AUTHOR=Lv Zunfu , Lu Guoquan 

TITLE=A New Curve of Critical Leaf Potassium Concentration Based on the Maximum Root Dry Matter for Diagnosing Potassium Nutritional Status of Sweet Potato

JOURNAL=Frontiers in Plant Science

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2021.714279

DOI=10.3389/fpls.2021.714279

ISSN=1664-462X

ABSTRACT=<p>Critical leaf nutrient concentrations have often been used to diagnose the nutritional status of crops. Determining critical leaf potassium (K) concentrations for the maximum root dry matter (RDM) will provide a reliable means of linking leaf K nutrient concentrations to the yield of sweet potato. Three field experiments, using varying K application rates (0–300 kg K ha<sup>−1</sup>) and two sweet potato cultivars, were performed in the Zhejiang Province of China. A new critical leaf K curve (K<sub>leaf</sub>) based on the maximum RDM was determined to assess K nutrition in sweet potato and described by the equation <inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mrow><mml:mtext>leaf</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>4</mml:mn><mml:mo>.</mml:mo><mml:mn>55</mml:mn><mml:mo>×</mml:mo><mml:mtext>RD</mml:mtext><mml:msubsup><mml:mrow><mml:mtext>M</mml:mtext></mml:mrow><mml:mrow><mml:mo class="qopname">max</mml:mo></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:mn>075</mml:mn></mml:mrow></mml:msubsup></mml:math></inline-formula>. A critical root K curve (K<sub>root</sub>) based on the maximum RDM was also determined to assess K nutrition and described by the equation <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mtext>K</mml:mtext></mml:mrow><mml:mrow><mml:mtext>root</mml:mtext></mml:mrow></mml:msub><mml:mo>=</mml:mo><mml:mn>2</mml:mn><mml:mo>.</mml:mo><mml:mn>36</mml:mn><mml:mo>×</mml:mo><mml:mtext>RD</mml:mtext><mml:msubsup><mml:mrow><mml:mtext>M</mml:mtext></mml:mrow><mml:mrow><mml:mo class="qopname">max</mml:mo></mml:mrow><mml:mrow><mml:mo>-</mml:mo><mml:mn>0</mml:mn><mml:mo>.</mml:mo><mml:mn>087</mml:mn></mml:mrow></mml:msubsup></mml:math></inline-formula>. The K nutrition index (KNI) was constructed to identify the situations of K-limiting and non-K-limiting treatments. The leaf KNI (KNI<sub>leaf</sub>) ranged from 0.56 to 1.17, and the root K KNI (KNI<sub>root</sub>) ranged from 0.52 to 1.35 during the growth period of sweet potato. The results showed that the critical leaf K concentration curve can be used as an accurate leaf K status diagnostic tool at critical growth stages that connected leaf nutrient concentration and sweet potato tuber yield. This K curve will contribute to K management of sweet potato during its growth period in China.</p>