Fig. 3. Volume of drainable porosity (VDP) as a function of polyacrylamide (PAM) molecular weight for 0.5- to 1.0- and 1.0- to 2.0-mm aggregate size and either deionized water (DW) or gypsum solution (GS). For a given soil, columns labeled with same letter are not significantly different at the P < 0.05 level. PAM(H) = high-molecular-weight PAM; PAM(M) = moderate-molecular-weight PAM.