At the off-season period, it is important to have adequate planning for good use of cultivation areas. Leaving crops fallow emerges as the worst option. Another fundamental factor lies in the role of increasing biodiversity as an alternative to improving cultural management in the production system soy/corn/cotton.
The safrinha, corn or sorghum, which emerged as an alternative to winter crops in regions less cold crops, mainly replacing wheat, currently exceeds, both in planted area, as in the average productivity, summer crop or harvest. This name of off-season is due more to the productivity potential, which is smaller in this case than the cultivated area itself. Thus, the cultivation of corn in succession to soybeans has become the perfect double in many regions, as soy fixes nitrogen (around 1 kg of N/harvested bag) so demanded by corn and this increases soil organic matter due to the residue left in the form of straw. Therefore, in these regions there are few alternatives for rotation of these cultures. On the other hand, crop rotation with different species plants is a fundamental practice for increasing biodiversity, for reduce phytosanitary problems due to a better biological balance (in the environment above and below the soil surface), increase the amount of matter organic and, consequently, give sustainability to production.
The rain delay that occurred that year and low corn prices in the last harvest led to a reduction in area sown with summer corn and increase in the area cultivated with soybeans. Those facts should raise some doubts to the producer regarding the cultivation options in the safrinha. Another factor that tends to affect the producer's decision for the next harvest has been the high incidence, in some regions, of diseases whose pathogens are transmitted by the corn leafhopper. Regarding the occurrence of other pests and diseases, the producer must pay attention to monitoring periodic, to interfere in the system whenever necessary, but following the recommendations based on action levels. The incidence of caterpillars, both in Soybeans, like summer corn, did not raise major concerns, largely due to the favorable climate conditions and the efficient activity of Bt events used in recent years. It is important to note that effective management of pests over the years tends to lower the overall pest population in the region. Also, no new records of insect resistance to Bt technologies in the field have been documented. The adoption of good agronomic practices such as: desiccation advance, the use of certified seeds, seed treatment, management effective control of weeds/tigueras and, mainly, the inclusion of areas of refuge in Bt cultures and the realization of periodic monitoring (which must be started even before sowing) constitutes the main strategy for effective phytosanitary management.
In areas sown with safrinha corn or to be cultivated, in addition to the observations already presented, seed treatment with systemic insecticides, such as those based on neonicotinoids to control suckers. Furthermore, it is essential monitor the incidence of leafhoppers soon after plant emergence to reduce the incidence of viruses and stunting in corn. In areas with history of incidence of these diseases or where the ideal window for planting the off-season corn has already passed, an alternative is to use the off-season corn sorghum, as, in addition to not being affected by diseases, as it is not a host to leafhopper, reduces its population for planting in the next harvest. Furthermore, sorghum is much more tolerant to water stress, typical in periods of dry season that occur in later plantings.
If there is no possibility of using all or part of the area with a culture commercial product in the off-season (corn, cotton or sorghum), it should not be left in fallow, as this is the worst option. In fallow areas, plant growth tiguera constitutes one of the main threats to the success of the next harvest, due to survival of pathogens and pests in the area. In this case, the opportunity arises to improve the quality and quantity of straw for the next harvest, using one or more cover crops. The increase in cost in function of new technologies introduced into the production system, and growth problems in the field such as, for example, the exhaustion of organic matter from soil and consequent higher incidence of nematodes, in addition to the increase in complexity of phytosanitary management, have worried producers.
Crop rotation is a ancient practice, always used successfully in conventional agriculture. That practice is considered an efficient way to reduce environmental impacts caused by monoculture, improving the physical, chemical and soil biological. Furthermore, rotation improves the environmental conditions above soil level, which promotes more efficient management of weeds, diseases and pests, especially those specific to each crop commercial.
Although crop rotation is a very beneficial practice for the production system, it is not always feasible. The modernization of agricultural activities is increasingly necessary, with the adoption of new technologies and large investments in infrastructure (machines, equipment and inputs) and training of the operational team (“know-how”), to make the activity more competitive, with gains in productivity and scale in production. Considering these and other factors, the economically viable crop options for rotation are very restricted. For example, in the Center-West region of Brazil, soybean cultivation predominates in summer and succession with off-season corn or cotton. Therefore, the options for farmer are really scarce and the solution to diversify species cultivated in the area is the rotation of cover crops, thus increasing the biodiversity in the agro ecosystem.
Many producers still do not have realized the benefits of cover crops and insist on leaving fallow areas. This is because most of them keep little record of their activities/results on the property. Thus, the small losses over the time or medium and long term gains are difficult to be perceived in function of commercial and environmental fluctuations. There are search results indicating that cultivating the soil with cover crops changes its structure, leaving its profile comparable to that of the native forest. So, an advance in the use of cultures of coverage, introducing its rotation, demands even greater effort. Therefore, how the benefits of cover crop rotation only have a medium to high return long term, your demonstration to the producer must be very convincing, to that this practice is widely adopted.
A concrete example lies in what has been carried out at Capuava Farm in Lucas do Rio Verde, Mato Grosso, by Agronomist José Eduardo de Macedo Soares Junior. Diversification and intercropping of cover crops in the agro-ecosystem promote many benefits for the producer and restores agricultural and environmental sustainability. In the short and medium term, it reduces the incidence of pests, diseases and plants weeds, while increasing the organic matter content of the soil, improving both fertility and moisture retention, reducing stress due to dry periods. The use of cover crops with a system Root system with high soil penetration capacity recycles mineral nutrients reducing leaching, improves rainwater penetration by increasing soil porosity, reducing compaction, erosion, and perennializes the springs between several other benefits.
The producer, when carrying out the transition of its production system, with or without the use of monoculture coverage, for cover crop rotation, you should be aware that it is a gradual process and must be aware of several factors. Little by little it will increase biological diversity, both of organisms living on the surface, like on the ground. Many of these organisms are beneficial and play an important role in maintain biological balance by feeding on pests that are important for commercial culture. The higher organic matter content in the soil allows survival of pathogenic microorganisms for underground pests such as, for example, nematodes. Therefore, the adoption of practices that protect beneficial organisms in the environment leads to a reduction in the use of pesticides in the field.
Pests that attack crops during the emergency are the great challenge for producers who begin to cover crop rotation, especially those using a single species of cover plant. Initially, the incidence of caterpillars leafcutter, slugs, wireworm and other pests challenge new practices, until the rotation of different cover crops begins to produce effects.
Even in systems direct planting, where there is little straw, hillside plots can suffer erosion due to soil compaction due to the low organic matter content, reducing drastically increase productivity. Therefore, initially it may be necessary to subsoiling. But this alone may not be enough and other practices may be necessary to maintain favorable soil conditions. Gradually the producer will discover that the rotation and intercropping of cover crops bring greater plant diversity to cultivated area, operating a true revolution for its production, reducing the use of pesticides to control pests, diseases and weeds, while increasing crop efficiency in use of fertilizers, recovering or increasing productivity. In addition Furthermore, the increase in organic matter content in the soil profile contributes to correction of acidity in the deeper layers, which allows greater development of the root system of commercial crops.
In the production system of annual crops, commercial crops soybeans, corn and cotton predominate. The rice, beans and sorghum are also used sporadically. In addition to these cultures, depending in the region, cover crops are also used to produce straw for direct planting. How commercial crop options for rotation are restricted, planned rotation of cover crops becomes essential to diversify the agro ecosystem during the seasons.
In the direct planting system, As important as the quantity (straw layer) is the quality of the material organic covering the soil. To maintain a good carbon/nitrogen (C/N) ratio in soil organic matter, it is essential to diversify straw sources, because grasses have a higher carbon content and legumes (proportionally) nitrogen. Thus, the combination of species of different groups improves the C/N ratio. The straw layer must be as thick as enough to protect the soil surface from the mechanical impact of water drops. rain, preventing the disintegration of soil particles, as well as their protection against desiccation by direct sunlight. The abundance of organic matter, retaining a higher moisture content, even allows for greater diversity of secondary organisms of soil fauna and flora, increasing thus biodiversity. Therefore, both the quantity and diversity of plant species to be used as cover are also important.
The gains are progressive with the incorporation of phytomass into the soil profile. Deepening the roots in the soil profile brings a series of benefits, as discussed previously. For Therefore, the neutralization of aluminum in the soil in the deeper layers is fundamental. In addition to soil improvers, organic matter plays a role relevant in this process. The phytomass produced by the roots is even more important than that produced by the aerial part of the plants. Experiments conducted with brachiaria have demonstrated that the phytomass of the roots results in greater gain in productivity than that of the aerial part of the plant, when evaluated separately. Furthermore, each crop has a root system with different ground penetration capabilities. As crops rotate coverage, the soil profile explored by the system deepens root of commercial plants, which can go from less than 80 cm to more than 2,5 m deep. Obviously, plants with a deeper root system their productive potential will be greatly increased.
There is strong evidence that the current bottleneck for increasing the productivity of annual crops in many properties is in the physical quality of the soil, as direct planting has been practiced with little straw and generally a single plant species. Thus, it remains a low content of organic matter, which limits the establishment of the population ideal plant, deepening roots and reduces plant tolerance to water deficit by exploiting only the surface layers of the soil, in addition to increase bedding. Apparently, the main advantage of cerrados, which resides in the depths, has been little used by the majority of producers.
Article published in issue 225 of Cultivar Grandes Culturas, February, 2018.
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