Rational fertilization increases the nutritional quality of cowpeas

Rational management of soil fertilization with higher doses of phosphorus and zinc significantly increases the nutritional quality and productivity of cowpeas (Unguiculata vine), also known as cowpea and macassar beans. A researcher study Francisco Brito,  Embrapa Mid-North (PI), revealed that  applications of doses of minerals in the soil increased the crude protein content in the grains by 8,3%, reaching a maximum value of 30,3%, a percentage considered high for the crop. Most cultivars reach 22% crude protein, according to Brito.

The other important result of the research that excited the scientist was grain productivity. Fertilization generated a net return about three times greater compared to crops that did not receive fertilizer. The experiment revealed a maximum value of 1,8 tons per hectare under rainfed conditions. The average productivity of cowpea varieties in Value of Cultivation and Use (VCU) trials, which is the protocol of the Ministry of Agriculture, Livestock and Supply (Map) for cultivar registration, reached up to 1,6 tons per hectare, also without irrigation. The ones that stood out the most were: BRS Guariba (1,4 tons), BRS Imponente (1,3 tons), BRS Itaim (1,6 tons) and BRS Aracê (1,2 tons).

The research into rational fertilization management was developed with the cultivar BRS Imponente, launched by Embrapa in 2016. The experiments were conducted in a soil classified as Oxisolo Amarelo Distrocoeso, of medium texture, in the municipalities of Magalhães de Almeida, in the eastern cerrado of Maranhão, 409 kilometers from São Luís; and Parnaíba, on the coast of Piauí, 370 kilometers from Teresina. 

The experiment The work was carried out over a year. The first stage, which corresponded to grain productivity, was carried out in the field using a randomized block statistical design, in a factorial scheme of four doses of triple superphosphate (0, 89, 178 and 267 kilos per hectare) associated with four doses of zinc (0, 10, 20 and 30 kilos per hectare), with  three replications. The zero dose corresponds to the experiment without the fertilizer (control). The maximum technical response to the doses was 102 kilos of triple superphosphate associated with ten kilos of zinc sulfate in grain productivity per hectare, reaching 1,8 tons.

The experiment

The work was carried out over a year. The first stage, which corresponded to grain productivity, was carried out in the field using a randomized block statistical design, in a factorial scheme of four doses of triple superphosphate (0, 89, 178 and 267 kilos per hectare) associated with four doses of zinc (0, 10, 20 and 30 kilos per hectare), with  three replications. The zero dose corresponds to the experiment without the fertilizer (control). The maximum technical response to the doses was 102 kilos of triple superphosphate associated with ten kilos of zinc sulfate in grain productivity per hectare, reaching 1,8 tons.

Producer revenue can be three times higher

The study showed that the cost-benefit ratio with rational fertilizer management was high and that it can improve the economic performance of the activity. For every real invested in management, there was a net return of R$8,07, considering fertilizer prices and the market value of a kilo of beans. Today, the price of a 25-kilo bag of triple superphosphate is R$71,16 and that of zinc sulfate, with the same quantity, costs R$204,99. The retail price for a kilo of beans is R$5,00. The research revealed that the producer's income per hectare is R$2.735,00 without the use of fertilizers, and R$8.500,70 with rational fertilization, discounting the cost of fertilizers, that is, a value three times higher.  

The researcher clarifies that only the variable cost of crops compared without and with fertilization was considered. The reason is that fixed costs are common for both.

Phosphorus and zinc are fundamental elements, according to the researcher. “Because tropical soils are poor in nutrients, these minerals need to be absorbed by plants to perform functions in metabolism, such as, in the case of phosphorus, the synthesis of carbohydrates and accumulation of energy”, explains the scientist. As for zinc, Brito explains that it is important in the synthesis of tryptophan, an essential amino acid for the plant, responsible for the formation of proteins. “It also acts as a regulator of a large number of enzymes, important in plant metabolism”, he adds. 

Increased crude protein content

In the second phase, the research investigated the nutritional quality of the grains, revealing a significant increase of 8,3% in the crude protein content. The maximum value achieved was 30,3%. In chemical analyses, the revealed values ​​of phosphorus and zinc in the grain were excellent. Phosphorus went from two to four milligrams. Zinc went from 43 to 53,4 milligrams. The analyzes were carried out in the Embrapa bromatology laboratory, in Teresina (PI). 

The result of the study, in the opinion of researcher Edson Bastos, from Embrapa Meio-Norte, “brings a great contribution to the technical-scientific community and cowpea producers in the region, as it identifies the doses of phosphorus and zinc that maximize both the productivity as well as the nutritional quality of the grains”. According to him, the other “valuable” contribution of the work was the finding that the higher zinc content in the soil increases the protein in the grain.

“With these results, cowpea producers in the region will be able to apply the appropriate amount of fertilizer and, therefore, achieve greater profits from the crop”, highlights Bastos, stressing that the farmer must always carry out a soil analysis before cultivation, as fertilization recommendations vary according to the fertility of the soil to be sown.

For the Embrapa researcher Henry Antunes, the research results are important, as in addition to discovering a way to increase productivity per area, they contribute to the generation of a product of better nutritional quality. “However, fertilization trials require more than one harvest, so that the results obtained can be consolidated and allow for safer recommendations”, considers Antunes. In this study, experiments were conducted in three harvests.

Work like this by Brito, according to Antunes, “shows the importance of the macronutrient phosphorus and the micronutrient zinc for soil fertilization programs”. The Cerrado biome naturally has low levels of minerals such as phosphorus and zinc, which has always been, according to the scientist, a major limitation to productivity in these areas. “Because of this, fertilization contributes to the calibration of optimal and economic doses, maintaining soil fertility and ensuring the longevity of production systems”, he declares.

Success numbers

Anchor of food and nutritional security among low-income consumers, mainly in the North and Northeast regions of Brazil, beans are rich in carbohydrates, fiber, vitamins and minerals such as iron, calcium, magnesium, zinc and phosphorus. In 2019, according to the Systematic Survey of Agricultural Production by the Brazilian Institute of Geography and Statistics (IBGE), the country produced just over three million tons of beans. The largest producers were, respectively, Paraná, Minas Gerais, Goiás, São Paulo, Bahia and Mato Grosso. The planted area was 2,8 million hectares. The harvested area reached 2,7 million hectares.

In 2019, Brazil maintained its pace in bean exports, although with a timid increase in numbers. According to the Brazilian Institute of Beans and Pulses (Ibrafe), headquartered in Curitiba (PR), the country exported more than 166 thousand tons to 81 countries, with revenues of almost US$113 million. According to the entity's president, Marcelo Eduardo Lüders, 55% of exports were cowpea. The rest was common beans. The main buyers were India, Vietnam and Pakistan, respectively. In 2018, bean exports reached just over 163 thousand tons, which totaled US$92 million in revenue.