A large number of factors can interfere with soybean crop productivity, such as climate, phytosanitary management, soil fertility and the environment in which soybeans are grown. However, the combination of all these factors corresponds to the periphery of management where the central point is the plant and its potential to use these factors to express its productive potential.
The basis of soybean cultivation is, without a doubt, the use of cultivars best adapted to the property's production system. Faced with materials with increasingly significant productive potential, the specificity of the region where it will be cultivated becomes fundamental for the expression of its genetics. Aspects such as the adaptation of the cultivar to the region, incidence of radiation, precipitation, wind, altitude, thermal amplitude, productive stability, cycle, tolerance to stress and diseases, resistance to herbicides and insects must be taken into consideration when choosing the cultivar. grow crops.
Recently, with the advance of soybean cultivation in the southern half of the state of Rio Grande do Sul, soils historically destined for the cultivation of irrigated rice are being cultivated with soybeans. In these floodplain soils or also called lowlands, soybeans have emerged as an alternative for rice farmers to diversify income and cultural management for rice monoculture until then. According to the Rio Grandense Rice Institute (Irga), in the 2012/13 harvest, more than 250 thousand hectares of floodplain area were cultivated with soybeans, suitable for the cultivation of irrigated rice.
Floodplain soils have characteristics of low infiltration and flat relief, making them easily waterlogged, as natural drainage is very poor, due to their proximity to the water table. This scenario provides an unfavorable environment for soybean cultivation due to the long flooded period and, therefore, without oxygen. Therefore, adapting the cultivar to the environment in which it is subjected is essential to achieving successful soybean production.
In this sense, research work was carried out in the city of São Sepé, Rio Grande do Sul, in the 2012/13 harvest, aiming to evaluate the behavior of soybean cultivars in floodplain and coxilha soil.
The two experimental areas were located close together, around 300m apart, but with very different soil characteristics that perfectly characterize the floodplain and coxilha (rainfed) conditions. The cultural treatments carried out were the same, therefore, only evaluating the effect of the cultivation environment. In the floodplain, the cultivars were sown on November 14th, and in the coxilha, sowing took place on December 15th. The plant population tested was the same for all materials, with 15 seeds being used per meter of row, and the spacing between rows was 0,5m.
Figure 1 – Soybean cultivars sown in floodplain areas. São Sepé, 2013
Figure 2 – Soybean cultivars sown in the Coxilha area - rainfed. São Sepé, 2013
The productive performance of the 15 commercial soybean cultivars in different growing environments is shown in Figure 1.
Graphic 1 - Productivity of soybean cultivars depending on the growing environment. São Sepé/RS 2013
The effect of the cultivation environment is directly linked to the adaptability of the cultivar, especially with regard to materials with greater tolerance to hypoxia (low oxygen content in organic tissues). Cultivars with greater amplitudes between productivity in the coxilha and floodplain represent the absence of this strategy in root development, being restricted to cultivation in the first area. Thus, the choice of cultivar for the floodplain environment is even more decisive than for the coxilha environment.
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Symptoms of hypoxia in leaves (left) and tips (right) of soybean plants in floodplains. São Sepé, 2013
In this sense, greater productive stability was observed in the cultivars NS 6211 RR, NS 4823 RR, NS 7100 RR and BMX Potência RR, showing less influence of the environment on productivity. On the other hand, the cultivars BMX Turbo RR, V Max RR, M-Soy 8000 and Monasca were those that had the greatest impact on productivity depending on the environment.
Furthermore, the sowing time factor becomes an important practice to be taken into consideration, given the cultivation environment and the development of cultivars (Figure 2). It was observed that the delay in sowing provided a better productive increase in soybean crops, for all cultivars. This result can be explained by the heavy rains that occurred in the last fortnight of December 2012. During this period, the soybean plants sown on 14/11/2012 were at more advanced stages, therefore, they may have been more damaged by waterlogging. from soil.
Graphic 2 - Productivity of soybean cultivars as a function of sowing date in the floodplain environment. São Sepé/RS 2013
From this work, it can be stated that the cultivars present completely different behaviors depending on the cultivation environment, that is, positive behavior in the floodplain does not mean that it will repeat its performance in the floodplain or vice versa. Furthermore, the sowing time is key to the expression of productive potential, and must be mainly linked to aspects of soil drainage and expected rainfall volume.
Click here to read the article in Revista Cultivar Grandes Culturas, issue 175.
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