Cover crops increase cotton productivity

Cultivating cotton after cover crops increases productivity by approximately 30% compared to the conventional cotton monoculture system. This is what Embrapa research reveals, which has been carried out at the Bahia Foundation's experimental field, in Luís Eduardo Magalhães, a municipality in western Bahia. The objective is to show the efficiency of cover crops in improving the physical and chemical characteristics of the soil for cotton cultivation, resulting in better use of water and greater fiber productivity.

Responsible for the experiment, Embrapa Algodão (PB) researcher Júlio Bogiani highlighted the potential of vegetation cover for soil and water conservation, ensuring superior productivity even in adverse weather conditions. "In recent years, the western region of Bahia has been facing problems of prolonged summers with drops in cotton productivity. When these summers occur in stages of high water demand by the plant, the losses are even greater. Alternatives such as the practice of the planting system direct (SPD) and the use of soil cover with biomass can minimize these problems, as they reduce water losses through evaporation, and consequently increase the efficiency of soil water use by crops", he notes.

According to Bogiani, in four years of studies, all alternatives for cotton cultivation in SPD showed greater productivity and productivity stability than cotton cultivated in a conventional soil preparation system (the most used in the western region of Bahia), especially in the years with greater problems of irregular rainfall, which lead to a huge drop in the productivity of cotton plants grown in conventional systems.

Direct vs. conventional planting

In the 2014-2015 harvest, two areas of the same size were cultivated, one with cotton and the other with soybeans. In the area cultivated with soybeans, immediately after harvesting the grains, desiccation was carried out to control weeds and volunteer soybean plants, followed by the implementation of five cover crop options for biomass formation. One area had only brachiaria ruziziensis and the other four had brachiaria ruziziensis in alternating rows with grain sorghum, Crotalaria ochroleuca, Crotalaria spectabilis and dwarf pigeon pea.

In the following harvest, the cotton plant grown after Brachiaria ruziziensis in an intercrop with sorghum showed the best productivity, reaching 5.493 kilos of seed cotton per hectare. "In this area we had an increase of 1.443 kilos per hectare, which represents a gain of more than 35% in relation to the productivity of the area with cotton monoculture in a conventional system", says Bogiani.

The average productivity of seed cotton in the area with cultivation of cover crops and sowing of cotton in SPD was 5.292 kg/ha, while in the area with cotton monoculture in conventional system the average productivity was 4.048 kg/ha. This means an increase of 30% (1.243 kg/ha) in cotton productivity in the direct planting system.

In the cotton monoculture area, the soil was prepared conventionally, with a subsoiler and harrows. In the area with the cover crops, the soil was not prepared mechanically, with the cover crops only being cultivated until desiccation with herbicides for direct sowing of cotton. Fertilization management and other cultural treatments were identical in both areas.

Other benefits

Embrapa Algodão researcher Alexandre Cunha de Barcellos Ferreira, who studies cover crop cultivation systems for direct sowing of cotton, emphasizes that in addition to gains in productivity, some cover crop species can improve the property's production systems, by minimizing pests, weeds, diseases and nematodes for successor crops; cycle nutrients extracted from deeper layers; increase the water and nutrient retention capacity and productive potential of the soil.

He warns to be careful when choosing crops in succession schemes. "When the producer grows certain crops in succession, it can encourage infestations of pests and diseases on the property. This is the case with cotton cultivation, in the off-season, after soybean cultivation, which is very common in the Cerrado. This type of succession can increase the population of some nematodes, insects and fungi", he states.

To prevent the spread of polyphagous pests (which affect several crops), nematodes and fungi, it is necessary to choose cover crops appropriately. In rotation schemes, the selection of crops that are not common hosts for pests and diseases is one of the fundamental strategies in agriculture for integrated management.

"There is no species that is ideal for correcting all problems in the production system. The choice of species must be based on the problem that you want to prevent or remedy", he points out.

The researcher points out that in addition to the medium and long-term benefits, some cover crops can be profitable in the short term. "In addition to producing dry matter for direct sowing of cotton and minimizing problems in the production system, they can also produce grains or seeds, which can be sold or used for animal feed, or even as seeds for cultivation in new areas", he says. .

Direct planting system

The direct planting system is a form of conservation management whose basic principles are soil cover, crop rotation and direct sowing into straw (with minimal soil disturbance). This layer of straw creates a favorable environment for plant development, helping to stabilize production and improve or maintain the physical, chemical and biological properties of the soil.

Cover plants have the function of producing biomass to form straw on the soil surface, leaving it protected and less susceptible to erosion. Over the years, the roots of cover crops increase the straw on the soil surface and the absence of soil disturbance improves its structure, nutrient cycling and water retention.

According to researcher Júlio Bogiani, it is common for producers to confuse planting on straw from crop residues from the previous harvest with the direct planting system. "Usually this straw is not enough to cover the soil and it degrades easily due to high temperatures," he explains.

This is the case of cotton, which in Brazil is normally grown in rotation or succession with soybeans. After the soybean harvest, the areas remain fallow during the off-season. "As soybean crop residues are quickly decomposed, during the autumn/winter/spring period, until the sowing of the cotton crop, the soil is poorly protected by crop residues. One strategy to produce dry matter after soybean cultivation is the cultivation of cover crops in the second harvest", recommends Ferreira.