Sweet potato fertilizer requirements can be calculated if you know your soil type and have a good idea of the yield potential of your land and climate. These are basic norms and your specific microclimate and variety can have an influence on the total amount applied. These norms do not take top dressings into account, only the total amount of N, P and K applied during the growth season. The fertilizer can be applied either through the irrigation system or as granular fertilizer. Consult your supplier on the effectiveness of these fertilizers on the various soils to make adjustments to these amounts.

Three soils are used in these tables:

  • S/SL – Sandy to Sandy Loam
  • SL/S – Sandy Loam to Sand
  • SCL/C – Sandy Clay Loam to Clay

Sweet potato fertilizer Nitrogen (N) application

Sweet potato fertilizer requirement ito nitrogen is easy. You don’t need a soil analysis just a good idea of your yield potential in the area. Be careful not to overestimate your potential yields as too much nitrogen will also have a negative effect on total yield and the quality of the sweet potato. High nitrogen content makes the plant more susceptible to insect damage and diseases. Too much nitrogen in the form of organic material will cause crooked and forked tubers which are not marketable. They can however be used in cutting and dicing industry.

Yield target t/ha S/SL SL/S SCL/C
0-40 70 – 90 60 – 70 50 – 60
41-50 90 – 110 80 – 90 90 – 100
51-60 120 – 140 110 – 120 100 – 120

Phosphorus (P) requirement – (Bray 1)

Phosphorus fertilizer requirements are based on Bray 1 lab analysis. If another method is used the values must be adjusted. The minimum amount applied is always about 20 kg P per hectare as P is not that mobile and a certain level of P must always be maintained in the soil.

 

P analysis (ppm) Yield target 0-99 t/ha
1-10 140-160
11-20 120-140
21-30 100-120
31-40 80-100
 41-60 60-80
 61-80 40-60
 81-100 20-40
 101-120 0-20
121-200 0

Sweet potato Potassium (K) fertilization

Potassium requirements are based on a soil analysis and yield estimates. Potassium is extremely important for flower formation and water regulation. Over fertilization can increase the salt content of the soil to such an extent that water uptake is reduced. Note that low nitrogen soil content will impair the translocation of potassium to other parts of the plant. A potassium deficiency in the plant will not be noticed as quickly as nitrogen or iron. Deficiency symptoms occur first in the older leaves as potassium is transferred to younger leaves first. Note that beans are sensitive to salt stress, so too high applications can reduce yields.

Soil type Soil analysis Yield t/ha
ppm 0-40 41-60 61-99
S/LS 1-20 200 230 265
SL/L 1-30 200 230 265
SCL/C 1-40 200 230 265
S/LS 21-40 160 194 227
SL/L 31-60 160 194 227
SCL/C 41-80 160 194 227
S/LS 41-60 120 158 185
SL/L 61-90 120 158 185
SCL/C 81-120 120 158 185
S/LS 61-80 85 122 155
SL/L 91-120 85 122 155
SCL/C 121-160 85 122 155
S/LS 81-100 48 86 115
SL/L 121-150 48 86 115
SCL/C 161-200 48 86 115
S/LS 101-121 25 50 80
SL/L 151-180 25 50 80
SCL/C 201-240 25 50 80
S/LS 121+ 15 30 40
SL/L 180+ 15 30 40
SCL/C 241+ 15 30 40

 

Below is the well known soil texture triangle on which the Sweet potato fertilizer recommendations are based. Most commercial agricultural soils are found in the left bottom corner as they are the most productive and provide the plant with best yield potentials.

Soil textural triangle for Sweet potato fertilizer requirements.1)https://commons.wikimedia.org/wiki/File:USDA_Soil_Texture.svg by Christopher Aragón

 

References

References
↑1 https://commons.wikimedia.org/wiki/File:USDA_Soil_Texture.svg by Christopher Aragón