Paddy: *Oryza sativa*

Paddy Overview

• Botanical name is Oryza sativa
• Part of the Gramineae family

Origin and Distribution

• Has been cultivated in Southeastern Asia since ancient times
• Likely originated in China and spread to India
• Now grown in Asia, Southern Europe, Africa, parts of Australia, and the Americas
• Initially grown on sugar plantations as food, later becoming a business in the early 20th century, largely by East Indians

Economic Importance

• A cornerstone of many countries' economies
• Second to sugar regarding most important agricultural industry
• Contributes about 20% of agricultural GDP and 12% of export earnings
• Involves over 12,000 farmers
• Benefits ~20% of the population
• Rice production increased from 171,000 metric tons in 1992 to over 500,000 metric tons in 2013
• By-products can be used for fuel, food, fertilizer (potash), and craft

Growth Phases of Rice Plant

• Consists of vegetative, reproductive, and ripening phases
• These phases are divided into different growth stages

Vegetative Phase

• Begins with seed germination, marked by the emergence of the radicle or coleoptile

Seedling stage

• It follows seed germination
• Seedling develops germinal and lateral roots
• Lasts from germination until the fifth leaf develops
• Seedling absorbs food from the endosperm

Transplanting stage

• Only transplanted rice plants undergo this stage
• Period of moving the seedling to full recovery

Tillering stage

• Begins with appearance of the first tiller from the auxiliary bud in one of the lower nodes
• Tillers increase rapidly (active tillering) until maximum tillers are reached
• Number of tillers declines and levels off
• The plant stops tillering after the production of tertiary tillers

Reproductive Phase

• Plant undergoes several stages

Panicle initiation stage

• Begins before maximum tiller production, during highest tillering activity
• Marked by initiation of the panicle primordial of microscopic dimension on the growing shoot

Booting and internode elongation stage

• Young panicle becomes visible to naked eye over a few days
• Marks the beginning of booting stage
• Time of internode elongation varies among varieties

Heading stage

• Marked by panicle tip emerging from the flag leaf sheath
• Emergence continues until 90% of panicles are out of sheaths

Flowering stage

• Begins with protrusion of the first dehiscing anthers in the terminal spikelet on panicle branches
• Flowering continues until all spikelets bloom
• Pollination and fertilization follow

Ripening Phase

• Rice grain develops after pollination and fertilization
• Grain development is a continuous process

Milk stage

• Caryopsis are first watery, then turn milky

Dough stage

• Milky caryopsis turns into soft dough then hard dough

Maturity stage

• Grain is mature when the caryopsis is fully developed in size, hard, clear, and free of greenish tint
• Completed when >90% of grains are fully ripened

Structure of the Rice Plant

• Monocotyledonous annual grass with a fibrous root system
• Culm (stem) is rounded, jointed
• Solid nodes and hollow internodes
• Node bears a leaf and a bud
• Buds in axils of lower leaves produce tillers
• Leaves are borne at an angle on the culm in two rows, one at each node
• Blade attached to the node by the leaf sheath
• Auricles: small, paired, ear-like appendages on leaf base
• Ligule: papery triangular structure just above auricles
• Rice plants have both auricles and ligule, Echinochola species weeds have neither

Panicle

• Group of flowers on the uppermost node of the culm above the flag leaf
• Grain develops after pollination and fertilization
• 99% of flowers are self-fertilized
• Mature grain covered by husk or hull
• Rice grain includes the embryonic shoot (plumule) and embryonic root (radicle) once the hull is removed
• Plumule is enclosed by the coleoptile
• Radicle is enclosed by the coleorhiza
• The rest of the grain is starchy endosperm

Climate and Soil Requirement

• Grows in 45°N - 40°S latitude
• Suitable for wet tropics, but grows elsewhere
• Generally grown under flooded culture
• Sown with early rains, harvested at the end of the monsoon during dry weather
• Needs abundant sunlight, especially in last 45 days
• High yields in areas with increased solar radiation, provided sufficient water (i.e., warm temperate countries)
• Low yields during wet, cloudy monsoon
• Heavy rain at flowering interferes with pollination, excess rain causes lodging
• Average temperature during growth season should be 20°C - 38°C
• Lower temperatures during early growth slow development and tillering
• Can grow on many soil types given adequate water, but clay and clayey/silty loams are preferable
• Clayey soils retain water and mineral nutrients due to less percolation and leaching
• Yield unaffected in pH range of 4-7

Varieties

• Adaptation led to geographical races
• 24 species in Oryza genus, 2 cultivated, 22 wild
• Cultivated species are Oryza sativa and Oryza glaberrima
  • Oryza sativa grown in Asia, Europe, and America
  • Oryza glaberrima grown in Western Africa
• Oryza sativa has three subspecies:
  • indica (India, Burma, Sri Lanka)
  • japonica (Japan, China, South Korea, Southern Europe, USA, South America)
  • javanica (mainly Indonesia)

Indica rice

• Suited for tropical monsoon climates (short day length)
• Hardy, tall, vigorous vegetative growth, high tillering
• Susceptible to lodging
• Long vegetative phase
• Broad, pale green color leaves
• Flag leaf is long, narrow
• Drooping after flowering
• Sensitive to long day length
• Resistant to pests/diseases
• Responds poorly to fertilizers but grows well under unfavorable conditions
• Matures late
• Narrow, long, flattened grain
• Cooked rice is non-cohesive

Japonica rice

• Suited for temperate areas
• Less vegetative, short, sturdy culms, moderate tillering
• Sensitive to long day length
• Narrow, dark green leaves
• Flag leaf is short, broad
• Remains erect after flowering
• Responds well to fertilizers (higher yields with more fertilizers)
• Moderately tolerant to unfavorable conditions
• Susceptible to pests
• Broad, short, thick grain
• Cooked rice tends to be sticky
• Most varieties are crosses between Indicas and Japonicas

Hybrid varieties

• Combine high-yield/fertilizer response of japonica with hardiness/adaptability of indica
• Dee-geo-woo-gen crossed with Peta is an example

Cultural Systems

• Two main cultivation systems:

Upland or hill rice culture

• Rain-fed crop with adequate rainfall (at least 30 inches over 3-4 months)
• ~10% of world rice production
• Seeds broadcast or row sown

Lowland or swamp rice culture

• Grown on flooded, low-lying lands
• Grown in water from planting until harvest
• Seeds broadcast, row sown, or transplanted from nursery beds
• Water supply is a main consideration
• Modifications such as dry land preparation followed by flooding are also used
• Accounts for 90% of world rice production

Seed Paddy

• Select seeds to obtain a uniform plant, vigorous seedlings, and high yield
• Seeds need to be matured, full and heavy
• Use certified seed paddy

Land Preparation

• Bunds (meres) are built to hold water uniformly, specifically on sloping sides
• Size and shape vary with topography
• Flat lands use fields of at least 0.4 hectare in size
• Clear land of dried rice straw, stubble, and weeds by fire during dry season or after harvesting

Reasons for Land Preparation:

• Soil in best physical condition for crop growth
• Soil surface should be level
• Control Weeds

Soil Tillage

• Required for fertilizer incorporation before planting
• Goal is to put soil in best physical condition for plant establishment and growth
• Soil must be tilled to a depth so plants develope roots and obtain key nutrients
• Soil disturbance should control weeds
• Tillage should leave soil level to improve water use efficiency and weed control
• Fields need drainage system for excess water removal

Primary Tillage

• First working after harvest, most aggressive operation
• Done under dry conditions, includes first and second cut with disc plough at 4-6 inches depth
• Done through harrowing via rome or disc plough

Secondary Tillage

• Done after primary tillage, usually shallower
• Less aggressive than primary tillage
• In inadequate rainfall, fields are irrigated for:
  • Harrowing or puddling with disc plough
  • Raking and leveling or dragging (henga or drag wood)
• Bunds (meres) are weeded and strengthened
• Cracks or holes sealed with mud
• Avoid draining turbid water to avoid loss of suspended clay and organic matter
• Fine leveling assists in control of weeds
• Fine leveling also helps in even distribution of water/fertilizer, allows for uniform emergence of seedlings
• Takes 4-6 weeks

Weed Control

• Weeds can lower rice yields
• Severe yield reduction if weeds are not controlled early (3-4 leaf stage)
• Weed growth can reduce yields by >30% in lowland fields, up to 75% in upland fields
• Weeds are worse in broadcast crops versus transplanted rice
• Flooding the paddy field during plant control growth, drying the land in the off-season controls weeds

Weeds Importance in Lowland Rice

• Grasses
• Sedges
• Broad leaf weeds

Weed Control- Integrated Program

• Weed control grouped under four broad categories
• Combines practices that have a direct or indirect impact on the weed population

Mechanical Control

• Ploughing, harrowing, puddling, and leveling destroys the initial weed population

Cultural Weed Control

• Clean implements and machinery to avoid weed spread
• Cattle out of rice fields, where possible, as weed species can remain viable
• Choice of variety: Varieties with good seedling vigor develop early and compete with weeds for environmental resources
• The use of weed free seeds: Prevents new weeds into fields
• Appropriate seed rate: Contribute to successful weed management
• Low plant density encourages weed development
• Proper water management
• Effective method for controlling non-aquatic weeds
• Early flooding of seedlings is effective
• Fields should be relatively level for proper drainage
• Field sanitation: Keep meres, dams, and water courses weed free

Manual Weed Control

• Rogueing: Manually pulling weeds when there is sparse population
• Should be done before seeds are produced or mature

Chemical Weed Control

• Use Weedicides or Herbicides
• Most effective when applied at seedling stage

Red Rice

• Serious weed in several rice-producing countries such as North and South America
• Panicle shatters readily before/during harvest
• Heavily infests fields with drop seeds, grows and remains viable, lowers market value

Interventions

• Early application of nitrogen fertilizer for early rapid growth
• Using varieties with early canopy cover
• Use high seed rate for plant competition
• Pre plant herbicide at tillage to destroy Red Rice seedlings
• Burning rice straw after harvesting to destroy weed seeds on soil surface

Nutrition

• 19 elements required for growth
• Nitrogen, Phosphorus and Potassium needed in large amounts and are macro elements.

Nitrogen

• Key plant nutrient given as urea
• Is associated with carbohydrate metabolism
• Is required for vigorous vegetative growth
• Is an important part of chlorophyll

Deficiency Symptoms

• Stunted growth
• Yellowing of leaves and tillers
• Reduced tillering

Sources

• Nitrogen fertilizer
• Nitrogen fixation
• Mineralization
• Nitrogen in irrigated water/rainfall

Phosphorous

• Second most important nutrient
• Given as Triple Superphosphate (TSP) with 46% P2O5

Other sources

• Mono Ammonium Phosphate (MAP)
• Di Ammonium Phosphate (DAP).

Functions

• Stimulates root growth
• Hastens crop maturity
• Improves straw strength
• Is a constituent on nucleic acid and phytins
• Aids in photosynthesis, the inter-conversion of carbohydrates, amino acids and fat metabolism, biological oxidation, the energy transfer process and a host of other life-process reactions

Deficiency Symptoms

• Stunted plants with few tillers
• Narrow leaves with erect shoots, dirty dark green
• Younger leaves healthier than older leaves
• Reddish or purplish color on leaves
• Reduced leaf number/length

Potassium

• Given as Muriate of Potash, at 60% K2O

Functions

• Important in photosynthesis and grain filling
• Associated with fungal disease resistance and lodging

Deficiency Symptoms

• Dark green leaves with yellowish brown margins
• Has dark brown necrotic spots, first on older leaves.

Control

• First fertilizer applied in 18-21 days after sowing
• Phosphorus /Potassium applied when prepping land
• Nitrogen (Urea) is split into three portions at 18-21, 42, and 60 days after sowing (DAS).
• Control for weeds before adding fertilizer

Urea application

• Ensure standing water will remain for 24 hrs to avoid loss
• Try to drain field before applying fertilizer/re-flood 1-4 inches 2-3 days after application

Current Fertilizer Rates

• Urea:75 kg/ha (1.5 bags/ac)
• Triple Super Phosphate: 40 kg/ha (1 bag/ac)
• Muriate of Potash: 40 kg/ha (1 bag/ac)

Disease

• 4 fungal diseases are major constraints

Leaf Blast

• Causal Agent: Pyricularia oryzae

Symptoms

• Lesions vary from small, dark, round spots to oval spots that are reddish-brown
• Spots become elongated, diamond or linear with points to end
• Lesions have gray with reddish brown in middle

Chemical Control

• Treat with fungicide -Carbendazim at a rate of 200-300 ml/acre -Fugi-One at a rate of 200-300 ml/acre

Sheath Rot

• Causal Agent:Sarocladium oryzae

Symptoms

• Affects at booting stage
• Uppermost leaf sheath has oblong/irregular spots (.05-1.5cm Long) w/ gray center and brown margin
• The boot leaf turns brownish black and is rotten
• The grains are discolored and not filled
• Spread by airborne condia

Notes

• Close planting, high humidity, injuries from ear-head bugs can cause diseases

Chemical Control

Treat with fungicide:

• Carbendazim at a rate of 200-300 ml/acre
• Fugi-One at a rate of 200-300 ml/acre

Sheath Blight

• Soil problems/irrigation are abundant
• Causal agent: Rhizoctonia solani

Symptoms

• Disease happens when the plant is older
• Can show one or few giant oblong irregular lesions on the leaf
• Advanced stages: lesions are bleached with an irregular purple/brown outline
• Drying of leaves during severe conditons

Chemical Control

• Treat with fungicide: -Carbendazim at a rate of 200-300 ml/acre -Fugi-One at a rate of 200-300 ml/acre

Brown Spot

• Causal agent: Bipolaris oryzae

Symptoms

• Infected seedling have short circle/oval brown lesions
• Infected becomes short/dies
• Underdeveloped lesions on older leaves are short, circular, and dark-purple
• Grown lesion on older leaves is oval, brown w/ white/gray middle w/ reddish edges
• Infected seeds have black spots/brown lesions

Notes

• Infected seeds cause infected seedlings with fungus that spread

Chemical Control

• Treat with fungicide: -Carbendazim at a rate of 200-300 ml/acre -Fugi-One at a rate of 200-300 ml/acre

Cultural Practices

• Avoid using infected seeds
• Apply moderate levels(80 - 100 kg/ha) in 3-4
• Avoid extra' N'; skip the final 'N' during 'sheath blight' infections
• Destroy weeds etc