Off-season corn: choice of seed or technology?

Without a doubt, choosing the seed is an important step to obtain high productivity from a crop, but it is in the field that it expresses its genetic potential. The use of technologies embedded in seeds and soil conservation technologies, such as corn-brachiaria consortium and direct planting, can provide greater harvest security to the farmer.

Especially in safrinha corn, the choice of seed must be more careful, as the risks of frost and/or prolonged drought during its cultivation were not enough, weeds, diseases and insect pests can appear, such as the corn leafhopper (Dalbulus maidis). This leafhopper is responsible for transmitting disease-causing pathogens: red and pale stunts, and the virus that transmits corn streak virus, drastically reducing crop productivity.

Considering that the leafhopper's longevity is 70 to 80 days, and that it only reproduces on corn plants, eliminating corn plants during soybean cultivation is a very important factor in reducing the population of these insects for the next corn harvest. But it's not that simple. The leafhopper feeds on several species, such as teosinte, sorghum, brachiaria and corn plants originating from grains/seeds lost on roadsides during crop transport.

Although it is an old problem, it was in 2022 that the leafhopper caused greater damage to corn crops, due to the previous soybean crop failure, where insect pest control was not carried out properly, multiplying in tiguera corn plants. . Corn hybrids with genetic resistance to stunting have been identified, but there are too few to cover the entire seed market. Therefore, integrated management must be used to avoid further damage.

Technologies for tolerance and/or resistance to insects and tolerance to herbicides to control invasive plants can be acquired via seeds and/or with the application of agrochemicals, but soil conservation is built gradually through the adoption of new and old technologies. The Direct Planting System is the oldest and most solid of these technologies, as cultivation with minimal soil disturbance, permanent coverage and crop rotation make up the three pillars of sustainability for the cultivation system.

In regions with a temperate climate, it is common sense to cultivate corn every four or five years, in order to incorporate large amounts of mass into the system. In regions with a tropical climate, it is simpler to produce large quantities of straw, however, it is difficult to keep this straw on the soil surface, due to its rapid decomposition, due to high temperatures and high humidity. Furthermore, the tropical region is marked by a rainy season and a dry season, and it is not always possible to establish a species for soil cover after harvesting safrinha corn, for example.

The off-season soybean-corn succession still faces conceptual resistance as it is not a perfect crop rotation, but it has already broken paradigms and supports grain production in the Central region of Brazil. It is even better when the off-season corn is grown in intercropping with brachiaria. The corn-brachiaria consortium is a simple technology for some, but for others it is an additional difficulty in the grain production system.

Brachiaria, as it is perennial and established together with off-season corn, has its roots growing in depth, during and after the corn harvest, when the water is more in the soil profile and less in the surface layer. The brachiaria straw left on the surface of the soil protects it from torrential rain, and the roots preserve nutrients in the soil, which will be used by soybeans in succession.

The expected benefit of the corn-brachiaria consortium is greater soybean productivity in succession. However, farming is like an open-air laboratory, with countless factors, many of them uncontrollable, interfering with the development of crops, and it is important to admit that not every year soybeans produce more where there was corn intercropped with brachiaria. But until we find a species for soil cover, with economic return, the corn-brachiaria consortium is an important technology to be used. This technology has been recognized since 2010 by the Ministry of Agriculture, Livestock and Supply (Mapa), through the Agricultural Climate Risk Zoning (Zarc).

However, it is increasingly important to master the details of the intercropping in the off-season soybean-corn production system. In work carried out by Embrapa Agropecuária Oeste, it was found that one brachiaria plant per square meter reduces corn productivity by 13 kg/ha to 42 kg/ha, if due care is not taken in the implementation and management of the consortium; and the highest dry mass productivity of the consortium was obtained with ten brachiaria plants per square meter.

A Brachiaria ruziziensis It is the most suitable species for intercropping, due to its morphological characteristics and ease of management. Brachiaria seeds must be purchased in advance to check their actual germination. Furthermore, the sowing method interferes with the final brachiaria stand and, therefore, an exclusive box for brachiaria seeds is recommended to adjust the seeding rate to the desired plant population.

Corn is cultivated as if it were single crop, but the growth of brachiaria is influenced by the sowing time, the spacing between rows, the type of hybrid and the plant population. Brachiaria grows in proportion to the light it receives, and in this sense, early sowing, hybrids with short stature and erect leaves allow greater growth of Brachiaria, making it possible to reduce the sowing rate.

To implement the consortium, two situations must be considered:

1) in clean crops (without weeds that are difficult to control), the smallest population of brachiaria plants can be used, with the application of the herbicide atrazine, sufficient to remove tiguera soybeans and weeds that are “easy” to control;

2) in dirty crops (with weedy plants that are difficult to control), it is important to increase the population of brachiaria plants, prioritize their implementation for emergence simultaneously with the emergence of corn, in order to be able to use another herbicide, such as mesotrione or nicosulfuron, to control of weeds and, at the same time, reduce the growth of brachiaria so as not to compete with corn.

In crops infested with broom sorghum (Sorghum arundinaceum), intercropping should be avoided, as the doses of herbicide that control it also eliminate brachiaria.

Other precautions still need to be observed when adopting the consortium. The use of corn hybrids with Bt technology, for example, recent research shows that brachiaria can be used as an alternative refuge for this technology. In this sense, the control of caterpillars, such as spodoptera, must be done with monitoring in brachiaria, also to ensure the formation of the consortium and, thus, control of bedbugs (Dichelops spp..), for example, mandatory in off-season corn, must be carried out with insecticides that also control these caterpillars.

The use of corn hybrids, tolerant to glyphosate, is a weak point in the off-season soybean-corn succession, due to the need for a graminicide herbicide to control tiguera corn in soybean crops, also tolerant to glyphosate. However, in the consortium, it is possible not to apply glyphosate post-emergence of brachiaria, with the aim of guaranteeing soil coverage for soybeans in succession.

Given the above, it is quite logical to conclude that the use of just one technology does not make the farmer's life easier, but rather the use of combined soil conservation technologies and crop management technologies and strategies that will allow plants to express their genetic potential in profitability for the farmer.

By Gessí Ceccon, agronomist at Embrapa Agropecuária Oeste