Nahuel Ignacio Reussi Calvo

Usefulness of Foliar Nitrogen-Sulfur Ratio in Spring Red Wheat

ABSTRACT Sulfur (S) availability indicators are necessary for a rational use of fertilizers. Experiments were carried out to evaluate the sensitivity and stability of nitrogen (N):S ratio in spring red wheat. Yield responses were determined in three replications over five experimental sites. Sulfur application did not increase N concentration in plant, whereas the effect on total S concentration was varied. Results showed 25, 35, 80, and 85% correctly diagnosed samples at stages Z22, Z24, Z31, and Z39, respectively. In treatments without S limitations, a decrease in N:S ratio was observed as the crop cycle advanced. Nitrogen: S ratio differed according to the site; however, these variations tend to decrease as the crop cycle advance. In summary, for spring red wheat, N:S ratio in plant is a useful method for S deficiencies diagnostic from the end of tillering to flag leaf.

Determination of Sulfate Concentration in Soil: Depth of Sampling

To diagnose sulfur (S) deficiency, methodologies based on soil sample analysis and simulation models have been used, all of which require determination of S availability. The objective was to evaluate the possibility of estimating sulfate concentration up to 60 cm deep, using values from soils 0–20 or 0–40 cm deep as predictive variables. A set of data from 22 fertilization experiments on winter and summer crops was used. For wheat, a close association (P < 0.0001) was determined between sulfate concentrations 0–20 and 0–60 cm deep (r2 = 0.88). When the sulfate concentration at 0–40 cm deep was used as predictive variable, the model r2 increased to 0.97. Similar results were obtained for summer crops (r2 = 0.68 and 0.94 for 0–20 and 0–40, respectively). The integration of all 22 experiments showed two linear models (P < 0.0001) to estimate sulfate concentration up to 60 cm deep (r2 = 0.79 and 0.95 for 0–20 and 0–40, respectively). These results help to simplify soil sampling and would enable more use of S diagnostic methods by producers.