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Environmentally Smart Nitrogen (ESN) is a polymer-coated urea fertilizer with potential to increase crop recovery of fertilizer nitrogen (N). Our research objectives were to characterize ESN N retention across time as affected by soil series, temperature, moisture, and incubation method. A rumen bag containing 38 to 44 mg ESN N was placed in 400 g soil, and the amount of ESN N remaining in prills was measured every 5 d for 40 d. Soil was incubated at 25 °C and 250 g H2O kg-1 soil, except in experiments where soil temperature or moisture was varied. Nitrogen retention in ESN was linear for three silt and sandy loams and curvilinear in two clayey soils with retention declining more rapidly in clayey soils. Soil temperature had the greatest effect on N retention with the rate of ESN N release increasing as soil temperature increased. Near complete release of ESN N was achieved by 40 d with temperatures ≥ 20 °C. [ABSTRACT FROM AUTHOR]

Radiocesium interception potential (RIP), a quantitative index of a frayed edge site of micaceous minerals, was investigated on test clay minerals (illite, kaolinite, montmorillonite and vermiculite) and soil clays formed under different pedogenetic conditions in the Kinki district of Japan and in northern Thailand to elucidate the effect of pedogenetic weathering on the amount of frayed edge site of micaceous minerals. A frayed edge site is defined as the wedge-shaped intermediate zone between non-expansible (1.0 nm) and hydrated (1.4 nm) interlayers, on which Cs is selectively adsorbed. The test clay minerals demonstrated unique RIP values closely associated with their charge characteristics. Very small RIP in non-micaceous test minerals (0.006 mol kg−1 in kaolinite; 0.1 mol kg−1 in montmorillonite) supported the fact that negative charges in these minerals do not show selective adsorption of 137Cs. Large RIP values in vermiculite (25.9 mol kg−1) compared with illitic minerals (4.3 mol kg−1 in silt size; 11.8 mol kg−1 in clay size) suggested that the frayed edge site increased as the expanded layer formed in the micaceous minerals. In northern Thailand soil clays, the absence of a vermiculitic expanded layer was indicated. Periodic wet–dry conditions may restrict K depletion from micaceous minerals in the region. It is concluded that micaceous minerals were weathered without layer expansion and, therefore, the amount of the frayed edge site was regulated by the content of micaceous minerals in northern Thailand. In Japanese soil clays, large RIP values were found in the EB and Bs horizons of a Podzodic profile (SW1), which had large vermiculitic expanded layers like the test vermiculite. However, the RIP values drastically decreased from the Bs to E horizon, maintaining a high vermiculitic layer charge. Thus, intensive weathering in highly acidic soils in Japan might reduce the frayed edge site. [ABSTRACT FROM AUTHOR]

A toxicological approach was taken to determine the heavy metal binding capacity of soils. A soil heavy metal binding capacity (SHMBC) methodology was developed and was based on the use of the MetPLATETM toxicity test kit, a bioassay that is specific for heavy metal toxicity. SHMBC test is based on the heavy metal binding capacity (HMBC) concept that has been considered in the assessment of the metal binding capacity of surface waters (Huang et al., 1999) and solid wastes landfill leachates (Ward et al., 2005). SHMBC is the ratio of the EC50 of an added metal in a soil sample divided by the EC50 of a metal in a reference soil (clean Ottawa sand). A higher SHMBC value indicates higher metal binding to soil and lower bioavailability and potential toxicity to the test bacteria. Five soils (two sandy soils, two organic soils and a clay soil) were used to determine their binding capacity towards Cu, Zn, and Hg, using the developed SHMBC test. The test measured the ability of the solids to reduce metal bioavailability and toxicity. SHMBC was highest for the clay soil and lowest for the sandy soils. The potential application of this relatively rapid (a few hours) test to predict metal toxicity to terrestrial plants is discussed. [ABSTRACT FROM AUTHOR]

Two separate field experiments were conducted to evaluate the effects of swine lagoon effluent relative to inorganic fertilizer at equivalent rates on phosphorus (P) status of an acidic Vaiden (very fine, montmorillonitic, thermic, Aquic Dystrudert) and an alkaline Okolona (fine, montmorillonitic, therimic, Typic Chromudert) silty clay soil. In each site, a randomized complete block design with a factorial arrangement of treatments was used. Treatments were replicated four times. Cumulative swine lagoon effluent P application rates for the year 1994 through 1996 were 0, 59, 121, and 175 kg P ha -1 on the Vaiden soil and 0, 72, 148, and 223 kg P ha -1 on the Okolona soil. In each replication, commercial fertilizer P at rates equivalent to swine effluent P application were also included. For both sites, soil P concentration increased with increasing swine effluent and commercial fertilizer P applications. No significant difference in soil P level was observed between two P sources. At high application rate, desorbed P was 1.20 and 0.59 mg P kg -1 in the Okolona and Vaiden soil respectively. In the Vaiden soil, P adsorption approached the maximum for equilibrium P concentration greater than 600 mg L -1 . However, Okolona soil displayed a linear adsorption potential with application of swine effluent P. Among P fractions, NH4Cl‐P and HCl‐P concentrations increased the most compared to the check in both Okolona and Vaiden soils. Results indicated that P status differs between the soils, but no significant differences in P concentration were obtained between swine lagoon effluent and commercial fertilizer, suggesting that both P sources had similar effect on soil P after 3 years of application. [ABSTRACT FROM AUTHOR]

Sorption and desorption properties of cadmium (Cd) and copper (Cu) in 5 clay types (montmorillonite, sericite, kaolinite, halloysite and allophane), which had been selected as representatives of commonly distributed minerals in the world soil environment, were investigated, with special reference to the charge characteristics of clays. Sorption properties of both Cd and Cu in all the clays were highly pH-dependent, resembling those in oxides. When the pH value at which 50% metal sorption on clays occurred was defined as pH-sorb50, the pH-sorb50 values of Cd in the five clay types ranged between pH 5 and 7. Sericite exhibited the highest affinity for Cd sorption. In montmorillonite, sorbed Cd in the high pH region was not desorbed at all by subsequent extraction. For Cu, the pH-sorb50 values were significantly lower than those for Cd, revealing the strong adsorption ability of Cu for all clay types. Sorption behavior of heavy metals was not parallel to the overall charge characteristics of clays and could not be easily predicted from the total charge such as cation exchange capacity or zeta potential. The higher sensitivity of 2:1 type clay minerals for Cd contamination was revealed. The critical role of edge surfaces on the sorption behavior was suggested because of the high charge density. The importance of pH control for the alleviation of Cd contamination was stressed for all clay types. [ABSTRACT FROM AUTHOR]