What it does
Phosphorus deficiency affects the major functions in energy storage and transfer of plants. Specifically, it affects tillering, root development, early flowering, and ripening.
Why and where it occurs
P deficiency is widespread in all major rice ecosystems and is the major growth-limiting factor in acid upland soils where soil P-fixation capacity is often large.
Soils particularly prone to P deficiency include the following types:
- coarse-textured soils containing small amounts of organic matter and small P reserves (e.g., sandy soils in northeast Thailand, Cambodia)
- highly weathered, clayey, acid upland soils with high P-fixation capacity (e.g., Ultisols and Oxisols in many countries
- degraded lowland soils (e.g., North Vietnam)
- calcareous, saline, and sodic soils
- volcanic soils with high P-sorption capacity (e.g., Andisols in Japan and parts of Sumatra and Java)
- peat soils (Histosols)
- acid sulfate soils in which large amounts of active Al and Fe result in the formation of insoluble P compounds at low pH
How to identify
The following are symptoms of P deficiency:
- Stunted plants
- Reduced tillering
- Leaves, particularly older ones, are narrow, short, very erect, and "dirty" dark green
- Stems are thin and spindly and plant development is retarded
- The number of leaves, panicles, and grains per panicle is also reduced
- Young leaves appear to be healthy but older leaves turn brown and die
- Red and purple colors may develop in leaves if the variety has a tendency to produce anthocyanin
- Leaves appear pale green when P and N deficiency occur simultaneously
Mild to moderate P deficiency is difficult to recognize in the field
P deficiency is often associated with other nutrient disorders such as Fe toxicity at low pH, Zn deficiency, Fe deficiency, and salinity in alkaline soils
Other effects of P deficiency include delayed maturity (often by 1 week or more).
When P deficiency is severe, plants may not flower at all. There are large proportion of empty grains.
When P deficiency is very severe, grain formation may not occur, and it will have:
- Low 1,000-grain weight and poor grain quality
- No response to mineral N fertilizer application
- Low tolerance for cold water
- Absence of algae in floodwater
- Poor growth (small leaves, slow establishment) of green manure crops
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How to manage
- Use high quality seed of a high yielding variety.
- Use rice cultivars that use P efficiently, particularly on acid upland soils.
- In rice-rice systems, carry out dry, shallow tillage (10 cm) within 2 weeks after harvest. On acid, low-fertility rainfed lowland and upland soils, all existing soil fertility problems (acidity, Al toxicity, deficiencies of Mg, K, and other nutrients) must be corrected before a response to P is obtained.
- Incorporate rice straw. Although the total amount of P recycled with the straw is small (1 kg P t-1 straw), it will contribute to maintaining a positive P balance in the long term.
- Apply optimum doses of N and K and correct micronutrient deficiencies.
- Replenish P removed in crop products by applying P fertilizers, farmyard manure, or other materials (night soil, compost).
- Apply fertilizers efficiently.
Learn more
View full fact sheet: Phosphorous deficiency on IRRI Rice Knowledge Bank