Mediation of gaseous emissions and improving plant productivity by DCD and DMPP nitrification inhibitors: Meta-analysis of last three decades.

Nitrification inhibitors (NIs), especially dicyandiamide (DCD) and 3,4-dimethylpyrazole phosphate (DMPP), have been extensively investigated to mitigate nitrogen (N) losses from the soil and thus improve crop productivity by enhancing N use efficiency. However, to provide crop and soil-specific guidelines about using these NIs, a quantitative assessment of their efficacy in mitigating gaseous emissions, worth for nitrate leaching, and improving crop productivity under different crops and soils is yet required. Therefore, based upon 146 peer-reviewed research studies, we conducted a meta-analysis to quantify the effect of DCD and DMPP on gaseous emissions, nitrate leaching, soil inorganic N, and crop productivity under different variates. The efficacy of the NIs in reducing the emissions of CO2, CH4, NO, and N2O highly depends on the crop, soil, and experiment types. The comparative efficacy of DCD in reducing N2O emission was higher than the DMPP under maize, grasses, and fallow soils in both organic and chemical fertilizer amended soils. The use of DCD was linked to increased NH3 emission in vegetables, rice, and grasses. Depending upon the crop, soil, and fertilizer type, both the NIs decreased nitrate leaching from soils; however, DMPP was more effective. Nevertheless, the effect of DCD on crop productivity indicators, including N uptake, N use efficiency, and biomass/yield was higher than DMPP due to certain factors. Moreover, among soils, crops, and fertilizer types, the response by plant productivity indicators to the application of NIs ranged between 35 and 43%. Overall, the finding of this meta-analysis strongly suggests the use of DCD and DMPP while considering the crop, fertilizer, and soil types.

Endophytic bacteria perform better than endophytic fungi in improving plant growth under drought stress: A meta-comparison spanning 12 years (2010-2021).

Drought stress is a serious issue that affects agricultural productivity all around the world. Several researchers have reported using plant growth-promoting endophytic bacteria to enhance the drought resistance of crops. However, how endophytic bacteria and endophytic fungi are effectively stimulating plant growth under drought stress is still largely unknown. In this article, a global meta-analysis was undertaken to compare the plant growth-promoting effects of bacterial and fungal endophytes and to identify the processes by which both types of endophytes stimulate plant growth under drought stress. Moreover, this meta-analysis enlightens how plant growth promotion varies across crop types (C3 vs. C4 and monocot vs. dicot), experiment types (in vitro vs. pots vs. field), and the inoculation methods (seed vs. seedling). Specifically, this research included 75 peer-reviewed publications, 170 experiments, 20 distinct bacterial genera, and eight fungal classes. On average, both endophytic bacterial and fungal inoculation increased plant dry and fresh biomass under drought stress. The effect of endophytic bacterial inoculation on plant dry biomass, shoot dry biomass, root length, photosynthetic rate, leaf area, and gibberellins productions were at least two times greater than that of fungal inoculation. In addition, under drought stress, bacterial inoculation increased the proline content of C4 plants. Overall, the findings of this meta-analysis indicate that both endophytic bacterial and fungal inoculation of plants is beneficial under drought conditions, but the extent of benefit is higher with endophytic bacteria inoculation but it varies across crop type, experiment type, and inoculation method.

Recent advances in bioremediation of heavy metals and persistent organic pollutants: A review.

Heavy metals and persistent organic pollutants are causing detrimental effects on the environment. The seepage of heavy metals through untreated industrial waste destroys the crops and lands. Moreover, incineration and combustion of several products are responsible for primary and secondary emissions of pollutants. This review has gathered the remediation strategies, current bioremediation technologies, and their primary use in both in situ and ex situ methods, followed by a detailed explanation for bioremediation over other techniques. However, an amalgam of bioremediation techniques and nanotechnology could be a breakthrough in cleaning the environment by degrading heavy metals and persistant organic pollutants.

Do soil conservation practices exceed their relevance as a countermeasure to greenhouse gases emissions and increase crop productivity in agriculture?

Globally, agriculture sector is the significant source of greenhouse gases (GHGs) emissions into the atmosphere. To achieve the goal of limiting or mitigating these emissions, a rigorous abatement strategy with an additional focus on improving crop productivity is now imperative. Replacing traditional agriculture with soil conservation-based farming can have numerous ecological benefits. However, most assessments only consider improvements in soil properties and crop productivity, and often preclude the quantitative impact analysis on GHGs emissions. Here, we conducted a meta-analysis to evaluate crop productivity (i.e., biomass, grain, total yield) and GHGs emissions (i.e., CO2, N2O, CH4) for three major soil conservation practices i.e., no-tillage, manures, and biochar. We also examined the yield potential of three major cereal crops (i.e., wheat, rice, maize) and their significance in mitigating GHGs emissions. None of the manures were able to reduce GHGs emissions, with poultry manure being the largest contributor to all GHGs emissions. However, pig-manure had the greatest impact on crop yield while emitting the least CO2 emissions. Use of biochar showed a strong coupling effect between reduction of GHGs (i.e., CH4 by -37%; N2O by -25%; CO2 by -5%) and the increase in crop productivity. In contrast, no-tillage resulted in higher GHGs emissions with only a marginal increase in grain yield. Depending on crop type, all cereal crops showed varied degrees of GHGs mitigation under biochar application, with wheat responding most strongly due to the additional yield increment. The addition of biochar significantly reduced CO2 and N2O emissions under both rainfed and irrigated conditions, although CH4 reductions were identical in both agroecosystems. Interestingly, the use of biochar resulted in a greater yield benefit in rainfed than in irrigated agriculture. Despite significant GHGs emissions, manure application contributed to higher crop yields, regardless of soil type or agroecosystem. Moreover, no-tillage showed a significant reduction in CH4 and N2O emissions under rainfed and irrigated conditions. Notably , biochar application in coarse while no-till in fine textured soils contributed to N2O mitigation. Most importantly, effectiveness of no-tillage as a countermeasure to GHGs emissions while providing yield benefits is inconsistent. Overall, the decision to use farm manures should be reconsidered due to higher GHGs emissions. We conclude that the use of biochar could be an ideal way to reduce GHGs emissions. However, further understanding of the underlying mechanisms and processes affecting GHGs emissions is needed to better understand the feedback effects in conservation agriculture.

Can Bacterial Endophytes Be Used as a Promising Bio-Inoculant for the Mitigation of Salinity Stress in Crop Plants?-A Global Meta-Analysis of the Last Decade (2011-2020).

Soil salinity is a major problem affecting crop production worldwide. Lately, there have been great research efforts in increasing the salt tolerance of plants through the inoculation of plant growth-promoting endophytic bacteria. However, their ability to promote plant growth under no-stress and salinity-stress conditions remains largely uncertain. Here, we carried out a global meta-analysis to quantify the plant growth-promoting effects (improvement of morphological attributes, photosynthetic capacity, antioxidative ability, and ion homeostasis) of endophytic bacteria in plants under no-stress and salinity-stress conditions. In addition, we elucidated the underlying mechanisms of growth promotion in salt-sensitive (SS) and salt-tolerant (ST) plants derived from the interaction with endophytic bacteria under no-stress and salinity-stress conditions. Specifically, this work encompassed 42 peer-reviewed articles, a total of 77 experiments, and 24 different bacterial genera. On average, endophytic bacterial inoculation increased morphological parameters. Moreover, the effect of endophytic bacteria on the total dry biomass, number of leaves, root length, shoot length, and germination rate was generally greater under salinity-stress conditions than no-stress conditions. On a physiological level, the relative better performance of the bacterial inoculants under the salinity-stress condition was associated with the increase in total chlorophyll and chlorophyll-b, as well as with the decrease of 1-aminocylopropane-1-carboxylate concentration. Moreover, under the salinity-stress condition, bacterial inoculation conferred a significantly higher increase in root K+ concentration and decrease in leaf Na+ concentration than under the no-stress condition. In SS plants, bacterial inoculation induced a higher increase in chlorophyll-b and superoxide dismutase activity, as well as a higher decrease in abscisic acid content, than in ST plants. Under salinity-stress, endophytic bacterial inoculation increased root K+ concentration in both SS and ST plants but decreased root Na+ concentration only in ST plants. Overall, this meta-analysis suggests that endophytic bacterial inoculation is beneficial under both no salinity-stress and salinity-stress conditions, but the magnitude of benefit is definitely higher under salinity-stress conditions and varies with the salt tolerance level of plants.

Does biochar accelerate the mitigation of greenhouse gaseous emissions from agricultural soil? - A global meta-analysis.

Greenhouse gaseous (GHGs) emissions from cropland soils are one of the major contributors to global warming. However, the extent and pattern of these climatic breakdowns are usally determined by the management practices in-place. The use of biochar on cropland soils holds a great promise for increasing the overall crop productivity. Nevertheless, biochar application to agricultural soils has grown in popularity as a strategy to off-set the negative feedback associated with agriculture GHGs emissions, i.e., CO2 (carbon dioxide), CH4 (methane), and N2O (nitrous oxide). Despite increasing efforts to uncover the potential of biochar to mitigate the farmland GHGs effects, there has been little synthesis of how different types of biochar affect GHGs fluxes from cropland soils under varied experimental conditions. Here, we presented a meta-analysis of the interactions between biochar and GHGs emissions across global cropland soils, with field experiments showing the strongest GHG mitigation potential, i.e. CO2 (RR = -0.108) and CH4 (RR = -0.399). The biochar pyrolysis temperature, feedstock, C: N ratio, and pH were also found to be important factors influencing GHGs emissions. A prominent reduction in N2O (RR = -0.13) and CH4 (RR = -1.035) emissions was observed in neutral soils (pH = 6.6-7.3), whereas acidic soils (pH ≤ 6.5) accounted for the strongest mitigation effect on CO2 compared to N2O and CH4 emissions. We also found that a biochar application rate of 30 t ha-1 was best for mitigating GHGs emissions while achieving optimal crop yield. According to our meta-analysis, maize crop receiving biochar amendment showed a significant mitigation potential for CO2, N2O, and CH4 emissions. On the other hand, the use of biochar had shown significant impact on the global warming potential (GWP) of total GHGs emissions. The current data synthesis takes the lead in analyzing emissions status and mitigation potential for three of the most common GHGs from cropland soils and demonstrates that biochar application can significantly reduce the emissions budget from agriculture.

Intercropping of Peanut-Tea Enhances Soil Enzymatic Activity and Soil Nutrient Status at Different Soil Profiles in Subtropical Southern China.

Intercropping is one of the most widely used agroforestry techniques, reducing the harmful impacts of external inputs such as fertilizers. It also controls soil erosion, increases soil nutrients availability, and reduces weed growth. In this study, the intercropping of peanut (Arachishypogaea L.) was done with tea plants (Camellia oleifera), and it was compared with the mono-cropping of tea and peanut. Soil health and fertility were examined by analyzing the variability in soil enzymatic activity and soil nutrients availability at different soil depths (0-10 cm, 10-20 cm, 20-30 cm, and 30-40 cm). Results showed that the peanut-tea intercropping considerably impacted the soil organic carbon (SOC), soil nutrient availability, and soil enzymatic responses at different soil depths. The activity of protease, sucrase, and acid phosphatase was higher in intercropping, while the activity of urease and catalase was higher in peanut monoculture. In intercropping, total phosphorus (TP) was 14.2%, 34.2%, 77.7%, 61.9%; total potassium (TK) was 13.4%, 20%, 27.4%, 20%; available phosphorus (AP) was 52.9%, 26.56%, 61.1%; 146.15% and available potassium (AK) was 11.1%, 43.06%, 46.79% higher than the mono-cropping of tea in respective soil layers. Additionally, available nitrogen (AN) was 51.78%, 5.92%, and 15.32% lower in the 10-20 cm, 20-30 cm, and 30-40 cm layers of the intercropping system than in the mono-cropping system of peanut. Moreover, the soil enzymatic activity was significantly correlated with SOC and total nitrogen (TN) content across all soil depths and cropping systems. The depth and path analysis effect revealed that SOC directly affected sucrase, protease, urease, and catalase enzymes in an intercropping system. It was concluded that an increase in the soil enzymatic activity in the intercropping pattern improved the reaction rate at which organic matter decomposed and released nutrients into the soil environment. Enzyme activity in the decomposition process plays a vital role in forest soil morphology and function. For efficient land use in the cropping system, it is necessary to develop coherent agroforestry practices. The results in this study revealed that intercropping certainly enhance soil nutrients status and positively impacts soil conservation.

Gluconacetobacter diazotrophicus Pal5 Enhances Plant Robustness Status under the Combination of Moderate Drought and Low Nitrogen Stress in Zea mays L.

Plant growth promoting endophytic bacteria, which can fix nitrogen, plays a vital role in plant growth promotion. Previous authors have evaluated the effect of Gluconacetobacter diazotrophicus Pal5 inoculation on plants subjected to different sources of abiotic stress on an individual basis. The present study aimed to appraise the effect of G. diazotrophicus inoculation on the amelioration of the individual and combined effects of drought and nitrogen stress in maize plants (Zea mays L.). A pot experiment was conducted whereby treatments consisted of maize plants cultivated under drought stress, in soil with a low nitrogen concentration and these two stress sources combined, with and without G. diazotrophicus seed inoculation. The inoculated plants showed increased plant biomass, chlorophyll content, plant nitrogen uptake, and water use efficiency. A general increase in copy numbers of G. diazotrophicus, based on 16S rRNA gene quantification, was detected under combined moderate stress, in addition to an increase in the abundance of genes involved in N fixation (nifH). Endophytic colonization of bacteria was negatively affected by severe stress treatments. Overall, G. diazotrophicus Pal5 can be considered as an effective tool to increase maize crop production under drought conditions with low application of nitrogen fertilizer.

Nitrous oxide emission from agricultural soils: Application of animal manure or biochar? A global meta-analysis.

Organic amendments (animal manure and biochar) to agricultural soils may enhance soil organic carbon (SOC) contents, improve soil fertility and crop productivity but also contribute to global warming through nitrous oxide (N2O) emission. However, the effects of organic amendments on N2O emissions from agricultural soils seem variable among numerous research studies and remains uncertain. Here, eighty-five publications (peer-reviewed) were selected to perform a meta-analysis study. The results of this meta-analysis study show that the application of animal manure enhanced N2O emissions by 17.7%, whereas, biochar amendment significantly mitigated N2O emissions by 19.7%. Moreover, coarse textured soils increased [lnRR‾ = 182.6%, 95% confidence interval (CI) = 151.4%, 217.7%] N2O emission after animal manure, in contrast, N2O emission mitigated by 7.0% from coarse textured soils after biochar amendment. In addition, this study found that 121-320 kg N ha-1 and ⩽ 30 T ha-1 application rates of animal manure and biochar mitigated N2O emissions by 72.3% and 22.5%, respectively. Soil pH also played a vital role in regulating the N2O emissions after organic amendments. Furthermore, > 10 soil C: N ratios increased N2O emissions by 121.4% and 27.6% after animal and biochar amendments, respectively. Overall, animal manure C: N ratios significantly enhanced N2O emissions, while, biochar C: N ratio had not shown any effect on N2O emissions. Overall, average N2O emission factors (EFs) for animal manure and biochar amendments were 0.46% and -0.08%, respectively. Thus, the results of this meta-analysis study provide scientific evidence about how organic amendments such as animal manure and biochar regulating the N2O emission from agricultural soils.

Nexus on climate change: agriculture and possible solution to cope future climate change stresses.

The changing climate scenarios harshen the biotic stresses including boosting up the population of insect/pest and disease, uplifting weed growth, declining soil beneficial microbes, threaten pollinator, and boosting up abiotic stresses including harsh drought/waterlogging, extremisms in temperature, salinity/alkalinity, abrupt rainfall pattern)) and ulitamtely  affect the plant in multiple ways. This nexus review paper will cover four significant points viz (1) the possible impacts of climate change; as the world already facing the problem of food security, in such crucial period, climatic change severely affects all four dimensions of food security (from production to consumption) and will lead to malnutrition/malnourishment faced by low-income peoples. (2) How some major crops (wheat, cotton, rice, maize, and sugarcane) are affected by stress and their consequent loss. (3) How to develop a strategic work to limit crucial factors, like their significant role in climate-smart breeding, developing resilience to stresses, and idiotypic breeding. Additionally, there is an essence of improving food security, as much of our food is wasted before consumption for instance post-harvest losses. (4) Role of biotechnology and genetic engineering in adaptive introgression of the gene or developing plant transgenic against pests. As millions of dollars are invested in innovation and research to cope with future climate change stresses on a plant, hence community base adaptation of innovation is also considered an important factor in crop improvements. Because of such crucial predictions about the future impacts of climate change on agriculture, we must adopt measures to evolve crop.