Soybean growth, solar energy conversion and seed vigour affected by different nitrogen (N) doses

The objective of this study was to evaluate soybean growth, conversion of solar energy and seed vigour of plants cultivated with different nitrogen doses. We carried out experiments using the cultivar BMX Potencia RR belongs to the maturation group 6.7, presenting an indeterminate growth habit. The experimental design was completely randomised with four replications in a 4 x 8 factorial scheme (four nitrogen doses and eight collection periods). In the Vn stage of soybean development, we applied four different nitrogen fertilisation doses, i.e. 0, 25, 50 and 75 Kg N ha-1 in the form of urea (45% of N). We evaluated leaf area (Af), leaf dry mass (Wf), stem (Wc), roots (Wr) and pods (Wv), dry matter production rate (Ct), relative growth rate (Rw), net assimilation (Ea), rate, leaf area ratio (Sa), solar energy conversion factor (ξ), leaf area ratio (Fa) and leaf mass (Fw), dry matter partition between plant structures, seedling emergence (E) and the emergence speed index (IVE) of the seedlings originated from the seeds produced. The experiment was conducted throughout the crop cycle. Nitrogen application positively impacted soybean growth; a nitrogen dose of 50 Kg ha-1 resulted in highest values of Wt. However, plants subjected to 75 Kg N ha-1 reached higher Rw and L values. Nitrogen fertilisation applied in the stage Vn facilitated plant growth, enhanced the conversion of solar energy and resulted in higher seed vigour.