The effects of continuous (1.0 mg/l) and concentrated (10 mg/l) irrigation
water-added polyacrylamide (PAM) on infiltration of a highly erodible Medit
erranean soil were studied using recirculating furrow infiltrometers. Polya
crylamide avoided the seal formation observed in the wetted surface of the
control furrow and helped to maintain higher infiltration rates for both PA
M treatments. Mean final cumulative infiltration for the continuous and con
centrated PAM experiments increased by 20 and 14%, respectively, as the res
ult of reduced seal formation and surface sealing. Steady-state furrow infi
ltration rates, evaluated with disc infiltrometers 15 h after irrigation an
d under soil water tensions of 40 and 100 mm, confirmed the infiltration be
nefit of PAM treatments. Unsaturated hydraulic conductivity calculated unde
r the same tensions revealed that the PAM-treated furrows were about 95% mo
re permeable than the control. Polyacrylamide application also increased av
erage saturated conductivity by 168% because of more unblocked pores in the
treated furrows. The ability of PAM to influence surface soil conditions a
nd improve infiltration can greatly enhance management of irrigated Mediter
ranean soils by allowing longer irrigation and higher inflow rates. Applica
tion of 10 mg/l in the inflow only during the advance phase of the irrigati
on can reduce labour, and ensures that loss of PAM from furrow tail water i
s minimized and that quantities applied during the season are reduced. (C)
2000 Silsoe Research Institute.