For obtaining potential yield of soybean
following recommendations and suggestions are applicable.
CLIMATIC REQUIREMENTS
Temperature:
Soybean can be grown successfully under a wide range of temperatures. The
minimum and maximum soil temperatures for germination of soybean seeds are
approximately 5 oC and
40 oC. Irrigations
(depending upon rains).oC, respectively. The optimum temperature for
rapid vegetative growth rate is about 30oC whereas, temperature
above 40oC has adverse effect on flower initiation and pod
retention.
Moisture: Moisture availability is particularly
critical during two periods of soybean germination and pod filling. However,
availability of adequate moisture during the pod filling period is critical. Water
stress during floral initiation, pollination, and seed development may greatly
reduce the seed yield significantly.
Photoperiod: Latitude and time of year
(sun declination) are the determents of photoperiod and temperature. Soybean is
short day plant (SDP) where flowering is promoted by day length shorter than a
critical maximum varies among varieties. Actual controlling factor is the
length of uninterrupted darkness or nyctoperiod. Photo periodically sensitive
varieties of soybean are adapted to a narrow latitude range (200-250 km).
SOIL AND FERTILIZER REQUIREMENTS:
Soil: Soybean can be grown on almost all
well-drained soils, however, crop is more productive on fertile loam soils.
Soybean is not sensitive to acidic soils as many other legumes. Soil with pH
6-7 is suitable for crop growth. In this pH range, adequate calcium and
magnesium are normally available. For efficient production, soil must be
managed properly to allow optimum uptake of water and nutrients.
Fertilizer: Fertilizer application is important
in the soybean production and has great effect on yield. Usually 25:50:50 (NPK)
kg /ha at the time of sowing
gives higher yields. Fertilizers are usually broadcasted during seed-bed
preparation. Under conditions fertilizer dose may vary according to the soil
fertility and status. Soybean in rotation with other crops, often provide some
nitrogen for the following crops and may reduce the need for pesticides by
limiting certain disease or insect problems.
Adding N fertilizer to soybeans usually decreases
nodulation and results in smaller amounts of N being symbiotically fixed.
Therefore, nitrogen is recommended only when adequate nodulation is not
achieved. However, supplemental N should not be applied within 30 days of
emergence but should be applied before flowering, which is usually early March
to spring crop and late July to autumn crop depending on maturity group of a
variety.
Seed-bed Preparation: Two to three
ploughings followed by plankings are sufficient to get proper tilth. This will
improve moisture conservation of the soil which is required for soil-seed
interaction, good seed germination, emergence, growth and development.
Seed Inoculum: The nitrogen fixing
bacteria (Rhizobia) that lives on soybean roots in nodules are not
native to most soils. The best way to introduce this bacteria is to inoculate
the seed. Once, introduced, the rhizobia population remains active in the soil
for a long time. In the presence of the appropriate inoculant ofRhizobium
japonicum, more nodules are formed on roots of soybean plant which can fix
atmospheric nitrogen from the air that is almost as effective as nitrogen
applied as fertilizer to promote growth and development of the plant.
Method of Inoculation: Inoculum is a black
powder containing nitrogen fixing bacteria which are mixed with ground peat or
some similar carrier and applied on seed just before planting time. Seeds are
moistened with concentrated sugar solution, inoculant is applied as 1250 gm per
100 kg seeds and then mixed thoroughly to have a uniform coating of inoculum on
the seeds. This process should be done in shady place. The use of fungicide in
case of seed treatment, may interfere with inoculated seed and with symbioses
of Rhizobium-soybean system. Thus, compatible fungicides (i.e. Benlate and Dithane
Z-78 (Zineb) with no toxicity to Rhizobia should be used. Treat seed
immediately before planting and use inoculum dose little higher than
recommended.
Varieties: Different soybean varieties of
American origin were selected afterconducting a large number of trials. These
varieties are NARC-1, NARC-2, Ajmeri, FS-85, Malakand-96, Swat-84 and Kharif-93
have been developed by the scientists of Oilseed Programme, NARC, Islamabad and
their provincial counter parts.
Planting Time: Variation in yield loss due
to delay in the planting is the result of variation in weather and its
influence on disease, plant height, flower abortion, amount of vegetative
growth, etc. Therefore, planting date is considered to be the one of the
important factor for maximum crop yield. Late planting may result in
significant decrease in seed yield. The optimum planting time for different
areas along with suitable varieties is presented below.
Seed Rate: Seed @ 40 kg acre-1 planted at a depth of 3 to 5 cm with
30 to 45 cm row spacing gives optimum population of 120,000 to 130,000 plants
per acre. As much as 20 to 24 plants per meter of row are generally
satisfactory. However, within a wide range of plant populations for a
particular row spacing, soybean yield do not vary significantly. However, low
populations result in low poding height and excessive branches but good lodging
resistance. Conversely, high plant populations result in increased lodging,
high poding height and less branching. Generally, soybeans in narrow rows are
higher yielding because they capture more of the sun's energy which drives
photosynthetic machinery of the plant. However, wide rows are used if the
varieties are tall and bushy type.
Method of Sowing: The method of sowing
should meet three objectives i) adequate and uniform depth of seed placement,
ii) adequate seed numbers and uniform distribution, iii) sufficient soil-seed
contact for germination. Under, existing conditions, soybean must be planted
with single row cotton drill or tractor drill because of their consistency in
producing good stands.
Irrigation: Number of irrigations varies
with climatic conditions, management practices and length of growing season.
Moisture stress during flowering, pod filling and seed development stages
reduces yield. Usually 6-7 irrigations are required for spring soybean and 2-3
irrigations for autumn crop depending upon the rains. Therefore, irrigation
must be given at the following stages:
·
Three weeks after germination
·
Initiation of flowering
·
Pod filling stage
·
Seed development stage
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