Soil Thickness Modifies the Nitrogen Sufficiency Index in Barley and Wheat

Abstract

In barley and wheat, remote sensing of nitrogen through the normalized differential vegetation index (NDVI) enable the estimation of nitrogen deficiencies. The relationship between the nitrogen sufficiency index (NSI) and the economic optimum nitrogen rate (EONR) has enabled NSI threshold definition for diagnostic models adjustment. The objectives of this study were to quantify the differences in yield formation and its relationship with NSI in barley and in wheat under contrastingsoil depth conditions. Nitrogen fertilization experiments were performed in 16 barley and wheat production sites located in the Pampas region of Argentina. Half of the experiments took place in (i) deep Typic Argiudolls and the other half were conducted in (ii) shallow Petrocalcic Hapludolls and Petrocalcic Argiudolls. The NDVI was measured at early growth stages, NSI was calculated, and yields were quantified. The EONR was associated with NSI values ranging from 0.95 to 0.97 inbarley and from 0.89 to 0.99 in wheat. Soil depth affected NSI only in wheat crops and at higher input-product price ratios (I: P = 6 and 10). The NSI effectively adjusts the nitrogen nutrition status in barley and wheat during their growth cycle. However, its application should account for site specific conditions such as soil depth and economic factors like the inputproduct price ratio.