Past attempts to use aggregate stability to predict soil susceptibility to seal formation indices (final infiltration rate and runoff) have yielded inconsistent results. We hypothesized that determining aggregate stability in a method in which a controlled wetting process was used to break aggregates will correlate well with seal formation indices, as the latter strongly depend on rate of aggregate wetting. We studied aggregate stability from soils varying in clay content, and exchangeable Na percentage (ESP), using the high‐energy‐moisture‐characteristics (HEMC) method. Aggregate stability indices were correlated with previously published seal formation data for the same soils. Aggregates were placed in a funnel equipped with a fritted disk, and wetted either fast (100 mm h−1) or slow (2 mm h−1), using a peristaltic pump. Thereafter, the aggregates were subjected to a stepwise increase in matric potential up to 5.0 J kg−1, to obtain a moisture retention curve, which served as the base for calculations of stability parameters. Aggregate stability correlated with clay content, but not with soil organic matter. Aggregate stability and sodicity correlated only in clay soils. Generally, poor correlation (R < 0.5) was obtained between aggregate stability and seal formation and runoff data, irrespective of soil ESP, when infiltration and runoff measurements were carried out on fast‐wetted soils. Conversely, aggregate stability significantly correlated (R > 0.70) with seal formation and runoff data from slow wetted soils for samples having ESP of <6.6. Our results suggest that aggregate stability determined with the HEMC method could serve as a predictor for soil susceptibility for seal formation only under the aforementioned specific conditions.

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Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 Â 40 Â 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m À3 ; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures.

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Adding anionic polyacrylamide (PAM) to soils stabilizes existing aggregates and improves bonding between and aggregation of soil particles. However, the dependence of PAM efficacy as an aggregate stabilizing agent with soils having different clay mineralogy has not been studied. Sixteen soil samples (loam or clay) with predominantly smectitic, illitic, or kaolinitic clay mineralogy were studied. We measured aggregate sensitivity to slaking in soils that were untreated or treated with an anionic high‐molecular‐weight PAM using the high energy moisture characteristic (HEMC) method and deionized water. The index for aggregate susceptibility to slaking, termed stability ratio (SR), was obtained from quantifying differences in the water retention curves at a matric potential range of 0 to −5.0 J kg−1 for the treatments studied. For the untreated soils, the SR ranged widely from 0.24 to 0.80 and generally SR of kaolinitic > illitic > smectitic soils. The SR of PAM‐treated aggregates exhibited a narrow range from 0.70 to 0.94. The efficiency of PAM in improving aggregate and structural stability relative to untreated soils ranged from 1.01 to 3.90 and the relative SR of kaolinitic < illitic < smectitic samples. These results suggest that the less stable the aggregates the greater the effectiveness of PAM in increasing aggregates stability (i.e., smectitic vs. kaolinitic samples). The effectiveness of PAM in improving structure and aggregate stability was directly related to clay activity and to soil conditions affecting PAM adsorption (e.g., electrolyte resources, pH, and exchangeable cations) to the soil particles and inversely to the inherent aggregate stability.

Recycling of organic wastes via their incorporation in cultivated lands is known to alter soil structural stability. Aggregate stability tests are commonly used to express quantitatively the susceptibility of soil structural stability to deformation. The objective of this study was to investigate the effects of biosolids addition, namely composted manure (MC) and activated sludge (AS), and spiking of the soils with orthophosphate (OP), phytic acid (PA) or humic acid (HA), on soil aggregate stability of semi-arid loamy sand, loam and clay soils before and after subjecting the soils to six rain storms (each 30 mm rain with a break of 3–4 days). Aggregate stability was determined from water-retention curves at high matric potential. The effects of the applied amendments on pre- and post-rain aggregate stability were inconsistent and soil-dependent. For the pre-rain state, all of the tested amendments improved aggregate stability relative to the control. For the post-rain condition, aggregate stability was lower in the MC, OP and PA treatments and higher in the AS and HA treatments than in the control. The coarse-textured loam and loamy sand soils were more affected by the soil amendments than the clay soil. For the pre-rain state, addition of organic matter significantly improved macro-porosity and hence the stability of apparent macro-aggregate (>250 μm). Our results indicate a possible advantage for separation of aggregates into macro- and micro-aggregates for more precise evaluation and understanding of the effects organic amendments might have on aggregate stability.

Surface sealing is determined by aggregate disintegration and clay dispersion, which in turn depend on aggregate wetting rate, and soil sodicity and texture. We hypothesised that soil susceptibility to seal formation increases when the aggregate wetting rate (WR) is increased, and that the effect of WR depends on soil texture and soil sodicity. The objective of this study was to investigate the effects of WR on seal formation, by observing infiltration rate (IR) and runoff, in cultivated soils varying in clay content and exchangeable sodium percent (ESP). Effects of 3 wetting rates (2, 8, and 64 mm/h) on IR and runoff from 6 Israeli soils exposed to 60 mm of simulated rain of deionised water were studied in the laboratory. The soils ranged in clay from 8.8 to 68.3% and ESP levels from 0.9 to 20.4. Effects of WR on soil infiltration rate and runoff depended on soil texture and soil ESP. In soils with low clay content (8.8%), the effect of WR on seal formation was negligible, whereas effect of ESP was significant. Conversely, in clay soils (>52.1%), WR had a predominant effect on IR and runoff, while the effect of ESP was notable yet secondary to that of WR. The soils with intermediate clay content (22.5-40.2% clay) were the soils most susceptible to seal formation, with WR and ESP having moderate effects on seal formation. Effects of WR on aggregate disintegration and seal formation increased with increasing clay content and aggregate stability. Conversely, the role of ESP in determining sealing decreased with an increase in clay content and in WR. A . I . M a m e d o v , G . J . L e v y , I . S h a i n b e r g , J . L e t e y S R 0 1 0 2 9 W e t t i n g r a t e a n d s o d i c i t y e f f e c t s o n s o i l s e a l i n g A . I . M a m e d o v e t a l .