Sweet Potato Nutrient Needs
First, all farmers should take into account the soil condition and characteristics of their field by performing semiannual or annual soil and tissue analysis before applying any fertilization method. There are no identical fields. Thus, no one can advise you on fertilization methods without considering your test data and crop history. However, below we will list some examples of sweet potatoes’ fertilization, as reported by farmers.
Sweet potatoes are tolerant plants to low fertilization and nutrient availability. However, most farmers apply fertilizers to boost their yields for commercial farming. In all cases, farmers are advised to invest in improving soil health and fertility by applying suitable practices (crop rotation – cover crops, use of green and animal manure, reduced tillage, etc.).
According to studies, sweet potatoes remove, on average, from one hectare: 100 kg of N, 90 kg of P, and 200 kg of K and Ca (90, 80, 180 lbs. per acre respectively). For this reason, in a field of 40,000 sweet potato plants per hectare, the plants need around 60-120 kg of nitrogen (N) per hectare (53-107 lb/acre) and 120 kg of potassium (K) per hectare (107 lb/acre), while phosphorus (P) is applied if the soil tests show deficiency. However, in many cases, farmers apply 34-130 kg of P per hectare (30-120 lb per acre).
Nowadays, farmers make from 0 to 4 fertilizer applications throughout the 4 to 6 months, from transplanting to harvesting to replenish the removed nutrients.
Many farmers apply well-rotted manure towards the rows about two months before planting. As a complementary or alternative measure, sweet potato farmers may incorporate a synthetic chemical fertilizer (broadcasted or in plants’ rows) 2 weeks before planting the crop.
Growers prefer to apply the entire phosphorus amount, with half of the required nitrogen and ¼ of the required potassium, as basal fertilization (a 5-10-10 fertilizer can be used). They divide the rest of the potassium and nitrogen into 2 sided-dressings, providing the first one 4-6 weeks after transplanting and the rest 6 weeks after the last application. In cases the soil pH is not at suitable levels (5.5 to 6.5) for sweet potato growth, farmers may apply lime or dolomite to correct the pH and enrich the soil with calcium (Ca). In the case complementary applications with Ca are needed, many farmers use gypsum. Micronutrients (copper, zinc, magnesium, boron, and iron) may also be applied by soil or foliar applications (in case of deficiency, symptoms are observed, and tissue analysis shows low levels). Most producers that have installed a drip-irrigation system use “fertigation” as a complementary fertilization method (apply of soluble fertilizers with irrigation). This way, they can provide the nutrients gradually and give the plant the proper time to absorb them.
However, these are just some fertilization examples. No one should follow them without personal research. Every field is unique and has different needs. Checking the soil condition and pH is vital before applying any fertilization method. You should always consult your local licensed agronomist.
Sweet Potato cultivation guide:
Sweet Potato Fertilization Requirements