Costs and benefits of conventional soybean cultivation

In 1995, in the United States of America, through the insertion of the cp4-epsps gene from the bacteria Agrobacterium sp., originated what is currently called glyphosate-resistant soybean, Raundup Ready soybean or simply RR soybean. Around the 2000s, RR soy arrived illegally (white bag) in Brazil, mainly via the borders with Argentina and Paraguay. It quickly became popular with producers and pressure for its regularization increased. It was argued during this period that weed control was beneficial, and species that presented great control difficulties, such as milkweed (Euphorbia heterophylla), black walleye (bidens pilosa) and viola string (Ipomoea spp.), were easily controlled with the use of glyphosate post-emergence of the crop and weed. Finally, in 2005, RR soybeans were legalized for commercialization and sowing in Brazil, and currently the country holds the record for the largest planted area in the world, with 34,86 million hectares, surpassing the United States, which have an area of ​​34,09 million hectares.

In the beginning, the producer gained a window of control, as it was difficult for the weed plant to escape the control stage, since the herbicide glyphosate has systemic and non-selective action. Furthermore, it resulted in lower production costs, as glyphosate herbicide has a low cost per area and provides less machinery input and greater operational capacity at the time of harvest. Soon after, other crops had their genetics modified to confer tolerance to the EPSPs inhibitor glyphosate, such as corn, cotton and canola. Therefore, in some areas there is currently a succession of crops that present tolerance to the same weed control action mechanism in their genetics.

In the Central-West region, for example, it was agreed to carry out the RR soybean/RR corn succession year after year, which generated dependence on the use of the herbicide glyphosate. This dependence and simplification of the weed control system would certainly not result in positive results. It is necessary to always remember that living organisms, whether weeds, insects or fungi/bacteria/viruses, show variability and may present individuals in their populations that are naturally resistant to a certain control action mechanism.

Therefore, the almost unique and exclusive focus on controlling weeds with glyphosate resulted in the selection of some resistant species, such as ryegrass (Annual ryegrass), horseweed (Conyza spp.), bittergrass (Digitaria insularis) and, more recently, in March 2019, a statement from Embrapa identified the resistance present in dairy individuals (Euphorfia heterophylla). The latter is of unique importance, as it is difficult to control by herbicides and now demonstrates biotypes with cross-resistance to ALS and Protox mechanisms of action, in addition to EPSPs inhibitors. Its control becomes difficult in the field and the options for herbicide action mechanisms that control it are increasingly scarce. It is clear that, with continued dependence on the use of glyphosate, resistant plants will increase in species and number of individuals, therefore, the producer may choose to increase the dose of glyphosate, higher than those recommended in the leaflet that control in the first place. This makes the problem worse. Another alternative is to combine the use of glyphosate with other mechanisms of action present. Due to its still efficiency and low cost, the use of glyphosate will continue in crops.

In this context, herbicides that had been drastically “excluded” from the soybean production system return to the management composition, to control resistant individuals. In general, the use of pre-emergent herbicides (diclosulam, sulfentrazone, etc.) has been observed, in addition to the association of glyphosate with latifolicides (2,4-D, etc.) or graminicides (clethodim, fluazifop-P-butyl, etc. .), as well as the association of glyphosate with soy-selective herbicides (chlorimuron, imazethapyr, etc.). These associations and uses vary depending on the flora present and resistant in each area.

In addition to the use of different action mechanisms, the management strategy must be modified. A clear example is the control of fleabane in RR soybeans. The best management of this weed consists of controlling it in the early stages during the off-season. Horseweed management in post-emergence of soybeans is not recommended, due to the few herbicide options that can be used (Table 1) and the development stage of the weed plant. Likewise, the best management of bittergrass is carried out in the initial stages, before the “clumping” process. After this process, it may be necessary to combine mechanical management (mowing) with the use of graminicidal herbicides in the post-sprouting period.

It is obvious that the incorporation of action mechanisms and management strategies can make the production system more expensive. The cost of control in areas with glyphosate-resistant bittergrass at an advanced stage of development can increase by 290% and if there is simultaneous horseweed infestation, the cost can be 403% higher. Bittergrass, for example, presents control difficulties with graminicides (fenoxaprop and haloxyfop) and its late control may require sequential applications that involve a first application with systemic herbicides (example: glyphosate and graminicides) and sequential applications with contact herbicides ( ammonium glufosinate and paraquat).

Given this, conventional soybeans are expanding due to comparisons between production profits in agricultural areas. Conventional soybeans are receiving a bonus of an average of R$7,76 per bag, mainly due to the consumer market, with high demand for a GMO-free product. In this way, despite production costs being relatively higher, sales values ​​are also more valued. It is also worth noting that conventional soybean production has financing programs, which helps to make production more profitable.

Regarding the total cost of implementing soybean cultivation, for the 2020/21 harvest, an estimated value of R$3.990,60 and R$4.102,84 per hectare is observed (Table 2), respectively for transgenic soybeans and conventional soybeans (Imea, 2020).

An advantageous example is shown in Table 3, where profits are obtained by calculating the harvest simulation, and for the 2019/2020 harvest an average productivity of 52,1 bags per hectare is expected. Profits from conventional soy were estimated at R$757,30 and from transgenic soy at R$677,14 per hectare. Although the expenses for conventional soybeans are higher (Table 2) and its productivity is slightly lower (Imea, 2020), the payment of the grain bonus at an average value of R$7,76 per bag makes its profitability per hectare higher .

RR soybeans were developed to resist the herbicide glyphosate, reduce the number of herbicide applications during the crop cycle, facilitate management and reduce costs. Its successive use, however, selected resistant species and currently its single use as a control measure is no longer efficient, therefore, the producer must opt ​​for other mechanisms of action, which tends to make management more expensive. It is therefore observed that RR soy generates management gains only in the first few years, as the continuous use of glyphosate predisposes the development of resistant weeds. And, from the fourth year onwards, transgenic crops require the same cultural treatment as conventional varieties or even greater quantities of herbicides.

There is also pressure from the consumer and import market, which encourages bonuses on conventional products at the time of sale. Thus, profitability of up to 10,6% higher (Table 3) can be achieved when using conventional soybeans. It is clear that glyphosate will continue to be a key part in the production system of the most varied crops, but it is time to put the feasibility of exclusively using cultivars that are resistant to this herbicide to the fore.

Emerson Trogello, UFV; Giovana Cândida Marques, Lucas Luis Faustino and Ana Caroline de Araújo, Instituto Federal Goiano