Occurrence, distribution and ecological risk assessment of herbicide residues in cropland soils from the Mollisols region of Northeast China.

The first systematic and comprehensive investigation of herbicide residues was conducted by identifying their spatial distribution, influencing factors and ecological risk in cropland soils from the Mollisols region covering 109 million hm2 in Northeast China. Fifty-six herbicides were detected with total herbicide concentrations ranging from 1.01 to 1558.13 µg/kg (mean: 227.45). Atrazine, its degradates deethyl atrazine (DEA) and deisopropyl atrazine (DIA), trifluralin and butachlor were the most frequently detected herbicides, while DEA, clomazone, nicosulfuron, fomesafen, and mefenacet exhibited the highest concentrations. Despite being less frequently reported in Chinese soils, fomesafen, nicosulfuron, clomazone, and mefenacet were found widely present. Although most of the compounds posed a minimal or low ecological risk, atrazine, nicosulfuron and DEA exhibited medium to high potential risks. The key factors identified to regulate the fate of herbicides were soil chemical properties, amount of herbicides application, and the crop type. The soybean soils showed highest herbicide residues, while the soil mineral contents likely adsorbed more herbicides. This study provides a valuable large-scale dataset of herbicide residues across the entire Mollisols region of China along with fine-scale characterization of the ecological risks. Mitigation and management measures are needed to reduce the herbicide inputs and residues in the region.

Interactive effects of phosphorus and Pseudomonas putida on chickpea (Cicer arietinum L.) growth, nutrient uptake, antioxidant enzymes and organic acids exudation.

Phosphorus (P) availability in alkaline soils of arid and semi-arid regions is a major constraint for decreased crop productivity. Use of plant growth promoting rhizobacteria (PGPR) may enhance plant growth through the increased plant antioxidation activity. Additionally, PGPR may increase nutrient uptake by plants as a result of induced root exudation and rhizosphere acidification. The current study was aimed to investigate combined effects of P and Pesudomonas putida (PGPR) on chickpea growth with reference to antioxidative enzymatic activity and root exudation mediated plant nutrient uptake, particularly P. Half of the seeds were soaked in PGPR solution, whereas others in sterile water and latter sown in soils. Plants were harvested 8 weeks after onset of experiment and analyzed for leaf nutrient contents, antioxidant enzymes activities and organic acids concentrations. Without PGPR, P application (+P) increased various plant growth attributes, plant uptake of P and Ca, soil pH, citric acid and oxalic acid concentrations, whereas decreased the leaf POD enzymatic activity as compared to the P-deficiency. PGPR supply both under -P and +P improved the plant growth, plant uptake of N, P, and K, antioxidative activity of SOD and POD enzymes and concentrations of organic acids, whereas reduced the rhizosphere soil pH. Growth enhancement by PGPR supply was related to higher plant antioxidation activity as well as nutrient uptake of chickpea including P as a result of root exudation mediated rhizosphere acidification.

Effect of buctril super (Bromoxynil) herbicide on soil microbial biomass and bacterial population

The present study aimed to evaluate the effect of bromoxynil herbicide on soil microorganisms, with the hypothesis that this herbicide caused suppression in microbial activity and biomass by exerting toxic effect on them. Nine sites of Punjab province (Pakistan) those had been exposed to bromoxynil herbicide for about last ten years designated as soil 'A' were surveyed in 2011 and samples were collected and analyzed for Microbial Biomass Carbon (MBC), Biomass Nitrogen (MBN), Biomass Phosphorus (MBP) and bacterial population. Simultaneously, soil samples from the same areas those were not exposed to herbicide designated as soil 'B' were taken. At all the sites MBC, MBN and MBP ranged from 131 to 457, 1.22 to 13.1 and 0.59 to 3.70 µg g-1 in the contaminated soils (Soil A), which was 187 to 573, 1.70 to 14.4 and 0.72 to 4.12 µg g-1 in the soils without contamination (soil B). Bacterial population ranged from 0.67 to 1.84x10(8) and 0.87 to 2.37x10(8) cfu g-1 soil in the soils A and B, respectively. Bromoxynil residues ranged from 0.09 to 0.24 mg kg-1 at all the sites in soil A. But no residues were detected in the soil B. Due to lethal effect of bromoxynil residues on the above parameters, considerable decline in these parameters was observed in the contaminated soils. Results depicted that the herbicide had left toxic effects on soil microbial parameters, thus confirmed that continuous use of this herbicide affected the quality of soil and sustainable crop production.

Changes in microbial biomass and P fractions in biogenic household waste compost amended with inorganic P fertilizers.

The present study was conducted to evaluate the changes in microbial biomass indices (C, N, and especially P) and in P fractions in compost amended with inorganic P fertilizers. In the non-amended control, the average contents of microbial biomass C, N, and P were 1744, 193, and 63 microg g(-1) compost, respectively. On average, 1.3% of total P was stored as microbial biomass P. The addition of KH(2)PO(4) and TSP (triple super phosphate) led to immediate significant increases in microbial biomass C, N, and P. Approximately, 4.6% of the added TSP and 5.8% of the added KH(2)PO(4) were incorporated on average into the microbial biomass throughout the incubation. Approximately, 4.7% of the 1mg and 5.8% of the 2mg addition rate were incorporated on average into the microbial biomass. In the amendment treatments, the average contents of microbial biomass C, N, and P declined by 44%, 64%, and 49%, respectively. Initially, the average size of the P fractions in the non-amended compost increased in the order (% of total P in brackets) resin P (0.7%)

Decomposition of heavy metal contaminated nettles (Urtica dioica L.) in soils subjected to heavy metal pollution by river sediments.

Two incubation experiments were conducted to evaluate differences in the microbial use of non-contaminated and heavy metal contaminated nettle (Urtica dioica L.) shoot residues in three soils subjected to heavy metal pollution (Zn, Pb, Cu, and Cd) by river sediments. The microbial use of shoot residues was monitored by changes in microbial biomass C, biomass N, biomass P, ergosterol, N mineralisation, CO(2) production and O(2) consumption rates. Microbial biomass C, N, and P were estimated by fumigation extraction. In the non-amended soils, the mean microbial biomass C to soil organic C ratio decreased from 2.3% in the low metal soil to 1.1% in the high metal soils. In the 42-d incubation experiment, the addition of 2% nettle residues resulted in markedly increased contents of microbial biomass P (+240%), biomass C (+270%), biomass N (+310%), and ergosterol (+360%). The relative increase in the four microbial properties was similar for the three soils and did not show any clear heavy metal effect. The contents of microbial biomass C, N and P and ergosterol contents declined approximately by 30% during the incubation as in the non-amended soils. The ratios microbial biomass C to N, microbial biomass C to P, and ergosterol to microbial biomass C remained constant at 5.2, 26, and 0.5%, respectively. In the 6-d incubation experiment, the respiratory quotient CO(2)/O(2) increased from 0.74 in the low metal soil to 1.58 in the high metal soil in the non-amended soils. In the treatments amended with 4% nettle residues, the respiratory quotient was constant at 1.13, without any effects of the three soils or the two nettle treatments. Contaminated nettle residues led generally to significantly lower N mineralisation, CO(2) production and O(2) consumption rates than non-contaminated nettle residues. However, the absolute differences were small.