Why does growing sweet potatoes without turning the vines give a higher yield?

I think everyone is very familiar with sweet potatoes. I remember when I was young, I often went to the fields with my grandmother to plant sweet potatoes. As I have grown older, the chances to work in the fields have become fewer and fewer, but I still eat sweet potatoes often.

Growing sweet potatoes without turning the vines gives a higher yield

Tests have shown that during the growth period of sweet potatoes (also called shan yu or di gua), not turning the vines can increase the yield by about 25% compared with plots where the vines are turned, and some can even reach 30%. The main reasons why turning the vines reduces the yield of sweet potatoes are:

Damage to vines and leaves. Practice has shown that each time the vines are turned, about 10 kg of vine and stem are broken per 667 sq m. If the vines are turned after rainy or overcast weather, they are even more likely to break because the vines have plenty of moisture. In addition, after turning the vines, the leaves are artificially piled up, which affects photosynthesis and causes phenomena such as severe yellowing of leaves, dead vines, and falling off.

Affecting the growth of underground tuberous roots. After turning the vines, the root base is severely twisted, some small roots are broken, and even the whole plant is twisted off, resulting in fewer tuberous roots, or even complete “root detachment”. According to experimental statistics in 2005, in a 0.13-hectare test field, for those whose vines had been turned 4 times, the average number of tuberous roots per plant was 2.7, weighing 0.34 kg; for those whose vines had never been turned, the average number of tuberous roots per plant was 3.8, weighing 0.56 kg, with an increase of 348 kg per 667 sq m.

Affecting photosynthesis. Turning the vines also causes the stems and leaves to shift and fall, disrupting the originally very ingenious natural distribution of the crop leaves. Each time the vines are turned, it takes 5 to 7 days for the stems and leaves to resume normal growth, and during this period the growth of the tuberous roots is affected.

Causing new branches to grow in clusters and consume a large amount of nutrients. When the vines are not turned, more and deeper waist roots are formed, the root system absorbs more nutrients, the vines are thick and strong, the leaves are thick and fleshy, photosynthesis is good, and drought resistance is strong. Some tuberous roots form on the waist roots, which can promote greater growth of sweet potatoes.

Planting time for sweet potatoes  

Sweet potatoes need to be raised as seedlings 2 months before transplanting. That is, spring sweet potatoes begin to be raised as seedlings in late January, autumn sweet potatoes in mid-to-late June, and early winter sweet potatoes in early-to-mid August. One-time seedling raising can be used, or propagation can be done in batches.  

The corresponding planting seasons and times for sweet potato seedlings:  

Spring sweet potatoes: late March to early April.  

Autumn sweet potatoes: around mid-to-late August.  

Winter sweet potatoes: around early-to-mid October.  

Mid-April is the suitable period for inserting seedlings. At this time, the usual early spring temperature has basically stabilized as it warms up. The suitable period for planting vines is when the 10 cm soil temperature reaches above 15°C after the late frost ends, and then planting can begin. In the previous winter or early that year, plow early to dry and whiten the soil, and when planting, form ridges and prepare the beds again. The bed width is 50 cm. In early and mid-April, according to the speed of seedling emergence in the seedbed, cut the seedlings successively and insert them for planting, using the line flat insertion method, increasing the number of nodes of the sweet potato seedlings buried in the soil to increase the number of tuberous roots set. Insert 3500-4000 plants per mu, with a plant spacing of about 33 cm.

Growth stages of sweet potatoes  

The growth period of spring sweet potatoes is 160-200 days, and that of summer sweet potatoes is about 110-120 days. According to the growth characteristics of spring sweet potatoes in the field and their relationship with climatic conditions, they are roughly divided into three growth stages:  

1. Early stage (from planting vines to closing of the canopy). Spring sweet potatoes take about 60-70 days, and summer sweet potatoes about 40 days. In this stage, stem and leaf growth is relatively slow, root development is relatively fast, and it is a period dominated by the growth of fibrous roots.  

2. Middle stage (from closing of the canopy to the peak of stem and leaf growth). Spring sweet potatoes take about 50 days, and summer sweet potatoes about 30 days. In this stage, tuberous root enlargement is relatively slow, and stem and leaf growth is fast, and it is a period dominated by the growth of stems and leaves.  

3. Late stage (from the beginning of decline of stems and leaves to harvest). For spring sweet potatoes, after late August; for summer sweet potatoes, after early September. This stage is the main period for tuberous root enlargement.     

Fertilization techniques for planting sweet potatoes  

1. Look at the seedling condition. During the branching and tuber-setting stage of sweet potatoes, the fertilizer requirement is very large, and a large amount of fertilizer needs to be applied as a top dressing to achieve the goals of strengthening the plants, promoting tuber formation, and fast but stable growth. Of course, do not apply blindly and excessively; fertilizer needs to be supplemented scientifically according to the growth of the sweet potatoes. For plots with relatively good growth, a small amount can be applied; for those with less optimistic growth, more needs to be applied. If the nitrogen application for the seedling-promoting or cluster-forming fertilizer is relatively large, the tuber-promoting fertilizer can apply only potassium fertilizer.  

2. Look at the time. About 45 days after planting the sweet potato vines, the tuber-promoting fertilizer can be applied, mainly potassium fertilizer as a top dressing. At this time, the aboveground part has already spread its vines down the ridges, and the tuberous roots have basically taken shape. Fertilizer can be applied by breaking open one side of the ridge, which not only supplements fertilizer for the sweet potatoes but also improves soil aeration through breaking the ridge, helping the tuberous roots expand.  

3. Look at moisture. In high-temperature and drought-prone areas in July-August, sufficient nitrogen fertilizer should be applied early to promote the stems and leaves to close the ridges before the drought. In years with a lot of autumn rain, the amount and frequency of top dressing should be appropriately reduced to prevent excessive growth of stems and leaves.  

4. Look at the soil texture. Sandy loam soil generally has good aeration and relatively poor fertilizer and water retention capacity. Soil fertilizer efficiency is short and easily lost, so attention must be paid to increasing the application of organic fertilizer to improve the soil, reducing the use of quick-acting fertilizer as much as possible, and appropriately increasing the number of top dressings. Clay soil has poor aeration, slow fertilizer decomposition, and strong fertilizer retention, so the number of top dressings can be appropriately reduced.

To increase the yield of sweet potatoes, there are many techniques. Not turning the sweet potato vines can indeed increase its yield, and reasonable fertilization can also increase its yield, but there are many points to pay attention to when fertilizing. You can exchange planting experience with others more often.