Nutrient Considerations

Most research has emphasized the application of synthetic fertilizers, particularly nitrogen fertilizers, for conventional sweetpotato production. In addition to nitrogen, macronutrients such as phosphorus and potassium are added to the agroecosystem often through synthetic fertilizer applications. For organic sweetpotato production, there is a greater focus on applying slower-release fertilizers comprised of various macronutrients and micronutrients. Regarding nitrogen, cover crops such as clover or hairy vetch may be planted prior to the sweetpotato growing season to promote nitrogen fixation and increase available nitrogen. Cover crop use may be implemented in conventional sweetpotato production but is more often implemented for organic sweetpotato production.

When identifying appropriate fertilizer applications, many factors must be considered. One important factor is the amount of the macronutrient that is provided, often through the application of synthetic fertilizers. Inadequate or excessive amounts can be detrimental to high-yielding and high-quality sweetpotato production. Further, the timing of fertilizer application must be taken into consideration. If improperly timed, there may be issues regarding contamination of surface and groundwater sources as a result of fertilizer leaching (Smith and Villordon, 2009). Additionally, improper timing and the resulting leaching can incur additional costs due to the loss of fertilizer.

Furthermore, it is important to consider that the cultivars utilized for production will have different nutrient requirements (i.e. different N requirements for Covington versus Beauregard). Other important factors include geographic locations, cropping seasons, and climate (Smith and Villordon, 2009). With all of these factors contributing to proper nutrition for the growing sweetpotato plant, it is critically important that nutritional consideration decisions are specific to the cultivar in the context of the specific production location (including registrations for products and the climate).

Below, there is additional information regarding nutrient considerations provided by each state associated with the SweetARMOR project.

North Carolina

Table 1. The below table has been adapted from the 2022 North Carolina Agricultural Chemicals Manual.

Desirable pH	Nitrogen (N) lb/acre	Recommended Nutrients Based on Soil Tests								Total Amount of Nutrient Recommended and Suggested Methods of Application
		Soil Phosphorus Level				Soil Potassium Level
		Low	Medium	High	Very High	Low	Medium	High	Very High
		P2O5 lb/acre				K2O lb/acre
5.8 to 6.2	50 to 80	200	100	50	0	200	175	150	0	Total recommended.
	0	150	60	30	0	75	50	30	0	Broadcast and disk in or sidedress 1 week after planting. Apply 30 to 40 lb/acre N for all sweetpotato varieties except Beauregard.
	50 to 80	0	0	0	0	125	125	120	120	Sidedress 21 to 28 days after planting. Apply all N for the Beauregard variety (50 lb/acre) and 40 to 50 lb/acre for all other sweetpotato varieties.
	Add 0.5 pound of actual boron (B) per acre 21 to 28 days after planting.

South Carolina

Table 2. The below table has been adapted from the 2022 Southeastern US Vegetable Crop Handbook.

Desirable pH	Nitrogen (N) lb/acre	Recommended Nutrients Based on Soil Tests								Nutrient Timing and Method
		Soil Phosphorus Level				Soil Potassium Level
		Low	Medium	High	Very High	Low	Medium	High	Very High
		P2O5 lb/acre				K2O lb/acre
5.8 to 6.2	50 to 80	200	100	50	0	300	200	150	120	Total recommended.
	0	150	60	30	0	150	50	30	0	Broadcast and disk-in.
	50 to 80	50	40	20	0	150	150	120	120	Sidedress 21 to 28 days after planting.
	Add 0.5 lb of actual boron (B) per acre 40 to 80 days after transplant.

Louisiana

Table 3. The below table has been adapted from the 2022 Southeastern US Vegetable Crop Handbook.

Desirable pH	Nitrogen (N) lb/acre	Recommended Nutrients Based on Soil Tests								Nutrient Timing and Method
		Soil Phosphorus Level				Soil Potassium Level
		Low	Medium	High	Very High	Low	Medium	High	Very High
		P2O5 lb/acre				K2O lb/acre
5.8 to 6.2	50 to 80	200	100	50	0	300	200	150	120	Total recommended.
	0	150	60	30	0	150	50	30	0	Broadcast and disk-in.
	50 to 80	50	40	20	0	150	150	120	120	Sidedress 21 to 28 days after planting.
	Add 0.5 lb of actual boron (B) per acre 40 to 80 days after transplant.

Mississippi

Table 4. The below table has been adapted from the 2022 Southeastern US Vegetable Crop Handbook.

Desirable pH	Nitrogen (N) lb/acre	Recommended Nutrients Based on Soil Tests								Nutrient Timing and Method
		Soil Phosphorus Level				Soil Potassium Level
		Low	Medium	High	Very High	Low	Medium	High	Very High
		P2O5 lb/acre				K2O lb/acre
5.8 to 6.2	50 to 80	200	100	50	0	300	200	150	120	Total recommended.
	0	150	60	30	0	150	50	30	0	Broadcast and disk-in.
	50 to 80	50	40	20	0	150	150	120	120	Sidedress 21 to 28 days after planting.
	Add 0.5 lb of actual boron (B) per acre 40 to 80 days after transplant.

California

Table 5. The below table has been adapted from the UC Vegetable Research and Information Center Sweetpotato Production in California Factsheet.

Nitrogen (N) lb/acre	Recommended Nutrients Based on Soil Tests		Nutrient Timing and Method
	P2O5 lb/acre	K2O lb/acre
125-175	50-100	200-250	Nitrogen: ⅓ to ½ of the crops expected requirement should be applied pre-plant, with the remainder applied through the drip tape or as a sidedness application between 30 and 90 days after transplanting. Considerations should be given for residual soil NO3-N, compost applications, and N in the irrigation water. Phosphorus: Applied before planting. Phosphorus response not expected if soil test > 20 ppm using Olsen P. Potassium: Sometimes applied through the drip tape. Apply potash to replace what was removed by the crop. Sweetpotatoes remove on average 5 lbs of K2O for every 1000 lbs harvested. No response has been observed to potassium, and no soil test recommendations have been developed. Preplant fertilizer should be placed in a band 9 inches to the side of the plant row at a depth of 8 to 10 inches. Alternatively, a banded application of potash directly beneath the drip tape in the middle of the bed can be used.