## 1 Introduction  
Currently, corn is one of the major global crops, along with other cereal crops like wheat or rice, being an essential source of food for humans. According to the Food and Agriculture Organization (FAO), the world production of corn has recently increased until 2018, where the production decreased by 1.31%, compared to 2017 [1]. If the situation of corn crops in Spain is considered, according to the FAO, it is one of the ten most important crops in this country. However, there has been a decrease both in production and in the cultivated area since 2013. In 2013, there was a harvested area of 442,300 hectares and a production of 4885 million tons, whereas in 2018, the harvested hectares were 322,373 and the production was 3842 million tons [1], which has implied a 21.35% decrease in five years. The low market prices, as well as other secondary factors, such as high water use, several pests or high international competition, have made this crop less attractive for Spanish growers. In a corn crop, a residue called corn stover, which is mainly composed of different parts of the plant like corn stalk, leaves and corncob waste, is produced. Currently, these wastes are left on the soil, being mechanically ground in order to be mixed with the soil after harvest. To a lesser extent, these wastes are used to produce bales to be used in biomass power plants or for livestock purposes. Formerly in Spain, corn stover was usually burned in the country, with the associated environmental risk and impact. Fortunately, this practice is in disuse. Concerning the production of corn stover generated during the corn harvest, [PERSON] et al. [2] established that the proportion of corn stover produced per corn plant (dry basis) was 0.65,whereas [PERSON] et al. [3] showed a corn stover ratio of 0.86; according to this data, and considering an average moisture of 20%, the production of corn stover in Spain in 2018 would be 1997 million tons and 3304 million tons, respectively. As it can be observed, different references showed disparate results about corn stover production, as its generation is dependent on the kind or variety of corn, the way of harvesting, the subsequent use of this crop and the area where the corn is grown, among other factors [2; 3]. In any case, the amounts of corn stover produced are significant enough to justify a study about the treatment of this waste for the competitiveness and economical improvement of corn crops. The harvesters, currently used in corn crops, usually cut and separate the corn grain, placing it in a hopper. The corncob waste and stalks come out, separately, from the rear of the harvester, although both parts are released jointly and remain on the soil. In order to transform this waste into bales, a previous swath process is necessary, followed by a baling process. Swathing can be carried out by the same harvester by incorporating a specific device or, at a later time, using other machinery. Afterwards, baling is carried out, which implies a partial soil dragging, increasing the proportion of impurities in the bale produced. As it was previously pointed out, swathing is, in many cases, a discontinuous process, existing for the period (even for several days) when the residue remains on the soil. In addition, bales are not immediately collected after their generation. Both periods can imply a degradation of this residue, due to weather conditions, which could limit its subsequent use. According to the literature, another study has reported other harvest systems that allows for the collection of corn stover before its contact with the soil, through a rolling system of wastes [4]. In any case, this system would not avoid the deterioration of bales due to their stay on the soil for several days, which will depend on the time of collection for their subsequent use. Thus, the baling system is not always economically profitable for corn growers as, on one hand, it implies an additional cost and, on the other hand, the profits are not competitive.