Diagnosis of Nitrogen Nutrition in Rice Leaves Influenced by Potassium Levels
Wenfeng Hou, Merle Tränkner, Jianwei Lü, Jinyao Yan, Siyuan Huang, Tao Ren, Rihuan Cong, Xiaokun Li
Abstract
Evaluation of the nitrogen (N) status by leaf color is a kind of classic nutritional diagnostic method. However, the color of the leaves is influenced not only by N, but also by other nutrients such as potassium (K). Two-year field trials with a factorial combination of N and K were conducted to investigate the effects of different N and K rates on soil plant analysis development (SPAD) readings and leaf N, K, magnesium (Mg), and chlorophyll contents. Visual inspections of leaf greenness revealed darker green leaves with the increasing N rates, while paler green leaves with the increasing K rates. Data showed that the SPAD readings, chlorophyll, N and Mg contents, and the chloroplast area increased significantly with the increase of N rates, while declined sharply with the increase of K rates due to the antagonistic relationships between K+ and NH4+ as well as Mg2+. It was also probably that the increase of K promoted the growth of the leaves and diluted the N and Mg content of the leaves. The paler leaf appearances resulted from the application of K may overestimate the actual demand for N in the diagnosis of rice N status, which was not a reliable estimate of N demand and grain yield. The strong antagonistic relationships among K+, NH4+ and Mg2+ should be considered in rice production and fertilization.