Prediction of nitrogen uptake by winter wheat (Triticum aestivum L.) by measurement of superior stem number and leaf color value, for decision-making regarding additional nitrogen fertilization

Abstract

To develop a technology to adjust the amount of additional nitrogen (N) fertilization after the flag leaf stage for the new winter wheat (Triticum aestivum L.) cultivar “Kitahonami”, we carried out the following. First, we defined the “superior stem” at the flag leaf stage (a stem whose auricle height is greater than 10 cm) and examined its suitability as an index. Second, we attempted to predict N uptake by the wheat at the flag leaf stage using the growth index [GI, superior stem number (m−2) × leaf color value]. Third, we analyzed the possibility of predicting the final N uptake by wheat at the mature stage from the N uptake at the flag leaf stage.The superior stem number at the flag leaf stage had a significant positive correlation with the spike number at the mature stage (r = 0.70, n = 169, p < 0.01). From the regression equation, it was estimated that a spike number of 700 m−2 was equivalent to a superior stem number of 900 m−2, which can also be used as an index to help prevent overabundance of stem numbers, causing lodging of Kitahonami wheat. The GI was closely related to N uptake at the flag leaf stage (r = 0.86, n = 268, p < 0.01). This indicates that the GI, which considers both the N content and the volume of the crop body, is suitable for predicting N uptake by wheat. N uptake at the mature stage was closely associated with N uptake at the flag leaf stage (r = 0.77, n = 147, p < 0.01), except in the case of soil having subsoil with unusually high N fertility. Excluding this case, N uptake at the flag leaf stage can be used to predict N uptake at the mature stage. On the basis of these results, we propose a method to predict N uptake by Kitahonami wheat at the mature stage and to decide the additional amount of N fertilizer required.