**2. Agronomic practices**

#### **2.1 Pregrowing season practices**

Soybeans are one of the most flexible crops in terms of production methods, geographical growing regions, and end use versatility. Therefore, there are multiple agronomic practices to consider when preparing a field for soybean production. While tillage and fertilization practices are common among producers, technique specifications can vary greatly due to preferences, environmental conditions, and cost. Historically, mechanized and non-mechanized tillage was considered a vital practice to maximize crop yield and value [8]. While tillage is still a useful tool, contemporary research has corroborated the dangers of over-tilling and the potential benefits from soil conservation and no-till operations. No-till practices and conservation tillage for soybean are wide-spread in areas of highly-erodible soil, and some research has shown that soybean yields remain the same or increase with decreased tillage [9–12]. However, other research has shown that rotational tillage practices will provide higher crop value than no-till practices, specifically because of herbicide costs and equipment requirements [13–15]. Given the need for proper soil maintenance, conservation tillage (<30% crop residue left on the soil surface) is a popular compromise, especially in herbicide tolerant soybean production [16, 17]. Research has further elucidated the benefits of conservation tillage and no-till practices on soil health by showing positive correlations with rhizobia and nematode populations [18, 19].

Pre-plant fertilization for a variety of macro and micronutrients is another common practice in soybean production. Soil fertility programs are designed to provide sufficient nutrients for a crop's needs which maximizes crop yield and farm efficiency while also minimizing environmental impact. To prepare a field for soybean planting, a farmer must start by determining what nutrients are already present in the soil; this can be accomplished by a variety of soil sampling and analysis methods [20]. The primary macronutrients, nitrogen (N), phosphorous (P), and potassium (K), should be examined first alongside critical secondary macronutrients and micronutrients such as sulfur (S), calcium (Ca), magnesium (Mg), zinc (Zn), manganese (Mn), boron (B), iron (Fe), and copper (Cu). General field nutrient requirement guidelines for soybean production are summarized in **Table 1**. While soybeans require a large amount of nitrogen, fertilization is usually unnecessary because of the symbiotic relationship with *Bradyrhizobium japonicum*,


**31**

**2.2 Growing season practices**

*Soybean Production, Versatility, and Improvement DOI: http://dx.doi.org/10.5772/intechopen.91778*

a bacterium that performs nitrogen fixation and provides plant available nitrogen [9, 21, 22]. Depending on field conditions, 25–75% of nitrogen in mature soybeans can originate from symbiotic nitrogen fixation [24]. Excess nitrogen has been linked to negative plant physiological conditions and inhibited rhizobia activity [25]. Thus, the best solution to limited field nitrogen is sometimes soil or seed-applied bacterial inoculation [21, 22, 25]. Soil pH is also a vital component of field management. It is well-documented that all nutrients have varying availability to plants depending on pH [22, 26, 27]. Generally, soybeans prefer a slightly acidic soil ranging from 6 to 7 pH [9, 22]. Liming a field is the optimum technique to raise pH, while the most

While yield is the driving factor for fertilization, recent market changes have adjusted soybean valuation with increased focus on seed composition quality. Amino acid profiles as descriptors for protein quality in human food and livestock feed as well as high oleic acid soybeans for increased functionality and performance are just two examples of possible premiums producers can receive through soybean seed composition. Research has shown that agronomic practices coupled with location-dependent, environmental variables can directly impact those premiums [28–30]. Nitrogen fertilization plays a limited role in seed composition as it is rarely needed due to the bacterial nitrogen fixation. However, excess nitrogen has been shown to decrease the levels of sulfur-containing amino acids and has an inconsistent effect on fatty acid concentrations [31, 32]. Phosphorous applications can increase protein quantity without adjusting the amino acid profile but also has a positive correlation with higher phytic acid and isoflavone concentrations [33–35]. Additionally, phytic acid has been shown to increase alongside zinc concentrations [33]. Pre-plant potassium applications have limited return on investment in regard to yield and seed composition; however, potassium deficient soybean plants are at a greater risk to insect pests, specifically aphids [36, 37]. Limited yield response is observed with sulfur applications. Although researchers have found the use of sulfur fertilizers to be economically viable, particularly on coarse soils, sulfur fertilization is rarely recommended [9, 21, 38]. Soil sulfur levels have also been shown to greatly impact the ratio between 11S and 7S seed storage proteins [39]. As markets continue to change and value differing soybean seed compositions, it will be critical for producers to fertilize with both yield and seed components in mind.

Soybean producers make decisions throughout the year that impact final yield,

value, and profit from their annual crop. Many of the most critical decisions occur at the beginning of and throughout the growing season. From the moment a soybean seed is planted to harvest, producers choose (or decide against) a multitude of practices including crop rotation, row spacing, population density, irrigation, post-emergence fertilization, and pest management. Maximizing a potential soybean crop is directly connected to previous field usage. Crop rotation or the process of growing different crops in sequenced seasons within the same field is a common practice in soybean production. Corn (*Zea mays*) and soybean rotations are advantageous because of corn's high nitrogen demand which can be alleviated through *Bradyrhizobium japonicum* nitrogen fixation in soybean nodules. Corn and soybean rotations also exhibit beneficial energy balance and grain yield improvement [13, 40]. Rotations including corn and soybeans as well as wheat (*Triticum*), oats (*Avena sativa*), barley (*Hordeum vulgare*), cotton (*Gossypium*), and forageable pasture have also shown potential for economic and environmental gains [22, 41, 42]. Although depending on crop sequences, new management practices may be needed. For example, alfalfa or clover following soybeans would require liming for maximum

production as those crops prefer a slightly higher pH [43].

common practice for lowering pH is elemental sulfur application.

**Table 1.** *Estimated nutrient uptake and accumulation for 3500 kg/ha<sup>−</sup><sup>1</sup> (52 bu/ac) soybean yield [21–23].*

#### *Soybean Production, Versatility, and Improvement DOI: http://dx.doi.org/10.5772/intechopen.91778*

*Legume Crops - Prospects, Production and Uses*

**2. Agronomic practices**

**2.1 Pregrowing season practices**

and western countries mainly utilize soybean indirectly in the food supply as livestock feed and food ingredients such as textured vegetable protein and protein isolates. However, as more consumers are looking for plant-based protein in their diet, soy foods will become a globally viable alternative to animal protein. As the soybean appetite has increased and transformed, scientific developments have also improved soybean production through agronomic, management, and genetic methods to meet demand.

Soybeans are one of the most flexible crops in terms of production methods, geographical growing regions, and end use versatility. Therefore, there are multiple agronomic practices to consider when preparing a field for soybean production. While tillage and fertilization practices are common among producers, technique specifications can vary greatly due to preferences, environmental conditions, and cost. Historically, mechanized and non-mechanized tillage was considered a vital practice to maximize crop yield and value [8]. While tillage is still a useful tool, contemporary research has corroborated the dangers of over-tilling and the potential benefits from soil conservation and no-till operations. No-till practices and conservation tillage for soybean are wide-spread in areas of highly-erodible soil, and some research has shown that soybean yields remain the same or increase with decreased tillage [9–12]. However, other research has shown that rotational tillage practices will provide higher crop value than no-till practices, specifically because of herbicide costs and equipment requirements [13–15]. Given the need for proper soil maintenance, conservation tillage (<30% crop residue left on the soil surface) is a popular compromise, especially in herbicide tolerant soybean production [16, 17]. Research has further elucidated the benefits of conservation tillage and no-till practices on soil health by showing positive

correlations with rhizobia and nematode populations [18, 19].

*Estimated nutrient uptake and accumulation for 3500 kg/ha<sup>−</sup><sup>1</sup>*

Pre-plant fertilization for a variety of macro and micronutrients is another common practice in soybean production. Soil fertility programs are designed to provide sufficient nutrients for a crop's needs which maximizes crop yield and farm efficiency while also minimizing environmental impact. To prepare a field for soybean planting, a farmer must start by determining what nutrients are already present in the soil; this can be accomplished by a variety of soil sampling and analysis methods [20]. The primary macronutrients, nitrogen (N), phosphorous (P), and potassium (K), should be examined first alongside critical secondary macronutrients and micronutrients such as sulfur (S), calcium (Ca), magnesium (Mg), zinc (Zn), manganese (Mn), boron (B), iron (Fe), and copper (Cu). General field nutrient requirement guidelines for soybean production are summarized in **Table 1**. While soybeans require a large amount of nitrogen, fertilization is usually unnecessary because of the symbiotic relationship with *Bradyrhizobium japonicum*,

 *(52 bu/ac) soybean yield [21–23].*

**30**

**Table 1.**

a bacterium that performs nitrogen fixation and provides plant available nitrogen [9, 21, 22]. Depending on field conditions, 25–75% of nitrogen in mature soybeans can originate from symbiotic nitrogen fixation [24]. Excess nitrogen has been linked to negative plant physiological conditions and inhibited rhizobia activity [25]. Thus, the best solution to limited field nitrogen is sometimes soil or seed-applied bacterial inoculation [21, 22, 25]. Soil pH is also a vital component of field management. It is well-documented that all nutrients have varying availability to plants depending on pH [22, 26, 27]. Generally, soybeans prefer a slightly acidic soil ranging from 6 to 7 pH [9, 22]. Liming a field is the optimum technique to raise pH, while the most common practice for lowering pH is elemental sulfur application.

While yield is the driving factor for fertilization, recent market changes have adjusted soybean valuation with increased focus on seed composition quality. Amino acid profiles as descriptors for protein quality in human food and livestock feed as well as high oleic acid soybeans for increased functionality and performance are just two examples of possible premiums producers can receive through soybean seed composition. Research has shown that agronomic practices coupled with location-dependent, environmental variables can directly impact those premiums [28–30]. Nitrogen fertilization plays a limited role in seed composition as it is rarely needed due to the bacterial nitrogen fixation. However, excess nitrogen has been shown to decrease the levels of sulfur-containing amino acids and has an inconsistent effect on fatty acid concentrations [31, 32]. Phosphorous applications can increase protein quantity without adjusting the amino acid profile but also has a positive correlation with higher phytic acid and isoflavone concentrations [33–35]. Additionally, phytic acid has been shown to increase alongside zinc concentrations [33]. Pre-plant potassium applications have limited return on investment in regard to yield and seed composition; however, potassium deficient soybean plants are at a greater risk to insect pests, specifically aphids [36, 37]. Limited yield response is observed with sulfur applications. Although researchers have found the use of sulfur fertilizers to be economically viable, particularly on coarse soils, sulfur fertilization is rarely recommended [9, 21, 38]. Soil sulfur levels have also been shown to greatly impact the ratio between 11S and 7S seed storage proteins [39]. As markets continue to change and value differing soybean seed compositions, it will be critical for producers to fertilize with both yield and seed components in mind.
