Protein and Oil Contents, Micro- and Macronutrients, and Other Quality Indicators of Soybean Cultivated in Lowland Fields

The cultivation of soybean is being expanded in traditional areas cultivated with rice, called the lowlands. However, soil characteristics are different from those in the highlands, which influences the exportation of nutrients to the grains. Therefore, this study aimed to determine the physical-chemical and technological characteristics of soybean grains harvested in lowlands in Brazil. Two-year crops (2021/22 and 2022/23) were used with two types of soil preparation (scarified and non-scarified) and six cover crop treatments (oats, clover, ryegrass, fallow, ryegrass + oats, and ryegrass + clover). The influence of these treatments was evaluated in terms of the grain yield, oil and protein contents, oil composition, quality indices (acidity, peroxide, iodine, and saponification), and contents of ash, carbohydrates, and micro- and macronutrients. Grain yield achieved an average of 3829.8 kg ha^-1. Soil scarification positively influenced grain yield and contributed to higher protein and oil contents, with maximum values of 32.7 wt% and 27.6 wt%, respectively. The main fatty acids in oil were oleic acid (22.13 ± 1.48-26.32 ± 0.98%) and linoleic acid (36.32 ± 1.57-52.18 ± 1.58%). The macronutrients phosphorus (5.12 ± 0.39-5.79 ± 0.37 kg ton^-1), calcium (2.79 ± 0.19-3.05 ± 0.18 kg ton^-1), magnesium (2.37 ± 0.14-2.57 ± 0.13 kg ton^-1), and sulfur (2.85 ± 0.18-3.19 ± 0.20 kg ton^-1), and the micronutrients copper (9.73 ± 1.42-11.68 ± 1.07 g ton^-1), iron (111.42 ± 6.86-122.02 ± 5.00 g ton^-1), and manganese (43.58 ± 3.34-47.08 ± 2.74 g ton^-1) were in agreement with the values reached in the highlands. For potassium (18.87 ± 0.38-29.29 ± 1.44 kg ton^-1) and zinc (30.02 ± 2.45-38.00 ± 1.03 g ton^-1), soil scarification allows higher levels of absorption. The use of ryegrass as a cover crop allows higher levels of nitrogen absorption, reaching up to 44.93 ± 2.74 kg ton^-1. Regarding the acidity (0.19-0.52%), peroxide (9.64-16.39 mEq O₂ kg^-1), iodine (85.34-91.91 mg KI g^-1), and saponification (182.33-203.74 mg KOH g^-1) indices of the oil, all values were obtained in accordance with the scientific literature. The conclusions of this study indicate that it is possible to cultivate soybean in lowlands after developing the proper soil preparation. Consequently, the yields are increased, and grains will benefit from higher protein and oil contents, enhancing soybean quality for commercialization.