High doses of limestone increase productivity in Matopiba

The use of high doses of limestone for growing first-crop soybeans in the Matopiba region guarantees an increase of up to 30% in productivity, in relation to the doses recommended by official documents. The practice does not cause an imbalance in soil fertility, although a decrease in nutrients may occur, which can be corrected with fertilization. These are the main conclusions of the studies that have been conducted by Embrapa Meio-Norte (PI) in the states of Piauí, Maranhão and Pará since 2019. Matopiba covers part of the states of Maranhão, Tocantins, Piauí and Bahia.

The research began following a request from the Association of Soybean Producers in the State of Piauí (Aprosoja-Piauí), which identified, together with some producers, the use of higher doses of limestone in some areas. Embrapa researcher Henrique Antunes explains that the practice has been adopted due to the value of this commodity.

“Producers have been opening areas with higher doses of limestone and are already planting soybeans, which bring a certain return. In other situations, they start with forage and in the second year they introduce soybeans,” he says.

The adoption of this practice, without technical-scientific support, makes it difficult for producers to access bank credit, “which is why research helps to generate new criteria that bring more security to the farmer”, believes Antunes.

He states that most of the official documents on soil fertility were prepared based on research from the 1980s and 1990s and that today farmers use soybean cultivars with different characteristics and nutritional demands, more intensive soil management systems and greater amounts of biological and nutritional inputs. “All of this justifies the need to review official documentation, especially for agricultural frontier regions with unique conditions,” he argues.

Embrapa's first study on the subject, conducted in partnership with the Federal University of Piauí (UFPI), sought to evaluate the effects of applying large amounts of limestone and gypsum in open areas on soil fertility, plant nutritional status and soybean productivity in the Cerrado region of Piauí. Gypsum combined with limestone helps improve soil characteristics by reducing its acidity.

Research

The experiment was conducted over two agricultural harvests (2019/2020 and 2020/2021) using the soybean cultivar BRS9180. Five doses of limestone (zero, 5, 10, 15 and 20 tons per hectare) and four of gypsum (zero, 1, 2 and 4 tons per hectare) were tested, in plots measuring 13,2 x 6,6 m. The doses of 5 tons per hectare of limestone and 1 ton per hectare of gypsum are the closest to the currently recommended standard.

The results indicate that limestone doses close to 15 tons per hectare practically neutralize soil toxicity due to aluminum. Doses between 10 and 15 tons per hectare increased the concentrations of phosphorus and potassium, but larger amounts (between 15 and 20 tons per hectare) reduced the concentrations of these elements and micronutrients, which caused a loss in grain yield.

Agricultural engineer Doze Batista de Oliveira, who wrote his doctoral thesis at UFPI based on the results of the project, explains that the application of a dose of 10 tons of limestone per hectare resulted in significant increases in soybean productivity, with increases of 18% and 12% in the 2019/2020 and 2020/2021 harvests, respectively. “This shows that liming promoted improvements in soil fertility, which boosted grain production. The combined use of gypsum and limestone provided a rapid improvement in the chemical characteristics of the soil, with a reduction in acidity at depth,” explains the agronomist.

After the initial studies in partnership with IFPI, Antunes has been conducting other research activities in the Matopiba region and in Pará with the support of the FertBrasil Network and resources from the Studies and Projects Financing Agency (Finep). According to him, subsequent data reveal an increase of 20% and even 30% in soybean production in areas where high doses of limestone and gypsum were used.

He explains that when soil characteristics are corrected by applying these amendments and there is good incorporation, plant roots are able to explore the soil better, reaching layers they were previously unable to reach. There, they find water and nutrients and go through the dry season under less stress.

“The use of correctives creates an environment conducive to the full development of plants, something fundamental especially in regions on the agricultural frontier, such as Matopiba, which has slightly more sensitive climate conditions and where soil fertility is still being created,” highlights the researcher.

The researcher draws attention to the decrease in the concentrations of phosphorus, potassium and micronutrients in the soil when high doses of limestone are used. This is reflected in the reduction of macro and micronutrients in the plants, so it is necessary for the producer to pay attention to fertilization that corrects these deficiencies.

Consultant Diógenes Brandalize has had a positive experience. He works on a 3-hectare property in the municipality of Água Branca (PI), where he grows soybeans, corn, sorghum and millet. He used to use 4 tons of limestone and half a ton of gypsum per hectare. Three years ago, he started using higher doses to increase production. The result was a 20% increase in productivity. Brandalize believes that producers in the region are beginning to adopt this practice. “There is a slow and gradual migration taking place; in some cases, producers are paying the higher total dose in installments. The difficulty in accessing credit is somewhat of a hindrance,” he says.

There are farmers who participate in the project, continue with traditional management and await the final results of the research. This is the case of Luís Fernando Devicari, who produces soybeans and corn, in addition to raising cattle and sheep on a 1.020-hectare property at Fazenda Barbosa in Brejo (MA). Devicari reports that he usually uses about three tons of limestone per hectare in open areas and, every two or three years, adds one ton per hectare. “In some areas with more deficits here in the region, producers use larger doses. Here on the farm, we analyze the soil every year and, when necessary, we add limestone,” he says.

Agricultural engineer and consultant Christofer Andre Garanhani, from Paragominas (PA), states that the studies have helped producers make decisions about the volume of limestone to be used on their properties. “With the extension of very clayey areas that we have, the doses of limestone need to be reviewed. And the work here has proven that we need increasing doses, mainly for composition, profile formation and then, logically, for replacements.”

He says that there was an expectation that even higher doses would be used, but with the results of the research they understood how limestone should be used, seeking balance for soil quality. Garanhani believes that the biggest barrier to adopting this practice is the higher cost. “In a border region, we have a lot of opening, construction and infrastructure costs, but I believe that most producers know that low doses no longer have the same effect, especially when we are dealing with cultivars that already have high genetic potential”, he analyzes.