Agricultural zoning and wheat sowing time

The Ministry of Agriculture adopts the “Agricultural Climate Risk Zoning” (ZARC) to define regions and times most appropriate for agricultural cultivation, considering rainfall, evapotranspiration, soil types, crop cycles, phenological phases and adaptation of cultivars. The main objective of ZARC is to support the definition of the “credit policy for official agricultural funding and private and public rural insurance”, aiming to reduce the risks of losses caused by climatic adversities. In traditional wheat growing regions in Brazil, the greatest risks of production loss are related to: 1) high temperature and water deficiency (in the tropical region); 2) frost in the ears; 3) excess rainfall after heading, causing diseases that are difficult to control, such as Fusarium head blight in the temperate region and blast in the tropical region; and 4) excess rain during harvest, causing the loss of technological quality of the grains.

The wheat sowing periods (by ten days), for each Brazilian municipality, are officially indicated by ZARC, whose annual review is previously made available on the internet (http://www.agricultura.gov.br/assuntos/riscos-seguro/risco -agriculture/decrees/decrees). It considers three groups of cultivars with similar cycles (early, medium and late), three groups of soils (sandy, medium texture and clayey) and three risk levels (20%, 30% and 40%). 

A limitation of ZARC is that it does not consider the probability of occurrence of wheat ear diseases (head blight and blast), due to the high difficulty in predicting the simultaneous occurrence of two environmental conditions necessary for fungal infection in the ears: high temperatures (20 to 25 ºC for Fusarium head blight and 24 to 28 ºC for blast) and long periods of rainfall (48 to 72 hours for Fusarium head blight and 15 to 40 hours for blast).

Therefore, the farmer needs to know the rainfall and temperature history of his property or municipality, to define the best wheat sowing date, avoiding post-earing weather conditions favorable to these diseases. As an example, in 2017, ZARC - considering the risk of losses of 20% - indicated the wheat sowing period in Londrina – PR from March 21st to May 10th, in order to minimize the risks of frost and excess water. rain at harvest. However, farmers and researchers have verified (in the 2009, 2011, 2015 and 2017 harvests) that wheat sowing carried out before April 20th intensifies the occurrence of blast in northern Paraná. Therefore, the sowing time must be chosen also considering the probability of the disease occurring.

We conclude that the sowing time based on ZARC is an important wheat crop management tool, as it reduces the risks of loss of grain productivity due to climatic adversities. Furthermore, the farmer who is well aware of the climate history of his property and how diseases spread will be better able to choose the ideal sowing time, which is a key factor in the success of the crop.