Amrakh I. Mamedov

Irrigation of calcareous soil with saline–sodic water can modify the composition of the soil solution and exchange complexes in agricultural land of arid and semi-arid regions with low water resources. The objective of this study was to monitor (medium-term) potential changes in a calcareous clay soil irrigated with two types of sodic waters without cropping. Irrigation water with two high sodium adsorption ratios (SAR = 20 and 40) and electrical conductivity (EC < 3 dS m−1) was prepared using NaCl and NaHCO3 salts. The sodic irrigation waters were applied (June–October) in three periods (1, 2, and 4; one period = five irrigations) to bare non-saline soil with drip irrigation during two growing seasons; no irrigation action was taken in the winter–spring rainy season (period 3). Sampling (0–30 cm) was made after each period to determine the changes in soil pH, EC, water-soluble Na+, Ca2+, Mg2+, K+, Cl−, and HCO3−. Relative to the control, irrigation with both sodic waters increased soil pH, EC, and water-soluble Na+ and decreased or did not change water-soluble cations (Ca2+, Mg2+). The Cl− concentration increased rapidly with NaCl-type water application, but it was leached away quickly by winter–spring rains. The HCO3− concentration increased with NaHCO3-type water application, yet it leached out slowly in the rainy period. The movement of HCO3− ions in the upper soil profile (0–30 cm) was significantly slower compared to Cl− ions. Dissolution of slightly soluble soil CaCO3 by irrigation increased the solution concentration of Ca2+ and its mobility, yet the kinetics of processes depended on water type and irrigation period. The released Ca2+ interacted with other cations in the soil, causing further significant positive physicochemical changes in the soil solution and exchange capacity (comparable with control soil) at the end of the irrigation period. The CaCO3 content in the soil would be a long-term guarantee of the Ca2+ resource in soils, even if the amount of water-soluble Ca2+ may decrease for the short-term period during irrigation. The results should be considered for rational irrigation management (with various water qualities) in semi-arid and arid regions.

Soils derived from loess are fertile but susceptible to accelerated degradation in response to agricultural practices. The objective of our study was to evaluate the long‐term effects of alfalfa ( Medicago sativa L.) integrated with contrasting organic amendments (29 years) to rejuvenate degraded loess via total soil organic carbon (SOC) sequestration. The replicated study was conducted in concrete lysimeter plots (2 m long × 1 m wide × 60 cm deep) filled with degraded loess materials followed by planting of alfalfa with cattle manure (60 Mg/ha) or vermicompost (27 Mg/ha) amendments. After 29 years, SOC concentration increased by 5.3–6.2‐fold under alfalfa–organic amendments compared to the control. A similar impact of alfalfa–organic amendments was observed on the humic acid, fulvic acid, and humin concentrations. There was an overestimation of SOC stocks (151 ± 48 kg/ha) when equivalent depth was used compared to equivalent mass of soil. While the SOC sequestration rates were 614 ± 129, 710 ± 69, and 744 ± 161 kg/ha/year at 0–10 cm depth under alfalfa, alfalfa–manure, and alfalfa–vermicompost treatments, respectively, the SOC sequestration rates decreased with depth. Significantly higher values of carbon pool index (CPI) and carbon management index (CMI) under alfalfa–organic amendments justified our results associated with the SOC sequestration; however, the SOC lability (CL) decreased under alfalfa–organic amendments, when compared to the control. A significant nonlinear inverse relationship ( R 2 = 0.80) between the CPI and CL suggested that SOC sequestration is significantly dependent on its lability or vice versa. Our results suggested that the impact of alfalfa–organic amendments significantly rejuvenated the degraded loess soils via SOC sequestration.