Potatoes - Fertility

Nitrogen

If manure is applied or legume sod is plowed down, reduce the nitrogen application. (See Table 1-8, Adjustment of Nitrogen Requirement Where Sod Containing Legumes Is Plowed Down, and Table 1-7, Average Amounts of Available Nutrients for Different Types of Manure, on page 9.)

See Table 9-65, Potato Nitrogen Recommendations, on page 153. If the total nitrogen-plus-potash applied is over 360 kg/ha (320 lb/ac), broadcast at least a portion before planting to avoid concentrating the fertilizer band near the seed piece and potato roots. Broadcasting or side-dressing nitrogen after potatoes are 20 cm high is not generally recommended, as it may delay maturity.

Phosphorus

Soil tests are required to determine phosphorus requirements. Where the soil test values are 51 mg P per L soil (ppm) or higher on mineral soils, phosphate applications may be reduced to 30 kg/ha (28 lb/ac). For soils testing lower than 51 mg P per L soil (ppm), see Table 1-10, Phosphorus Requirements: Vegetables on Mineral Soils, on page 12.

On muck soils with soil test P values of 61 mg P per L soil, potatoes are unlikely to respond to additional phosphorous applications. For muck soils testing lower than 61 mg P per L soil (ppm), see Table 1-11, Phosphorus and Potassium Requirements: Vegetables on Muck Soils, on page 13.

Table 9-65. Potato Nitrogen Recommendations

On mineral soils testing medium or low for phosphate, place some or all of the phosphate fertilizer in bands 2.5 cm (1 in.) below and 6 cm (2¹/₂ in.) to each side of the seed piece at planting time. On muck soils or on mineral soils testing high for phosphate, placement is less critical and fertilizer may be broadcast.

Potassium

Soil tests are required to determine potassium requirements. Where the soil test values are 181 mg K per L soil (ppm) or higher, potatoes are unlikely to respond to additional potash applications. For soils testing lower than 181 mg K per L soil (ppm) see Table 1-12, Potassium Requirements: Vegetables on Mineral Soils, on page 14, or Table 1-11, Phosphorus and Potassium Requirements: Vegetables on Muck Soils, on page 13.

Petiole/Plant Analysis

When used in conjunction with a soil analysis, plant analysis is a useful tool for diagnosing crop problems or for evaluating a fertilizer program. The objective of a good fertilizer program is to maintain tissue nutrient concentrations on the lower side of the sufficiency range. Attempting to bring the nutrient analysis up to the higher end of the range could possibly result in over-fertilization and may not be economical. For more information, see the section, Plant Analysis, on page 3.

Only use sufficiency ranges as a reference and a guideline. Plant analysis does not replace soil testing or a sound soil fertility program. Samples for plant analysis should be taken, in the morning, at early bloom. Sample at least 50 plants distributed throughout the chosen area. Take the fourth leaf from the tip, including the petiole. Sample problem areas separately. See Table 9-66, Potato - Interpretation of Plant Analysis, right.

Table 9-66. Potato - Interpretation of Plant Analysis

Values apply to the fourth leaf, including stem, from the growing tip sampled at early bloom.

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

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

Related Links

• Publication 363 - Vegetable Production Recommendations

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