Soils in arid and semi-arid regions are strongly affected by the accumulation of carbonates, gypsum and other, more soluble, salts.Carbonates and gypsum both have a considerable influence on soil properties, especially the chemical properties of the soil solution. The development of reliable, fast and inexpensive methods to quantify the amounts of carbonates and gypsum in soil is therefore important. Visible and near infrared (vis-NIR) spectroscopy is a non-destructive, rapid and cheap method for measuring several soil properties simultaneously. However, research on vis-NIR spectroscopy in quantifying carbonates and gypsum is limited. Therefore, this study evaluated the efficiency of vis-NIR spectroscopy in quantifying carbonates and gypsum in surface soils using partial least-squares regression (PLSR) compared with standard laboratory methods and compared PLSR with a feature-specific method using continuum removal (CR). Carbonates and gypsum in a total of 251 sieved and air-dried topsoil samples from Isfahan Province in central Iran were measured by standard laboratory methods and vis-NIR spectroscopy (350-2500 nm wavelength range). In parallel, PLSR and the feature-specific method based on CR spectra were used to predict carbonates and gypsum. The PLSR model efficiency (E) for carbonates and gypsum in the validation set was 0.52 and 0.80, respectively. The PLSR model resulted in better predictions than the feature-specific method for both soil properties. Because of the unique absorption features of gypsum, which did not overlap with other soil properties, predictions of gypsum resulted in higher E values and lower errors than predictions of carbonates.

This study tested and evaluated a suite of nine individual base learners and seven model averaging techniques for predicting the spatial distribution of soil properties in central Iran. Based on the nested-cross validation approach, the results showed that the artificial neural network and Random Forest base learners were the most effective in predicting soil organic matter and electrical conductivity, respectively. However, all seven model averaging techniques performed better than the base learners. For example, the Granger–Ramanathan averaging approach resulted in the highest prediction accuracy for soil organic matter, while the Bayesian model averaging approach was most effective in predicting sand content. These results indicate that the model averaging approaches could improve the predictive accuracy for soil properties. The resulting maps, produced at a 30 m spatial resolution, can be used as valuable baseline information for managing environmental resources more effectively.

Numerous studies have been conducted to determine the positive effects of Neotyphodium endophye-tall fescue symbiosis on plant resistance to different stresses. However, its effects on the uptake of potassium (K) and transformation of K-bearing minerals are not yet known. The objective of this research was to investigate the possible effects of such symbiosis on the transformation of clay-sized micaceous minerals. Tall fescue genotype 75B, both infected and non-infected with natural Neotyphodium endophyte, was cultivated in a mixture of quartz sand and phlogopite or muscovite. Pots were irrigated with distilled water and complete or K-free nutrient solutions for a period of 140 days. K concentrations in shoot and root were determined using a flame photometer and the clay-sized particles in each pot were analyzed using an X-ray diffractometer. Results revealed vermiculitization of phlogopite under both nutrient solutions. In addition to vermiculite, smectite was detected as a newly formed mineral in phlogopiteamended pots. In contrast, a very weak rate of vermiculitization was observed in muscovite-treated media. The rate of phlogopite transformation was significantly higher under the endophyte-infected plants, particularly when the K-free nutrient solution had been applied. Also, the significant decrease in pH value in the rhizosphere of infected plants confirmed the positive effect of endophyte-tall fescue symbiosis on mineral transformation.

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