The Agricultural Climate Risk Zoning (Zarc) is more complete, as it now has six different types of water classes available in the soil. Previously, there were three divisions that only took into account the concentration of clay in the composition. In the new way of identifying land types, there is a formula that involves the percentage proportion between clay, silt and sand, correlated with the amount of water that can be stored in the soil, the so-called Available Water index (AD). In practice, from now on, producers will have to download an application and/or a spreadsheet to identify their soil class according to the new rules. The first crop to adopt the new parameters will be soybeans in the 2023/24 harvest.
The rules for the new classification are in Normative Instruction (IN) 1/2022, from the Agricultural Policy Secretariat (SPA) of the Ministry of Agriculture, Livestock and Supply (Mapa), in force since July 1st. The old standard (IN SPA/Mapa 2/2021), which establishes soil types based on clay concentration, remains in force. This is because all Zarc ordinances use the current methodology, valid until a new one is published, which always happens before the start of the harvest, if any.
The new methodology was developed and validated by the Brazilian Agricultural Research Corporation (Embrapa) Solos, with participation from the production sector. “The systematic methodology updates began in 2017, the year in which we had a meeting at the headquarters of the FAEP/SENAR-PR System, in which the changes and technical criteria were presented by the Embrapa team for soybean Zarc”, recalls Ana Paula Kowalski, technician from the Technical and Economic Department (DTE) of the FAEP/SENAR-PR System.
In view of the change, the producer needs to know, to stay up to date with his obligations, that the new class method from AD1 to AD6 considers the three soil fractions (clay, silt and sand). “The new formula that classifies soils is more complex, better considering the interactions that result in the water storage capacity of the different soils we have. This is one of the main parameters for determining the recommended planting period for each crop in the Zarc methodology”, explains Ana Paula.
Zarc defines the best time to cultivate in Brazil, as it indicates the probability of production losses for a given crop and by municipality, signaling sowing periods with lower climate risk. This zoning is obtained from a broad official database, systematized by Embrapa, which involves historical climatological series, soil types, behavior and requirements of the planted species, types of cultivars and production systems. Based on this, the risk classifications are 20%, 30% and 40% (these strata remain unchanged).
Complying with Zarc is a mandatory requirement for granting agricultural financing by financial institutions, within the scope of rural credit and access to Proagro and Proago Mais. Furthermore, planting within the Zarc periods is also mandatory for those who access the federal subsidy when contracting agricultural insurance, and insurers may even be more restrictive in the periods or types of soil accepted for contracting.
Hugo Borges Rodrigues, general coordinator of agricultural risk at Mapa, explains the changes in soil classification and the impacts on national agriculture:
Why did the Map change the soil classification?
Zarc is a technical-scientific tool whose methodology was developed in the 1990s. The new soil classification in Zarc is part of a set of advances in methodology and parameters. Estimating soil water storage capacity is fundamental for studies of agricultural production risks in simulation and planning models such as Zarc. The direct assessment of the volume of Available Water (AD) is quite costly, as it involves the collection of undisturbed samples and evaluations carried out by specialized laboratories. This difficulty has led researchers to look for indirect ways of estimating soil AD. With the publication of the new normative instruction, the classification was simplified to be estimated based on the granulometric composition of percentage contents of sand, silt and clay. This will allow for a greater range of classified soils.
How did you arrive at this model of six types?
The new classification methodology was based on the research “Prediction of water available in the soil based on granulometry for use in risk analyzes in Agricultural Climate Risk Zoning”, by Embrapa. The work was a request from Mapa for improvements to the Zarc methodology.
When will the new way of classifying soils be adopted?
Zarc studies are updated by culture at the national level. It is natural that some cultures take between three and five years to be updated with new methodologies. Thus, Zarc's studies carried out in the format of three types of soils remain valid until a new study is carried out for culture. The first crop that will have a new format, already valid for the 2023/2024 harvest, will be soybeans, the results of which (Zarc ordinances) will be released in December 2022. The anticipation of the release of the results (which have already been validated with the agents interested parties) aims to provide greater predictability for adapting to the new format.
In practice, what does the producer need to do in relation to what he was doing?
The producer needs to have a soil particle size analysis that is representative of the planting area. In practice there is no change, as to classify the soil in the previous format (three types of soil) it is also necessary to know the contents of sand, silt and, mainly, clay. Therefore, existing analyzes are valid for classifying soils in the two formats used by Zarc. It is worth noting that in the “Zarc Plantio Certo” application it is possible to enter the sand, silt and clay contents to classify soils into six AD classes and a calculator is also available on the map website to facilitate classification.
What benefits does the new classification model bring to the producer?
The main thing is the best indication of the risk to which the producer is exposed. There is also a greater coverage of Brazilian soils (more than 90%), as the previous classification did not consider soils with less than 10% clay content, and with more than 35% clay they were classified in just one class.
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