When comparing the results obtained by both methods of study , no profound limitations to the substitutive method were found to the point of not allowing its use or to put in check its results, as reported in some studies . We agree, however, that in finalistic studies under field conditions or in situations where it needs more directly applicable inferences, the additive method should primarily be adopted. If from one side there are disadvantages, from the other side the substitute method has the advantage of obtaining information as to the community as a whole, providing evidence about the nature of competition between species involved—if it occurs for the same resources, or if one of the species is able to avoid the competition. In addition, discrete varietal differences in competitive ability against weeds are probably best captured by substitutive experiments. Soybean is one of the leading economical crops grown in Brazil, with about 27.7 million hectares planted in the 2013/2014 cropping season. Soybean yields in Brazil had significantly increased in the last decades, and current Brazilian average yield is 3035 kg∙ha−1 .

Among the factors which limit crop yield, the occurrence of weed species can be highlighted as one of the most relevant facts . Recent GMO technologies have aimed to employ herbicide resistance to soybean varieties and the weed infestation have drastically reduced in most fields with such technologies. Lack of Government regulation and Farmer’s mismanagement of such technologies cannabis grow tray, however, led to the selection of weed species tolerant or resistant to the herbicides applied with these technologies . The glyphosate-resistant Roundup Ready® soybean was widely used in Brazil for at least ten years, and currently Conyza bonariensis, C. canadensis, C. sumatrensis, Digitaria insularis, Lolium multiflorum  and Eleusine indica  are resistant to this herbicide, due to its extensive and almost uncontrolled use in Roundup Ready soybean. This abuse, moreover, resulted in the selection of weed species naturally more tolerant to glyphosate, namely Ipomoea spp., Richardia brasiliensis and Commelina benghalensis , among others. These facts have made researchers and companies retreat from the excessive reliability in GMO crops and has provided new possibilities to researches that regard integrated weeds management and integrated cropping systems Researchers also started to notice that it is important to know the key traits of weed plants intended to be eliminated from the system, in order to develop management techniques that are efficient to the controlling of such species .

One of the main management practices which contribute to the reduction in weeds infestation is the continuous maintenance of straw on the soil surface , which limits weeds access to light. In addition, some plant species produce chemicals which usually exudate to soil through the root system, inhibiting germination and/or growth of other plant species. This phenomenon is called Allelopathy . The intercrop of corn second crop  with Brachiaria ruziziensis was developed to allow the maintenance of a bold layer of mulching from the forage on soil after corn is harvested , thus soil would not be exposed to direct rainfall and sunlight when crop is not present. The crop succession soybean-corn + B. ruziziensis year after year, however, also started to select pests and weed species, urging for diversification at the second cropping season in Brazilian Savannah. In addition,vertical grow systems for sale the demand for partial or total substitution of petroleum-based fuel oil for biofuels has become a topic of strategic security for many countries , aiming to meet both the increasing demand for energy and the new required limits for emission of gases responsible for the greenhouse effect . Radish , crambe  and rapeseed  are promising for producing biofuels , being these winter oilseed crops good choices for a profitable second crop while keeping soil protected during fall/ winter; they can be planted later than corn, developing well even when planted after march 10th, which is a deadline for corn planting in the Brazilian Savannah .

Even being a profitable option to replace corn after soybean, the potential of these oilseed crops suppress the occurrence of weed species in areas where these are rotated with soybeans that need to be assessed. Oilseed crops could either demand additional herbicide application in the cropping system throughout the year for not suppressing weeds, or reduce herbicide demand supposing the most important weed species that are properly suppressed—the latter would be a highly desired side-effect. This study aimed to evaluate the potential of oilseed crops planted following soybean, in terms of their ability to inhibit the occurrence of weed species under Brazilian Savannah cropping systems. Sampling precision proved most areas were precisely sampled, according to the demanded by Bordeau  and Goldsmith & Harrison , who stated the variance of sample means increases as the number of sampled quadrats per area decreases.