The potential for rhizobial inoculation to increase soybean grain yields on acid soils in Ethiopia

In Ethiopia, inoculation of soybean with rhizobial inoculants is not common practice, but could provide an option to increase grain yields in low nitrogen (N) acidic soils. In these acid soils, the selection of acid tolerant rhizobia is one strategy that may increase the performance of soybean. In this study, rhizobial strains isolated from Ethiopian soils were evaluated for their acid tolerance and symbiotic N fixation efficiency with soybean, in controlled environments. Following this, four isolated rhizobial strains were evaluated in six field experiments in major soybean growing areas of Ethiopia. Inoculation with the commercial strain or with one of two locally sourced isolates, that were developed as inoculants, improved soybean yield. The yield increase due to inoculation with the commercial strain was consistent and greater than other treatments, while the increase due to the two locally sourced strains was comparable to, or greater than, application of 46 kg N/ha in soils, where the resident rhizobial population was ≤1.4 × 10³ cfu/g soil. For soils with high background rhizobial populations, there was no response to inoculation. In one of the experimental sites (Bako), the percentage of N fixed (%Ndfa) was 55 for the commercial strain and 35 for the local strain, ES3. This study demonstrated that field validation is a necessary step in the selection of acid-tolerant strains of rhizobia to increase soybean production for Ethiopia.     

Internal Mechanisms of Plant Adaptation to Aluminum Toxicity and Phosphorus Starvation in Three Tropical Forages

Many tropical forage grasses and legumes grow well in acid soils, adapting to excess aluminum (Al) and phosphorus (P) starvation stresses by using mechanisms that are still unclear. To determine these mechanisms, responses to Al toxicity and P starvation in three tropical forages were studied: two grasses, Brachiaria hybrid cv. ‘Mulato’ (B. ruziziensis clone 44-06 × B. brizantha cv. ‘Marandú’) and Andropogon gayanus, and one legume, Arachis pintoi. The tropical grasses tolerated high levels of Al toxicity and P starvation, with the Brachiaria hybrid maintaining very low levels of Al concentration in shoots. ²⁷Al Nuclear Magnetic Resonance spectroscopy (NMR) analysis revealed that, in the Brachiaria hybrid, Al makes complexes with some ligands such as organic-acid anions in the root symplast. The forages probably adapted to P starvation through high P-use efficiency. These experiments provide the first direct evidence we know of that organic acid anions within root tissue help detoxify Al in non-accumulator species such as the Brachiaria hybrid.     

Role of Salicylic Acid in Alleviating Cadmium Toxicity in Rice Roots

In order to understand how salicylic acid (SA) is involved in modulating rice responses to cadmium (Cd) toxicity, particularly in Cd immobilization, a series of hydroponic experiments were conducted to examine changes in cell wall composition, activities of the enzymes related to lignin synthesis including phenylalanine ammonia-lyase (PAL), peroxidase (POD), and polyphenol oxidase (PPO), subcellular Cd distribution, levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and lignin and non-protein thiols (NPT) in rice roots under Cd stress with or without the pretreatment of SA. Results showed that Cd treatment decreased root biomass by 40% compared with the control (no Cd treatment) and pretreatment with SA significantly mitigated the Cd-induced inhibition of root growth. There was no significant difference in root cell wall composition or lignification between the treatment with Cd alone and the treatment with Cd with SA. No effects were observed for SA pretreatment on the activities of PAL, POD, or PPO under Cd stress. Furthermore, soluble Cd concentrations in root cells were significantly higher in the treatment with Cd with SA than in the treatment with Cd alone. However, H₂O₂ and MDA concentrations in rice roots were significantly lower but NPT levels were higher in the treatment with Cd with SA than in the treatment with Cd alone, which indicated that SA alleviated Cd-induced oxidative damage. It seems to suggest that SA-mediated enhancement of Cd tolerance was not due to enhanced Cd retention in the cell wall but to enhanced Cd bindings with thiols (─SH) group. The effects of SA-enhanced Cd tolerance were discussed with regard to H₂O₂ signaling pathways.     

Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on -glucosidase, -glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0–5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton ( Gossypium hirsutum L.) or in cotton rotated with peanut ( Arachis hypogaea L.), sorghum ( Sorghum bicolor L.), rye ( Secale cereale) or wheat ( Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C ( r -values up to 0.90, P< 0.001), and were correlated among each other ( r -values up to 0.90, P <0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61±0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86±0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.Trade names and company names are included for the benefit of the reader and do not infer any endorsement or preferential treatment of the product by USDA-ARS     

Growth and interactions of arbuscular mycorrhizal fungi in soils from limestone and acid rock habitats

Arbuscular mycorrhizal (AM) development in different soil types, and the influence of AM fungal hyphae on their original soil were investigated. Plantago lanceolata, which can grow in soils of a very wide pH range, was grown in two closely related limestone soils and an acid soil from rock habitats. Plants were colonised by the indigenous AM fungal community. The use of compartmented systems allowed us to compare soil with and without mycorrhizal hyphae. Root colonisation of P. lanceolata was markedly higher in the limestone soils (30-60%) than in the acid soil (5-20%), both in the original habitat and in the experimental study. Growth of extraradical AM fungal hyphae was detected in the limestone soils, but not in the acid soil, using the signature fatty acid 16:1ω5 as biomass indicator. Analysis of signature fatty acids demonstrated an increased microbial biomass in the presence of AM fungal hyphae as judged for example from an increased amount of NLFA 16:0 with 30 nmol g⁻¹ in one of the limestone soils. Bacterial activity, but not soil phosphatase activity, was increased by around 25% in the presence of mycorrhizal hyphae in the first harvest of limestone soils. AM fungal hyphae can thus stimulate microorganisms. However, no effect of AM hyphae was observed on the soil pH or organic matter content in the limestone soils and the available P was not depleted.     

不同腐殖酸复合肥施用量对辣椒产量及其养分利用率的影响

试验研究不同腐殖酸复合肥施用量对辣椒产量及其养分利用率的影响结果表明 ,随施肥量的增加而辣椒叶片N、P、K累积量逐渐增大 ,果实N、P、K累积量呈二次抛物线趋势变化 ,且施肥量过大时不利于营养元素向果实中的转移。肥料生产效率及N、P、K养分利用率均随施肥量的增大而降低 ,肥料对辣椒产量的贡献率以及辣椒产量随施肥量的变化与辣椒果实营养元素累积量变化趋势相一致     

Arsenic-contaminated soils phytotoxicity studies with sunflower and sorghum

Background, Aim and Scope  Environmental pollution caused by arsenic (As) is a major ecological problem. There has been intense worldwide effort to find As-hyperaccumulating plants that can be used in phytoremediation—the green-plant-assisted removal of chemical pollutants from soils. For phytoremediation, it is natural to prefer cultivated rather than wild plants, because their agriculture is well known. This study was conducted to evaluate the tolerance of common sunflower(Helianthus annuus L.) and sugar sorghum(Sorghum saccharatum Pers.) for soil-As contents of 10–100 mg As kg^-1 soil, with sodium arsenite as a model contaminant. Methods  Plants were grown in a growth chamber for 30 days. Microfield experiments were conducted on experimental plots. To study the phytoremediation effect of the auxins indole-3-acetic acid (IAA) and 2,4-dichlorophenoxyacetic acid (2,4-D), we treated 1- and 3-day-old plant seedlings with water solutions of the auxins (concentrations 10^-5, 10^-7, and 10^-9 g l^-1). The soil and plant-biomass samples were analyzed for total As by using the color reaction of ammonium molybdate with As. Results and Discussion  Phytotoxicity studies showed that 100 mg As kg^-1 soil poisoned sunflower and sorghum growth by 50%. There was a linear correlation between soil-As content and As accumulation in the plants. Laboratory experiments showed that the soil-As content was reduced two- to threefold after sunflower had been grown with 10–100 mg As kg^-1 soil for 30 days. Treatment of sunflower and sorghum seedlings with IAA and 2,4-D at a concentration of 10^-5 g l^-1 in microfield experiments enhanced the phytoremediation two- to fivefold as compared with untreated control plants. The best results were obtained with 3-day-old seedlings. Conclusion, Recommendation and Outlook  (a) Sunflower and sorghum are good candidates to remediate As-polluted soils. (b) Phytoremediation can be improved with IAA or 2,4-D. (c) Mixed cropping of sorghum and sunflower may be another way of improving phytoremediation.     

Effect of Foliar Salicylic Acid Applications on Growth,Chlorophyll, and Mineral Content of Cucumber Grown Under Salt Stress

The objective of this study was to determine the effect of foliar salicylic acid (SA) applications on growth, chlorophyll, and mineral content of cucumber grown under salt stress. The study was conducted in pot experiments under greenhouse conditions. Cucumber seedlings were treated with foliar SA applications at different concentrations (0.0, 0.25, 0.50, and 1.00 mM). Salinity treatments were established by adding 0, 60, and 120 mM of sodium chloride (NaCl) to a base complete nutrient solution. The SA was applied with spraying two times as before and after transplanting. Salt stress negatively affected the growth, chlorophyll content and mineral uptake of cucumber plants. However, foliar applications of SA resulted in greater shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight as well as higher plants under salt stress. Shoot diameter and leaf number per plant increased with SA treatments under salt stress. The greatest chlorophyll content was obtained with 1.00 mM SA treatment in both saline and non-saline conditions. Leaf water relative content (LWRC) reduced in response to salt stress while SA raised LWRC of salt stressed cucumber plants. Salinity treatments induced significant increases in electrolyte leakage. Plants treated with foliar SA had lower values of electrolyte leakage than non-treated ones. In regard to nutrient content, it can be interfered that foliar SA applications increased almost all nutrient content in leaves and roots of cucumber plants under salt stress. Generally, the greatest values were obtained from 1.00 mM SA application. Based on these findings, the SA treatments may help alleviate the negative effect of salinity on the growth of cucumber.     

Effect of pre-harvest foliar application of amino acids and seaweed (Ascophylum nodosum) extract on growth,yield, and storage life of different bell pepper (Capsicum annuum L.) cultivars grown under hydroponic conditions

The study was set up to evaluate the efficiency of amino acids and seaweed on vegetative growth, reproductive phase, yield, and postharvest storage quality of hydroponically grown bell pepper cultivars “Sven Rz F-1” and “Red Knight.” Different concentrations of amino acid and seaweed were sprayed on bell pepper plants under hydroponic conditions. Pre-harvest foliar application of amino acids and seaweed significantly increased plant height, number of leaves, leaf area, yield per plant, number of marketable fruits per plant, average fruit diameter, fruit wall thickness, and average single fruit weight. Amino acid and seaweed significantly improved postharvest physicochemical quality of both bell pepper cultivars under extended cold storage conditions. Conclusively, amino acid as well as seaweed extract not only improved growth, development, yield, and overall quality of bell pepper cultivars but also increased storage life with reduced weight loss and decay along with better physicochemical quality.