Effects of polyacrylamides with different hydrolysis degrees and molecular weights on water holding capacity of sandy yellow soil

A simulation experiment was carried out to identify the optimal polyacrylamide (PAM) formulations (hydrolyis degree, HD; molecular weight, MW) for increasing the water holding capacity of sandy yellow soil distributing widely in Chongqing City. The results indicated that different formulations of PAM could maintain the soil moisture and reduce soil water evaporation rate to some extent. Compared with the control, the treatments amended by PAMs having a MW of 8 million but with different HDs of 10%, 20%, 30%, and 40% reduced the cumulative evaporation rate from sandy yellow soil by a range of 7.76% to 20.17%, while increased the mean soil moisture by a range of 2.65% to 5.96%, with the PAM having a HD of 40% showing the maximum water holding capacity. On the other hand, the treatments amended by PAMs having a HD of 40% but with different MWs of 4, 6, 8, 10 million reduced the cumulative evaporation rate from sandy soils by 14.37% to 20.74%, but increased the mean soil moisture by 4.85% to 6.11% when compared to the control, with the PAM of 10 million MW showing the maximum capacity to hold soil water. Therefore, with the dosage of 0.02% the PAM product with a HD of 40% and a MW of 10 million can be recommended as the optimal formulation for increasing water retention in sandy yellow soil.