Growing Soybean crop nutrition advice

What soil type, pH and climate do soybeans prefer?

Soybeans prefer well-drained, loamy soils with slightly acidic to neutral pH levels and warm temperatures during the growing season.

• Soil Type: Soybeans thrive in soils with a loamy texture, but they can also grow well in sandy loam and clay loam soils. In compacted soils, the hypocotyl may break easily during emergence if under pressure and the root system may not be deep.
• pH: Soybeans prefer slightly acidic to neutral soil pH levels, ideally ranging from 6.0 to 7.0. Maintaining proper pH levels is crucial for optimal nutrient uptake and overall plant health.
• Climate: Soybeans are adaptable to various climates, but they generally prefer warm temperatures for optimal growth. Adequate sunlight and moisture are also essential for soybean cultivation.
• They thrive in regions with a warm, temperate climate, with temperatures ranging from 77°F to 86°F during the growing season. Temperature below 60°F can cause delayed germination and emergence, with increased potential for some diseases. Temperatures above 100°F have an adverse effect on the growth rate, increased flower abortion, and decreased capacity to retain pods. The occurrence of water deficits exacerbates these problems.
• Moisture: Water availability for high soybean yield is ideally 35% during the vegetative growth phase and 65% during the reproductive phase. Lack of water for some days during flowering (dry spells) dramatically reduces yield, especially in sand soils and areas where the root system is superficial due to calcium deficiency or aluminum toxicity in depth (in Brazilian Cerrado, there are reports of losses ranging from 10 to 70% depending on the number of days with a lack of rain). Dry weather is necessary for ripening.

What nutrients are most important for soybean yield and quality?

Soybeans require a balanced supply of macro and micronutrients for optimal growth, development, and yield. Some of the most important macro and micronutrient fertilizers for soybeans include:

Macronutrients

• Nitrogen (N): This is the most important plant nutrient for the soybean crop and the one that is required in the largest quantity. 80 Kg of N is needed to produce 1000 kg of soybean. Soybeans, like other legumes, have a symbiotic relationship with nitrogen-fixing bacteria known as rhizobia. While this means can fix atmospheric nitrogen through symbiosis with rhizobia bacteria, they still require nitrogen for early vegetative growth before nodulation occurs. Excessive nitrogen application, however, can lead to vegetative growth at the expense of nodulation and nitrogen fixation.
• Phosphorus (P): Has a function in the plants directly related to energy storage. Phosphorus is essential for root development, flowering, and seed formation in soybeans. Adequate phosphorus availability is crucial, especially during early growth stages.
• Potassium (K): Potassium plays a vital role in various physiological processes, including water regulation, enzyme activation, and stress tolerance. Soybeans require potassium for overall plant vigor and reproductive development.
• Sulfur: Besides these essential macros, sulfur (S) is also considered important for soybean nutrition, as it plays a role in protein synthesis and nitrogen metabolism. While sulfur is often obtained from atmospheric deposition and organic matter decomposition, sulfur deficiency can occur in soils with low organic matter content or under high-yield production systems.
• Polysulphate is proven to improve both corn and soy yields and provides sulfur, potassium, calcium and magnesium in one gradual release granule.

Micronutrients:

• Zinc (Zn): Zinc is involved in enzyme activation and various metabolic processes in soybeans. Zinc deficiency can lead to reduced growth, delayed maturity, and poor seed quality.
• Iron (Fe): Iron is essential for chlorophyll synthesis, photosynthesis, and nitrogen fixation in soybeans. Iron deficiency can result in chlorosis and reduced plant growth.
• Manganese (Mn): Manganese is required for enzyme activation and photosynthesis in soybeans. Manganese deficiency can manifest as interveinal chlorosis and reduced growth.
• Boron (B): Boron is involved in cell wall formation, flower development, and pollen germination in soybeans. Boron deficiency can lead to abnormal flower and pod development.
• Our Nova line of water-soluble fertilizers offers a range of micronutrient solutions designed for pulse crops and solutions that complement comprehensive fertility programs.
• Our US research trials suggest that foliar-applied macro and micronutrients can increase soybean yields, especially when the application coincides with the transition from vegetative to reproductive growth.

Nutrient requirements 

Requirements in temperate region, Mollisols, USA 

Source: Bender et al., 2015, USA. Average for 3 varieties and yield 3.4 t/ha

Dynamic of nutrient uptake over a crop season in soybean

Soybean has been grown in the most varied types of soil in the world, for example Molisols and Alfisols (neutral to alkaline, with high fertility) to Oxisols and Ultisols (acidic, with low fertility). It is important to correctly manage the fertility of each type of soil to seek profitable production for the producer. 

Very similar in terms of offtake nutrients in the regions, except to P, higher in grains in richer soils. 

Dynamic of nutrient uptake

• Increment of uptake during pods and grain development

• • N, P, Ca and Mg – 50-55% of uptake until R4; 45-50% after)
  • S – 45% until R4 (55% after)
  • K – 50% until R2 (50% after)

• Possible higher response to split fertilization in sandy soils (specially for K and S)

Source: Bender et al., 2015, USA. Average for 3 varieties and yield of approximately 60 bushels/A. 

Nutrient deficiencies

Sources: Embrapa, Brazil; IPNI; IPI

Key aspects in nutrition and fertilization of soybean

• Soybean requires a good nutrition for its growth and development – non- availability results in abnormal or sub-normal plant growth. Plants show characteristic nutrient deficiency symptoms.
• Soybean is a high-protein crop and requires a large quantity of nitrogen (N) to synthesize aminoacids and protein (@ 80 kg N/t grains). The main source of N to crop is the biological nitrogen fixation (BNF), a. conversion in the root nodules of atmospheric N 2 into ammonium (NH 4 + ).
• To improve the biological nitrogen fixation (BNF) without applying nitrogen fertilizer, the farmer must inoculate with Bradyrhizobium (minimum 1.2 million viable cells per seed).
• Ideal pH range in soil is 5.5-7.0. The liming must be done to raise the pH of acidic soils above 5.5, providing Ca and Mg, neutralizing Al, increasing the efficiency of fertilization and BNF.
• The soybean root system needs good calcium amount in the soil profile and has low tolerance to high concentrations of aluminum in soil. To reduce or eliminate Al toxicity and increase Ca in layers deeper than 20 cm must be used the gypsum (CaSO 4 ) or fertilizers containing it in its composition.
• P and K may present enough availability in soil.
  • In general, soil P level must be kept at least in 20 mg/dm3 or more. In slightly acidic to alkaline soils, where the more used extractors of P are Bray-1 and Olsen, the P2O5 rates vary from 20 to 90 kg/ha in function of the amount of in soil. On the other hand, in more acidic soils with a greater capacity for fixing P by iron and aluminum oxides, the main extractant is Mehlich-1, and the nutrient doses are higher, at least 60 kg/ha of P2O5, reaching values more than 150 kg/ha; in these cases, it is recommended to apply the part prior to planting (as a corrective) and the remainder during sowing. Water soluble fertilizers must be used to maintain the yield potential of the crop, and the main sources are single superphosphate (SSP), triple superphosphate (TSP) and MAP.
  • K level must be above 120 mg/dm3. The main source is KCL, but there are some alternatives sources to supply K and other macronutrients (for example Polyhalite to supply K, Ca, Mg and S). Rates are variable in function the amount of K in soil, from 50 kg/ha to 120 kg/ha of K2O.
• In areas where the gypsum was not applied to reduce Al toxicity, sulfur should be applied together with PK fertilization. In Oxisols and Ultisols the suggested doses range from 3 to 5 kg per tons of grains produced. In Molisols and Alfisols usually without economic response in soils with high organic matter content, slightly acidic to alkaline. However, it is suggested to apply the nutrient in fields with a history of low productivity for crops such as alfalfa and corn at doses ranging from 10-15 kg/ha of S
• Ca and Mg are normally supplied by liming. However, in Oxisols with lower CTC, responses to applying these nutrients through fertilizers with water solubility have shown a positive response. The suggestion would be to provide 15-20 kg/ha of Ca and 5-10 kg/ha of Mg.
• The presence of micronutrients in fertilization, including Mo and Co to support biological nitrogen fixation. In acidic Oxisols and Ultisols, the main deficiencies are boron (B), copper (Cu), molybdenum (Mo), manganese (Mn) and zinc (Zn), and the forms to the application could be by seeds, soil or foliar. In Alkaline soils the main deficiencies are iron(Fe), manganese (Mn) and zinc (Zn).

What are common nutrient management challenges for soybean growers in the United States (USA)?

In the context of the US being one of the largest soybean producers and exporters globally, soybean growers across America face several nutrient management challenges:

• Nitrogen management: Balancing nitrogen levels is crucial for early vegetative growth before nodulation. The goal is to optimize growth without excessively relying on synthetic fertilizers.
• Phosphorus and potassium deficiency: Addressing soil deficiencies in these essential nutrients is critical for root development, flowering, and seed formation, which in turn ensure high yields.
• Micronutrient imbalances: Managing deficiencies or imbalances in micronutrients like zinc, iron, manganese, and boron is essential for optimal growth and yield, maintaining the quality of soybean crops.
• pH management: Maintaining proper soil pH levels is necessary to ensure nutrient availability and uptake by soybean plants, maximizing their growth potential.
• Sustainable nutrient management: It is increasingly important to implement practices that balance crop nutrient requirements with environmental stewardship. This includes precision fertilization and conservation tillage to minimize environmental impact while meeting the demands for sustainably produced soybeans and adhering to certification programs such as the Roundtable on Responsible Soy (RTRS). Compliance with regulations related to pesticide use, water quality, soil conservation, and greenhouse gas emissions is also important in this context.

Soybean growers should conduct soil tests to accurately assess nutrient availability and deficiencies. Based on the results of these tests and crop requirements, growers can develop nutrient management plans that include fertilization strategies to address specific nutrient deficiencies and optimize soybean yield and quality. ICL can help.