Journal of Soil Science and Plant Nutrition

The current study aimed at evaluating the effects of different sewage sludge (SS) amendment rates as biofertilizers on growth of Corchorus olitorius plants and soil properties, with an emphasis on heavy metal (HM) allocation in plant parts and postharvest soil. Then, the soil was supplemented with various SS rates (0, 10, 20, 30, and 40 g kg−1). The effects of these SS amendment rates on different growth parameters of Corchorus olitorius and soil properties were investigated. The SS amendment rate of 20 g kg−1 triggered the highest growth rates of Corchorus plants. Micronutrient HMs, including Co, Cu, Mn, and Ni, increased in the shoots of plants grown in soils amended with 20 g kg−1, but with levels sufficient for normal plant growth and below the phytotoxic limits. The sludge application significantly increased the content of organic matter in postharvest soil from 1.38 to 4.83% at the amendment rate of 20 g kg−1. Furthermore, our data showed that the quantities of the estimated HMs remaining in postharvest soils were below (Cu, Fe, Mn, Mo, Zn, and Pb) or within (Co, Ni, Cd, and Cr) the maximum permissible concentrations in agricultural soils at all of the SS amendment rates. Taken together, our findings suggest that soil application of SS can provide a sustainable safe practice for SS disposal and improve plant growth, while exerting no environmental threats provided there is no accumulation of HMs to toxic levels in shoots of the grown plants or in the amended soils.

Salinity stress is one of the important factors reducing the growth and yield of crops such as legumes in many parts of the world, especially in arid and semi-arid regions. The combined use of silicon (Si) and plant-associated beneficial bacteria in mitigating environmental stresses including salinity has gained importance in recent years. However, there is limited information on the plant growth-promoting (PGP) potential of the non-rhizobial bacteria that colonize within root nodules of legumes alone or in the combination with Si to improve the tolerance of legumes to salinity stress. In this study, the PGP potential of the non-rhizobial bacteria of root nodules alone or in the combination with Si to alleviate salinity stress in alfalfa plant was investigated. Based on the results of a series of evaluations, among 60 bacterial isolates, isolated from the root nodules of alfalfa plants irrigated with saline water (EC, 8.60 dS m−1), two bacterial isolates, 40 K and N44, were selected as effective non-rhizobial strain and rhizobial one, respectively, for further study. A pot-experiment in a completely randomized design with factorial arrangement in three repetitions under greenhouse conditions was adopted to assay the effect of non-rhizobial strain 40 K alone or in combination with Si on the growth of alfalfa plant inoculated with its rhizobial symbiosis, N44 strain, under salinity stress. Experimental treatments included: Si factor at three levels of 0, 1, and 4 mM Si from potassium silicate source, nodule non-rhizobial strain factor at two levels of B0 (control), and non-rhizobial strain 40 K, and salinity (saline water) factor at three levels of 0, 5, and 15 dS m−1. Salinity stress reduced plant biomass, chlorophyll content, and the concentration of potassium and nitrogen of plant and increased the concentration of sodium in shoot tissue and the activity of antioxidant enzymes (catalase and superoxide dismutase) in alfalfa plant. However, the use of non-rhizobial strain and Si improved the morphological and physiological characteristics of the plant, reduced the plant sodium concentration, and increased the potassium concentration of alfalfa plants. The highest improvement in plant growth indices (shoot N concentration) was recorded in plants inoculated with non-rhizobial strain in the presence of Si at a concentration of 4 mM. Based on 16S rRNA sequence analysis, 40 K and N44 isolates were identified as Advenella incenata and Ensifer meliloti, respectively. The results of this study showed that Si fertilization can be suggested as a sustainable strategy for improving the plant growth promoting effects of non-rhizobial bacteria on the growth of alfalfa (increased shoot N concentration) and encouraging ecological adaptability of this plant under saline water irrigation.

A pharmacological study was conducted to analyze the impact of inhibitors of Na+-H+ antiporters (amiloride 100 µM) and cation-chloride-cotransporters (bumetanide 200 µM) on two cultivars of the African rice species (Oryza glaberrima Steud) differing in salt resistance (TOG5307: salt-resistant and TOG5949: salt-sensitive) exposed to 75 mM NaCl during 3 days. Amiloride increased Na+ accumulation in roots and leaves to a higher extent in salt-resistant TOG5307 than in salt-sensitive TOG5949. Bumetanide reduced Cl− accumulation in both cultivars as well as K+ accumulation in TOG5307 and Na+ accumulation in TOG5949, suggesting that the cation-chloride-cotransporter in O. glaberrima does not necessarily strictly behave as a Na+:K+:2Cl− transporter. Inhibitors mainly acted on the absorption step but had low impact on root-to-shoot translocation process. The salt-resistant cultivar TOG5307 was able to efficiently regulate Na+ uptake and to cope with high concentration of accumulated toxic ions, as demonstrated by a higher cell viability index and a higher concentration of protein and photosynthetic pigments in NaCl-exposed plants comparatively to salt-sensitive TOG5949.

The present study was performed to verify that the exogenous application of proline as an antioxidant can effectively reduce the damage of the herbicide Basagran® on fenugreek (Trigonella foenum-graecum). Sterilized healthy seeds were soaked in proline (7 mM) with or without the herbicide Basagran® (10–4 M) applied as a foliar spray. Performance was evaluated based on the plant’s physiological and biochemical attributes. Results revealed that herbicide stress caused seedling growth inhibition, which could be due to hydrogen peroxide (H2O2) accumulation with an increase in malondialdehyde (MDA) level and electrolyte leakage (EL). As a consequence, proline metabolism was affected, including the activity of proline dehydrogenase (PRODH) and pyrroline-5-carboxylate synthetase (P5CS), and levels of pyrroline-5-carboxylate (P5C) and proline (Pro) as well as glutathione (GSH) level, total antioxidant capacity (TAC), and activity of catalase (CAT) and glutathione-s-transferase (GST) were affirmatively influenced. However, the exogenous application of proline attenuated the harmful effects of Basagran® by improving growth performance, which might be related to enhanced antioxidant activities, total chlorophyll, relative water content (RWC), and GSH levels. Proline treatment also reduced the damage caused by increased MDA levels and reactive oxygen species (ROS) by regulating the enzymatic and non-enzymatic defense systems. Principal component analysis showed that increased oxidative damage and water imbalance were the most important contributors to herbicide stress-induced damage; however, the proline-mediated antioxidant defense was the crucial determinant of herbicide tolerance in fenugreek. Collectively, findings obtained from this study revealed that externally used proline protects against herbicide stress by enhancing cellular defense mechanisms. These results indicate the capacity of proline to improve the tolerance of fenugreek plants subjected to herbicide constraints.

In this study, we have compared three sampling designs and two modeling methods applied in the spatial prediction of available P in the soil. The study was conducted in a 160 ha where three sampling methods were tested — simple regular grid (RG) with a fixed distance between points, spatial coverage sampling (SCS) containing points over short distances, and simulated annealing sampling considering the marginal distribution of environmental covariates (DIST) — as a basis for prediction of the available phosphorus content in the soil, at a depth of 0–10 cm. Thus, each calibration set contains 160 samples, which were used to calibrate two predictive models: kriging with external drift (KED), considered a mixed model because it encompasses the geostatistical and deterministic approaches; and ordinary kriging (OK). The results were validated with an external and independent set containing 50 points. The best prediction result was found by combining the DIST sampling with the KED model, which has a lower mean absolute error (MAE) = 14.62 mg dm−3, mean error (ME) = −3.12 mg dm−3, and root mean squared error (RMSE) = 23.44 mg dm−3 and higher Nash-Sutcliffe efficiency (NSE) = 0.13. Sampling designs that consider environmental covariables contribute to the increase in the quality of the predicted available phosphorus maps. The most accurate map was generated from the DIST sampling combined with KED modeling.

Previous studies recorded positive impact of ZnO NPs on plants stressed with salinity. The current work was performed to study the effect of two different concentrations of biosynthesized ZnO NPs (50 and 100 mg L−1) on faba bean plants under salinity stress. The zinc oxide nanoparticles (ZnO NPs) were synthesized using Mentha extract, and their shape and size were characterized using X-ray diffraction and transmission electron microscope while diffuse reflectance spectra were measured using UV–Vis spectrophotometer. The generated ZnO NPs were spherical with a particle size 9.4 nm and had a rod form with particle size 15.2 in length and 3.5 nm in width. The response of faba been plants to the foliar spray of ZnO NPs concentrations (0, 50, and 100 mg L−1) alone and in combination with salt stress at 150 mM NaCl was studied. Salinity induced reduction in faba bean root and shoot length and dry/fresh weights, while an enhancement was recorded in response to foliar treatment with ZnO NPs at 50 and 100 mg L−1 either in presence or absence of salinity stress. The highest amounts of chlorophyll a, b, carotenoids, and total pigments were recorded in plants received 50 mg L−1 ZnO NPs compared to the alternative control. Secondary metabolites (phenols, flavonoids, and tannins) were accumulated in salinity-stressed plants and further accumulation in response to ZnO NPs treatment was noticed. Amino acids, proline, glycine betaine, and total soluble sugars, as well as enzymatic and non-enzymatic antioxidant contents, increased almost onefold in salinity-stressed plants as compared to control plants while the 50 mg L−1 ZnO NPs treatment resulted in higher accumulation of the previously mentioned substances. In contrast, plants oxidative stress was reduced in response to ZnO NPs treatments. The nitrogen, phosphorus, potassium, calcium, zinc, and iron contents of faba bean plants were recorded under salinity stress and in response to the two applied concentrations of ZnO NPs. Faba bean plants stressed with 150 MN NaCl showed growth decline that may be attributed to osmotic stress and low water availability imposed by salinity. The treatment of stressed plants with 50 mg L−1 ZnO NPs induced an enhancement in plant growth as well as an accumulation of antioxidants, osmolytes, and secondary metabolites that could help plants overcome the negative effects of salinity.

The purpose of this study is to evaluate modified spent coffee grounds (SCG), together with three SCG hydrochars as Zn bio-chelates. These by-products were intended to increase Zn in lettuce (Lactuca sativa) by a biofortification process. SCG and three SCG hydrochars (produced at 160, 180, or 200 °C) were activated with NaOH and functionalized with Zn sulfate. Lettuce was grown for 40 days in soils amended with the described substrates at the rate of 1.75 g kg−1 soil. Plant growth parameters and Zn, Fe, and Mn content in the plant were measured. No significant phytotoxic effect on lettuce growth was detected. In all cases, a significant increase in the Zn content in plant was observed with a maximum of 318.2% for the hydrochar at 180 °C with respect to the control. Both SCG and hydrochars promoted similar Zn levels in plant (0.30–0.35 mg Zn 100 g−1 fresh weight), although lower than those generated by the commercial chelate (0.45 mg Zn 100 g−1 fresh weight). In addition, other micronutrients such as Fe and Mn were also increased in the plant. Zn bio-chelates derived from SCG and SCG hydrochars have biofortified lettuces in Zn and also in Fe and Mn, without significantly limiting plant growth. The behavior of the different bio-products used is similar, and therefore, any of them could be used in Zn biofortification. This is a novel strategy in the reuse of SCG.

Sulfur availability depends upon the distribution of S forms in soil, interaction among them, and soil microbial properties. Organic amendments play a vital role in maintaining adequate S reserves in soil. However, two important questions in this regard are (i) the effect of microbial activity on sulfur oxidation in soil, and (ii) the relationship of sulfur fractions to available S pool in soil. The present experiment was designed to assess the effect of organic amendments on sulfur fractions, availability, and microbial properties in soil. Two alkaline subtropical soils belonging to Missa (silt loam Typic Ustochrept) and Kahuta (sandy loam Udic Haplustalf) soil series were amended with organic amendments, viz. farmyard manure (FYM), poultry litter (PL), and sugarcane filter cake (SF), at 1% w/w and incubated at 25 °C for 56 days maintaining soil moisture at 50% WHC. CO2-C evolution rate, the ∑CO2-C, and also the ∑CO2-C to microbial biomass C differed with the soils and were higher in poultry litter–amended soils. Dissolved organic C (DOC), microbial biomass C (MBC), and dehydrogenase activity (DHA) were also higher in poultry litter while the microbial biomass S (MBS) and arylsulfatase activity (ASA) were higher in the sugarcane filter cake–amended soils. Organic amendments significantly increased plant-available SO42− and enhanced C-bonded S, and inorganic S fractions in the following order: sugarcane filter cake > poultry litter > farmyard manure. Organic amendments significantly improved microbial activity and S availability in soil depending upon their labile organic C, organic S, and available S contents.