No abstract

The familiarity of mankind with gypsum and its simple composition are in contrast with the frequent mistakes reported for its behavior and role in nature. Gypsum has been studied as a raw material, as a rock constituent, as an indicator of geological and archaeological conditions, and from other points of view. However, its role in Earth surface processes, its relationship to life through calcium in the equilibrium of carbonates and its structural water molecules, seems overlooked. Moreover, errors of gypsum formulation, analysis, and behavior obscure some of its roles within nature. The semi‐solubility of gypsum explains its actions in many soils. The softness, fragility, and crystal water of gypsum are often not considered. Routinely drying at 105°C and pulverizing samples for lab analyses casts suspicion on all analytical results because gypsum becomes anhydrite and/or bassanite at this temperature. Specific physicochemical models are needed to predict the behavior of soils mainly composed of gypsum.

Glossic Fragiudalfs comprise several million hectares of agronomically important soils within the silty uplands of the lower Mississippi River Valley (Major Land Resource Area [MLRA] 134). These soils are typified by a fragipan within 100 cm of the surface overlain by a 5‐cm‐thick, or more, glossic horizon containing bleached coatings (albic material) along primary ped faces, indicating fragipan degradation. Concentrations of Fe–Mn nodules also occur in horizons above the fragipan. There is limited documentation regarding the in situ morphology of the nodules or their relationship to the underlying fragipan. The objectives of this study were to document (i) the profile distribution of nodules, (ii) variations in nodule morphology with depth, and (iii) the role of fragipans in nodule formation. Nodules were most common and largest directly above the fragipan horizons. Field and micromorphological observations suggested the nodules formed in remnants of the brittle fragipan matrix as a result of the conversion of Btx material to E′ material (albic material) that isolated and surrounded brittle fragipan peds. The brittle peds that are the precursors to nodules appeared to decrease in size and became more highly impregnated with Fe and Mn oxides with distance above the fragipan. Spatial relationships of Fe concentrations and argillans within the nodules illustrated that the nodules were being formed in place and were not transported despite having distinct borders. With time the glossic horizon expands at the expense of the fragipan, resulting in a horizon consisting of Fe–Mn nodules and a few isolated brittle peds in a matrix of albic material.

Pots containing mine soil treated with lime, fertilizer, and bleached, primary papermiil sludge (at the rate of 56, 112, and 224 Mg/ha added alone or in combination with fertilizer [P and K]) were planted to subterranean clover (Trifolium subterranean L.) in the first phase of a two‐phase study. Fertilizer was found necessary to revegetate the mine soil, and the addition of sludge and fertilizer significantly (α<0.05) increased yield over the fertilizer only. This favorable effect of sludge was observed during the second harvest, with 112 Mg/ha giving the maximum yield. Biological N2 fixation and native N did not raise the N concentration in clover within the normal range (2.9–3.8%). Fertilizer application improved N uptake by the forage. The N concentration in clover declined with successive harvests. However, sludge application minimized this decline. Phosphorus was found to be at normal range (0.1–0.2%) in all cases, except at the sludge rate of 112 and 224 Mg/ha without fertilizer. Excessive tissue concentrations of K, Ca, S, Fe, Cu, Zn, and Al were observed in the unfertilized mine soil and K, Ca, Zn, and Al were excessive in all treatments.

Soil salinity encroachment is an increasing concern in many irrigated lands, because of the undesirable effects of soluble salts on agricultural production and on water quality. From this point of 10 view, the design and management of irrigation districts can be evaluated by monitoring the soil salinity.There are few cases in the world where comparisons can be undertaken from 'historic' data sets for extents other than individual plots. We demonstrate a monitoring procedure using electromagnetic induction (EMI) survey in an irrigated district in Spain. This district is the only one having an established soil salinity baseline. The EMI data acquired at the same plots were converted to soil 15 electrical conductivity by calibrating with augered soil samples. The presented calibrations improve the baseline for future comparisons and for the treatment and understanding of new acquisitions of field data in next surveys. A shortcoming inherent to destructive soil sampling is its potential for biasing effects on long-term monitoring of soil salinity by means of GPS or other means of accurate localization and relocalization of soil sampling, the herein called "localization paradox", rarely treated 20 in scientific papers. The localization paradox is relevant for any variable soil property requiring repeated sampling. This issue is discussed, and a way for its overcoming by using EMI readings displaced from the augering is presented. EMI needs calibration with a reduced number of soil samples analyzed in the lab. The adoption of our data treatment procedures will facilitate soil salinity monitoring. 25