IAC survey shows that balanced micronutrients benefit the productivity and quality of citrus

Several factors are taken into consideration in citrus production, some of which may be almost imperceptible to the naked eye. However, researchers from the Agronomic Institute (IAC), of the São Paulo State Department of Agriculture and Supply, are attentive to all stages of cultivation and warn about the importance of micronutrient supplies in the soil and leaves for the health of orchards. . IAC studies show that boron, manganese and zinc are the most limiting micronutrients for citrus production. The results are the result of a survey carried out with samples sent to the IAC laboratories by producers from the Brazilian Citrus Belt, in the State of São Paulo and Triângulo/Southwest of Minas Gerais. The samples sent by citrus growers represent 10% to 15% of the citrus area planted in Brazil.

The IAC soil and plant laboratories are references in Brazil and adopt analytical methods developed in the IAC System. According to IAC researcher Rodrigo Marcelli Boaretto, the survey is essential to provide guidance to citrus growers, considering that nutritional imbalance, caused by a lack or excess of a nutrient, can compromise the productivity and quality of citrus fruits. "Based on the survey carried out, we found that around 25% of the soil samples sent to the IAC laboratories showed lower than adequate boron and manganese levels, while for zinc this value was close to 50%", he says. As for leaves, the average percentage of samples with micronutrient levels lower than adequate were 8,2%, 22,4% and 36,7%, respectively for boron, manganese and zinc.

According to Boaretto, the increase in productivity in Brazilian citrus farming is one of the factors that most impacts micronutrient deficiency. In the 2019/2020 harvest, the average productivity in the Citrus Belt was 42 tons per hectare, whereas at the beginning of the 1980s this productivity was less than 20 tons per hectare per year. Other factors can also intensify the demand for micronutrients, such as early production, climate change and cultivation of materials that are more demanding in micronutrients. For example, the Citrumelo Swingle rootstock, which represents around 70% of new plantings, has a greater demand for boron than Cravo lemon, a rootstock that previously occupied around 90% of national orchards.

The researcher comments that, associated with factors that have intensified the demand for micronutrients by citrus crops, there has been an increase in the number of products in the spray tank mixture, due to the greater incidence of phytosanitary problems. This procedure increases the chances of incompatibility between the components and can reduce the efficiency in the absorption of micronutrients by the leaves. "Although foliar fertilization has always been carried out in conjunction with the application of pesticides, in order to reduce operational costs, this procedure affects the efficiency of nutrient absorption by the leaves", he states.

The researchers recommend that zinc and manganese corrections should be made via foliar spraying. Boron should preferably be applied via soil. "However, foliar applications with boron can be carried out in situations in which sufficient amounts of this nutrient cannot be supplied via the soil", advises the researcher. On average, producers spend between R$100,00 and R$400,00 on micronutrients, depending on management, productivity and age of the orchard.

Over the last 20 years, the IAC citrus nutrition team has been seeking information in order to establish parameters for optimizing fertilization in orchards. The research is supported by the São Paulo Research Foundation (FAPESP), the National Council for Scientific and Technological Development (CNPq) and partnerships with the private sector.

The current IAC recommendations suggest that in orchards under development, less than four years old, four to six annual applications with boron, manganese and zinc should be made to the leaves. This management must be adopted from September to May. In orchards in production, the recommendation is three to four sprays with manganese and zinc per year. These applications must be made from the beginning of spring until the end of the rains, trying to reach the new shoots, with the leaves already expanded on the plant. For greater micronutrient absorption efficiency, these foliar applications must provide good wetting of the plants.

"Dosages of foliar fertilization with micronutrients consist of preparations of solutions containing nutrients in proportions, per liter, of 200 to 300 milligrams of boron; 300 to 700 milligrams of manganese; and 500 to 1000 milligrams of zinc; in addition to the adjuvant based on urea of ​​five grams per liter", explains the IAC researcher, from the São Paulo Agribusiness Technology Agency (APTA).

Still according to Boaretto, the greater incidence of Citrus Canker and other fungal diseases has intensified the use of copper-based pesticides in orchards in the Brazilian Citrus Belt, which has been increasing copper levels, both in the soil and in the leaves, to very low values. higher than those considered appropriate. "The producer must pay attention to the intensive use of copper-based pesticides, seeking to associate other phytosanitary management strategies, in order to reduce the quantities of this micronutrient, as, in some situations, it can compromise the productivity of Brazilian orchards", advises