PART I SELECTING AND GROWING
SWEETPOTATO FOR LIVESTOCK
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1 Technology for growing dual-purpose and forage purpose sweetpotato in
the Northern Midlands of Vietnam
1.1 Characteristics of the Northern Midlands of Vietnam
1.1.1 Soil characteristics
The agricultural land of the Northern Midlands of Vietnam consists of
the old alluvial bed area and valleys of the plain areas. Erosion-has
led to soil acidity and low soil organic matter, phosphorus and nitrogen.
This restricts yield potential of cultivated crops.
The plains areas of the valleys are more fertile, with soil composition
from loamy to less loamy and mixed sandy soil, suitable for sweetpotato
as well as for corn, beans, and groundnut. The plains areas are 30 m above
sea level and the slope varies from 10-30 %. There is mainly one crop
a year, and the utilisation rate of agricultural land is low.
1.1.2 Climatic conditions
Climate of the Northern Midlands of Vietnam is a monsoon tropical climate.
The dry season lasts from November to April, with early north-east winds.
It is considered the coldest area of the country. Therefore, winter crop
sweetpotato needs to be planted early with cold-tolerant varieties.
Rainy season is from May to October, with the greatest concentration
between June and September. There is potential for flood during this period.
Heavy rains and floods cause serious erosion. On the other hand, dry season
runs from October/November to March/April, and the drought and low temperature
tend to stunt crop growth. The most serious drought usually happens at
the end of December and the beginning of January.
1.1.3 Population and density
The population density of this area is fairly low, ranging from 70 to
140 persons/km2, with Kinh people occupying more than 60% and various
ethnic minority groups occupying the other 40%. The main income comes
from crop production, mostly from a single food crop, yielding relatively
tow living standards. The food/head/year averages between 220 kg and 302
kg. Low income leads to low investment and poor cultivation technology.
Irrigation and water systems are not well developed, especially in the
upland and mountainous areas. It is necessary to select varieties suitable
for these conditions.
1.1.4 Crops and production systems
For crop purposes, the Northern Midlands of Vietnam is divided into
two parts: upland and plain fields. The following crop rotations are recommended:
- On upland:
Sweetpotato or autumn corn
Spring sweetpotato - Winter rice (upland rice) - Winter soybean
Spring-Summer bean - Winter rice (upland rice) - Winter sweetpotato
Sweetpotato under permanent fruit trees
- On the plains:
Spring sweetpotato - Winter rice
Spring-Summer bean - Early winter rice - Winter sweetpotato
Late spring rice - Early winter rice - Winter sweetpotato
Spring sweetpotato - Early winter rice - Winter corn
1.2 Geographical location
The Northern midlands of Vietnam consist of the following provinces:
Quang Ninh, Bac Giang, Bac Ninh, Vinh Phuc, Phu Tho, Thai Nguyen, Ha Tay,
Hoa Binh. The following recommendations also apply to some neighbouring
provinces that share similar topographical, soil and planting characteristics.
1.3 Recommended sweetpotato varieties suitable for root and
vine dual-purpose and their characteristics
1.3.1 The characteristics of yield, agronomic performance, and growing
period
| Distinguishing characteristics |
Variety |
| |
Hoang long |
KB1 |
K51 |
TQ2 |
KL5 |
| Root yield (ton/ha) |
21-35 |
13-17 |
14-29 |
11.94 |
20-22.5 |
| Vine yield (ton/ha) |
18-35 |
29-40 |
19-32 |
28.70 |
20-36 |
| Root DM yield (ton/ha)* |
2-7 |
1-2.5 |
1.51 |
2.85 |
1-5.2 |
| Root starch yield (ton/ha)* |
1.4-4.9 |
0.7-1.75 |
1.05 |
2.14 |
0.7-3.5 |
| Season suited to planting |
Winter |
Winter |
Spring |
Spring |
Winter,spring |
| Tolerance performance: |
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|
|
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|
Good |
Good |
Medium |
Medium |
Good |
| |
Medium |
Bad |
Fair |
Fair |
Good |
| |
Medium |
Good |
Medium |
Medium |
Fair |
| |
Good |
Medium |
Fair |
Good |
Medium |
| |
Poor |
Poor |
Medium |
Good |
Medium |
| Growing time (days) |
140 |
150 |
150 |
120 |
120 |
*Root DM yield=Root yield x Dry Matter (DM) content in root
* Root starch yield=Root DM yield x starch content in DM
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1.3.2 The characteristics of utilization, vine, root and storage
Distinguishing
characteristics |
Variety |
Hoang long |
KB1 |
K51 |
TQ2 |
KL5 |
| Root palatability1:
- For human (boiled)
- For pigs (cooked)
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High DM
Good |
High DM
Good |
Low DM
Fair |
Low DM
Fair |
Med DM
Good |
Vine palatability:
- For humans (boiled)
- For pigs (fresh)
|
Bitter
Bitter |
Not sweet
Not sweet (Should be cooked) |
Sweet
Sweet
(Should be cooked) |
Not sweet
Not sweet |
Sweet
Sweet
(Should be cooked) |
Method of storage:
- Time (month)
- Way to store
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3-4
Fresh, dried |
3-4
Fresh, dried |
3-4
Fresh,dried |
3
Dried |
3-4
Fresh, dried |
Root morphology:
- Color of skin
- Color of root flesh
- Shape of root
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Red-pink
Yellow Roundish |
White
White
Roundish |
Pink
Yellow
Slender |
White
White
Slender |
Light red
White
Slender |
Vine morphology:
- Shape of leaf
- Color of tender leaf
- Color of adult leaf
- Color of stem
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Heart shape White
Dark blue
Violet |
Heart shape Violet
Green
Purple green |
Heart shape Violet
Green
Green |
Saw-tooth Green
Dark green Purple green |
Lobe
White
Green
Green |
1 For human consumption as a staple, instead of a vegetable,
in which the level of DM is important to establish palatability.
Palatability for pigs, on the other hand, was established by pigs' reaction
when fed with certain varieties.
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1.4 Sweetpotato varieties suitable for forage purpose and their characteristics
1.4.1 The characteristics of yield2, agronomic performance
and growing period
Distinguishing
characteristics |
Variety |
Rau muong |
KL5 |
TQ1 |
T2 |
SN16 |
Fresh vine yield (ton/ha) |
42 |
50 |
37.83 |
63.61 |
47.58 |
Fresh leaf yield (ton/ha) |
10.72 |
7.6-13.5 |
11.99 |
13.25 |
14.01 |
Leaf DM yield (ton/ha)* |
2.48 |
2.99 |
2.22 |
2.74 |
2.59 |
Leaf CP yield (ton/ha)* |
0.55 |
0.58 |
0.49 |
0.53 |
0.47 |
Season suited to planting |
Spring |
Winter, spring |
Spring, winter |
Spring |
Spring |
Tolerance performance: |
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Good |
Good |
Fair |
Medium |
Medium |
|
Fair |
Good |
Fair |
Fair |
Fair |
|
Fair |
Good |
Fair |
Medium |
Medium |
|
Good |
Good |
Good |
Good |
Fair |
- Twisted leaf virus tolerance
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Good |
Good |
Good |
Fair |
Fair |
Branching and regrowth |
Strong |
Strong |
Strong |
Strong |
Strong |
* Leaf DM yield=Fresh leaf yield x leaf DM content (excluding vines)
* LeafCP (crude protein) yield = Leaf DM yield x CP% in DM
2 The vine yield of the same variety grown for
forage-purpose would be higher than that which was grown for
dual-purpose which was not cut frequently in order to allow for root development.
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1.5 Technologies that can be applied to increase vine and root
yield
1.5.1 Selecting the appropriate variety
Growing purpose |
Spring crop |
Winter crop |
Dual purpose |
TQ1,K51,KL5,KB1 |
TQ2,KB1,Hoanglong,KL5,SN3 |
Vine purpose |
Raumuong,T2,KL5,TQ1,SW6,KB1 |
TQ2,SN3,KB1,KL5,Hoanglong |
1.5.2 Planting season
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Spring crop |
Winter crop |
Planting season |
- 20 February-15 March
- For vine purpose, it can be planted whenever the soil is moist.
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- 20 September-5 October
- For vine purpose, it can be planted whenever the soil is moist.
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Favorable conditions |
- From planting to harvesting the temperature and moisture is
rather suitable.
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- During planting time, moist soil and high temperature provide
good conditions for vines to grow.
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Unfavorable conditions |
- Need to prevent flooding at the end of the season and too much
vine growth.
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- At the end of season, soils are dry and temperatures low, roots
may not develop well.
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1.5.3 Soil characteristics
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Spring crop |
Winter crop |
Proper soil type |
Sandy-light loamy soil |
Loamy soil, light loamy soil, sandy
mixed soil |
Land type |
High land, upland, bedy
land |
Upland, low land, low land |
1.5.4 Soil preparation
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Spring crop |
Winter crop |
Requirements |
Prepare the soil deeply, porous and
friable, well ploughed, good water drainage by the end of season |
Prepare the soil in order to maintain
moisture during growing season |
Size of bed |
Width: 1 .1-1 .2 m; height:40-45 cm.
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Width: 1.0m; height: 35-40 cm |
Distance btwn beds |
10-20cm |
10-20 cm |
Direction of beds |
Depending on the plot, but East-West
direction is recommended |
East-West direction |
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1.5.5 Planting method
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Spring crop |
Winter crop |
Vegetative multiplication |
- The stems from winter crop or garden crop can be multiplied.
- Choose the stems that are not infested with viruses or insects.
No nitrogen fertilisation before cutting
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- Multiplication season is the end of June and beginning of July
- Plant in mounded beds or flat beds. Irrigate, cut tops early
to pro mote multiple branches.
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Multiplication method of planting material
from root
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- Choose the small or medium roots with no scratches, no virus,
or insect infestation
- Prepare the soil well, the soil clods must be as fine as for
veg etables. The top of the bed is flat, with 1.2 m width,
20 cm height, fertilise 10 tons of manure/ha before planting as
basic fertiliser.
- Planting density: 40 x 40 cm/hole, the big root should be cut
into parts then dipped into ash, planting depth is about 3 cm,
cover the surface of the bed with chopped rice straw, water them
to keep the plants and soil moist.
- After the shoots have grown out of the soil surface about 5
cm, cut off weak shoots, leave only 2-3 shoots in a hole. When
the shoots are 20- 25 cm long, cut the top to allow branching,
50 - 60 days later cut the stem to plant.
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Preparation before cutting planting
material |
7-10 days before cutting,
apply additional P and K fertiliser (1-2 kg K/ sao*), do not water
or apply nitrogen |
Standards of good planting material |
Adult stem, thick and hard,
with no root, no virus and insect infestation |
Method of cutting planting material |
Cut the 1st and the 2nd
section, avoid damaging the stems and leaves |
Length of stem (cm)
Node number/stem |
25-30
6-8 |
20-25
5-7 |
Planting method |
Put the stem horizontally
in the direction of the bed, exposing the top 3-5 cm, cover with
soils from both sides and pat down the soil next to the stem. Lay
the stem down flat and no need to leave space between plantlets.
Keep the stem fresh. Better plant in the evening. In winter, avoid
planting during the north-east windy days. |
Planting density
(stem/m of bed) |
5-6 stem/ m |
4-5 stem/m |
* sao : An area unit of northern Vietnam, 1 sao equals 360m2
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1.5.6 Fertilization
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Spring crop |
Winter crop |
Ratio and total amount of fertilizers
(kg / sao*) |
300 -400 kg manure
3 kg urea (N)
10 kg superphosphate(P)
6 kg potassium chloride (K) |
300-400 kg manure
4-5 kg urea (N)
10 kg superphosphate (P)
4.5 kg potassium chloride (K) |
Basic fertilization |
All manure
All P fertilizer
1 kg urea |
All manure
All P fertilizer
1 kg urea |
Frist additional fertilization
Timing
Amount (kg/sao) |
15-20 days after planting
2 kg urea
2 kg potassium chloride |
20-25 days after planting
2-2.5 kg urea
2-2.5 kg potassium chloride |
Second additional fertilization
Timing
Amount (kg/sao) |
45-60 days after planting
The remaining potassium chloride (4 kg) |
45-60 days after planting
The remaining amount:
1-1 .5 kg urea
2-2.5 kg potassium chloride |
* sao : An area unit of northern Vietnam, 1 sao equals 360m2 |
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1.5.7 Cultivation technology
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Spring crop |
Winter crop |
Pinch off young shoots |
- At 20 days after planting pinch off the tops to promote branching
and optimize vegetative development.
- At 80-90 days after planting, if vegetative development is too
strong, cut 30-40 % of vine.
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- At 20 days after planting pinch off the tops to promote branching
and optimize vegetative development.
- No cutting
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Weed control,
re-mounding the bed |
- Link with the 1st additional fertilization
- Dig small holes on both sides of the bed, let the soils dry
for 1 day. Fertilize 2 kg of potassium chloride in holes, cover
fertiliser with soil. During this process, excess roots are cut
off to promote better root growth.
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- Mulch to protect the plants from cold and drought while keeping
the soil surface moist.
- Use rice straw to cover both sides of the bed when it is dry
and cold.
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Irrigation |
- Water while applying 1st additional fertilization. Drain to
avoid the crop sub merged in water.
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- Water while applying 1st additional fertilization. During drought,
irrigate rows between beds to keep soil moist.
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Vine lifting |
- When too much vegetative growth, lift up the stems to break
off excess roots on stems to limit vegetative growth and allow
nutri ents to concentrate in roots. Avoid damaging the stems
and leaves.
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- No need to lift up the stems because this crop does not have
much vegetative growth.
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1.5.8 The vine-cutting method for forage varieties
Cutting method |
Spring crop |
Winter crop |
First vine harvest
- Time to start harvest
- Harvest criteria
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- At 40-45 days after planting
- Choose 2-3 longest stems of a plant, use a sharp knife to cut,
leaving 10-1 5 cm.
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- At 45-50 days after planting
- Choose 1 -2 longest stems of a plant, use a sharp knife to cut,
leaving 15-20cm.
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Subsequent vine harvest
- Harvest interval
- Stems and amount to cut
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- Cut stems every 10-15 days until the last harvest.
- Depending on vegetative growth, cut 2-3 longest stems, up to
4 stems if much growth, leaving 1 5-20 cm. More stems can be cut
near the end harvest.
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- Cut stems every 10-15 days until the last harvest.
- Cut 2-3 longest stems of a plant, leaving 15-20 cm. Irrigate
while applying addi tional fertiliser after cutting.
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1.5.9 Main insects and protection
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Spring crop |
Winter crop |
Weevil
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- The most serious for spring crop. The drier and hotter the
weather is, the more weevil attack. Less serious in sandy soils
than in loamy soils. Cracked soils are most susceptible to weevils.
Storage roots are also often attacked, so it is necessary to cover
the roots with nylon or sand.
- Rotate sweetpotato with paddy rice and other crops. Use biological
control such as introduction of natural enemies, manipulation
of habitat, conservation of natural enemies through avoidance
of pesticide use or trap weevils to eliminate them.
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Sweetpotato Hornworm (Agnus convolvuli) |
- The most serious attack is in spring when they eat all the
leaves.
- Protection by planting in rotation with other crops or pick
them out by hand.
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Borer |
- The larvae attack the main stems and petioles and decrease
the vegetative growth. Vine yield is decreased. For dual-purpose
varieties, in the case of too much vegetative development, borer
attack is good because it limits vegetative growth, allowing the
nutrients to go into roots. In this case, protection is not necessary.
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Black rot |
- Plant sweetpotato in rotation with other crops such as paddy
rice. Clear all the remaining parts of the previous crops, do
sanitation of the field.
- Plant sweetpotato in rotation with other crops. Do not use black
rot- infected roots and stems for breeding material. Avoid damaging
the roots during harvest. Clean fields after harvest.
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1.5.10 Harvest
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Spring crop |
Winter crop |
Methods of identifying the time for
harvest |
- Most appropriate time for harvest depends on the timing of
rotation with other crops.
- Harvest when two thirds of the leaves have turned yellow or
fallen off. Another indication is when tubers no longer have any
roots attached.
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Date of harvest |
From 20 June to 5 July |
From 5 February to 20 February |
Methods of harvest |
Sunny and dry days are
best for harvesting. First, dig out both sides of the bed, then
hoe to pick out the roots. Avoid damaging the roots, clean soils
off of the roots and store in cool place. |
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1.5.11 Storage
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Spring crop |
Winter crop |
Root storage
Root storage Methods
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- Put roots in a heap, cover the heap with a layer of sand before
covering with a sheet of nylon. The roots can be stored up to
2-3 months.
- Slice the roots with or without the skin to make dry chips <0.5
cm in thickness. Avoid molding. The experience of the farmers:
soak slices in salt water (in concentration of 8-10% for 1 hour)
before drying to avoid molding. When completely dried, put chips
in nylon bags for storage.
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Storage duration |
From July to February |
From March to June |
Remarks during storage |
Susceptible to rotting or weevil attacks.
Check regularly to eliminate rotting or weevils or dry the slices
again. |
Due to high humidity, storage roots
are often molded or rot ten. |
Vines storage
Methods to store vines
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- Chop vines into 0.5-1 cm lengths, dry thoroughly and store
in nylon bags and feed them to pigs regularly.
- Chop vines into 0.5-1 cm lengths, pre-wilt, then ensile with
additives*.
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Storage duration |
From July to February |
From March to June |
Remarks during storage |
Susceptible to molding. |
Due to high humidity, storage roots
are often molded or rotten. Bags need to be air tight. |
* Ensiling methods will be covered in Chapter 2.
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1.5.12 Recommended utilization
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Spring crop |
Winter crop |
Vine |
Use dried or ensiled vine |
Use fresh or ensiled vine or sell the
surplus vine |
Root |
Big root, slice and dry to make chips
or starch noodles |
Small root, high moisture content,
feed fresh or ensiled roots to pigs
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