Liming is a crucial practice for the production of soybeans and other crops in the Mato Grosso savanna. The Mato Grosso Agricultural Research Support Foundation (MT Foundation) has been conducting an experiment for 15 years that evaluates different production systems involving the management of this practice, divided into ‘Liming in soybean crops’ and ‘Crop rotation in soybeans’. The experiment is conducted at the institution's Learning and Diffusion Center, in Itiquira/MT (CAD Sul).
The production systems in the crop rotation experiment include oilseed monoculture, crop succession with a focus on soybeans and crop rotation involving soybeans, sunn hemp and corn crops or second crops intercropped with brachiaria, varying over time. The ‘Liming in soybean cultivation’ experiment involves three production systems (monoculture, succession and crop rotation) and different doses of lime.
Felipe Bertol (photo above), researcher in Soils, Nutrition and Production Systems at Fundação MT and responsible for the experiment, highlights that the objective has always been to guide farmers about the impact of their decisions on farming and defend more sustainable agriculture. These objectives were updated and renewed over time.
Researcher Felipe Bertol found that in the first six years of a trial, there was no significant difference between the systems tested. If the experiment had ended during this period, the conclusion would be that the adoption of straw and soil degradation did not generate different results.
However, due to a series of events, such as the increase in the soybean cyst nematode population (Heterodera glycines), the introduction of varieties with a shorter cycle and the occurrence of water deficits, crop succession and rotation systems began to present better results than monocultures.
According to Bertol, this difference remained over time, reaching a maximum production of 91 bags per hectare in a record year. However, in the last three years, climate variability and the increase in cyst nematodes have caused differences between production systems, but it is still not possible to clearly predict the impact of crop rotation and succession on soybean productivity.
Another important point observed in one of the monoculture systems is the soil disturbance, where the introduction of brachiaria three years ago led to a rapid and evident increase in soybean productivity. In three harvests, the amount of straw on the surface provided by brachiaria in the second harvest resulted in production ceilings similar to those of crop succession in a short space of time, compared to soil disturbance. The researcher adds that the conclusion is still inconclusive and requires further studies.
“What the farmer is doing is not completely inadequate.” This was one of the main findings of the experiment, according to the expert, however, there is the caveat that, if the producer maintained so-called conventional agriculture, that is, with fallow and/or soil disturbance, the scenario would be devastating. Furthermore, the results indicate that corn, as a second crop, is good for the system and is on par with the other cover crops tested when it comes to crop succession.
In parallel, the research demonstrates the importance of crop rotation in managing nematodes and also in promoting better straw conditions, which stand out in years with water deficit. “This happens in all systems, whether rotation or succession, which contribute organic material and soil structure”, defines the expert.
Finally, regarding soil, the researcher states that the pillar: physics – chemistry – biology has a great impact on productive potential. “Chemically the systems are very similar, but the production ceilings are much lower in monocultures in relation to crop succession and rotation and the reasons are the biological and physical conditions of these environments”, explains Bertol.
In the 10th and 11th year of the experiment, the researchers involved began to observe an increase in nematode populations in some of the cultivation systems, which, despite already being present, grew because the environment began to provide conditions for this. The species found were Heterodera glycines, Pratylenchus brachyurus e Rotylenchulus reniformis.
Rosangela Silva, nematologist and researcher at Fundação MT who has been following the experiment since the beginning, explains that in the case of the cyst nematode, the increase in doses of lime and the lack of coverage in the environment (organic matter) greatly favored the growth of populations .
“Especially when it was prioritized to cultivate susceptible soybeans, thinking only about the productivity of the material and leaving aside the problem with the nematodes that occur”, he adds.
In the rotated system, the specialist says that the cyst populations were smaller, due to the diversity of coverage and the increase in microorganisms antagonistic to the cysts. “In a more biologically diverse or biologically more active environment, the nematode population was smaller and there was an increase of 17 bags of soybeans compared to the soybean-fallow system”, she explains.
The message that remains after the long period of experiment, according to Rosangela, is that even in a diverse environment for the cyst nematode, if the resistant cultivar is not prioritized there will be losses in productivity.
“The environment helps, but other management tools cannot be forgotten, so the first thing to know is which species do you have? How big is the problem, how is it distributed in the area and which management tools should be prioritized? Thus, the producer can expect the desired productivity, paying the production costs”, advises the nematologist.
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