Dose and form of nitrogen supply in the relationship dynamics of wheat ear components with yield in cropping systems
Nitrogen management distinctly influences the expression and magnitude of relationships between wheat ear components and grain yield. We sought to determine the variables linked to wheat ear that are more responsive to changes in the dose and form of nitrogen supply and to determine the direct and indirect effects on grain yield by single and fractional nitrogen supply in soybean/wheat and corn/wheat succession systems. The study was conducted in 2018 and 2019 in a randomized block experimental design with four replications, in a 3 x 3 factorial, for N-fertilizer doses (30, 60, 120 kg ha-1) and forms of supply [single dose (100 %) in phenological stage V3 (third expanded leaf); fractionated dose (70% and 30%) at the V3/V6 phenological stage (third and sixth expanded leaf) and; fractionated dose (70% and 30%) at phenological stage V3/R1 (expanded third leaf and beginning of grain filling)], respectively, in the soybean/wheat and corn/wheat succession systems. The increase in the nitrogen doses promotes productivity due to the greater contribution of grain mass and ear length in the V3 stage and ear grain mass in V3/V6 and V3/R1, in a soybean/wheat system. In the corn/wheat system, the increase in nitrogen promotes productivity, with a greater contribution of grain mass in the ear, regardless of the form of supply. Nitrogen supply in single dose (V3) and fractionated in theV3/V6 gave similar productivity, with a reduction in V3/R1. The grain mass of the ear showed greater contribution of alteration by the form of single and fractioned nitrogen supply, regardless of the dose and succession system. The grain mass of the ear shows a high correlation with yield, regardless of the dose and form of nitrogen supply in the soybean/wheat system, with a positive indirect effect by the ear mass. In the corn/wheat system, ear grain mass shows a high correlation with yield, when nitrogen is supplied in a single dose at 30 and 60 kg ha-1, with a positive indirect effect due to ear length.