Today’s, adverse effects of off-site erosion, namely damages received from sediment, is a serious bioenvironmental problem. One of the methods for temporary soil stabilization before permanent rehabilitation of vegetation cover, especially on slopes, for mitigating of bioenvironmental contaminants, is using materials having property to cementate the dispersed particles on the soil surface. Gypsum is a material having ability to flocculate and bind the separate particles and aggregates on the soil surface. It can also prevent from soil detachment against abrasive forces. The objective of this study is to evaluate the optimum application of gypsum to reduce runoff and sediment yield and enhancing shear strength of soil surface and aggregate stability on unstable sloping marly hills of Zanjan province using small flume facility and rainfall simulator, torvane and wet sieving apparatus. These marly hills are overhang to one of the biggest water reservoirs of Iran (Sefidrood Dam) and due to their large amounts of clay particles cause numerous problems for this area. Results showed that mixing of different amounts of gypsum with upper 5 mm of soil surface reduced runoff and sediment rates between ranges of 0-13% and 11-92% respectively compared with the control treatment. Also at 30% slope and under 75 mm h-1 rainfall, the effectiveness of 20 Mg ha-1 gypsum in reducing sediment concentration diminished 35 min after runoff initiation. Whereas, the effect of 30 Mg ha-1 gypsum on sediment reduction in the same slope and rainfall intensity did not decrease even 60 min (1 hour) after initiation of runoff. In addition, it was revealed that using of gypsum because of improvement of soil physical properties and formation of water stable aggregates (WSA) on steep slopes reduced soil particle detachment and ultimately decreased soil erosion. Therefore with respecting to relatively cheap purchasing price of gypsum, the dispersed particles of soil surface on sloping areas can be economically stabilize and this leads to reduce different pollutions related to dispersed particles.

Continuous evaluation and measurement of soil moisture content are necessary for irrigation management and planning. One common instrument for measuring soil moisture is the gypsum block method, which can be done easily and quickly. However, soil salinity can cause errors in measuring water content using the gypsum block model 5910-A. In this research, the effect of different irrigation salinities (1, 2, 6, 10, 18) dS m-1 was investigated on gypsum blocks in three textural classes; clay-loam, loam, and sandy-loamy. The study was conducted in a completely randomized laboratory experiment with two replications and correction functions were investigated using the response surface method to determine the effect of parameters on the correction value. Correction functions were developed for each texture at different salinities using response surface method. Results showed that the response surface method (RSM) could estimate correction functions with an error probability of less than 0.0001 using two variables; moisture suction and salinity, or considering just the salinity factor. The accuracy of correction functions slightly decreased in different textures of clay loam, sandy loam and loam. The response surface method showed that the best salinity correction model was based on the salinity variable and the amount of soil matric suction for all three soil texture. Soil matric suction was determined from the soil moisture curve using the Parabolic model with a goodness of fit (R2) of 0.96 for loamy soil, and 0.94 for clay-loam and sandy-loam textures. To minimize correction under maximum salinity and soil suction conditions in different textures, the response surface method showed that the lowest moisture modification in clay-loam texture could be0.075 (cm3/cm3) at a suction of 8 (bar) and salinity of 18 (dS m-1) with an acceptance degree of 1. The desirability degree for loam soil and sandy-loam was calculated as 0.96 and 0.95 respectively. The results indicated that moisture correction values increased with soil salinity, but the accuracy of estimation functions for moisture correction values also increased. The changes in the moisture modification function were sinusoidal and quadratic in relation to the soil salinity and matric suction variables, respectively.

Irrigation planning and management requires continious monitoring and measurements of soil moisture content. Application of Gypsum blockes (GB) is common in soil moisture measurements. GB readings are subjected to its geometry and soil solution concentration. This study was carried on 90 GB in research greenhouse of Faculty Agricultural, Ferdowsi University of Mashhad. At the begining, all GB were calibrated in distilled water. Further, readings were collected in four solutions of 2, 6, 10 and 18 dS/m salinity. Then, three soil media with different textures (sandy loam, loam, clay loam) at 5 levels of salinity rate (trace, 2, 6, 10 and 18 dS/m of saturated extract) were studied, as 15 treatments. GB readings, at different soil moisture contant, were made by ELE-5910A. For each treatment, readings vs. soil moistures were plotted. These curves were compared with that of standard (same soil texture with trace salinity). Finally, some corrector functions were developed to eliminate the salinity effects from GB readings.

Remediation of Saline and sodic soils is usually done using leaching of excess salt and physical, chemical and biological methods and by application of mineral and organic amendments. An incubation experiment using poly ethylene columns was conducted to study the effect of using four organic and mineral amendments in a saline sodic soil (SAR=33, EC= 18. 7 dS. m-1). The treatments included: green manure, animal manure, plant residue and gypsum along with control. The water from the area (Akhtar Abad) was used to irrigate the columns. Change in some salinity and sodicity indices and the concentration of some elements in soil solution were measured and compared in soil sub-samples at 40, 80, 120, 160 days of incubation and for 0-10, 10-20 and 20-30 cm depths. The results indicated that all organic amendments especially green manure decreased soil pH compared to control (P<0. 01). Application of all amendments increased soil EC compared to control (P<0. 01). Highest EC was in green manure followed by gypsum, plant residue and animal manure, respectively. The gypsum and green manure decreased the SAR in soil compared to control (P<0. 01). The animal manure treatment did not change SAR but the plant residue treatment significantly increased SAR. In the gypsum and green manure treatments the concentration of Ca and Mg in soil solution increased significantly (P<0. 01).

In the current study, the effects of hysteresis on calibration curve of gypsum block affected by soil texture and compaction were investigated. For this, calibration curve of gypsum block in 3 soil texture including Sandy Loam, Loam and Silty Clay in three bulk density (natural in the farm and plus 10% and minus 10%) for two phases of wetting and drying were provided. The results showed that block calibration curves were different in two phases of wetting and drying in the different soil compaction and texture. By reducing soil compaction, hysteresis and its effect on shape of calibration curve of block were increased because of fine pores reduction and more non-uniformity of soil pores distribution. The effect of soil compaction on block calibration curve was different during drying and wetting phases such as for specific soil moisture, with increasing soil compaction, the block electric resistance increased and reduced during drying and wetting phases, respectively. During drying and wetting phases, increasing of soil compaction caused 16% increase and 3% decrease in field capacity, respectively. Accordingly, it is recommended that soil compaction of installation place of gypsum block and around be equal.

Sodic soils are widely spread in arid and semiarid regions. To use sodic soils for crop production, reclamation of physico-chemical properties of these soils is necessary. To study the effects of different levels of gypsum (0, 50 and 100% of gypsum requirement) alone and with three levels of organic carbon (0, 1. 5 and 3% w/w) from different sources (alfalfa and corn residue, saw dust and date fruit waste) on some properties of a sodic soil, a factorial experiment was conducted with 27 treatments and three replications using a completely randomized design. After application of gypsum or gypsum+ organic matter to the sodic soil, the physic-chemical properties of it were measured every 15 days. The studied soil was leached at the end of the incubation time. The results showed that the physicochemical characteristics of the sodic soil improved with the increase in incubation time. Before performing leaching treatment, the application of gypsum equal to gypsum requirement had the greatest impact on decreasing SAR, ESP, and dispersible clay (DC). Maximum microbial respiration rate was obtained from the application of 3% organic carbon from date fruit waste. The application of organic materials + gypsum had the greatest impact on improvement of sodic soil behaviors after leaching. The addition of organic matter caused some characteristics of sodic soil to become undesirable before leaching. After leaching, pH, SAR, ESP, DC and hydraulic conductivity (HC) decreased in all treatments. The treatment of gypsum at the rate of 100% gypsum requirement + 3% organic carbon from date fruit waste was the most effective reclamation treatment for the sodic soil. The organic materials + gypsum had the maximum reclamation effect on sodic soils, when the soils had been leached two months after incubation.

Saline-sodic soils have improper physical, chemical and biological condition and the crop productivity is low in these conditions. Application of conditioners often can be a proper solution for reclamation and improving the productivity of saline-sodic soils. In order to study the effect of some conditioners on soil chemical characteristics and yield of maize (SC260 cultivar) in a saline-sodic soil, an experiment was carried out as a completely randomized design with 3 replications in a research greenhouse of Ferdowsi university of Mashhad. The studied treatments included control and 10 ton/ha of compost (MC), vermi-compost (VC), poultry manure (PM), and gypsum powder (G). The results showed that poultry manure and vemi-compost treatments increased significantly (p<0.05)dry weight of shoots, grain yield, weight of 1000 grains, and height of maize in relation to control. Application of studied conditioners in this research cause to increase electrical conductivity (ECe) and decrease sodium absorption ratio (SAR), significantly compared to control (p<0.05)  

To measure soil water content (or soil matric suction) in thin layers of about 30mm, conventional gypsum blocks are not suitable. To carry out the task, mini-gypsum blocks were constructed using plaster of Paris in an innovative fashion. A power relationship was found between the soil water content and the mini-gypsum blocks’ readings in kΩ. The calibration results showed that readings of mini-gypsum blocks were sensitive to temperature. A normalized resistance deviation method was adopted to compensate for the effect of temperature on the sensor readings. After calibration, the high coefficient of determination obtained ensured the use of the mini-gypsum blocks for further experiments.

Background. Dental plaster, white orthodontic gypsum, and construction gypsum have β-hemihydrate particles. Setting time is an essential property of dental gypsum, which can affect the strength of the material. This research aimed to compare construction gypsum, dental plaster, and white orthodontic gypsum’ s initial and final setting times. Methods. Three groups were included in this experimental laboratory study: construction gypsum (A), dental plaster (B), and white orthodontic gypsum (C). Each group consisted of 10 samples. Gypsum manipulation consisted of using 120 gr of powder and 60 mL of water. Gypsum powder and water were mixed using a gypsum mixer at 120 rpm. A homogeneous mixture was poured into a mold, and the setting time was measured using a Gillmore needle, according to ASTM C03-266. The initial setting time test was measured using 113. 4 grams and a-2. 12mm needle. The final setting time was measured using 453. 6 grams and a-1. 06mm needle. This test was repeated until the needle failed to penetrate the gypsum’ s surface. All the data were analyzed with one-way ANOVA and post hoc Tukey tests using SPSS 23. Results. The average initial setting time for groups A, B, and C were 1. 40± 16. 17, 1. 19± 10. 39, and 1. 51± 24. 46, respectively. The average final setting time for groups A, B, and C were, 0. 79± 15. 97 0. 88± 24. 31) and 0. 66± 33. 37, respectively. One-way ANOVA and post hoc Tukey tests showed significant differences in the initial and final setting times between the three groups (P<0. 05). Conclusion. There were differences in setting time between dental plaster, white orthodontic gypsum, and construction gypsum. The construction gypsum’ s setting time is suitable as a type II dental gypsum, according to ADA No. 25.

The effect of adding waste materials (gypsum and calcite) for the remediation of a soil contaminated by pyritic minerals was examined. Materials were characterised in terms of their acid neutralisation capacity (ANC), sorption capacity and structural components. Their effect on the contaminant leaching in soil + material mixtures over a wide range of pH was also evaluated. Results at laboratory and pilot plant scales were compared to account for the potential variability in the material efficiency when applied at larger scale. The use of gypsum permitted its valorisation, although calcite was a more effective amendment because its addition led to a greater increase in the pH and acid neutralisation capacity, and thus in the sorption capacity in the resulting soil + material mixture. In the same way, when the combination of gypsum + calcite was added to the soil, it led to an increase in the pH from 2.5 to 6.9 and in the ANC from -86 to 1,513 meq/kg. As a result, the concentration of extractable heavy metals and As was reduced, and they were successfully immobilised both at laboratory and at pilot plant scales. Thus, the use of these materials induced a significant reduction in the contaminant mobility and permitted the valorisation of waste materials.