.9 g·kg⁻¹、4.2 mg·kg⁻¹、142 mg·kg⁻¹、143 mg·kg⁻¹及24 mg·kg⁻¹。采用边界线法、以达到95%最高产量为目标，得到的氮、磷、钾、钙、镁、铜、铁、锰及锌适宜范围依次为：34.4~44.7 g·kg⁻¹、1.7~2.9 g·kg⁻¹、18.6~23.6 g·kg⁻¹、8.8~13.7 g·kg⁻¹、2.3~3.5 g·kg⁻¹、3.1~5.4 mg·kg⁻¹、73~210 mg·kg⁻¹、104~181 mg·kg⁻¹及22~27 mg·kg⁻¹。