Soil Science Society of America Journal

Chertkov, V. Y.; Ravina, I.; Zadoenko, V.

doi: 10.2136/sssaj2004.1807pmid: N/A

Soil shrinkage is characterized, along with the shrinkage curve, by a partition of the volume change of the soil matrix between contributions of cracks and soil subsidence. This partition is determined by the shrinkage geometry factor (rs). Knowledge of the value of rs is important for the consideration of water and solute transport in swelling and cracking soils. The rs concept was recently used for the generalization of flow equations in the case of the axially symmetric two‐dimensional deformation of shrink‐swell soils. Sufficient accuracy of the rs value is very essential for all these applications. However, the theoretical definition and available measurement method of the rs factor include some implicit assumptions that are disturbed in real conditions. These disturbances, which are not accounted for in rs measurements, can lead to distortion of the rs value. The objectives of the work are: to explicitly formulate the assumptions; to introduce a new presentation of the rs concept based on a comparison between different shrinkage curves of a soil; to suggest an approach for estimating the rs values corrected by taking into account the disturbance of one of the assumptions; and to experimentally illustrate the approach using the simplest case of pure‐clay paste samples when they dry, shrink, and crack. The results show the necessity and practical possibility of considering the rs factor as a function of soil moisture and introducing to the factor the multiplicative correction that is connected with accounting for possible macrocracks in soil samples to be used for experimental estimation of the rs factor.

Haws, Nathan W.; Liu, Bingwu; Boast, C. W.; Rao, P. S. C.; Kladivko, E. J.; Franzmeier, D. P.

doi: 10.2136/sssaj2004.1818pmid: N/A

Determining representative infiltration rate parameters for use in modeling field‐scale flow and transport processes is difficult because of the spatial variability of soil properties. To determine how steady‐state infiltration rate variability is affected by support scale, steady‐state infiltration rates (Is) were measured at three spatial scales (local, hillslope, and landscape) along a 710‐m transect on a swell–swale landscape in Indiana. Spatial variability at the local scale was studied using measurements in a 1 × 1 m2 array of 100 ring infiltrometers (7.2‐cm diam.) for three soils at three horizons each. Studies were conducted at the hillslope and landscape scales using three nested infiltrometers of sizes 20 × 20, 60 × 60, and 100 × 100 cm2 Geostatistical analyses show a decrease in the sample variance of the Is values and an increase in spatial correlation of Is with depth. They also suggest that an area >10, 7.2‐cm diam. rings (i.e., approximately >400 cm2) is needed to provide a representative measurement area (RMA; i.e., area needed to filter out smaller‐scale heterogeneities) at the local scale. Hillslope‐ and landscape‐scale tests indicate that Is measurements with infiltrometers require an infiltrometer with a support area greater than the local‐scale RMA to show the spatial correlation of the larger scales. In addition, these infiltrometer measurements may not provide appropriate effective Is estimates at these greater scales unless they are averaged over a domain that extends across the landscape's range of variability, estimated from the computed semivariograms to be 120 to 200 m for this study.

Rodgers, M.; Mulqueen, J.; Healy, M. G.

doi: 10.2136/sssaj2004.1827pmid: N/A

Accumulation of biomass and deposition of suspended solids at the surface of a sand filter can lead to clogging of the filter media. A laboratory intermittent sand filter column, which included three sand strata, was operated for a period of 806 d before failure occurred through surface clogging. Upon dismantling the column, the cause and effects of the surface clogging were investigated. The main mechanism responsible for sand clogging appeared to be biomass buildup. Maximum loss on ignition of filter media samples was 2.35%, and it occurred in the upper 0.01 m of the sand. There was a reduction in field‐saturated hydraulic conductivity in the top 0.01 m of the upper sand stratum from a value of 1.9 × 10−3 ± 1.7 × 10−4 m s−1 (for virgin sand with an effective size, d10, of 0.45 mm) to 3.5 × 10−5 ± 7.5 × 10−6 m s−1 The soil‐water characteristic curve, which relates the volumetric water content (θv) to the soil suction, also reflected the changes in the filter media due to clogging. The water‐holding capacity greatly increased as biomass accumulated in the filter media. Scanning electron microscopy (SEM) confirmed the existence of a clogging organic layer on the surface of the top sand layer.

Hanke, M.; Perry, D.; Kung, K.-J. S.; Bubenzer, G.

doi: 10.2136/sssaj2004.1833pmid: N/A

Rainfall simulators with high uniformity and low intensities are required in many research areas related to environmental quality. To examine the characteristics of field‐scale macropore‐type preferential flow, we designed a portable water application system suitable to apply water with intensity < 5 mm h−1 for long‐term steady‐state infiltration experiments under different climatic conditions. Our results showed that, when water was applied at 345 kPa pressure, the system could deliver 4.36 mm h−1 of water to 19.2 by 2.7 m with 80 to 85% uniformity, while uniformity of the inner 16.2 by 2.1 m reached 94 to 97%. The performance of this system was not influenced by the ambient wind speed. Lower intensities of water application can be achieved by applying water intermittently.

Yamaguchi, Noriko; Hiradate, Syuntaro; Mizoguchi, Masaru; Miyazaki, Tsuyoshi

doi: 10.2136/sssaj2004.1838pmid: N/A

We investigated the influences of humic acid on the removal of Al tridecamer (Al13) from a hydroxyaluminum (HyA) solution at various humic acid/Al ratios. The Al species contained in the solution were analyzed by using a liquid‐state 27Al‐NMR and an atomic absorption spectrometer and fractionated into three Al species: (i) Al13, (ii) Al monomer and dimer (AlSYM), and (iii) other undefined species including aggregated/precipitated Al (AlNON). By the addition of humic acid to the HyA solution, the concentration of Al13 was rapidly decreased within 0.007 d (10 min). The decrease in Al13 and the increase in AlNON were more pronounced at a higher humic acid/Al ratio. When the molar ratio of humic acid carboxylic groups to Al exceeded 0.8, Al13 was undetected from solution within 0.007 d. The formation of Al13–humic acid complexes and the aggregation/precipitation of those complexes were a predominant mechanism in removing aqueous Al13 at the early stage of the reaction. Approximately 10 mol of carboxylic groups in humic acid were required to remove 1 mol of Al13 from the HyA solution. Aqueous Al13 had greater preference in precipitating with humic acid than AlSYM After 5 to 570 d of aging, the concentration of Al13 and AlNON also decreased and increased, respectively, both in the presence and absence of humic acid. In conclusion, aqueous Al13 would not exist in soil solution under a high humic acid condition.

Kjaergaard, Charlotte; Hansen, Hans Christian B.; Koch, Christian B.; Villholth, Karen G.

doi: 10.2136/sssaj2004.1844pmid: N/A

Mobility of colloids depends in part on the release from aggregates and the stability in suspension. This study determined the soil dispersibility of the different horizons in a Typic Agrudalf. Water‐dispersible colloids (WDC) from bulk horizons and macropore deposits were characterized for mineralogy and physical chemical properties. The effect of solution pH and ionic strength on ζ‐potential and flocculation behavior was evaluated using dynamic light scattering, and the role of colloid associated organic C (OC) and sesquioxides were elucidated. The soil dispersibility did not reflect the contrasting physicochemical conditions, but was directly correlated with total clay content. Generally, WDC were enriched in OC and sesquioxides. Water‐dispersible colloids from the Ap‐horizon and from macropore deposits differed markedly from the remaining WDC‐fractions due to a significantly higher content of OC (14–35 g kg−1), AlCBD (9.3–10.6 g kg−1) and a much smaller N2–adsorption surface area (14–25 m2 g−1). Treatment with Na2S2O8 for removal of OC increased the surface area by 171–225%, indicating surface coatings of OC. The contribution of OC to the colloidal stability was inferred from: (i) a more negative ζ‐potential and larger suspension stability of WDC with larger content of OC, and (ii) reduced negative ζ‐potential as well as suspension stability after OC removal. Large variations were observed in the flocculation behavior for WDC with rather similar mineralogical composition. A two‐fold increase of the initial particle diameter occurred at an electric conductivity of 91 μS cm−1 for the least stable colloids and at 1023 μS cm−1 for the most stable and OC‐rich colloids. The effect of solution pH on flocculation was significant only at pH below 4.5.

Mikutta, Christian; Lang, Friederike; Kaupenjohann, Martin

doi: 10.2136/sssaj2004.1853pmid: N/A

Recent N2 adsorption studies have suggested a ‘pore clogging’ effect on mineral soil phases caused by organic matter coatings. For methodological reasons, this pore clogging effect has been studied only after drying. Our hypothesis was that pore clogging is affected by drying of organic coatings. In our study, we used AlOOH, which has been equilibrated with dissolved organic matter (DOM) and polygalacturonic acid [PGA; (C6H8O6)n]. To test our hypothesis, we determined the porosity of moist and freeze‐dried AlOOH samples. Freeze‐dried samples were analyzed by N2 adsorption, moist samples by 1H‐nuclear magnetic resonance (NMR). In addition, the samples were characterized by environmental scanning electron microscopy—energy dispersive x‐ray spectroscopy (ESEM‐EDX). Both, DOM and PGA significantly reduced specific surface area (SSABET) of AlOOH by 34 m2 g−1 (15%) and 77 m2 g−1 (36%). The reduction in SSABET normalized to the amount of C sorbed was 1.0 m2 mg−1 DOM‐C and 5.9 m2 mg−1 PGA‐C. Dissolved OM reduced the pore volume of micro‐ and small mesopores <3 nm whereas PGA also reduced the volume of larger pores. The 1H‐NMR results of moist samples showed that PGA sorption reduced the amount of water in pores <4 nm. In addition, the pore size maximum of AlOOH increased by 150%. Polygalacturonic acid coatings created new interparticle pores of about 10‐ to 70‐nm size that are not stable upon freeze‐drying. Porosity changes upon DOM‐treatment were not commensurable by 1H‐NMR. Our results indicate that clogging of micro‐ and small mesopores is not an artifact of freeze‐drying. Polygalacturonic acid seems not only to cover the mouth of AlOOH‐nanometer pores but also to fill them.

Carrizosa, María José; Koskinen, William C.; Carmen Hermosín, María

doi: 10.2136/sssaj2004.1863pmid: N/A

We determined the sorption mechanism of the acidic herbicides bentazon [3‐(1‐methylethyl)‐1H‐2,1,3‐benzothiadiazin‐4(3H)‐one 2,2‐dioxide] and dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) on two organoclays, octadecylammonium (ODA)‐ and hexadecyltrimethylammonium (HDTMA)‐exchanged Arizona montmorillonite (SAz‐1), as part of a study to determine their potential use as sorbent materials for ionizable organic pollutants. To determine the mechanisms involved in the sorption process, herbicide‐organoclay complexes were characterized by x‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). In general, the d001 values of SAz‐HDTMA and SAz‐ODA organoclays expanded after herbicide saturation, indicating interlayer sorption of the herbicide. Also, FTIR spectroscopic studies suggested weak hydrophobic interactions between these herbicides and the interlayer organic phase of the organoclays. However, H bonding between these herbicides and the monosubstituted amino group in SAz‐ODA reinforced the strength of the hydrophobic interactions resulting in nonreadily reversible sorption on that organoclay. These results suggest that organoclays can be used to remove this type of pollutants from water or soils.

Shi, Wei; Miller, Bruce E.; Stark, John M.; Norton, Jeanette M.

doi: 10.2136/sssaj2004.1867pmid: N/A

Dairy wastes are commonly applied to croplands as N fertilizers, but the dynamics of N release and transformations during the growing season are difficult to predict. We compared N mineralization kinetics and examined microbial N transformations in soil receiving dairy‐waste compost vs. lagoon effluent. Mineralization kinetics was examined with a 70‐d laboratory incubation, and a first‐order model was used to derive mineralization parameters. Measurements of N transformations were conducted with 15N pool dilution techniques in silage corn field plots that were unfertilized or fertilized with ammonium sulfate, lagoon effluent, or compost at two rates equivalent to 100 or 200 kg available N ha−1 The N mineralization potential was higher and the first‐order rate constant was lower in soil receiving compost than lagoon effluent. Approximately 6% of compost N was mineralized within 2.5 mo; in contrast, up to 90% lagoon effluent organic N was released. However, silage yield was greatest in the compost treatment, showing that synchronization of N availability is as important as the amount mineralized. The field 15N measurements indicated that microbial NO−3 consumption was negligible despite the treatments. Microbial NH+4 immobilization in soil receiving dairy wastes was similar to that in soil unfertilized or fertilized with inorganic N. Soil treated with the high‐rate compost had the highest rates of mineralization and nitrification, which led to the highest soil NO−3 accumulation. Our observations suggest that peak plant demand is met by the compost N; however, its high N mineralization potential makes the management of dairy compost a difficult task.

Acosta-Martínez, V.; Zobeck, T. M.; Allen, Vivien

doi: 10.2136/sssaj2004.1875pmid: N/A

Continuous monoculture systems can reduce soil organic matter because of low organic inputs and disturbance from tillage practices. Integrated cotton (Gossypium hirsutum) cropping and livestock production systems in West Texas may provide more sustainable alternatives to the traditional continuous cotton system and improve soil quality. Our study was conducted on a Pullman soil (Fine, mixed, thermic Torrertic Paleustolls) after 5 yr as a complete randomized block design (three replications) that compared continuous cotton and an integrated livestock‐crop system with a perennial warm‐season grass pasture (Bothriochloa bladhii) paddock and two paddocks (two stages) of a rotation (wheat [Triticum aestivum]‐fallow‐rye [Secale cereale]‐cotton). Total N (average: 1.0 g kg−1 soil) remained similar among systems and soil pH was >8.1. Organic C was higher (13.5 g kg−1 soil) in perennial pasture compared with continuous cotton (9.0 g kg−1 soil) at 0 to 5 cm. A similar trend was found for the soil aggregate stability. Soil microbial biomass C (Cmic) was greater in perennial pasture (193 mg kg−1 soil) and the rotation under rye and cotton (237 mg kg−1 soil) compared with continuous cotton (124 mg kg−1 soil) at 0 to 5 cm, and in perennial pasture at 5 to 10 and 10 to 15 cm. Soil microbial biomass N (Nmic) showed similar trends. Soil enzyme activities were greater in perennial pasture and the rotation (under rye and cotton) than under continuous cotton at 0 to 5 cm. The integrated crop‐livestock system had higher protozoa (20:4ω6c = 1.98%) and fungi (18:3ω9c = 1.30%) than continuous cotton (20:4ω6c = 1.09%; 18:3ω9c = 0.76%). These findings suggest positive differences in soil function and sustainability of the integrated crop–livestock system compared with continuous cotton.