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

Zunfu Lv,Guoquan Lu

doi:10.3389/fpls.2021.714279

Abstract

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−1) and two sweet potato cultivars, were performed in the Zhejiang Province of China. A new critical leaf K curve (Kleaf) based on the maximum RDM was determined to assess K nutrition in sweet potato and described by the equation . A critical root K curve (Kroot) based on the maximum RDM was also determined to assess K nutrition and described by the equation . The K nutrition index (KNI) was constructed to identify the situations of K-limiting and non-K-limiting treatments. The leaf KNI (KNIleaf) ranged from 0.56 to 1.17, and the root K KNI (KNIroot) 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.

Highlights

Sweet potato (Ipomoea batatas L.) is an essential food crop, and based on its cultivation area and yield, it is ranked as the fourth major food crop after rice, wheat, and corn in China (Ma et al, 2012)
The root dry matter (RDM) of sweet potato gradually increased during the growth period of sweet potato (Figure 1; Table 2)
RDM increased initially and stabilized as the K application rate increased for two sweet potato cultivars

Summary

Introduction

Sweet potato (Ipomoea batatas L.) is an essential food crop, and based on its cultivation area and yield, it is ranked as the fourth major food crop after rice, wheat, and corn in China (Ma et al, 2012). China cultivates sweet potato on a large scale, and the annual average total yield and planting area are ranked first in the world (Tang et al, 2018). Unlike N and P nutrients, K does not become a part of the chemical structure of the plant. K plays many regulatory roles in plant nutrition, i.e., it promotes root growth, activates enzymes, improves photosynthetic capacity, transports sugar and starch, and causes earlier tuber initiation (Liu et al, 2013). Since K application plays a significant role in the distribution and accumulation

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