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Soil quality and crop productivity can be improved by the combined soil application of organic amendments and synthetic fertilizers. We evaluated the sole and combined effects of sugarcane-bagasse ...

Magnesium (Mg) is an essential plant macronutrient responsible for modulating many physiological or biochemical processes such as photosynthetic activity, amino acid synthesis and nucleotide metabolism. Agricultural soils with a more-than-adequate availability of calcium (Ca) have inherent Mg deficiency, potentially resulting in overall reduced soil productivity and crop yield potential. We conducted a field experiment to investigate the optimum soil application of Mg to increase crop growth and productivity under calcareous soil conditions. In addition to recommended soil application of mineral fertilizers, we applied the following four levels of Mg to the soil in the form of anhydrous MgSO4: control, 4 kg Mg ha−1 (Mg4), 8 kg Mg ha−1 (Mg8) and 16 kg Mg ha−1 (Mg16). Results showed that Mg16 application enhanced the plant height (21%), number of grains (18%), 1,000 grains weight (20%), grain yield (20%) and biological yield (9%) over control (p ≤ 0.05). Chlorophyll a, chlorophyll b and total chlorophyll were generally higher at the Mg8 and Mg16 levels than at the control level. Contrasting to increases in growth traits, the concentration of K significantly decreased in grains, leaves and shoots of maize along the soil’s Mg gradient (p ≤ 0.05). We suggest that Mg16 overcomes the deficiency of soil Mg and can increase the crop yield traits in calcareous soils. More investigations of the effect of soil Mg on various crops grown in calcareous soils may add to our knowledge related to the stressing impact of soil Mg on plant K concentration.

A formidable challenge in suburban agriculture is the sustainability of soil health following the use of wastewater for irrigation. The wastewater irrigation likely toxifies the crop plants making them unconsumable. We used a multivariate, completely randomized design in a greenhouse, comparing the phytoextraction capacities of Brassica juncea, Eruca sativa, Brassica rapa, and Brassica napus—all grown on silt loam soil irrigated with industrial wastewater, canal water, and a 1:1 mixture, during 2018. The studied Brassica plants were generally closely efficient in remediating toxic metals found in wastewater irrigated soil. Substantial differences between Brassica and Eruca plants/parts were recorded. For example, B. napus had significantly higher metal extraction or accumulation compared to E. sativa for Zn (71%), Cu (69%), Fe (78%), Mn (79%), Cd (101%), Cr (57%), Ni (92%). and Pb (49%). While the water and plant were the main predictors of metal extraction or accumulation, an interaction between the main effects substantially contributed to Cu, Mn, and Fe extractions from soil and accumulations in plants. Significant correlations between biological accumulation coefficient and biological transfer coefficient for many metals further supported the metal extraction or accumulation efficiencies as: B. napus > B. juncea > B. rapa > E. sativa. Root-stem mobility index correlation with stem-leaf mobility index indicated the metal translocation along the root-stem-leaf continuum. Therefore, we suggest that these crops may not be used for human or animal consumption when grown with industrial wastewater of toxic metal concentrations ≥ permissible limits. Rather these plants may serve as effective remediators of toxic metal-polluted soil.

Among various heavy metals, nickel (Ni) is a potential pollutant that accumulates in broad-leaf vegetables and is reported to be carcinogenic. Biochar (BC) is a nutrient-rich and effective organic amendment for immobilization of Ni in soil. Fenugreek (Trigonella corniculata L.), a broad-leaf vegetable, is commonly cultivated due to its all-inclusive composition of nutrients such as calcium and iron and β-carotene and vitamins. Therefore, a field-pot study was conducted to examine the effectiveness of cotton-sticks-waste biochar (BC) for soil immobilization of Ni in fenugreek crop cultivated between early-October to end-November 2015. Fenugreek was grown in a sandy-loam soil experimentally contaminated with various Ni levels (0, 25, 50, and 100 mg Ni kg−1 soil) under three BC levels (0, 3, and 5%; w/w). Overall, results showed increasing plant lipid peroxidation (assessed via malondialdehyde) and ascorbic-acid concentration with increasing Ni toxicity level without BC application (p ≤ 0.05). Application of 3% BC increased the chlorophyll a (20.0%), chlorophyll b (49.1%), total chlorophyll (27.6%), carotenoids (21.6%), anthocyanin (27.2%), photosynthetic rate (112%), transpiration rate (45.0%), and sub-stomatal CO2 concentration (19.9%) in fenugreek as compared to control (0% BC) under 50 mg Ni kg−1 soil. Higher BC application rate (5%) was more effective in increasing the chlorophyll a (33.6%), chlorophyll b (81.1%), total chlorophyll (43.9%), carotenoids (71.7%), anthocyanin (77.8%), photosynthetic rate (127%), transpiration rate (42.2%), and sub-stomatal CO2 concentration (23.5) over control under 100 mg Ni kg−1 soil. We suggest that the consistent increases in dry mass, carbon flux rate and, protein, amino acids, and sugar contents of fenugreek (cultivated in a soil toxified with Ni and amended with 5% BC) seems to be caused by the reduction in the mobility of Ni in the presence of BC in a sandy-loam soil.

Beaver dam analogues (BDAs) are becoming an increasingly popular stream restoration technique. One ecological function BDAs might help restore is suitable habitat conditions for fish in streams where loss of beaver dams and channel incision has led to their decline. A critical physical characteristic for fish is stream temperature. We examined the thermal regime of a spring-fed Canadian Rocky Mountain stream in relation to different numbers of BDAs installed in series over three study periods (April–October, 2017–2019). While all BDA configurations significantly influenced stream and pond temperatures, single- and double-configuration BDAs incrementally increased stream temperatures. Single and double configuration BDAs warmed the downstream waters of mean maxima of 9.9, 9.3 °C by respective mean maxima of 0.9 and 1.0 °C. Higher pond and stream temperatures occurred when ponding and discharge decreased, and vice versa. In 2019, variation in stream temperature below double-configuration BDAs was lower than the single-configuration BDA. The triple-configuration BDA, in contrast, cooled the stream, although the mean maximum stream temperature was the highest below these structures. Ponding upstream of BDAs increased discharge and resulted in cooling of the stream. Rainfall events sharply and transiently reduced stream temperatures, leading to a three-way interaction between BDA configuration, rainfall and stream discharge as factors co-influencing the stream temperature regime. Our results have implications for optimal growth of regionally important and threatened bull and cutthroat trout fish species.

Midlatitude treed bogs represent significant carbon (C) stocks and are highly sensitive to global climate change. In a dry continental treed bog, we compared three sites: control, recent (1–3 years; experimental) and older drained (10–13 years), with water levels at 38, 74 and 120 cm below the surface, respectively. At each site we measured carbon dioxide (CO2) fluxes and estimated tree root respiration (Rr; across hummock–hollow microtopography of the forest floor) and net primary production (NPP) of trees during the growing seasons (May to October) of 2011–2013. The CO2–C balance was calculated by adding the net CO2 exchange of the forest floor (NEff-Rr) to the NPP of the trees. From cooler and wetter 2011 to the driest and the warmest 2013, the control site was a CO2–C sink of 92, 70 and 76 g m−2, the experimental site was a CO2–C source of 14, 57 and 135 g m−2, and the drained site was a progressively smaller source of 26, 23 and 13 g CO2–C m−2. The short-term drainage at the experimental site resulted in small changes in vegetation coverage and large net CO2 emissions at the microforms. In contrast, the longer-term drainage and deeper water level at the drained site resulted in the replacement of mosses with vascular plants (shrubs) on the hummocks and lichen in the hollows leading to the highest CO2 uptake at the drained hummocks and significant losses in the hollows. The tree NPP (including above- and below-ground growth and litter fall) in 2011 and 2012 was significantly higher at the drained site (92 and 83 g C m−2) than at the experimental (58 and 55 g C m−2) and control (52 and 46 g C m−2) sites. We also quantified the impact of climatic warming at all water table treatments by equipping additional plots with open-top chambers (OTCs) that caused a passive warming on average of ~ 1 °C and differential air warming of ~ 6 °C at midday full sun over the study years. Warming significantly enhanced shrub growth and the CO2 sink function of the drained hummocks (exceeding the cumulative respiration losses in hollows induced by the lowered water level × warming). There was an interaction of water level with warming across hummocks that resulted in the largest net CO2 uptake at the warmed drained hummocks. Thus in 2013, the warming treatment enhanced the sink function of the control site by 13 g m−2, reduced the source function of the experimental by 10 g m−2 and significantly enhanced the sink function of the drained site by 73 g m−2. Therefore, drying and warming in continental bogs is expected to initially accelerate CO2–C losses via ecosystem respiration, but persistent drought and warming is expected to restore the peatland's original CO2–C sink function as a result of the shifts in vegetation composition and productivity between the microforms and increased NPP of trees over time.

To quantify the effects of water table drawdown and soil warming on CH4 fluxes, we used a static chamber technique during the growing seasons (May–October) of 2011–2013 at hollow and hummock microforms at three sites of a continental bog near the town of Wandering River, Alberta, Canada: (1) Control, (2) Experimental drained, and (3) old Drained. To simulate climatic warming, we used open top chambers to passively warm half of the hollows and half of the hummocks at each of the water level treatment sites. Water table drawdown significantly reduced CH4 flux by 50% in 3 years and 76% in 13 years of drainage. The hollows showed greater reduction of efflux as compared to hummocks. A persistent functional relationship of CH4 flux with water level was found across all sites in all years. The relationship revealed that the contribution of change in vegetation type at hollows and hummocks to CH4 production and emission was relatively less important than that of the water level. Hummocks and hollows responded to warming differently. At the control, experimental and drained sites, warming increased flux at hollows by 16, 21 and 26%, and reduced flux at hummocks by 4, 37, and 56%, respectively. The combined effect of lowered water table and warming on CH4 emission was overall negative, although the interaction between the two contributing factors was not significant. Therefore, whereas climatic warming and subsequent lowering of water table are expected to reduce CH4 efflux from dry ombrotrophic bogs of Alberta, different microforms at these bogs may respond differently with accelerated emissions at warmed, wetter (hollows) and reduced emissions at warmed, drier (hummocks) microforms. Overall, CH4 efflux from Alberta’s dry continental bogs that are not underlain by permafrost might be affected only slightly by the direct effect of predicted climate warming, although initial water table position will be an important control on the overall response.

Chromium (Cr) is becoming a potential pollutant with the passage of time. Higher intake of Cr does not only affect the productivity of crops, but also the quality of food produced in Cr polluted soils. In the past, foliar application of Fe is widely studied regarding their potential to alleviate Cr toxicity. However, limited information is documented regarding the combined use of PGPR and foliar Fe. Therefore, the current study was conducted to screen Cr tolerant PGPR and examine effect of foliar Fe with and without Cr tolerant PGPR under Cr toxicity (50 and 100 mg kg−1) in maize (Zea mays) production. Out of 15, two Cr tolerant PGPR were screened, identified (Agrobacterium fabrum and Leclercia adecarboxylata) and inoculated with 500 μM Fe. Results confirmed that Agrobacterium fabrum + 500 μM Fe performed significantly best in improving dry weight of roots and shoot, plant height, roots and shoot length and plant leaves in maize under Cr toxicity. A significant increase in chlorophyll a (51.5%), b (55.1%) and total (32.5%) validated the effectiveness of A. fabrum + 500 μM Fe to alleviate Cr toxicity. Improvement in intake of N (64.7%), P (70.0 and 183.3%), K (53.8% and 3.40-fold) in leaves and N (25.6 and 122.2%), P (25.6 and 122.2%), K (33.3% and 97.3%) in roots of maize at Cr50 and Cr100 confirmed that combined application of A. fabrum with 500 μM Fe is a more efficacious approach for alleviation of Cr toxicity and fortification of Fe comparative to sole foliar application of 500 μM Fe.

Mango (Mangifera indica L.), the sixth most important fruit crop worldwide, is likely at risk under a climate change scenario of accelerated soil organic matter mineralization and constrained plant nutrient supplies such as zinc (Zn) and boron (B). We identified the optimum nutrient formulation and application method to possibly rectify nutrient deficits in mango plants grown in one of the warmest and driest regions&mdash, Multan, Pakistan. We evaluated the yield and physiological (quality) responses of 20-year-old mango trees to seven treatments of foliar and soil applications of Zn and B. Combined soil application of B and Zn resulted in optimum increases in leaf mineral B and Zn and fruit-set, retention, yield, pulp recovery and total soluble solids at ripening (p = 0.021), while reducing titratable acidity and early fruit shedding (p = 0.034). Additionally, this treatment improved fruit quality (taste, flavour, texture, aroma, acceptability, p &le, 0.05). Yield was found to be correlated with retention percentage (P &le, 0.001, R2 = 0.91), which was in turn related to fruit-set number panicle&minus, 1 (P = 0.039, R2 = 0.61). Therefore, we suggest that combined soil application of B and Zn mitigates leaf mineral deficiencies and improves the yield and quality of mango more efficiently than other individual or combined foliar or soil treatments used in this study.

In the Athabasca oil sands region near Fort McMurray, Alberta, Canada, peatlands are disturbed extensively in order to recover bitumen below the surface. Hence, following oil sands mining, landscape reclamation is a part of the mine closure process in order to return functioning ecosystems, including peatlands, to the region. This study was conducted at a pilot fen reclamation project and three other diverse natural (poor, rich and saline) fens in the oil sands region during the growing seasons of 2013 and 2014, the first and second year post-construction. Ecosystem functioning of the constructed fen (CF) was evaluated with reference to natural fens based on pore water dissolved organic carbon (DOC) concentration and chemistry. Significant variation of DOC concentration among the reference fens was observed, varying from an average of 42.0mg/L at the rich fen (RF) to 70.8mg/L at the saline fen (SF). Dissolved organic carbon concentration at CF was significantly lower than at all reference fens, but increased significantly over the first two years. Seasonal variation of DOC concentration was also observed in each site with concentration increasing over the growing season. At CF, DOC was comprised of larger, more humic and complex aromatic compounds than reference fens in the first year post-construction based on its spectrophotometric properties; however, these differences were reduced in the second year. Initial DOC concentration and chemistry at CF was indicative of the source being largely the peat placed during fen construction. Changes in chemistry and increasing concentration of DOC in the second growing season likely resulted from increasing inputs from plants established on site. These results suggest that DOC concentration is likely to increase in future at CF as vascular plant productivity increases and in response to salinity sourced from tailing sand used to construct the catchment.

Changes in atmospheric temperature and lowering in water-table (WT) are expected to affect peatland nutrient dynamics. To understand the response of peatland nitrogen (N) and phosphorus (P) dynamics to warming and drainage in a continental wooded-bog of hummock – hollow microtopography, we compared three sites: 1) control, 2) recently drained (2-3 years; experimental), and 3) older drained (12-13 years; drained), during 2013. The WT was lowered at experimental and drained sites to 74 cm and 120 cm, respectively, while a warming of ~1 °C was created at one half of the microforms using open-top chambers. Responses of peat total-inorganic-nitrogen [TIN = nitrate nitrogen (NO3--N) + ammonium nitrogen (NH4+-N)] and phosphate-P [PO43--P] pools and, vegetation C:N ratio, δ13C and δ15N to the experimental treatments were investigated across sites/microforms and over time. Peat TIN available and extractable pools increased with deepening of WT and over time, and were greater at hummocks relative to hollows. In contrast, the PO4 pools increased with short-term drainage but reverted to very close to their original (control) nutrient values in the longer-term. The WT and warming driven change in the peat TIN pool was strongly reflected in the vascular vegetation C:N ratio and, shrub δ13C and δ15N, while moss nutrient dynamics did not vary between sites. Therefore, we suggest that atmospheric warming combined with WT deepening can increase availability of mineral N and P, which then can be reflected in vascular vegetation and hence modify the productivity and ecosystem functioning of the northern mid-latitude continental wooded bogs in the long-term.

Mid-latitude treed bogs are significant carbon (C) stocks and are highly sensitive to global climate change. In a dry continental treed bog, we compared three sites; control, recent (1–3 years; experimental) and older drained (10–13 years; drained) with water levels at 38, 74 and 120 cm below the surface, respectively. At each site we measured carbon dioxide (CO2) fluxes and tree root respiration (Rr) (across hummock-hollow microtopography of the forest floor) and net primary production (NPP) of trees during the growing seasons (May to October) of 2011–2013. The carbon (C) balance was calculated by adding net CO2 exchange of the forest floor (NEff–Rr) to the NPP of the trees. From cooler and wetter 2011 to driest and warmest 2013, The control site was a~C sink of 92, 70 and 76 g m−2, experimental site was a C source of 14, 57 and 135 g m−2, and drained site was a progressively smaller source of 26, 23 and 13 g m−2, respectively. Although all microforms at the experimental site had large net CO2 emissions, the longer-term drainage and deeper water level at the drained site resulted in the replacement of mosses with vascular plants (shrubs) at the hummocks and lichens at the hollows leading to the highest CO2 uptake at drained hummocks and significant losses at hollows. The tree NPP was highest at the drained site. We also quantified the impact of climatic warming at all water table treatments by equipping additional plots with open-top chambers (OTCs) that caused a passive warming on average of ∼1 °C and differential air warming of ∼6 °C (at mid-day full sun) across the study years. Warming significantly enhanced the shrub growth and CO2 sink function of the drained hummocks (exceeding the cumulative respiration losses at hollows induced by the lowered water level × warming). There was an interaction of water level with warming across hummocks that resulted in largest net CO2 uptake at warmed drained hummocks. Thus in 2013, the warming treatment enhanced the sink function of control by 13 g m−2, reduced the source function of experimental by 10 g m−2, and significantly enhanced the sink function of the drained site by 73 g m−2. Therefore, drying and warming in continental bogs is expected to initially accelerate C losses via respiration but persistent drought and warming is expected to restore the peatland's original C sink function as a result of transitional shift of vegetation between the microforms and increased NPP of trees over time.

Northern peatland ecosystems represent large carbon stocks that are susceptible to changes such as accelerated mineralization due to water table lowering expected under a climate change scenario. During the growing seasons of 2011 and 2012 we monitored CO2 fluxes and plant biomass along a microtopographic gradient (hummocks-hollows) in an undisturbed dry continental boreal treed bog (control) and a nearby site that was drained (drained) in 2001. Ten years of drainage in the bog significantly increased coverage of shrubs at hummocks and lichens at hollows. Considering measured hummock coverage and including tree incremental growth, we estimate that the control site was a larger sink in 2011 of −40 than that of −13 g C m−2 in 2012 while the drained site was a source of 144 and 140 g C m−2 over the same years. We infer that, drainage induced changes in vegetation growth led to increased biomass to counteract a portion of soil carbon losses. These results suggest that spatial variability (microtopography) and changes in vegetation community in boreal peatlands will affect how these ecosystems respond to lowered water table potentially induced by climate change.