The Brazilian sugarcane production estimate is 671,9 million tons, which places the country as the largest producer in the world (Conab, 2014). The high production is also due to the constant renewal of sugarcane fields, which according to Conab (2013) accounted for around 20% of the cultivated area with an expenditure of 15t stalks/ha for traditional planting and 20t stalks/ha for mechanical planting.
The stalks used as seedlings when planting new sugarcane fields must be free from pests and disease-causing pathogens. To obtain stalks with considerable health for planting, the sugarcane producer needs to form sugarcane fields with constant health inspections, known as nurseries.
Practices such as heat treatment (immersing the stalks in water at 52°C before planting to eliminate pathogens), rouging (inspections with the removal of clumps infected by pests or pathogens) and irrigation, burden the formation of nurseries. When considering the current need for stalks for planting sugarcane (15t to 20t of stalks to plant 1ha) the producer needs to expand nursery sugarcane fields, which further increases costs for commercial planting.
In an attempt to reduce the consumption of stalks for planting, options such as the use of pre-sprouted seedlings (MPB) have provided advantages to producers, who, instead of using stalks, start using seedlings directly. According to Landell et al (2013) in the MPB system, stalk consumption is reduced between 0,5t of stalk/ha to 1t of stalk/ha, in addition to optimizing the use of fertilizer and providing better management of pests and diseases such as scald and rickets.
Producers interested in MPB (Figure 1) can form their own plants according to the methodology recommended by Landell (2013). The booklet was developed by the team at the Sugarcane Center of the Campinas Agronomic Institute (IAC) and is available on the Institute's website. Another option is for the producer to purchase MPB from producing companies, such as the factory itself where the producer is a supplier of sugar cane.
The idea of MPBs arose from the need for the IAC Sugarcane Program to deliver material free of Sphenophorus levis (pest that colonizes sugarcane stalks). Therefore, since 2009, the team has invested in the formation of MPB, which in addition to preventing the spread of the pest also reduces the volume of material to be transported.
MPB planting is done in lines spaced 1,50m and 0,50m between plants. The furrows are shallower than the traditional planting system and can also be replaced by holes, generally made mechanically.
The formation of nurseries was the first use of MPB, but currently sugarcane mills have found other uses for the new technology. The second job is to replant sugarcane in the absence of commercial planting, so that with less effort the producer can maintain the sugarcane stand.
The third use is in nursery areas, however, in the “meiosi”, which involves planting two rows of sugar cane with MPB (spaced 1,5m apart), a larger space (closer to 15m), planting another two rows with MPB and so on. In the 15m spaces between the double rows of sugar cane, another crop is grown (peanuts, soybeans or sunflower). After harvesting, the sugarcane stalks formed in the double rows are used to plant the 15m unoccupied spaces.
The plants have also given MPB a fourth use, which is known as the revitalization of ratoons. In this modality, MPB are planted in the faults of the ratoons, commonly caused by the harvesters being broken down. As a result, some plants have been able to maintain sugarcane productivity for longer, that is, increasing the longevity of the ratoon crop.
Use of herbicides
The chemical management of weeds in planting with MPB still needs to be better elucidated. In the field, it has been observed that herbicide treatments traditionally used in crops harm plants in the MPB system, particularly if applied shortly after transplanting. In an attempt to alleviate the issue, a proposal is made for chemical management that allows MPBs not to receive herbicides immediately after transplantation (setting phase), but rather before planting and after establishment (40 days of transplantation) of the seedlings. (Figure 2).
Preliminary studies in a greenhouse at the IAC demonstrated that the superficial planting of MPBs allowed the roots to remain in the same layer of soil as the herbicides, which were subsequently applied. As a result, pronounced intoxication symptoms were observed in MPBs, which is common in young plants due to the lack of development of plant tissue that facilitates the dynamics of herbicides in plants.
To minimize the intoxication of MPBs, herbicides can be applied before planting with subsequent incorporation (pre-planting incorporated - PPI). The choice of herbicides must be based on the physical chemistry of the molecules, so that there is an option for use at all times of the year (dry or rainy). As well as meeting the diverse weed flora typical of crops in the tropics.
The answer to the problem certainly lies in specific management that reduces the period of coexistence between MPBs and herbicides in the soil. Applications of herbicides in pre-incorporated planting (PPI) seem to be an interesting practice, as the period in which the herbicide molecule is available in the soil occurs before the crops are planted.
The application of herbicides in PPI is common in areas with high weed infestation, but its success depends on the incorporation of the herbicide into the soil and also on the minimum waiting time until planting, which can be up to 60 days. PPI herbicide applications minimize the weed seed bank in the soil and subsequent infestations are less severe. If MPBs are transplanted during this period, the crop plants will be little harmed by the interference imposed by weeds, even without the need to apply herbicide immediately upon planting (Figure 3).
After planting, herbicides should not be applied immediately, allowing MBPs to establish themselves only influenced by the applications of herbicides applied in PPI. As a result, the selectivity of treatments is improved and the seedlings develop better.
However, due to the diversity and population density of weed flora present in tropical regions, there is a need to complement PPI applications when MPBs are in the second month after transplantation. The choice of herbicides for post-emergence use must also follow the physicochemical characteristics of the molecules. This way, the producer will have options for use at all times of the year, while also serving the diverse weed flora.
Therefore, complementary herbicide management can be directed post-emergence of the weeds, if necessary after the first month of transplanting. In these cases, the application of the herbicide will be carried out when the seedlings are already more developed, approximately 40 days after transplantation (planting), consequently, with the structures of the plant tissue more developed.
In traditional sugarcane plantations, post-emergent herbicides are applied after the second month of sugarcane plantation installation (after “breakthrough”) and even then they are selective to most cultivars. From preliminary experiments carried out at IAC, it was observed that plants from MPB have a similar size to plants originating from setts when both reach 40 days of development.
Studies on the best method of weed control in a planting system with MPB have not yet been elucidated. However, the application of herbicide treatments prior to planting and in addition after 40 days of planting MPBs has demonstrated selectivity.
Figure 2 - Proposal for the application of herbicides in a sugarcane planting system with pre-sprouted seedlings (MPB). Campinas Agronomic Institute, Centro de Cana, Ribeirão Preto, 2014
Figure 3 - Field planted with MPB after 60 days of application and incorporation (PPI) of herbicides. Agronomic Institute, 2013
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