THE RELATIONSHIP BETWEEN THE SOLUBLE AND EXCHANGEABLE MAGNESIUM IN NILE DELTA SOILS.

Salt affected soils exist in several parts of Nile Delta of which are high-magnesium soils with improper properties. The identifying of rich-magnesium soils requires estimation ofthe exchangeable magnesium percentage (EMgP) and/or the exchangeable magnesium to exchangeable calcium ratio (EMg/ECa). The EMgP value and EMg/ECa ratio on soil surface are important statements that have an obvious equilibrium with the relative values of Mg and Ca in soil solution. Preliminary study was carried out to create proper relationship between the soluble magnesium in soil solution and exchangeable magnesium on the exchange complexes in Nile Delta soils. To derive the relations between both soluble and exchangeable magnesium in soil, 90 soil samples were collected during winter season (2015/2016) from Kafre El-Sheikh, El-Hamoul, Borollus, Motobus and El-Mahalla Districts to represent non saline- , medium saline- and high saline- soils. The soluble cations in soil paste extract and the exchangeable cations on soil surface were determined. Chemical analysis of soil paste extract showed that the soluble magnesium percentage (SMgP) ranged from 9.0 to 36 and SMg/SCa ratio in soil solution ranged from 0.2 to 3.5. The determination of the exchangeable cations on soil surface indicated that EMgP value ranged from 8 to 29 and EMg/ECa ratio ranged from 0.12 to 2.0. Three empirical equations were derived to represent the relationships between: 1- SMg/SCavs. EMg/ECa: EMg/ECa = - 0.245 + 1.362 (SMg/SCa) -0.246 (SMg/SCa)2 (R² = 0.858) (1) 2- SMgPvs. EMgP: EMgP= -9.298 + 2.191(SMgP) -0.032(SMgP)2(R² = 0.817) (2) 3- SMgP vs. EMgP after the suitable transformation: EMgP=-0.432+3.098(ASIN (SQRT (SMgP/100))-2.438(SQRT (SMgP/100))2(3) (R² = 0.830) The coefficients of determination for the obtained relations aremost proper; consequently, EMg/ECa ratio and EMgP valueon soil surface can be safely predicted from their values in soil solution using these equations.