Identifying sulfur deficient fields by using sulfur content; N:S ratio and nutrient stoichiometric relationships in soybean seeds

Sulfur (S) fertilization has increasingly become an important issue in crop management. In Argentina S deficiencies have been reported, but there has been no success in finding soil tests for predicting soybean response to S fertilization. The objectives of this study were to: (i) evaluate seed S and N:S ratio as a tool for identifying S deficient soybean crops in field conditions and (ii) determine shifts in stoichiometric relationships among nitrogen (N), phosphorus (P) and S in soybean seeds which can be used for identifying S responsive sites under field conditions. Seed samples from 20 field experiments designed to explore response to S fertilization in soybean were collected in a large area in the Argentinean Pampas region. Seed yield (SY) and P (%P), S (%S) and N (%N) concentration in seeds were determined. Different data analyses were tested in order to find an S deficiency index. Moderate SY responses to S fertilization were observed in the present study (i.e. relative SY was never below 75%). seed S concentration increased in response to S fertilization in most responsive sites, and N:S ratio was governed by variations in seed S concentration. Stoichiometric relationships were more accurate for identifying S responsive sites than using single variables (e.g. seed S concentration or N:S). The isometric variations among N, P and S suggest that the accumulation of these nutrients is proportional in seed tissue. A significant increase in the intercept of the stoichiometric relationship between N and S in S deficient crops was observed. An S deficient index (SDI) was calculated based on this difference that can be used as a diagnostic tool for identifying S responsive sites in soybean. The present study shows a novel approach for using stoichiometric concepts in fertilizer management in soybean. Fil: Salvagiotti, Fernando. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Oliveros; Argentina Fil: Ferraris, Gustavo Nestor. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Quiroga, Alberto Raul. Instituto Nacional de Tecnología Agropecuaria. Centro Regional La Pampa-San Luis. Estación Experimental Agropecuaria Anguil; Argentina Fil: Barraco, Mirian Raquel. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires. Estación Experimental General Villegas; Argentina Fil: Vivas, Hugo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Santa Fe. Estación Experimental Agropecuaria Rafaela; Argentina Fil: Prystupa, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina Fil: Echeverria, Hernan Eduardo. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina Fil: Gutiérrez Boem, Flavio Hernán. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones en Biociencias Agrícolas y Ambientales; Argentina