Impact of monovalent cations on soil structure. Part I. Results of an Iranian soil

Abstract

A b s t r a c t. This study investigated the impact of monovalent cations on clay dispersion, aggregate stability, soil pore size distribution, and saturated hydraulic conductivity on agricultural soil in Iran. The soil was incubated with treatment solutions containing different concentrations (0-54.4 mmol l -1 ) of potassium and sodium cations. The treatment solutions included two levels of electrical conductivity (EC=3 or 6 dS m -1 ) and six K:Na ratios per electrical conductivity level. At both electrical conductivity levels, spontaneously dispersible clay increased with increasing K concentration, and with increasing K:Na ratio. A negative linear relationship between percentage of water-stable aggregates and spontaneously dispersible clay was observed. Clay dispersion generally reduced the mean pore size, presumably due to clogging of pores, resulting in increased water retention. At both electrical conductivity levels, hydraulic conductivity increased with increasing exchangeable potassium percentage at low exchangeable potassium percentage values, but decreased with further increases in exchangeable potassium percentage at higher exchangeable potassium percentage. This is in agreement with earlier studies, but seems in conflict with our data showing increasing spontaneously dispersible clay with increasing exchangeable potassium percentage. Our findings show that clay dispersion increased with increasing K concentration and increasing K:Na ratio, demonstrating that K can have negative impacts on soil structure.

Impact of monovalent cations on soil structure. Part II. Results of two Swiss soils

“…The results with regard to the impact of K on soil structure presented in this paper are apparently in contradiction to the findings presented in Part I of this series of papers (Farahani et al, 2018). Here, we demonstrate that clay dispersion was little affected by K and tended to decrease with increasing K concentration (Fig.…”

“…1), while we found that K strongly increased clay dispersion in Part I of our work ( Fig. 1 in Farahani et al, 2018). The si l soil used in this paper had a similar texture as the soil used in Part I, and the experimental procedure (the addition of monovalent cations in treatment solutions and incubation for one month) and treatment concentrations (K in the range of 0-60 mmolc l -1 ) were similar in both studies.…”

“…In our study, we applied K in the range of 0-60 mmolc l -1 , and the results indicated that in the Iranian soil containing muscovite, K ions were not fixed and had a negative effect on soil structure (Part I of this series of papers; Farahani et al 2018), whereas in the Swiss soils containing illite, K ions were fixed, which prevented the negative effects of K on soil structure (this paper). We hypothesise that higher K concentrations have negative effects on soil structure in soils containing illite when the amount of K exceeds the 'K fixing potential' of illite.…”

Effect of different K:Na ratios in soil on dispersive charge, cation exchange and zeta potential

“…There was no correlation between net dispersive charge and Na concentration (sum of water‐soluble and exchangeable Na). Furthermore, the percentage of dispersible clay increased significantly with increasing K concentration ( r = 0.92, P = 0.004 and r = 0.77, P = 0.04 for EC 3 and 6 dS m −1 , respectively) and K:Na ratios ( r = 0.74, P = 0.05 and r = 0.78, P = 0.03 for EC 3 and 6 dS m −1 , respectively), but no relation was obtained between clay dispersion and Na concentration (Farahani et al ., ). Similar results, for a negative effect of K on soil structure, especially clay dispersion, have been reported in soils with different textures (sandy loam, loamy sand, loam, clay loam and clay) and clay mineralogy (mixture of kaolinite and illite, illite, kaolinite and smectite) in the literature (Czyz et al ., ; Rengasamy & Marchuk, ; Marchuk & Rengasamy, ; Emami et al ., ).…”

Methodological aspects of the quantification of dispersible clay and their relations with soil properties along a catena under no-till system

“…Cropping system management plays an important role in the construction and modification of the geomorphology and soil structure of sloping agricultural landscapes (De Alba et al, 2004;Arnáez et al, 2015). Inadequate conservation practices can promote a continuous degradation of soil structure (Nunes et al, 2017), resulting in the dispersion of particles as a result of the presence of unstable aggregates, impeding the retention of rainwater and favouring the displacement of these particles, thereby facilitating erosion (Beutler et al, 2001;Farahani et al, 2018a).…”