Soybeans: Fertility

Excerpt from Agronomy Guide for Field Crops (Chapter 4)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Nitrogen
2. Phosphate and Potash
   • Phosphate and Potash Recommendations for Soybeans Based on OMAFRA-Accredited Soil Tests - Table 4-14
   • Methods of Application
3. Plant Analysis
   • Interpretation of Plant Analysis for Soybeans - Table 4-15
4. Micronutrients
   • Manganese
5. Updates on Soybeans: Fertility
6. Related links...

Nitrogen

Nitrogen fertilizers are not usually required for soybeans. (See the section Inoculation. Research into nitrogen fertilizer applied at planting time has shown that nitrogen, even in small amounts, can delay nodule fixation.

If nodulation does not occur, and the soybeans are pale green and N-deficient, the recommended remedial measure is to apply 50 kg/ha of N at first flower, as urea or calcium ammonium nitrate, when the foliage is dry.

| Top of Page |

Phosphate and Potash

Phosphate and potash recommendations for soybeans are given in Table 4-14, Phosphate and Potash Recommendations for Soybeans Based on OMAFRA-Accredited Soil Tests.

100 kg/ha = 90 lb/ac

¹ Where manure is applied, reduce fertilizer applications according to the amount and quality of manure (see the section Manure. Example of fertilizer application: If a soybean crop is not manured, and the soil tests are 9 for phosphorus and 85 for potassium, the phosphate requirement is 40 kg/ha and the potash requirement 40 kg/ha (see above). These nutrients can be supplied by broadcasting or banding 200 kg/ha 0-20-20 fertilizer.

² For a nutrient that has an excessive rating by soil analysis, the application of this nutrient in fertilizer or manure may cause problems due to reduced crop yield or quality. Phosphate additions may jeopardize water quality. Potash additions may induce magnesium deficiency on soils low in magnesium.

For information on the use of this table or if an OMAFRA-accredited soil test was not completed, refer to the section Fertilizer Recommendations.

Occasionally, potassium deficiency will appear in soybeans as yellowing or browning of margins in older leaves (see Plate 51).

Plate 51: Potassium (K) deficiency appears as yellowing or browning of leaf margins on older leaves.

| Top of Page |

Methods of Application

Fertilizer should not be placed in contact with soybean seeds due to the sensitivity to fertilizer salts. Unlike corn, there is no yield advantage to this practice. The fertilizer may be broadcast and plowed down or worked into the soil either in the fall or spring. A planter with a separate attachment for fertilizer placement may also be used to place the fertilizer 5 cm (2 in.) to the side and 5 cm (2 in.) below the seed. For further information, see Table 2-30, Maximum Safe Rates of Nutrients.

| Top of Page |

Plant Analysis

For soybeans, sampling the top fully developed leaf (three leaflets plus stem) at first flowering is recommended. Refer to Table 4-15, Interpretation of Plant Analysis for Soybeans. For sampling at times other than first flower, samples should be taken from both deficient and healthy areas of the field for comparative purposes. A soil sample should be taken from the same area and at the same time as a plant sample.

Refer also to the section Plant Analysis in the Soil Management and Fertilizer section.

Values apply to the top fully developed leaf (3 leaflets plus stem) at first flowering.

¹Yield loss due to nutrient deficiency is expected with nutrient concentrations at or below the "critical" concentration.

²Maximum normal concentrations are more than adequate but do not necessarily cause toxicities.

| Top of Page |

Micronutrients

Manganese

Manganese is the only micronutrient deficiency diagnosed in soybeans in Ontario, although zinc deficiency may show up in the future where the surface soil has been lost by erosion.

The symptoms of manganese deficiency are upper leaves ranging from pale-green (slight deficiency) to almost white (severe deficiency) with green veins (see Plate 52).

Plate 52: Manganese (Mn) deficiency. Upper leaves appear pale green to almost white with green veins.

Soil tests and plant analyses are useful in predicting where manganese deficiencies are likely to occur. Both are available at the OMAFRA-accredited laboratories listed in Appendix B, Accredited Soil-Testing Laboratories in Ontario.

Correct the deficiency as soon as detected by spraying the foliage with 2 kg of actual manganese/ha from manganese sulphate (8 kg of manganese sulphate/ha) in 200 L of water. A "spreader-sticker" in the spray is recommended. If the deficiency is severe, a second spray may be beneficial.

Caution should be taken when applying micronutrients with a sprayer that has been used to apply herbicides. Cleaning out the spray tank is essential for avoiding crop injury. See the section Herbicide Injury, for more details.

Soil application is not a recommended method of applying manganese regardless of the source because of the large amounts required. Application of manganese chelates to the soil has resulted in yield reductions.

In general, beans will give a profitable response to manganese in the parts of the field where manganese deficiency is showing. There is no benefit to applying manganese to beans without deficiency symptoms.

| Top of Page |

Updates on Soybeans: Fertility

• Phosphorus Requirement Table - Field Crops
• Potassium Requirement Table - Field Crops
• Magnesium Soil Test Ratings and Interpretations for All Crops
• Manganese Requirement Table and Zinc Requirement Table

| Top of Page |

Related links...

• Soybeans
• Soil Fertility & Crop Nutrition

| Top of Page |