Early Sowing and Soil Scarification Improve Protein and Oil Contents in Soybean Grains Cultivated in Lowlands

Soybean cultivation in lowlands has increased over the years. In this case, further studies on soybean composition based on management practices are required. This work evaluated the contents of oil, protein, and micro and macronutrients from soybean sown in Brazilian lowlands in November and December, with and without soil scarification, and with medium, high, and very high fertilization. Two crop years were evaluated: 2018/2019 and 2021/2022. Sowing in November and soil scarification contributed to the increase in protein content, with averages of 19.41 and 33.50 wt% for 2018/2019 and 2021/2022. The average oil contents were 16.24 and 21.03 wt% for 2018/2019 and 2021/2022. Linoleic (37.67–50.23 wt%), oleic (14.80–28.26 wt%), and palmitic (8.86–14.06 wt%) acids were the main fatty acids found in the oil, while the earliest sowing season (November) showed the highest percentages of these fatty acids. Soil scarification contributed to increasing N absorption in grains, yielding 29.10 kg t−1 in 2018/2019 and 57.9 kg t−1 in 2021/2022. In most of the treatments, sowing in November increased Ca, Mg, Cu, Fe, and Mn in the grains. Soybean cultivation in lowlands is a promising alternative to crop rotation in traditional rice crops. This work demonstrates the need to improve the soybean production system in lowlands with a high-quality index, mainly oil and protein.