Effect of polyacrylamide applying on soil–rock mixture detachment and prediction of detachment capacity using machine learning

Runoff and soil loss affect both farmland productivity and environmental quality. This study tested the interaction effects among polyacrylamide (PAM) application rate, PAM molecular weight, and slope gradient on runoff and soil loss under simulated sprinkler irrigation in laboratory. Experimental treatments consisted of four PAM application rates of 0 (control), 0.5, 1.0, and 2.0 g m-2, two PAM molecular weights of 12 and 18 Mg mol-1, and three slope gradients of 5o, 15o, and 25o. Results indicated that compared with the control treatment, PAM application generally decreased total runoff volume but increased soil loss. Total runoff volume and soil loss increased with the increased PAM application rate. Under control treatment, total runoff volume increased with the increased slope gradient. However, total runoff volume was similar for different slope gradients when PAM application rates were 0.5 and 1.0 g m-2, but it decreased with the increased slope gradient when PAM application rate was 2.0 g m-2. Total soil loss increased with the increase of slope gradient under experimental conditions. Polyacrylamide molecular weight did not affect total runoff volume but did soil loss significantly atP< 0.001, and a high PAM molecular weight resulted in less soil loss than a low one did. Statistical analysis demonstrated that there existed a significant interaction effect atP< 0.001 between PAM application rate and soil slope gradient on runoff volume and soil loss. The interaction effects between PAM molecular weight and slope gradient or among PAM application rate, PAM molecular weight, and slope gradient on soil loss were also significant atP< 0.01. A PAM application rate less than 2 g m-2is suggested to control water and soil loss on sloped lands under sprinkler irrigation.

Controlling Runoff and Erosion in Sloping Land with Polyacrylamide under a Rainfall Simulator

Effect of polyacrylamide on the erodibility factor of a loam soil

Interaction effects of polyacrylamide application and slope gradient on potassium and nitrogen losses under simulated rainfall

Soil Erosion as Affected by Polyacrylamide Application Under Simulated Furrow Irrigation with Saline Water

Alternative erosion control practices using polyacrylamide (PAM) have received increased attention. This study examines the effect of PAM applied to soil when rainfall intensity, rainfall kinetic energy (KE), and PAM applied all interact, influencing time to runoff (ROt), cumulative runoff (ROc), and cumulative soil detachment (Dc). This study evaluated the response of a silt loam soil to aqueous PAM rates of 0 (untreated control), 20, and 40 kg ha-1 when applied to an initially air-dried soil. A total of 0.5 L of reverse osmosis water was sprayed on all soil beds. Simulated rainfall using a gravity-fed rainfall simulator was applied from 13.8 and 0.8 m fall heights at application rates of 64, 96, and 128 mm h-1. Results show significant benefit, as evidenced by increased ROt and reduced ROc and Dc for 20 and 40 kg ha-1 PAM application levels. This was true for all rain rates and durations up to 75 min whether rainfall was at or less than terminal velocity. Polyacrylamide was less effective at increasing ROt as rain rate increased. There was no difference in ROt with 40 kg ha-1 PAM compared to 20 kg ha-1 PAM; thus, the greater PAM application rate would not be recommended for this purpose. The benefits of reduced ROc and Dc with PAM were always greater for lower KE-rain (29% lower KE) than for higher KE-rain at a given rainfall intensity. Although both PAM application levels reduced ROc, for high KE-rain, only application of 40 kg ha-1 was significantly less than the untreated soil. For low KE-rain, ROc was significantly less with either PAM application level. Results show that PAM alone has a limited effect for maintaining infiltration rate; therefore, it is likely that regions with fewer intense convective storms would receive greater benefit from an increased PAM application rate. The greatest benefit of PAM was in reduced Dc where justification can be made for using increased PAM rates for high KE-rain, as documented by significantly less Dc for 40 kg ha-1 PAM compared to 20 kg ha-1 PAM at rain rates of 96 and 128 mm h-1. Under these conditions, both PAM rates significantly reduced Dc compared to untreated soil. With low KE-rain, Dc was significantly less for 20 kg ha-1 PAM compared to the untreated control, but 40 kg ha-1 PAM did not significantly reduce Dc since soil loss was so small.

Effect of Polyacrylamide Application on Runoff, Erosion, and Soil Nutrient Loss Under Simulated Rainfall

ABSTRACT: Irrigation reduces infiltration rates for subsequent irrigations or rains, thus decreasing the efficiency of water use and impacting watersheds in agricultural areas. Reduced infiltration causes greater runoff with its accompanying erosion, pollution, and sedimentation. Small rates of polyacrylamide (PAM) improve infiltration and reduce erosion on irrigated fields. The effects of PAM on infiltration of rainwater, the longevity of the effects of various rates of PAM, and the effects of repeated or intermittent PAM applications are not understood. This study measured the effects of four PAM application rates (0, 10, 25, and 40 ppm) on the subsequent infiltration of wastewater or simulated rainwater for seven weeks following the initial treatments. Also, effects of repeated and intermittent PAM applications on infiltration were determined. Hydraulic conductivity was determined for each soil column using the falling head method. Two soil types from the coastal plain of south Texas were tested — a soil high in clay (Victoria) and a sandy loam (Willacy). Effects of PAM rates were significant, but effects of water type were not (P > 0.05). Benefits from single PAM applications disappeared within two weeks. Water enriched with PAM is so viscous and infiltrates so slowly that applying PAM in every irrigation event may not be feasible. However, repeating PAM applications every two weeks maintained high infiltration rates on the alternate weeks. This intermittent application of PAM may be a practical approach for improving infiltration rates on irrigated lands.

Natural hillslopes are mostly composed of complex slope shapes, which significantly affect soil erosion. However, existing studies have mainly focused on uniform slopes to simplify complex hillslopes, and the mechanisms responsible for the influence of slope shape on soil and nutrient losses are still not well understood, especially in the application of soil improvers to reduce soil loss. To investigate the effects of slope shape and polyacrylamide (PAM) application on runoff, soil erosion and nutrient loss, this study conducted artificial field rainfall experiments involving two PAM application rates and nine slope shapes. The results indicate that the average amount of soil loss from convex slopes was 1.5 and 1.3 times greater than that from concave and uniform slopes, respectively, and the average amount of ammonia nitrogen loss and phosphate loss increased by 24.0%–58.6%. Soil and nutrient losses increased as the convexity of the convex slopes increased. For runoff, there was little difference between concave and convex slopes, but the runoff amount for both slopes was greater than that for uniform slopes. After PAM application, the soil loss decreased by more than 90%, and the nutrient loss decreased by 28.2%–68.1%. The application of PAM was most effective in reducing soil erosion and nutrient loss from convex slopes, and it is recommended to appropriately increase the PAM application rate for convex slopes. A strong linear relationship between ammonia nitrogen and phosphate concentrations and sediment concentrations was found in the runoff on slopes with no PAM application. However, this linear relationship weakened for slopes with PAM application. The findings of this study may be valuable for optimizing nonpoint source pollution management in basins.

Estimating sheet erosion on purple soil hillslope treated with polyacrylamide (PAM) in the Three Gorges Reservoir area

Modelling soil detachment capacity by rill flow with hydraulic variables is essential to understanding the rill erosion process and developing physically based rill erosion models. A rill flume experiment with non-erodible flume bed and small soil samples was conducted. Seven flow discharges and six steep slope gradients were combined to produce various flow hydraulics. The soil detachment capacity increases with the increase in slope gradient and flow discharge. The critical slope gradients of 21.26 and 26.79% cause the detachment capacity to increase at a slow pace. The soil detachment capacity can be defined by a power function of flow discharges and slopes. The contribution rates of slope gradient and flow discharge to soil detachment capacity are 42 and 54%, respectively. The soil detachment capacity increases with shear stress, stream power and unit stream power; the increase rates of these parameters are greater under gentle slopes than steep slopes. Stream power is the superior hydrodynamic parameter describing soil detachment capacity. The linear model equation of stream power is stable and reliable, which can accurately predict soil detachment capacity by rill flow on steep loessial hillslopes. This study can help to sufficiently clarify the dynamic mechanism of soil detachment and accurately predict soil detachment capacity for steep loessial hillslopes.

Soil type may influence soil detachment process by overland flow, but few studies have quantified the effect fully and systematically. This study was undertaken to quantify the effects of soil type on soil detachment capacity using undisturbed soil samples collected from 11 soil types from the Beijing Region. The soil samples were placed in a 5.0-m long and 0.38-m wide hydraulic flume and eroded by overland flow under three slope gradients (17.4%–34.2%) and three unit discharges (1.32–5.26 × 10−3 m2 sec−1). The results showed that soil detachment capacities were significantly affected by soil types. Aeolian Sandy Soil was the most easily detached, whereas Wet Meadow Soil was the hardest. Soil detachment capacity was significantly affected by soil properties. For soil texture, loamy sand had the largest detachment capacity, followed by sandy loam, loam, and silt loam. Furthermore, detachment capacity was negatively correlated to clay and silt content and positively related to sand content and median diameter of soil particles. Both shear strength and organic matter content were negatively correlated to detachment capacity. Detachment capacity could be predicted reasonably well by stream power, clay content, and organic matter content (r2 = 0.743) with a coefficient of Nash-Sutcliffe efficiency of 0.644. An equation was developed to estimate detachment capacity based on stream power and soil properties (r2 = 0.704; Nash-Sutcliffe efficiency, 0.702). Rill erodibility ranged from 0.73 to 85.22 × 10−3 sec m−1, and the critical shear stress changed from 0.683 to 7.978 Pa. The results are helpful to understand the mechanism of soil detachment process under different soil types and to develop the process-based erosion models.

Impact of raindrop diameter and polyacrylamide application on runoff, soil and nitrogen loss via raindrop splashing

The nutrient loss caused by soil erosion is the main reason for soil degradation and environmental pollution, and polyacrylamide (PAM) as a common soil amendment has a great influence on runoff and erosion processes at the slope. In order to investigate the mechanism of nutrient transport with runoff, a field experiment was conducted and a simple mathematical model was developed in this study. Four PAM application rates (0, 1, 2, and 4 g·m−2) and two rainfall intensities (50 and 80 mm·h−1) were applied in the field experiment. The results revealed that runoff rate of 2 g·m−2 PAM application treatments decreased by 5.3%-10.6% compared with the control groups, but it increased by10.9%-18.7% at 4 g·m−2 PAM application treatments. Polyacrylamide application reduced ammonium nitrogen concentrations of runoff by 10.0% to 44.3% relative to the control groups. The best performance with correlation coefficient (R2) and Nash–Sutcliffe efficiency (NSE) showed that the ammonium transport with runoff could be well described by the proposed model. Furthermore, the model parameter of the depth of the mixing layer (hm) linearly increased with an increase in flow velocity, but exponentially decreased with an increase in PAM application rate.

Soil erosion is one of the most critical environmental problems currently facing Iran, and soil conservation is crucial for managing natural resources. The objective of this study was to investigate the effect of a vetiver cultivation system, known to be a valuable bioengineering technique, and polyacrylamide (PAM) addition on runoff, sediment load (SL) and cumulative water infiltration under field conditions in a loamy soil. The experimental treatments were vetiver cultivation, PAM (applied at 20 and 40 kg ha–1) and a mixture of vetiver and different PAM application rates. Three simulated rainfall intensities of 15, 30 and 45 mm h–1 were applied on the treated soils. Runoff and SL were collected at different time steps. The results showed that vetiver significantly decreased runoff and SL and increased cumulative water infiltration at different rainfall intensities, whereas the effect of PAM on runoff, SL and cumulative water infiltration depended on the PAM level. At the 15 mm h–1 rainfall intensity, PAM application increased the runoff, but decreased SL and cumulative water infiltration. At the 30 mm h–1 rainfall intensity, the 20 kg ha–1 PAM level decreased the runoff and SL. At the 45 mm h–1 rainfall intensity, the higher PAM level was more effective to enhance the cumulative water infiltration and to reduce the runoff and SL. In general, although simultaneous application of vetiver and PAM significantly decreased the runoff volume and SL and increased water infiltration compared with the control, vetiver considerably decreased the runoff and SL. This suggests that vetiver may sufficiently decrease soil erosion and PAM is therefore unnecessary in controlling runoff and soil erosion where vetiver is applied.