Journal Articles

Now showing 1 - 3 of 3

Copper induces nitrification by ammonia-oxidizing bacteria and archaea in pastoral soils
(Wiley, 12/12/2022) Matse D; Jeyakumar P; Bishop P; Anderson C
Copper (Cu) is the main co-factor in the functioning of the ammonia monooxygenase (AMO) enzyme, which is responsible for the first step of ammonia oxidation. We report a greenhouse-based pot experiment that examines the response of ammonia-oxidizing bacteria and archaea (AOB and AOA) to different bioavailable Cu concentrations in three pastoral soils (Recent, Pallic, and Pumice soils) planted with ryegrass (Lolium perenne L.). Five treatments were used: control (no urine and Cu), urine only at 300 mg N kg-1 soil (Cu0), urine + 1 mg Cu kg-1 soil (Cu1), urine + 10 mg Cu kg-1 soil (Cu10), and urine + 100 mg Cu kg-1 soil (Cu100). Pots were destructively sampled at Day 0, 1, 7, 15, and 25 after urine application. The AOB/AOA amoA gene abundance was analyzed by real-time quantitative polymerase chain reaction at Days 1 and 15. The AOB amoA gene abundance increased 10.0- and 22.6-fold in the Recent soil and 2.1- and 2.5-fold in the Pallic soil for the Cu10 compared with Cu0 on Days 1 and 15, respectively. In contrast, the Cu100 was associated with a reduction in AOB amoA gene abundance in the Recent and Pallic soils but not in the Pumice soil. This may be due to the influence of soil cation exchange capacity differences on the bioavailable Cu. Bioavailable Cu in the Recent and Pallic soils influenced nitrification and AOB amoA gene abundance, as evidenced by the strong positive correlation between bioavailable Cu, nitrification, and AOB amoA. However, bioavailable Cu did not influence the nitrification and AOA amoA gene abundance increase.
Organic carbon content controls the severity of water repellency and the critical moisture level across New Zealand pasture soils
(Elsevier BV, 15/03/2019) Hermansen C; Moldrup P; Müller K; Jensen PW; van den Dijssel C; Jeyakumar P; de Jonge LW
Organic matter can render soil hydrophobic and cause soil water repellency (SWR) which has large implications for agriculture. Consequences such as fingered flow, uneven wetting patterns, and increased overland flow reduce irrigation efficiency and plant nutrient availability. The phenomenon of SWR is a transient soil property depending, inter alia, on soil water content (w). Soil can exhibit SWR from oven-dry w until the critical w where it again becomes fully wettable (wNON). The total SWR can be obtained from the nonlinear SWR-w relationship as the integrated trapezoidal area under the SWR-w curve (SWRAREA). We analyzed 78 soil samples, representing five dominant soil orders in the South Island of New Zealand. The soils had a large range in clay (0.000–0.520 kg kg−1) and organic carbon (OC) content (0.021–0.217 kg kg−1). The degree of SWR was measured on soils at air-dry conditions (SWRAD) and after heat-pretreatment at 60 (SWR60) and 105°C (SWR105). Further, SWR was measured in small w increments above air-dry w until wNON was reached. The SWR-w curves were either unimodal or bimodal, or no SWR occurred. SWRAREA ranged from 0.16 to 26.82 mN m−1 kg kg−1. Among the five soil orders tested, the Podzols exhibited the highest severity in SWR, whereas the Semiarid soils were the least hydrophobic soils. In conclusion, OC was the main factor for controlling the severity of SWR. Though, pH also had minor effects on SWR. Further, an upper limit critical water content was derived from the simple relationship between the wNON and OC, which could be applied to improve irrigation practices of pastoral soils. However, there is a need for further testing on different soils and land uses.
Enhanced removal of arsenic and cadmium from contaminated soils using a soluble humic substance coupled with chemical reductant.
(1/03/2023) Wei J; Tu C; Xia F; Yang L; Chen Q; Chen Y; Deng S; Yuan G; Wang H; Jeyakumar P; Bhatnagar A
Soil washing is an efficient, economical, and green remediation technology for removing several heavy metal (loid)s from contaminated industrial sites. The extraction of green and efficient washing agents from low-cost feedback is crucially important. In this study, a soluble humic substance (HS) extracted from leonardite was first tested to wash soils (red soil, fluvo-aquic soil, and black soil) heavily contaminated with arsenic (As) and cadmium (Cd). A D-optimal mixture design was investigated to optimize the washing parameters. The optimum removal efficiencies of As and Cd by single HS washing were found to be 52.58%-60.20% and 58.52%-86.69%, respectively. Furthermore, a two-step sequential washing with chemical reductant NH2OH•HCl coupled with HS (NH2OH•HCl + HS) was performed to improve the removal efficiency of As and Cd. The two-step sequential washing significantly enhanced the removal of As and Cd to 75.25%-81.53% and 64.53%-97.64%, which makes the residual As and Cd in soil below the risk control standards for construction land. The two-step sequential washing also effectively controlled the mobility and bioavailability of residual As and Cd. However, the activities of soil catalase and urease significantly decreased after the NH2OH•HCl + HS washing. Follow-up measures such as soil neutralization could be applied to relieve and restore the soil enzyme activity. In general, the two-step sequential soil washing with NH2OH•HCl + HS is a fast and efficient method for simultaneously removing high content of As and Cd from contaminated soils.

Journal Articles

Browse

Filters

Settings

Sort By

Results per page

Search Results