Investigating the Effect of Polyacrylamide Concentration and Slope Position on Soil Erosion and Leaching of Elements

Due to erosion, soil structure is destroyed, plant elements are removed from the soil by runoff and destroyed, soil fertility is reduced and, as a result, the production and productivity of the soil is reduced. The use of modifiers such as polyacrylamide while reducing runoff production and soil erosion can be useful in reducing the wastage of soil nutrients, especially in sloping lands. The aim of the present study was to investigate and compare the rate of sediment and runoff production and nutrient loss in three slope positions and four concentrations of polyacrylamide using a rain simulator. Direct measurement of runoff and sediment, efficiency and repeatability in different intensities, durations and amounts of rain are among the advantages of using a rain simulator in investigating surface runoff, erosion, and sediment (Jahanbakhshi et al., 2016). Therefore, in order to investigate and study soil erosion and direct measurement of runoff and sediment, rain simulators can be used.

The present research endeavor was conducted to investigate the effect of using different amounts of anionic polyacrylamide superabsorbent in controlling the erosion and wastage of soil nutrients in sloping lands. The experiment was performed as a factorial experiment in a completely randomized design with three replications. The first factor of the slope was determined in three positions (slope toe, slope foot, and shoulder slope) and the second factor was the concentration of polyacrylamide at five levels (0,0/4, 1, 3, and 6 g/m2). The test area was located on the campus of Mohaghegh Ardabili University being exposed to a 10-minute rainfall with an intensity of 35 mm/hour; it was checked that the intended rainfall was simulated by a rain simulator. A total of 45 experiments were performed by the rain simulator on plots measuring 2 m2. After conducting each rain simulator test in the plots, runoff and sediments were collected in a collection tank and the amount of sediment, runoff volume and amounts of sodium, potassium, calcium, magnesium, phosphorus and organic carbon were measured in the laboratory.

The effects of slope position on all soil characteristics were significant (P <0.01) increasing from 0.35 kg/ha to 0.55 kg/ha. The effect of slope position on organic carbon loss was significant at the 5% level and other elements at the 1% level. The effect of polyacrylamide concentration was significant only on phosphorus loss at the level of 1%. Also, the interaction effect of slope and concentration on calcium loss was significant at the level of 5%. By changing the position of the slope from the toe slope to the foot slope, the average runoff volume increased from 3.84 to 14.8 liters, and the average phosphorus loss increased from 0.035 kg/ha to 0.55 kg/ha. The effect of PAM in higher concentrations was greater than in lower concentrations in reducing runoff, sediment, and then the loss of nutrients in the soil. The results showed that the maximum production of sediment due to the simulated rain on the surface of the plot is 192.36 grams per square meter. This is the value of the control plot at the foot slope (S0) which is significantly different from other treatments. The lowest amounts of sediments were related to the treatment of 6 grams per square meter of PAM in the position of the toe slope (F6) with an average production sediment of zero, and the treatment of 6 grams per square meter of PAM in the position of the toe slope (F3) with an average sediment production of 1.69 grams per square meter.

The highest amount of sediment and runoff was produced at the foot slope. The greatest loss of nutrients was observed at the foot slope. It was observed that the effect of PAM in higher concentrations is greater than in lower concentrations in reducing runoff, sediment, and then the loss of nutrients in the soil. It can be concluded that the use of anionic polyacrylamide has an important effect on reducing soil erosion and consequently reducing the wastage of elements such as phosphorus and organic matter in sloping lands, because the release of these elements from the soil mainly happens attached to the soil particles. This research showed that the effect of PAM in reducing runoff, sediment and then the loss of nutrients of soil, in higher concentrations is greater than in lower concentrations but from a certain concentration onwards (3 grams per square meter) the impact of PAM does not increase.