Causes of Deformed Sweet Potato Storage Roots and How to Prevent Them
During the cultivation of sweet potatoes, we have all encountered the phenomenon of sweet potatoes forming some deformed storage roots. Some grow “misshapen,” some are big at the head and small at the tail, forming burdock roots, some develop cracks, and some storage roots become hard, as if “red blood streaks” have grown inside them, and so on. The occurrence of these phenomena seriously affects the commercial value of sweet potatoes.
How are deformed storage roots formed? To understand this, it helps to start with how sweet potato storage roots form. The young roots growing from the potato vines or seed potato sprouts are all called fibrous roots, and the storage roots are formed when the cambium cells beneath the epidermis of these fibrous roots rapidly divide, grow, and expand. However, different fibrous roots have different conditions for growth and development, and the roots they form are also different. Some expand to form storage roots, some do not expand or thicken and remain fibrous roots, and those in between form burdock roots (woody roots). Whether a fibrous root can form a storage root is affected by many factors. Under conditions of sufficient sunlight, good soil aeration, and suitable fertilizer and water conditions, the cambium activity of the fibrous root can be enhanced, its lignification is inhibited, and this favors thickening of the root to form a storage root; on the contrary, high soil moisture, poor aeration, or excessive nitrogen fertilizer favors the formation of fibrous roots; during the process of storage root formation, if unfavorable conditions such as dry, hard soil and poor aeration are encountered, the expansion of the storage root will be hindered, thus forming burdock roots. Therefore, to avoid this deformed growth, scientific and reasonable methods must be adopted in soil selection, fertilization, irrigation, and other aspects.
1. Although sweet potato is not strict about soil requirements, it is still best to choose loose topsoil, well-drained, organic-matter-rich, deep sandy loam and loam. Soil with too much sand should be improved by applying more organic fertilizer and mixing in clay. Although clay-heavy plots have strong water retention, they are not conducive to the formation and expansion of storage roots.
2. Fertilize reasonably according to the fertilizer requirements of sweet potato. Throughout the life of sweet potato, potassium fertilizer is needed in the largest amount, nitrogen fertilizer next, and phosphorus fertilizer the least. The demand for nitrogen fertilizer is mostly concentrated before the rows close; during the storage root formation period, excessive nitrogen fertilizer must be avoided. If the content of available nitrogen in the soil is too high at this time, the pith cells of the young roots age and form fibrous roots, making it difficult to expand into storage roots. Therefore, when fertilizing, be sure to emphasize nitrogen in the early stage and potassium in the later stage.
3. Strengthen water management. Some deformed sweet potatoes are caused by improper soil dryness and wetness. The cracks that appear during the expansion of some sweet potato storage roots are often caused by watering or rain after drought. Therefore, maintaining suitable moisture during production, keeping the field at 70-80% of maximum water-holding capacity during the branching and storage root formation stage, and keeping the field at 60-70% of maximum water-holding capacity during the rest of the period, can avoid the appearance of split sweet potatoes and “red blood streaks” and obtain more “well-shaped” storage roots.