This research conducted in the District of Concepción, Concepción Department, Paraguay, involved the use of a randomized complete block design consisting of four treatments and five repetitions. The general objective was to evaluate the effect of Cajanus cajan L. species with different planting densities on soil compaction and as specific objectives; measure the compaction of the soil at the beginning and end of the crop cycle, determine the soil moisture percentage as well as the root development of the species at the end of the crop cycle. The data obtained were subjected to analysis of variance (ANOVA) and the means compared through the Tukey test at 5%. Determinations of resistance to soil penetration before the crop establishment and at the end of the crop cycle were not influenced positively; except at 20 cm of density that showed difference at the end of the cycle, the soil moisture percentage was not significant and for root development highly significant differences were found. As regards the soil compaction, it was found that the biological material used with different planting densities had positive effects in the compaction of the soil. Thus, the recommended density is 114,284 plants per hectare.