• impairs plant growth
• obstructs root development
• restricts water supply to the roots
• results in deficiencies in phosphorus and zinc
• Iron deficiency and boron toxicity may also occur

• discoloration of leaves starting at tip
• scorched appearance in more susceptible plants
• depressed tillering and growth
• pattern of damage is patchy

• with high levels of exchangeable sodium
• relatively rare especially in irrigated rice systems
• occurs in semiarid region soils
• often associated with salinity
• damage occurs throughout the growth cycle of the rice crop

• Discoloration of leaves ranging from white to reddish brown starting from the leaf tips
• Discoloration spreads down the leaf giving the plant a scorched appearance in more susceptible plants and in severe alkaline conditions
• Growth and tillering depressed

Plant stand is patchy and has a poor growth (IRRI).

Soil and plant tests can be used to detect alkalinity. However, there is no direct test available for plants. The soil can be checked for potential alkalinity if the exchangeable sodium > 15% and a soil pH > 8.

Strongly alkaline soils can also be phosphorus and zinc deficient.

Alkalinity is relatively rare especially in irrigated rice systems.
Alkaline soils have high levels of exchangeable sodium usually more than 15%.

Alkalinity occurs in semiarid region soils and is often associated with salinity. Thus, a number of combinations can occur:

	Saline soil	Alkali soil	Saline-Alkali
ECe x 10-3	Above 4	Below 4	Above 4
ESP	Below 15	At least 15	At least 15
PH paste	Below 8.5	8.5-10.0	usually < 8.5

ECe = Electrical conductivity of soil extract with water

ESP = Exchangeable sodium percentage

The high percentage of sodium in alkaline soils usually causes soil structural problems, which can be a problem in aerobic or upland crop systems. The high percentage of sodium can also have a direct effect on some cultivars. Alkalinity impairs plant growth and obstructs root development. It also restricts water supply to the roots. The strong basic properties of alkaline soils result in deficiencies in phosphorus and zinc. Iron deficiency and boron toxicity may also occur in these soils.

The damage caused by alkalinity occurs throughout the growth cycle of the rice crop.

Alkalinity is relatively rare, especially in irrigated rice systems.

The objective of rehabilitating alkaline soils is to replace the sodium ions in the soil with calcium ions. This is a long-term process. Sources of calcium to be applied include:

Name	Formula	Content	Comments
Lime	CaCO3	40% Ca
Dolomite	MgCO3 + CaCO3	13% Mg, 21% Ca	Slow-acting, content of Ca and Mg varies
Gypsum	CaSO4 . 2 H2O	23% Ca, 18% S	Slightly soluble, slow-acting
Partly acidulated rock phosphate	Ca3(PO4)2	10–11% P	>1/3 water-soluble
Rock phosphate, finely powdered	Ca3(PO4)2	11–17% P, 33–36% Ca	Very slow acting (25–39% P2O5)
Single superphosphate	Ca(H2PO4)2 . H20 + CaSO4 . 2H20	12% S, 7-9% P, 13-20% Ca	Soluble, quick acting