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Few studies have attempted to investigate the combined effects of soil matric potential (Ψm) and osmotic potential (Ψs) on plant production and water use efficiency (WUE). The purpose of this study...

Salinity, water scarcity, and nitrogen (N) deficiency are the main limiting factors for plant production. However, over-irrigation and excessive N utilization can also limit the growth and biomass yield of leafy vegetables. The aim of this study is to investigate the growth regulation of spinach (Spinacia oleracea L.) under different levels of irrigation water salinity, water utilization, and nitrogen supply. Combinations of five salinity levels (1, 4, 7, 9, and 11 dS m−1) with three levels of water consumption including deficit irrigation (W–), full irrigation (W0) and over-irrigation (W+), and four levels of N supply (0, 50, 75, and 100% of N requirement) were examined under controlled greenhouse conditions. The least plant biomass, evapotranspiration (ET), and nitrogen use efficiency (NUE) were observed when high-saline water was applied in combination of water and N deficiency. However, the osmotic/drought effect is a short-term effect of salinity that can be further exacerbated by the condition W–. With increasing the fertilizer rate up to 150 mg N kg−1 soil, the plant growth traits increased significantly for all salinity levels; however, an excessive N utilization caused no significant increase. Water stress caused a morphological adaptation in the plant by reducing leaf area and ET, resulting in improved water use efficiency (WUE). With increasing salinity, WUE increased then decreased significantly. In other words, both the relative ET and relative yield were reduced with increasing salinity; however, at intermediate salinity levels (4 and 7 dS m–1), further decline in the former than in the latter resulted in higher WUE values. The stepwise regression analysis showed that the plant yield was affected mostly by WUE, ET, and leaves number (R2 = 0.983***). The findings of this study revealed that the reduced leaf area was the main growth regulation in the spinach plant under stress conditions, which ultimately could enhance WUE.

Study of the simultaneous effect of wind and rain is of great importance in the environmental studies of erosion for more accurate measurement and modeling of soil loss. There is little information on the combined effects of rain and wind on soil erosion as well as soil organic carbon (SOC) loss. The purpose of this study was to investigate interrill erosion in relation to SOC loss and enrichment ratio (ERoc) as influenced by rain intensity and wind velocity linking to flow hydraulic characteristics. Three rain intensities of 20, 40 and 60 mm h−1 and four wind velocities of 0, 6, 9 and 12 m s−1 were generated on three different soil samples (sandy, sandy loam and loam), each at three replicates (totally 108 runs). The SOC loss was determined through the concentration of organic carbon in sediment and the measured sediment load. The values of SOC loss and ERoc ranged from 0.04 to 4.04 mg m−1 s−1 and from 0.52 to 9.40, respectively. The measured interrill erosion rates and SOC losses increased at higher wind velocities and rain intensities, especially when wind velocity became more than a threshold value of 9 m s−1. For each soil, a direct linear relationship was distinguished between the losses of soil and SOC. Accordingly, SOC loss accounted for 0.36%, 0.17%, and 2.19% of the total soil loss in the sandy, sandy loam and loam soils, respectively. The ERoc was nearly constant for each soil and not changed with the increased soil erosion rate. Finally, flow velocity and unit stream power were found as the best predictors of soil and SOC losses in a wind-driven interrill erosion system.

Few studies have considered the effect of organic amendments on soil microbial activity and its contributions to hydraulic conductivity under field conditions in semiarid region soils with different textures and degrees of aggregate stability. This study was performed to investigate the relationship between selected soil properties and hydraulic conductivity in response to different types and application rates of organic amendments. For this purpose, urban municipal solid waste (MSW) compost and alfalfa residue (AR) were applied at different rates of 0 (control), 10 Mg ha− 1 and 30 Mg ha− 1 to clay loam and loamy sand soils under field conditions. Results show that after two years, MSW-treated soils had lower soil organic carbon (SOC) compared to those treated with AR due to higher CO2 emissions from the soils treated with MSW. Higher microbial respiration and mineralization quotient (qmC) in the MSW-treated soils resulted in higher levels of water stable aggregates (WSA > 0.25 mm) and more macro-pore fraction, leading to greater hydraulic conductivity, with larger increases at the higher rate of application (i.e. 30 Mg ha− 1). Relative to the control treatment, the application of MSW caused greater increases in microbial respiration in the clay loam soil than in the loamy sand soil, whereas the reverse was found for AR. Apart from soil texture, aggregate size was found to play an important role in controlling the carbon stock and microbial respiration of soils and consequently hydraulic conductivity. The macro-pore fraction was more sensitive than the micro-pore fraction to the application of organic amendments. Correlation analysis indicated that during the reclamation process higher levels of microbial respiration, SOC, water stable aggregates and macro-pore fraction were associated with greater soil hydraulic conductivity.

Soil salinity and sodicity are escalating problems worldwide, especially in arid and semi-arid regions. A laboratory experiment was conducted in soil columns to investigate redistribution of soluble cations through soil profile after reclaiming process of a calcareous saline sodic soil (CaCO3 = 20.7%, EC = 19.8 dS m−1, SAR = 32.2 (meq L−1)0.5). Two series of reclamation experiments, consisting of soil and water treatments were applied. The soil amendments were comprised of control, cattle manure (50 g kg−1), pistachio residue (50 g kg−1), gypsum (5.2 g kg−1; equivalent of gypsum requirement), manure + gypsum and pistachio residue + gypsum. After one month incubation, two types of water quality, including untreated and treated with sulfuric acid, were applied with irrigation for four months. The results showed that the concentration of all monovalent and bivalent cations as well as EC and SAR differed significantly (α = 0.01) among soil amendments. In contrast, the effect of applied sulfuric acid in the irrigation water was negligible on the final soil EC, but it was significant on soil SAR. Soluble Na+ and K+ showed a higher mobility than Ca2+ and Mg2+ within the soil. At the end of experiments, soil EC and SAR decreased significantly even for the unamended soil. This can be caused by solute leaching. In absence of sulfuric acid, pistachio residue was the best amendment in reducing soil EC and SAR. This study brings up some synergistic or antagonistic behaviors between gypsum and organic amendments in particular for the monovalent cations.

Macronutrients deficiency is one of the most important limitations of saline sodic soils. This study is focused on redistribution of nitrogen (N), phosphorous (P) and potassium (K) as well as microbial respiration in ameliorating process of a calcareous saline sodic soil. The experimental work was performed with five soil treatments: cattle manure, pistachio residue, gypsum, manure + gypsum and pistachio residue + gypsum, plus the control. One water treatment (with sulfuric acid) plus the control and three replications were applied. After one month of incubation, four intermittent irrigation events with a monthly frequency were applied. The results indicated that concentrations of N and K increased with soil depth while, the highest P concentration was observed in surface soil. The organic matter-amended soils showed the highest concentrations of N. It was found that P availability increased due to the application of amendments except for gypsum which showed an antagonism influence. Application of organic matters increased the absorbable K, but part of its concentration came from their chemical composition. Compared to the untreated water, sulfuric acid had positive impacts on P and K availability, however its influence on N concentration was negligible. Measurement of microbial respiration showed that cattle manure had the highest rates of carbon mineralization. The application of gypsum as well as sulfuric acid had no significant effects on microbial respiration. Results showed that pistachio residue is an efficient amendment to reclaim saline sodic soils, and to improve availability of macronutrients.

Soil salinity and sodicity are escalating problems worldwide, especially in arid and semiarid regions. A laboratory experiment was conducted using soil column to investigate leaching of soluble cations during reclamation process of a calcareous saline–sodic soil (CaCO3 = 20.7%, electrical conductivity (EC) = 19.8 dS m−1, sodium absorption ratio (SAR) = 32.2[meq L−1]0.5). The amendments consisted of control, cattle manure (50 g kg−1), pistachio residue (50 g kg−1), gypsum (5.2 g kg−1; equivalent of gypsum requirement), manure + gypsum and pistachio residue + gypsum, in three replicates which were mixed thoroughly with the soil, while sulfuric acid as an amendment was added to irrigation water. To reflect natural conditions, after incubation period, an intermittent irrigation method was employed every 30 days. The results showed that EC, SAR, and soluble cations of leachate for the first irrigation step were significantly higher than those of the subsequent leaching runs. Moreover, the concentration of removed soluble cations was lower for the control and gypsum-treated soils. It was found that among applied amendments, treatments containing cattle manure showed higher concentrations of sodium, calcium, and magnesium in the leachate, while due to pistachio residue application, further amount of potassium was removed out of soil column. The addition of pistachio residue resulted in the highest reduction in soil salinity and sodicity since the final EC and exchangeable sodium percentage dropped to 18.0% and 11.6% of their respective initial values, respectively. In the calcareous soil, solubility of gypsum found to be limited, in contrast, when it was added in conjunction with organic amendments, greater amounts of sodium were leached.

Spatiotemporal assessment of groundwater quality for irrigation is essential for agricultural management. This study was conducted to quantify the spatiotemporal changes of Kerman groundwater irrigation quality during 1999–2010 using geostatistical analysis combined with a new method established based on regression coefficient (RC). Result showed that among the main soluble ions, Na+ and Cl− had the highest concentrations. Except Ca+2, the average concentration of all other soluble ions and also EC were higher than the maximum permissible levels for drinking, however, Na+, SO 4 −2 and EC showed no limitations for agricultural irrigation. Based on the proposed RC, soluble Na+, Ca+2, Cl−, total cations, total anions and EC have gradually increased over the years. Soluble Cl− with 0.18 meq l−1 y−1 showed averagely the highest value of RC. Also, EC exhibited an increasing trend with an average value of 16.8 µS cm−1 y−1. In contrast, Mg+2, SO 4 −2 and SAR exhibited negative values of RC, while the value for HCO3 − was zero. Based on nugget-to-sill ratios, the groundwater variables had moderate to strong spatial structure. Finally, the spatiotemporal changes of groundwater salinity (EC) and sodicity (SAR) have been mainly controlled by Na+ and Cl−.