Performance of seedlings and yield of soybean genotypes under soil compaction

The identification of soybean genotypes tolerant to soil compaction makes it possible to reduce productivity loss under stress conditions. Added to this, the prior selection of these genotypes will result in greater assertiveness in the positioning of cultivars in the field. Thus, the objective was to evaluate the susceptibility of soybean genotypes to compaction in greenhouse and field conditions; verify which characteristics of seedlings under high resistance to root penetration are correlated with crop production in compacted soil; and to validate the substrate mechanical impedance method for evaluating the susceptibility of plant genotypes to soil compaction. Seeds of 20 genotypes were sown in a substrate mechanical impedance system under controlled conditions. The characteristics evaluated were total root length, total root surface area, mean root diameter, total root volume, taproot length, shoot length, root dry matter and seedling shoot dry matter. In the field experiment, half of the planting area was compacted, constituting two treatments, soil with and without compaction. The percentage of seedling emergence, initial plant height, stem diameter, number of nodes, internode length, number of lateral branches, shoot dry matter, final plant height, absolute and relative growth rate, number of pods, weight of 100 seeds and grain yield. In addition, the number of days between soybean sowing until plant flowering and grain harvest was recorded according to genotype and soil compaction level. In a controlled environment, genotypes tolerant to soil compaction show greater plasticity of root characteristics and smaller alterations in the shoot of seedlings. In the field, these genotypes show smaller reductions in growth rate, height, number of pods and grain yield. The shoot dry matter and the root dry matter of soybean seedlings in a mechanical impedance system present a positive and negative correlation, respectively, with soybean yield in compacted soil, indicating that the genetically determined susceptibility to soil compaction stress was similar throughout ontogenesis. The substrate mechanical impedance system used to evaluate the performance of soybean seedlings under stress, facilitates the decision-making in breeding programs focused on identifying genotypes expressing soil compaction tolerance.