2007 - Texas A&M AgriLIFE Research Center at Beaumont - Texas ...

Planting after the optimum planting dates reduces the
opportunity to produce high yields. It has been estimated
that a 5 percent reduction in first crop yield can be expected
for each week’s delay in planting after April 21.
Seeding Rates
G. N. McCauley, L. Tarpley and M. F. Jund
Uniform stands of healthy rice seedlings pave the way
to a productive rice crop. Growers generally can achieve the
desired plant population of 15 to 20 seedlings per square foot
(9 to 12 seedlings per 7-inch drill row foot) by drill seeding
70 to 90 pounds of rice seed per acre the first week of April.
Lower seeding rate and plant populations (15 seedlings
per square foot) are preferred when planting high tillering
varieties, such as Cypress and Jasmine 85, and when disease
pressure is expected to be high after canopy closure.
These recommendations assume average seed size (Cocodrie,
Cypress and Cheniere at 18,000 to 19,000 seed per
pound), well prepared seedbeds, planting at recommended
depths, good quality seed and near optimum conditions for
April 1 planting.
Adjusting seeding rate for variety
When planting a variety with seed that is larger than
average (Jefferson with 16,000 seed per pound) or smaller
than average (Dixiebelle or hybrid seed with 20,000 to
21,000 seed per pound), adjust the seeding rate to ensure that
you get the desired number of seed per square foot.
For example, Jefferson ought to be planted at a 10
percent higher rate than that used for Lemont and Gulfmont,
15 percent over that used for Cypress and Cocodrie and
25 percent over that used for Dixiebelle, assuming similar
germination and survival of each variety.
This higher seeding rate will help ensure that varieties
with lower-than-average numbers of seed per pound (such
as Jefferson) will have a plant population similar to other
varieties. Table 4 shows the effect of seed size on seed per
square foot.
Further increasing the seeding rate of Jefferson can be
justified because of its lower tillering and vigor. Compared to
Cocodrie, Jefferson has lower tillering capacity. This makes
it difficult for Jefferson to yield as well when stands are less
than the recommended 20 to 25 seedlings per square foot.
Table 4. Recommended seeding rates adjusted for seed size and
tillering for March 20 to April 1 planting on good seed beds.
Variety
Jefferson
Lemont, Gulfmont
Priscilla, Wells
Cypress, Saber,
Bolivar and Cocodrie
Drill
seeded
90-100
80
70-80
60-70
Seeding rate (lb/A)
Broadcast
(dry)
110-120
100
100
80-90
Water
planted
120-130
120
120
110
Low plant populations of Jefferson (such as 12 live seedlings
per square foot or about 40 pounds of seed per acre, assuming
80 percent seedling emergence) will yield well if the
seedlings are uniformly distributed and enough nitrogen is
applied early.
Adjusting seeding rate for conditions
Below are recommendations and considerations when
adjusting seeding rate according to planting conditions:
• For broadcast seeding, use an additional 20 pounds of
seed per acre above the 70 to 90 pounds per acre of
drilled seed.
• If the seedbeds are rough or poorly prepared, increase
the seeding rate by 10 pounds or more.
• For each week the crop is seeded before March 15,
you may need an additional 10 pounds of seed because
earlier planting usually means cooler weather.
• You might not need to increase the seeding rate if soil
and air temperatures are 70 degrees or above. However,
growers who have had problems achieving recommended
stands should use higher seeding rates.
• When drilling to moisture in stale seedbed conditions,
you can generally reduce the seeding rate by 10 to 15
percent from conventional seedbed conditions.
• If soil conditions require a germination flush and Command
will be applied preplant, increase the seeding rate
to 10 percent above conventional recommendations.
• You can reduce the need for higher seeding rates by
using gibberellic acid as a seed treatment, which can
increase seedling vigor.
Replanting is not recommended unless stands have fewer
than 8-10 seedlings per square foot over most of the field
for semidwarf varieties and 5 seedlings per square foot for
hybrids. If there are fewer than 15 seedlings per square foot,
you can improve plot yields by increasing early nitrogen
applications by 30 to 50 pounds per acre.
Rice producers who commonly achieve optimum planting
density recognize that actual seedlings per square foot (plant
population) is a better measure for comparing field performance
than seeding rate because plant population is the final
product of:
• Seeding rate
• Live seed per pound of seed (determined by percent
germination and seed size)
• Percent emergence (determined by planting conditions,
such as seed depth and vigor, soil moisture, temperature,
seedling disease and bird feeding)
Measuring seedling stand density
Growers are encouraged to count seedlings per square
foot for a given seeding rate. This information becomes
very important in subsequent years when the seeding rate
is adjusted for variety and planting conditions. The best
measurements of stand density can be made at the three- to
four-leaf rice stage. After the fourth leaf, tillering makes
stand counts very difficult.
In broadcast rice, stand density can be measured using
square or circular hoop of 1, 2, 3 or more square feet. The
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