Key Check 5. Sufficient nutrients from tillering to early panicle initiation and flowering.
Importance. Sufficient nutrients from tillering to EPI, and
flowering will ensure good crop growth, panicle development, and
attainment of yield potential. The optimum panicle density could be
associated with the attainment of yield potential.
Assessment of Key Check. - From tillering to early panicle initiation (EPI) and flowering, apply N fertilizer (1.5 bags urea per hectare in dry season or 1.0 bag urea per hectare in wet season) if LCC reading is below 4 for transplanted and below 3 for direct wet-seeded rice (see Table 2 and Table 3 for application of fertilizer).
- Transplanted rice and Direct Wet-seeded rice. At flowering, achieve at least 300 panicles/m2 for transplanted rice, and 350 panicles/m2 for direct wet-seeded rice.
To assess panicle density, randomly select 3 sampling sites in a diagonal line across the field. The sampling sites should be at least 1 m from the edge of the field. Count the number of panicles using a 1 m x 1 m quadrat (1 m2). Add the number of panicles and divide the total by 3 to get the average number of panicles/m2. Recommendations to achieve Key Check- Know and manage the nitrogen
needs of your plants based on LCC and assess other nutrients based on
MOET or Nutrient Omission Plot (Box 3).
Proper management of
nutrients improves crop growth and yield. It means giving the right
kind and amount of nutrients at the right time.
Rice plants grow and respond better to fertilizer when there is more sunlight.
Conduct
the Minus One Element Technique (MOET) test 30 days before
transplanting or direct wet seeding and assess nutrient status based on
visible plant nutrient deficiency symptoms and growth response (i.e.,
plant height and tiller number) but not plant biomass.
Use
the leaf color chart (LCC) every 7 days from early tillering to early
flowering to assess the crop need for nitrogen (N) fertilizer. LCC and
MOET are simple tools that can assess nutrient deficiency, guide
fertilizer application, and generate savings in fertilizer use.
Aside
from nutrient deficiency, consider mineral toxicity in deciding on the
nutrients to apply. In the lowlands, iron toxicity is most common,
especially where there is permanent flooding during crop growth. Iron
toxicity-affected rice plants have tiny brown spots on the lower leaves
starting from the tip or have orange-yellow to brown leaves.
To
manage iron toxicity, use intermittent irrigation and avoid continuous
flooding on poorly drained soils, balanced fertilizers, and perform dry
tillage after harvest to increase iron oxidation during the fallow
period.
- Nitrogen.
Use the LCC every 7 days from 14 days after trans-planting (DAT) or 21
days after seeding (DAS) until early flowering. But if 14-14-14-12S is
applied at 14 DAT or 21 DAS (Table 2 and Table 3), LCC reading starts
at 21 DAT or 28 DAS.
Nitrogen
affects many processes contributing to yield. It increases plant
height, tiller number, leaf size, spikelet number per panicle,
percentage filled spikelets, and grain protein content. Thus, if N is
deficient, plants become stunted and yellowish.
If
there is too much N, particularly between panicle initiation and
flowering, the rice plant becomes prone to lodging and pests. Excess N
is also costly.
The LCC helps farmers determine the
right time of N application by measuring the leaf color intensity. If
more than 5 out of 10 leaves have readings below the critical value of
4, apply 1.5 bags of 46-0-0 (urea) or 3.5 bags of 21-0-0-24S (ammonium
sulfate) during the DS and 1 bag of 46-0-0 or 2 bags of 21-0-0-24S
during the WS.
Ammonium sulfate is used instead of
urea when plant shows sulfur deficiency (i.e., thru MOET or visual
symptoms shown in p.35), or if sulfur-containing fertilizer like
14-14-14-12S is not used.
- Phosphorus and potassium.
Compound fertilizers, (i.e., 14-14-14-12S, 16-20-0) or single carrier
fertilizer (i.e., 0-18-0 or 0-0-60) can be used and dependent on
cropping season, soil type, yield target, and market availability
(Table 2 and Table 3).
Phosphorus
fertilizer is important for root development, tillering, early
flowering, and ripening. Phosphorus-deficient plants are stunted with
greatly reduced tillering. Leaves are narrow, short, very erect, and
dark green. Stems are thin and plant development is retarded. The
number of leaves, panicles, and grains per panicle are also reduced.
Potassium
improves root growth and plant vigor and helps prevent lodging. It also
enhances crop resistance to pests and diseases. Potassium deficiency is
often not detected because its symptoms are not as easy to recognize as
those of N deficiency, and appear during the later growth stages.
Potassium-deficient
plants are dark green with yellowish brown leaf margins, i.e., similar
to those of tungro disease but affecting whole field, not patches. Dark
brown spots can also be seen on the leaf surface.
- Sulfur. The
amount of sulfur in 14-14-14-12S (with 12% sulfur) as recommended in
Table 2 and Table 3 is adequate to correct usual sulfur deficiency.
Sulfur
deficiency is often mistaken for nitrogen deficiency. Unlike N
deficiency where older leaves are affected first, sulfur deficiency
results in yellowing (chlorosis) of young leaves.
Other
symptoms include yellowish seedlings in seedbed, high seedling
mortality after transplanting, stunted growth (but plants are not
dark-colored as in P or K deficiency), reduced tiller number, fewer and
shorter panicles, reduced number of spikelets per panicle, and delayed
maturity.
- Zinc. Apply 25 kg zinc sulfate/ha at 14 DAT once a year during the DS.
Zinc
deficiency is the most widespread micronutrient-related problem in
rice. Its symptoms appear between 2-4 weeks after transplanting.
These
include dusty brown spots on old leaves, yellowish young leaves at the
base and midrib, stunted plants, uneven plant growth, and patches of
poorly established hills in the field.
Rice plants,
however, can recover from symptoms soon after the field is drained.
Severe deficiency, on the other hand, results in reduced tiller number
and delayed maturity.
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Nutrient Management
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