Co-limitation and stoichiometry capture the interacting effects of nitrogen and sulfur on maize yield and nutrient use efficiency

Nitrogen (N) and sulfur (S) deficiencies, individually and in combination, produce gaps between actual and potential yields in maize (Zea mays L.). Our objectives were to evaluate the effect of N and S status and their interaction on yield gap, and nutrient use efficiency (yield per unit of nutrient supply) using frameworks of co-limitation and stoichiometry. Factorial trials were established combining two N (unfertilized, N-fertilized) and two S (unfertilized, S-fertilized) treatments in five site-years. Yield ranged from 6.7 to 15.4 Mg ha(-1). In a scale from 0 (no stress) to 1 (maximum stress), N stress varied from 0 to 0.67, and S stress from 0 to 0.66. Yield gap varied from 0 to 10 Mg ha(-1), diminished as both N and S stresses reduced, and with higher N-S co-limitation. Both N and S use efficiencies increased with reductions in nutrient stresses and with increases in some of the N-S co-limitation indices. Co-limitation between N and S was maximized with N:S ratio similar to 9.6 in shoot biomass and similar to 11.2 in grain, indicating the balanced nutrient ratio in each plant organ at maturity. Both co-limitation and stoichiometry frameworks captured the interacting N and S effects on yield and nutrient use efficiency.