( Exchangeable sodium percentage(ESP) ESP is the percentage of exchangeable sodium ions to the total soil exchangeable cations of all types in the soil sample. ESP=(exchangeable sodium ions )/(soil cations exchangeable capacity) X100 Alkalinization-If a high proportion of exchange sites is occupied by sodium ions, soils can become very basic with pH values of 8.5 to 10. 5. These soils can become impermeable to water because small soil particles that are dispersed by the sodium are entrapped in the pores and seal them. These impermeable soils keep a water layer on the surface, which cannot infiltrate, and these areas appear wet longer than other adjacent soils Classification of solonetz in China: Light alkali-affected soil, ESP 5-10%: Middle alkali-affected soil. ESP: 10-15%6 Strong alkali-affected soil esP: 15--20% Alkali soil. ESP>30%（二）Exchangeable sodium percentage (ESP） ESP is the percentage of exchangeable sodium ions to the total soil exchangeable cations of all types in the soil sample. Alkalinization-If a high proportion of exchange sites is occupied by sodium ions, soils can become very basic with pH values of 8.5 to 10.5. These soils can become impermeable to water because small soil particles that are dispersed by the sodium are entrapped in the pores and seal them. These impermeable soils keep a water layer on the surface, which cannot infiltrate, and these areas appear “wet” longer than other adjacent soils. Classification of solonetz in China: Light alkali-affected soil, ESP : 5－10％ ; Middle alkali-affected soil, ESP : 10－15％; Strong alkali-affected soil, ESP : 15－20％ Alkali soil, ESP>30%. ESP = [(exchangeable sodium ions )/(soil cations exchangeable capacity)]×100