Application of polyacrylamide (PAM), gypsum, or their combination generally decreases erosion and runoff. However, their benefits are uncertain for soils with varying properties. The objectives of this study were to evaluate the effects of 5 Mg ha⁻¹ (2 tn ac⁻¹) gypsum (5G), 20 kg ha⁻¹ (18 lb ac⁻¹) PAM (20P), 40 kg ha⁻¹ (36 lb ac⁻¹) PAM (40P), and 20 kg ha⁻¹ (18 lb ac⁻¹) PAM with 5 Mg ha⁻¹ gypsum (20P+5G) for increasing time to initial runoff (TRO), decreasing cumulative runoff (RO), and decreasing cumulative sediment loss (SL) after 1 hour of a simulated rainfall on soil samples from two soil series (Hoberg and Brussels). Soils were packed to a bulk density of 1.3 Mg m⁻³ (81 lb ft⁻³) in test beds 0.3 × 0.3 × 0.15 m (12 × 12 × 6 in) set to a slope of 20% and subjected to a 61 mm h⁻¹ (2.4 in hr⁻¹) simulated rainfall with a kinetic energy of 1.5 kJ m⁻² h⁻¹ (103 ft lb ft⁻² hr⁻¹). Differences in TRO, RO, and SL for four soil samples (two sample depths per soil series) and four amendments plus an unamended check were all significantly different (p < 0.01). Amendments of 20P, 40P, and 20P+5G increased TRO for soil samples with ≤0.5% organic matter (OM). The 5G amendment increased TRO for an acid soil sample (pH 4.1) with low OM (0.2%). The 20P+5G amendment produced an average 25% reduction in RO. Other amendments reduced RO by an average of 9% to 10%. The 40P amendment did not reduce RO, except for a Brussels silt loam surface soil that showed a 41% decrease. The 20P+5G amendment reduced SL by an average of 47% for soil samples, except for a high OM (3.7%) soil sample where OM likely interfered with soil-PAM bonding. The order of the amendment effectiveness for increasing TRO, and reducing RO and SL was 20P+5G > 40P > 20P > 5G. Generally, the 20P+5G amendment was the best, irrespective of soil calcium (Ca⁺⁺) content. On average, this amendment increased TRO by 69%, decreased RO by 25%, and decreased SL by 36%. When this amendment was used on an acid soil sample with low OM (0.2%) and low cation exchange capacity (9.2 cmol_c kg⁻¹), it increased TRO by 71% and reduced RO and SL by 45% and 74%. The amendment effectiveness was influenced by soil properties, including texture, clay mineralogy, cation exchange capacity, and OM.

#	Concept	H-Index	Publications	Citations
1	Engineering	1	1	51
2	Civil Engineering	1	1	51
3	Environmental Engineering	1	1	51
4	Hydrology	1	1	51
5	Environmental Remediation	1	1	51

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