Bioneutralization of alkaline bauxite residues (BR) may be achieved through in situ organic acids produced from fermentative decomposition of carbohydrates-rich organic matters (e.g., plant ...residues), which are driven by organophilic and heterotrophic prokaryotes tolerant of extremely saline and alkaline conditions. The present study investigated if the resilience of tolerant prokaryotes in soil microbial inoculums could be improved by pre-culturing them in carbohydrate-rich plant residues, leading to enhanced bioneutralization efficacy in strongly alkaline BR. In a 2-week microcosm experiment with BR (pH ~ 10.5), it was found that the resilience of prokaryotic communities and their functional modules and bioneutralization efficacy were significantly boosted in BR admixed with plant residues (i.e., SM: sugarcane mulch, LH: Lucerne hay) pre-cultured with soil microbial inoculum. The results showed that 10–20% of the initially inoculated soil prokaryotic features were recovered in treatments with pre-cultured plant residues. Besides, the enriched diverse prokaryotes formed highly clustered networks in the amended BR. These modules actively drove C and N mineralization and sustained 0.8–2.0 units of pH reduction, despite the buffering effects of alkaline minerals in BR solid phase. In contrast, soil microbial inoculation cultured in the growth medium lost >99% of the original prokaryotic features in soil inoculums, resulting in merely 0.2–0.7 unit pH reduction in the treated BR. Therefore, pre-culturing soil inoculum in plant residues would be preferred as an integral system to treat BR for effective bioneutralization.
Display omitted
•Growth medium based soil inoculum lost 99% prokaryotes in amended bauxite residues.•Plant residues enriched bacteria were diverse and resilient in amended bauxite residues.•Plant biomass amendments with pre-enriched bacteria sustained pH reduction.•Initial alkaline mineral content and salinity determined bioneutralization efficacy.
Nitrogen (N) is a major fertiliser for agriculture and food production. About 67.84 million tons of N are annually applied to agricultural fields, without which nearly half of the world’s population ...would not be alive today. Returning plant residues to the soil is an alternative and sustainable way of N fertilisation. Although impacts of returning plant residues on plant available N in soil have been widely studied, there is still no systematic review of their mechanisms and models. In this review we highlight the following advances: (1) When plant residues are returned to the soil, N undergoes biotic immobilisation–remineralisation, abiotic immobilisation, soil organic N mineralisation and plant residue organic N mineralisation. (2) Plant residues modify inorganic N fate using three mechanism mineralisation, immobilisation–mineralisation and immobilisation, depending on plant residue nature and soil properties. (3) The use of plant residue C/N ratio is not always effective to predict the effect of plant residues. Instead, soil properties and the forms of carbon and nitrogen should be considered. (4) Mineralisation always promotes N uptake by crops and increases the risk of N loss. In addition, although net immobilisation is involved in immobilisation–mineralisation and immobilisation, it does not necessarily induce lower crop nitrogen uptake. Results also depend on the synchronism between the changing soil inorganic N and the crop N uptake. (5) N loss during mineralisation can be reduced by an immobiliser. Net N immobilisation during immobilisation–mineralisation and immobilisation can be reduced by changing the timing of ploughing and fertilising or by changing the plant residues placement.
•Assess the role of soil fungi and bacteria to decomposition of maize residues and macroaggregate formation.•We used PLFA and 13C in specific PLFA.•Amount of and maize-derived C in fungal PLFA ...correlated with macroaggregate amount.•Quality of plant residues determines composition and activity of the soil microbial biomass.•Fungal activity is of importance in the formation of macroaggregates.•Actinomycetes may take over the role of soil fungi in the decomposition of soil organic matter.
Although microbial-derived carbon (C) inputs to soil are increasingly acknowledged as an important source of soil organic matter (SOM), the contribution of different microbial compounds to soil C transformation and their role in aggregation remain poorly understood. This study assessed the contribution of soil fungi and bacteria to the decomposition of maize residues by means of extracted phospholipid fatty acids (PLFAs) and 13C in specific PLFAs and investigated the importance of soil fungi in the formation of macroaggregates. Sieved soil (<250μm) was incubated for 28 days with and without addition of maize residues and fungicide. Our results show a significant relation between the amount of fungal PLFA 18:2ω6 and the amount of macroaggregates. Further, the amount of macroaggregates was higher in the treatment with the higher amount of maize-derived C in fungal PLFA, suggesting that fungal activity is important for macroaggregate formation. Based on an increased incorporation of maize-derived C into actinomycetes in fungicide treatments, we suggest that actinomycetes may take over the role of soil fungi in the decomposition of SOM. Our study underpins the important role of soil fungi in the decomposition of organic matter and structure formation in the soil, and shows that during inhibition of soil fungi other soil microorganisms are promoted and adopt their function in the soil food web.
Selenium (Se) biofortification via crops is one of the best strategies to elevate the daily Se intake in areas where soil Se levels are low. However, Se fertilizer recovery (SeFR) is low and most of ...the Se taken up accumulates in non‐harvested plant parts and returns to the soil with plant residues. A pot experiment with soil was undertaken to study the efficiency of inorganic Se (Na2SeO4) and Se‐enriched plant residues for biofortification, as well as to identify the bottlenecks in Se utilization by Brassica napus L. The soil was fertilized with Na2SeO4 (0 and 7 µg Se kg−1) or with Se in stem or leaf residues (0 and 7 µg Se kg−1). A treatment with autoclaved soil was included (0 and 7 µg kg−1 as Na2SeO4) to unravel the impact of microbial activity on Se uptake. The Se‐enriched plant residues produced a lower Se uptake efficiency (SeUPE) and SeFR than did inorganic Se, and soil autoclaving enhanced Se accumulation in the plants. The time required for decomposition seems to preclude crop residues as an alternative source of Se. Furthermore, B. napus had a limited capacity to accumulate Se in seeds. The study shows that the bottlenecks in Se biofortification appear to be its low bioavailability in soil and poor loading from the silique walls to seeds. Thus, improved Se translocation to seeds would be a useful breeding goal in B. napus to increase SeFR.
Plants are subjected to low use efficiency of water and nutrients in marginal lands such as calcareous soils. Moreover, plant wastes are not utilized optimally by the farmers. Hence, field trials ...were carried out in 2018 and 2019 summer seasons to find the practicable model which can be emerged through addition of sugar beet residues as mulching material and irrigation treatments in maize field. The amount of these residues were 0, 2.4, 7.2 and 12.0 ton ha
−1
(denoted M
0
M
1
M
2
and M
3
, respectively). Irrigation treatments were 60%, 80% and 100% of crop evapotranspiration (signed as W
60
, W
80
and W
100
, respectively). The study was established in a strip plots design with three replications. Findings exhibited that W
80
x M
3
or M
2
were as similar as W
100
x M
2
in improving biological, straw and grain yields ha
−1
. Similar beneficial effect of W
100
or W
80
on nutrient uptake was obtained under mulching soil with M
3
or M
2
. Moreover, M
1
x W
80
or W
100
achieved the maximally available phosphorus (P) in soil. As well, M
3
x W
80
showed stable improvement in water use efficiency during the two studied seasons. Due to irrigation and soil mulching combinations, calcium carbonate (CaCO
3
) was reduced by 5.6.1-32.6% compared to the initial CaCO
3
in soil (25.42%). Generally, application of sugar beet residues at a rate of 7.2 ton ha
−1
and moderate irrigation water supply, that is 80% of crop evapotranspiration may be considered a promising quixotic practice for regulating deficit irrigation in maize grown in calcareous soils. Continuous application of compatible irrigation regime and soil mulching, for example, 80% of crop evapotranspiration plus soil mulching could have the potentiality to improve calcareous soil properties year after year.
•Intercropping with different N levels were tested on cauliflower followed by lettuce.•With 75 kg N ha−1, N uptake and growth of the intercropped cauliflower were maximized.•Under no N supply, both ...cauliflower growth and N uptake were hampered by clover intercrop.•Lettuce growth and N uptake were enhanced by the preceding intercropping system.
Cauliflower (Brassica oleracea var. botrytis L.) requires large amounts of nitrogen (N) fertilizer to produce high yields. The intercropping of cauliflower with a leguminous species may help farmers to reduce N fertilizer rates, production costs and environmental pollution. Moreover, the recycling of crop residues can contribute to the nutritional support of subsequent crops in a rotation. In this study, cauliflower was cultivated in year one either alone or intercropped with annual clover (Trifolium resupinatum L.), using four N fertilization rates: 0, 75, 150, and 300 kg N ha−1 (referred to as N0, N1, N2, and N3 respectively). Following crop residue incorporation in year two, iceberg lettuce (Lactuca sativa var. capitata (L.) Janchen) was cropped on the same field without the supply of N fertilizer to assess the effect of cauliflower and clover residues as well as of residual N fertilizer rates on the growth and N uptake of lettuce.
The presence of clover did not affect the marketable yields of the intercropped cauliflower, which were similar to the cauliflower sole-cropped. The N1 and N2 fertilizer rates maximized both growth and N uptake of the intercropped cauliflower, while with the N3, crop development was limited. In the N0 plot, the legume competed for N and depressed growth and N absorption of cauliflower. The sole-cropped cauliflower was, on the contrary, unaffected by the N fertilizer rates. The iceberg lettuce cultivated in succession benefited from the presence of clover in plots N1 and N2. When succeeded to the sole-cropped cauliflower, however, the iceberg lettuce produced less biomass and absorbed less N. Results from this study suggest that the intercropping system cauliflower-clover can be a sustainable tool to optimize N input and reduce N fertilizer requirements for the successive crop.
Background and aims Crop residues and soil types play an important role in soil C and N storage. The objectives of this study were to quantify the effects of crop residue quality and interactions ...with soil type on soil C and N, in the short- and medium-term, and to determine the responses related to the priming effect (PE). Methods Residues of vetch (Vicia sativa L.), pea (Pisum sativum L.) and wheat (Triticum aestivum L.) crops with different chemical compositions and labelled with ¹³C and ¹⁵N were left to decompose on the surface of either a sandy-loam soil or a clay soil incubated under laboratory conditions at 25 °C for 360 days. We measured the total CO₂-C and CO₂-¹³C emitted during decomposition, the soil mineral N content and the amounts of ¹³C and ¹⁵N remaining in both the surface residue particles and the bulk soil. Results Over the short-term, the vetch residues decomposed faster than those of wheat and pea on the soil surface due to their more favourable chemical composition for biodegradation; after one year, however, this difference disappeared. We observed extra soil C mineralization in all cases, i.e., the PE was positive for all treatments and was directly related to the water-soluble (vetch > pea > wheat) and soil C contents (clay soil > sandy-loam soil). Conversely, the fete of the added ¹⁵N and net N mineralization differed considerably between the three residues and was strongly related to the initial N content of the residue. Conclusions Crop residue quality and soil type affected the soil PE and soil C balance but not the fate of crop residue-C after one year. Net soil N mineralization was observed in all crop residues, with large early differences (vetch > pea > wheat), which were maintained on a medium-term basis. Our results emphasize the need to jointly consider C and N dynamics as well as short-and medium-term effects to manage agricultural and environmental services provided by the recycling of crop residues to agricultural soils.
The world's soils store more carbon than is present in biomass and in the atmosphere. Little is known, however, about the factors controlling the stability of soil organic carbon stocks and the ...response of the soil carbon pool to climate change remains uncertain. We investigated the stability of carbon in deep soil layers in one soil profile by combining physical and chemical characterization of organic carbon, soil incubations and radiocarbon dating. Here we show that the supply of fresh plant-derived carbon to the subsoil (0.6-0.8 m depth) stimulated the microbial mineralization of 2,567 226-year-old carbon. Our results support the previously suggested idea7 that in the absence of fresh organic carbon, an essential source of energy for soil microbes, the stability of organic carbon in deep soil layers is maintained. We propose that a lack of supply of fresh carbon may prevent the decomposition of the organic carbon pool in deep soil layers in response to future changes in temperature. Any change in land use and agricultural practice that increases the distribution of fresh carbon along the soil profile could however stimulate the loss of ancient buried carbon.
The treatment of synthetic wastewater containing azo dyes present in textile industry wastewater was carried out by biological method (anaerobic microbial) in Linnaeus University in Sweden and ...chemical treatment method (catalytic wet peroxide oxidatin, CWPO) in Ege University in Turkey.
Display omitted
► High residence time, yeast extract, microorganism were effective on dye removal. ► The highest removal obtained by microbial process was approximately 89%. ► In CWPO, optimum activated carbon, H
2O
2 loading, temperature, pH were determined. ► The highest removal obtained by CWPO was approximately 93%. ► Dye removal was accomplished by 60% adsorption and by 40% oxidation.
The treatment of synthetic wastewater containing azo dyes found in textile industry wastewater was carried out by anaerobic biological method and chemical oxidation. The main target of this study was to compare different treatment methods and to evaluate the effect of different parameters on treatment effectiveness. In the microbial process, the results have shown that increasing the residence time, the amount of yeast extract and the addition of microorganisms originally growing on forest residues had positive effects on the dye removal. In the catalytic wet peroxide oxidation process, CWPO, the reaction conditions were optimized at 0.5
g/L activated carbon loading with 2
mL H
2O
2/300
mL solution (35
wt%), at 80
°C, in 2
h with pH
=
3. At the optimum conditions, approximately 93% of the dye was removed. At these optimized conditions, the CWPO process was tested with real textile industry wastewater. The percentage of dye removal with this wastewater was 50%. The adsorption effect of the activated carbon was also investigated. At pH
=
7, the removal by just adsorption was around 15%. But in acidic conditions (pH
=
3) and at higher temperatures the adsorption effect of activated carbon increased. Adsorption and oxidation performances were compatible at 80
°C, however, at lower temperatures the adsorption effect was more considerable than the oxidation. It can be concluded that, generally the decolorization was accomplished by 60% adsorption and by 40% oxidation.
PDF
