Table 2 shows the average physical property evaluations of forty soybean seed cultivars. The axis corresponding to seed length averaged 8.116 mm, with variations of 9.300 mm from cultivar FLECHA IPRO to 7.040 mm for cultivar NS 7447. The average seed width was 7.464 mm, with variations of 8.180 mm from cultivar FLECHA IPRO to 6.620 mm for cultivar NS 7447. Seed thickness presented average values of 6.890 mm, with variations of 7.900 mm from cultivar FLECHA IPRO to 6.175 mm for cultivar NS 6823 RR.
The average seed volume was 219.447 mm³, with variations of 314.515 m³ from cultivar FLECHA IPRO to 159.230 mm³ for cultivar TMG 1180GX RR. Seed roundness averaged 0.920, with 0.994 variations from cultivar CZ26 B42 IPRO to cultivar 1180GX RR with 0.835. The average sphericity of the seeds was 0.903, with 0.983 variations of cultivar NS 7447 to 0.839 of cultivar KWS RK 6813 RR2. The average equivalent diameter of the seeds was 7.321 mm, with variations of 8.261 mm of cultivar FLECHA IPRO to 6.599 mm for cultivar TMG 1180GX RR.
The projected area of seed cultivars had average values of 47.65 mm², with variations of 59.71 mm² from cultivar FLECHA IPRO to 36.58 mm² for cultivar NS 7447. The surface area of seed cultivars had a mean value of 168.62 mm², ranging from 214.27 mm² for FLECHA IPRO cultivar to 136.73 mm² for the TMG 1180GX RR cultivar. The surface-volume-ratio averaged 0.773, ranging from 0.834 for 2686 IPRO to 0.681 for FLECHA IPRO. The friction coefficient as a function of seed displacement averaged 1.147, and it ranged from 1.902 for cultivar 6139 RR to 0.650 for cultivar M6410.
The average resting angle was 23.08°, ranging from 28.68° from cultivar KWS RK 6813 RR2 to 20.32° for cultivar 8473 RR. The average unit mass of seeds was 0.186 g, ranging from 0.251 g of cultivar FLECHA IPRO to 0.115 g of cultivar TMG 1180GX RR. The unit-specific mass of the seeds presented an average of 1030.67 kg m-3, ranging from 1649.155 kg m-3 of cultivar KWS RK 6813 RR to 813.679 kg m-3 of cultivar 6139 RR. The average apparent specific mass for soybean cultivars was 718.70 kg m-3, ranging from 783.030 kg m-3 to 598.723 kg m-3 of cultivar FLECHA IPRO for cultivar 8473 RR, respectively. The average porosity of seed mass was 39.20%, ranging from 43.83% of cultivar MAMBA RR to 36% of cultivar 8473 RR.
According to Table 3, the seed lots of the different cultivars present variability in their physical properties, which were possible to characterize in groups of larger seeds (LS), intermediate-larger seeds (ILS), intermediate-smaller seeds (ISS), smaller seeds (SS). Among the groups, there was a predominance of ILS seeds, followed by LS, ISS and SS. Soybean seed cultivars have heterogeneous physical characteristics that are distinguishable between FLECHA IPRO, 6139 RR and MAMBA RR cultivars from larger seeds, and NS 7447, 2686 IPRO and 8473 RR cultivars from smaller seeds, while the other cultivars prevailed as seeds of size averages.
The cultivar UNIGEL 8473 RR Desafio had greater differentiation in apparent specific mass and porosity, while the cultivar KWSRK 6813 RR achieved greater differentiation for physical properties of unit specific mass and angle of repose. In the evaluation of the unit mass, the cultivar FLECHA IPRO differed from all other cultivars, except the cultivars NS 6823 RR and TMG 1180GX RR which were similar between them and with FLECHA IPRO. The cultivar AVANTSEED 96139 RR obtained greater differentiation with the other cultivars for the physical property coefficient of friction.
The cultivar AVANTSEED SMANBA RR had higher differentiation for porosity. Given the importance of uniformity of seed lots for optimal regulation of postharvest equipment, in a research realized with three soybean cultivars, separating them by size in to improve sowing quality and grain distribution. In the evaluation of the physical properties length, width, sphericity it was observed that the seed cultivar UNIGEL NS 7447 differed from the other cultivars, while for the physical properties thickness, volume, equivalent diameter, projected area, surface area and area ratio, however for the surface/volume the highest differentiation occurred with cultivar FLECHA IPRO, however, for the physical property circularity, cultivar M7739 IPRO stood out.
By Pearson’s correlation network Figure 2, it can be noted a high positive correlation between VxPA, VxED, VxSA, EDxSA, EDxW, WxV, PAxL, PAxW, and LxV. Moderate positive correlations were verified between LxED, EDxT, TxV, and CrxSp. On the other hand, there were high negative correlations between WxSVR, PAxSVR, VxSVR, EDxSVR, SVRxSA, and moderate negative correlations between SVRxL, SVRxT, CrxFC, SpxFC, USMxW, USMxPA, and USMxEd. The other correlations had low magnitude, and for this reason, they were not mentioned here. From these results, it is possible to infer about the positive relationship between the size-related properties volume, length, width, projected and surface areas, equivalent diameter, and thickness, while these variables showed low or no correlation with the other physical properties of the seed, such as those related to shape and mass.
Figure 3 shows the results obtained by principal component analysis, which revealed the existence of two clusters (G1 and G2). Cluster 1 (G1) was formed by the cultivars 3980 RR, 6139 RR, CERTA IPRO, KWS RK 6813 RR2, KWS RK 6813 RR, M7739 IPRO, 5947 IPRO, 7337 RR, TMG 1180 GXRR, TMG 1264 RR, 98Y30, 98Y52, 96Y90, 8579 RSF, 2686 IPRO, and NS 7447. In turn, the cultivars 68H0 RSF IPRO, 6968 RSF RR, 7166 RSF, ATRIA RR, GURIA RR, MAMBA RR, BRS 7380 RR, 2728 IPRO, 2687 RR, 2737 RR, CZ26 B42 IPRO, FLECHA IPRO, GXM 7148 IPRO, GXM 8372 IPRO, 8573 RR, 74178 IPRO EXTRA, ULTRA IPRO, M6410, NS 7007 IPRO, NS 6823 RR, NS 7505 IPRO, DESAFIO, TMG 7062 IPRO, and 8473 RR constituted the cluster 2 (G2). Unit specific mass (USM) was the physical property that most contributed to the formation of G1. This finding is supported by the boxplot of physical properties, where it can be noted a marked difference between clusters for USM, for which cluster G1 showed higher means (Figure 4). The surface-to-volume ratio (SVR) and friction coefficient (FC) were the other properties for which G1 showed means higher than G2, however, they did not contribute to the formation of G1 by the PCA. The other physical properties contributed to the formation of G2. In Figure 3, it can be verified that G2 showed higher means for length (L), width (W), thickness (T), volume (V), circularity (Cr), sphericity (Sp), equivalent diameter (ED), projected and surface areas (PA and SA, respectively), indicating that these cultivars have larger seeds than the ones allocated in G1.
Based on the results provided by PCA and boxplot of the physical properties, we infer that the soybean cultivars comprising the G2 are more similar to each other for all properties assessed, except for USM, which in turn is the property for which the cultivars allocated to the G1 group are most similar. This similarity between soybean cultivars suggests a higher homogeneity in seed lots regarding these physical properties. In this sense, the cultivars allocated in G2 show to be homogeneous for volume, length, width, thickness, circularity, sphericity, equivalent diameter, projected area, surface area, surface-to-volume ratio (SVR), friction coefficient, unit mass, apparent specific mass, rest angle, and porosity of seeds, while G1 has a greater heterogeneity for these same properties.