Field Selection and Considerations

Field Selection

Before planting, ensure that the field intended for sweetpotato planting material is free of pathogens and pests. Pathogen sampling can include taking soil samples for soil-borne pathogens such as nematodes or taking samples from weeds or other wild plants growing in the uncultivated field. Given that some pathogens can jump from wild hosts or weeds onto crops such as sweetpotatoes, sampling these plants before preparing the field for sweetpotato planting may be a helpful indicator for potential pathogen or pest presence.

Other than sampling for pathogen or pest presence, ensure that the field has the right soil composition. Generally, soils utilized for sweetpotato production range from sand to loamy sand, drain well, and have low salt levels (Stoddard, 2013). Although sweetpotatoes can grow in heavier soils or compacted soils, the quality and quantity of the storage roots will be negatively impacted. Additionally, avoid high levels of organic matter within the soil, as it can promote scurf in sweetpotatoes (Kemble et al., 2022) Sweetpotatoes are somewhat sensitive to salts and a reduction in yield can be observed if the soil’s electrical conductivity exceeds 2 dS/m (Stoddard, 2013). Additionally, storage roots grown in salty soil conditions are more likely to develop tip rot after a few months in storage (Stoddard, 2013). Further, a pH of 5.8 to 6.2 is optimal for sweetpotato production (Kemble et al., 2022).

Further, ensure that the field is in a location that is easily accessible to large machinery including sweetpotato transplanters, machinery used to up-root storage roots during harvest, and machinery for the application of pesticides like fungicides or insecticides.

Row Spacing and Plant Population

Between-row spacing is quite dependent on the machinery that the grower has available for use. If the grower also produces other transplanted crops like tobacco, the row spacing of the machinery may be very different than the machinery a sweetpotato only producer has readily available. With this level of variance, between-row spacing can range from 36 inches to 48 inches (Jennings et al., 2019). However, most commercial sweetpotato growers utilize 42 or 44 inches between-row spacing (Jennings et al., 2019). Narrower row spacing potentially provides the benefit of more effective weed control due to increased vegetation (canopy) cover for the row middles. Further, in theory, the narrower between-row spacing would increase yield, given that there would be a greater number of plants transplanted into the field.

In-row spacing can similarly vary, with in-row spacing ranging from 8 inches to 14 inches (Jennings et al., 2019). The placement of plants within a row may be a strategy for managing root sizing for the purpose of altering harvest times (Jennings et al., 2019). Narrower in-row spacing promotes competition between plants, which can delay root sizing and thus extend the time within the field. Meanwhile, wider in-row planting can reduce competition between plants, which can promote storage root sizing and thus reduce the time within the field. Like narrower between-row spacing, narrower in-row spacing potentially provides the benefit of more effective weed control due to the reduced time for canopy convergence. The convergence of plants’ canopies reduces the amount of light available for the germination of weeds between plants.

Plant populations are entirely dependent on the in-row and between-row spacing utilized for transplanting sweetpotato slips into the field. Further, the mature plant population is dependent on the number of plants that grow to maturity, as some plants may die soon after transplanting or throughout the season. Generally, plant populations per acre can range from 12,500 (12 inch in-row) to 15,000 (10 in-row), with both approximates having 42 inch between-row spacing (Jennings et al., 2019). Larger plant populations result in more plant costs, including costs for planting material and compounds to reduce pest incidence (e.g. insecticides, fungicides, etc.). When planting, one should make considerations for plant costs and further time for roots to grow to an adequate size (related to harvest time).