Abstract
ABSTRACT: Brazil is the largest exporter and second largest producer of soybean grains. Most of this production is from plants grown under no-tillage system (NT). This research evaluated the effect of soil compaction, and different amounts of black oat residues on the soil surface on soybean growth and grain yield in lowland under NT. The experiment was conducted in a completely randomized design with seven treatments and four replications, in the 2016/2017 and 2017/2018 crop seasons. The treatments consisted of: 1) winter fallow without soil compaction (WF); 2) winter fallow with soil compaction (WF-C); 3) black oats and complete removal of surface residues, with soil compaction (0R-C); 4) black oats and removal half of surface residues, with soil compaction (0.5R-C); 5) black oats without surface residue removal, with soil compaction (1R-C); 6) black oats without surface residue removal, plus the residues from treatment 3, with soil compaction (2R-C); 7) black oats without surface residue removal, without soil compaction (1R). When the soybean plants were at the phenological stage R2, they were evaluated nodule, root and shoot dry matter, nitrogen contents, plant height, and grain yield. The soil physical properties were evaluated in the 0.0-0.05, 0.10-0.15 and 0.20-0.25 m layers. The soybean aerial dry matter is > 38% in non-compacted soil in year with soil water excess, regardless of the amount of surface oat straw. In year with small water deficit, soil with more surface oat straw produced > 5% shoot dry matter and > 4% of soybean grain, regardless of compaction. The plant growth and grain yield soybean in lowland varied according to the water conditions, and were affected by soil compaction and amounts of black oats residues on soil surface.
Highlights
Soybean (Glycine max (L.) Merrill) is the main oilseed produced and consumed in the world, having great food and economic importance
bulk density (BD) was higher in treatments with additional soil compaction, regardless of the amount of black oat residues on soil surface, in the 2016/2017 crop season (Table 1)
According to GUBIANI et al (2018), tillage reduces BD and increases porosity in the soil surface layer; according to SILVA et al (2012), this effect decreases over time and remains less than a year because of the restructuring and natural densification of the soil
Summary
Soybean (Glycine max (L.) Merrill) is the main oilseed produced and consumed in the world, having great food and economic importance. Soybean crops have been grown in the state of Rio Grande do Sul, Brazil, in rotation with irrigated rice in lowlands. These soils have different dynamics and characteristics when compared to well-drained highlands. BEUTLER et al (2014) reported that flooded soil for 16 days at soybean reproductive stage resulted in a decrease of up to 29% in grain yield In this context, the use of cover crops, like black oats, improves the soil structure and superficial straw reduce water evaporation when water deficit occurs, mainly in soybean reproductive stage when water demand is greater and water deficit is common. The objective was to evaluate the effect of soil compaction and amounts of black oat residues on the soil surface in soybean growth and grain yield in lowland under no-tillage system
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