Autochthonous halotolerant plant growth-promoting rhizobacteria promote bacoside A yield of Bacopa monnieri (L.) Nash and phytoextraction of salt-affected soil

Phytoremediation is a promising approach for reclamation of salt-affected soil. Phytoextraction is the most commonly used process, which exploits plants to absorb, immobilize, and accumulate salt in their shoots. In this study, halotolerant plant growth-promoting rhizobacteria (PGPR) were isolated from the rhizosphere of wild grasses growing naturally in salt-affected areas of Lucknow, Uttar Pradesh (India) and were tested for their efficacies of salt-tolerance and plant growth-promoting (PGP) abilities. Based on 16S rRNA sequences, the most efficient halotolerant isolates possessing PGP traits were identified as Pseudomonas plecoglossicida (KM233646), Acinetobacter calcoaceticus (KM233647), Bacillus flexus (KM233648), and Bacillus safensis (KM233652). Application of these isolates as bio-inoculants significantly (P < 0.05) increased the growth and bacoside A yield of a medicinal plant, Bacopa monnieri (L.) Nash, grown on natural salt-affected soil. The phytoremediation of salt-affected soil was evident by the substantial increase in shoot Na⁺:K⁺ ratio of bio-inoculant-treated plants. When compared to un-inoculated control plants, the soil physico-chemical properties of bio-inoculant-treated plants were improved. The shoot and root biomass (fresh and dry weights), soil enzymes, and soil nutrient parameters showed significant positive correlations with the shoot Na⁺:K⁺ ratio. Consequently, the halotolerant PGPR screened in this study could be useful for the reclamation of saline soils concomitant with improved plant growth and bacoside A yield.     

Effect of organic matter on the distribution, extractability and uptake of cadmium in soils

Distribution and plant uptake of soil Cd as influenced by organic matter and soil type were investigated in a greenhouse experiment. Three soils (a sand, sandy loam and clay loam) were used. The rates of organic matter in its moist state added were 0,20,40, 80, 160 and 320 g kg^-1 of the air-dried soil on mass basis. Ryegrass (Lolium multörum L.) was used as a test crop. Soil Cd was analysed by a sequential extraction technique and by extraction with 1 M NH₄NO₃ and 0.005 M DTPA. The exchangeable fraction of Cd as determined by 1 M MgCl₂ in the sequential extraction procedure increased, whereas the Fe-Mn oxidebound fraction decreased, with increasing levels of organic matter addition in all three soils. The dry matter yields of ryegrass were not affected by the addition of organic matter, but the Cd concentrations in both cuts of ryegrass decreased with increasing amounts of organic matter added. The plant Cd was highly but negatively correlated to soil CEC. At any level of organic matter addition, the decrease in Cd concentration of ryegrass was in the order: sand > sandy loam > clay loam.     

The effect of soil pH and high urea concentrations on urease activity in soil

The rate of hydrolysis of urea in soil over the wide range of concentrations, up to 10 moles N per dm³ soil solution, found in fertilizer practice, was examined in Begbroke sandy loam adjusted to different pH values. On rewetting air-dry soil, urease activity increased rapidly, reached a maximum within the first 24 h and then decreased slowly to level off after about 4 days. Pretreatment of the soil with urea or ammonium had no effect on the urease activity. Urease activity increased with substrate concentration, reached an optimum value and then decreased with rising urea concentration. The results could be explained by substrate inhibition at higher urea concentrations, and the data are well described by a modified Michaelis-Menten equation involving three parameters, V_max, K_m and K_i where K_i is an inhibition constant. K_m decreased linearily with rise in pH whereas K_i increased slightly between pH 4.9 and 7.0 and steeply between 7.0 and 8.4. V_max increased with rise in pH, reached a maximum value at pH 6.0 and then declined at higher pHs. There was a further reaction, reaching a maximum rate at a urea concentration of about 0.2 molar N in the soil solution, that followed Michaelis-Menten kinetics. K_m for this high affinity reaction increased up to pH 7.2 and then decreased at higher pH values; V_max increased up to pH 6.8 and then decreased. The contribution of the high affinity reaction was small except at low concentrations of urea.     

THERMODYNAMICS OF THE EXCHANGE OF NICOTINE ON ALUMINIUM-MONTMORILLONITE

The ion exchange equilibria involving the interaction of nicotine with Almontmorillonite was studied thermodynamically. The exchange isotherms at 30° and 60°C indicated a preference for Al ions by montmorillonite as compared with nicotinium ions. A separation factor supported the conclusion. The enthalpy gain indicated tighter binding of Al. The entropy gain indicated a diffused and disordered arrangement of nicotinium ions in the Goüy layer with Al forming a more ordered arrangement in the Stern layer.     

A VERSATILE METHOD FOR TREATMENT OF CLAY SOILS FOR THIN-SECTION FABRIC STUDIES

In an earlier investigation three different methods had to be used for the treatment of laboratory-compacted clay soils prior to the preparation of thin sections for use in fabric studies. The three methods, viz., the Carbowax method, the Araldite-resin impregnation method, and the Aquax method, had limited application depending on the degree of saturation and the clay-mineral composition of the soil. A new method has been developed which can be applied to all clay soils irrespective of their mineralogy and degree of saturation. In this method, the pore water of the soil specimen is first replaced with monostyrene using a two-step diffusion process. Then the specimen is impregnated with an Araldite-resin mixture which can be cured at a temperature of 55°C. The method has yielded better thin sections than those obtained by any of the three previous methods. Pure montmorillonite soils can be treated with a greater degree of success than hitherto possible.     

Diffusion of urea, ammonium and soil alkalinity from surface applied urea

A model for predicting the concentration profiles of urea, ammonium and soil pH in a soil column following diffusion from a surface application of urea is developed, using independently derived parameters, and tested experimentally. The following processes within the model were studied separately under the same conditions as those in the diffusion run. The rate of urea hydrolysis as a function of substrate concentration and pH in the soil solution, and the sorption of urea and ammonium by the soil from solution. A theory for the propagation of changes of pH in soils was applied to describe the diffusion of soil alkalinity arising from urea hydrolysis. These processes were linked by three diffusion equations—for urea, NH₄ and soil alkalinity, which were solved numerically using finite difference methods. There was good agreement between experimental and predicted concentrations of urea and NH₄, and soil pH values at the two times tested.     

Effects of long-term 2,4-D application on microbial populations and biochemical processes in cultivated soil

Summary The effects of 15 years of field applications of 2,4-dichlorophenoxy acetate (2,4-D) on soil microbial population and biochemical processes were studied in a field cropped with maize followed by potatoes. Amine or ester formulations at the rate of 0.95 kg 2,4-D per hectare applied in May and October every year. Fungal, bacterial, and actinomycete populations, and microbial biomass C and N were reduced by the 2,4-D treatment, the reduction being more marked where the ester was used. N mineralization, nitrification, and potentially mineralizable N were reduced by the 2,4-D ester only, while urease activity was depressed by both formulations. Dehydrogenase activity and soil microbial respiration tended to be temporarily increased by the amine, but were reduced substantially by the ester, indicating that the ester probably interfered with nutrient cycling.     

Experiences with Rice Grown on Permanent Raised Beds: Effect of Crop Establishment Techniques on Water Use,Productivity, Profitability and Soil Physical Properties

In recent years, conventional rice production technologies have been leading to deterioration of soil health and declining farm profitability due to high inputs of water and labor. Conservation agriculture(CA) based resource-conserving technologies i.e. zero-tillage(ZT), raised-bed planting and direct-seeded rice(DSR) have shown promise as alternatives to conventional production technologies to overcome these problems. Present study was undertaken during 2009–2012 to establish an understanding of how permanent raised bed cropping system could be practiced to save water at the field application level to improve water productivity and also have the capability to enhance productivity, profitability and soil physical quality. The results showed that among different crop establishment techniques, conventional-tilled puddle transplanted rice(CT-TPR) required 14%-25% more water than other techniques. Compared with the CT-TPR system, zero till direct-seeded rice(ZT-DSR) consumed 6%–10% less water with almost equal system productivity and demonstrated higher water productivity. Wide raised beds saved about 15%–24% water and grain yield decrease of about 8%. Direct-seeded rice after ZT or reduced tillage or on unpuddled soil provided more net income than CT-TPR. The CTTPR system had higher bulk density and penetration resistance due to compaction caused by the repeated wet tillage in rice. The steady-state infiltration rate and soil aggregation( 0.25 mm) were higher under permanent beds and ZT and lower in the CT-TPR system. Under CT-TPR, soil aggregation was static across seasons, whereas it improved under no-till and permanent beds. Similarly, mean weight diameter of aggregates was higher under ZT and permanent beds and increased over time. The study reveals that to sustain the rice productivity, CA-based planting techniques can be more viable options. However, the long-term effects of these alternative technologies need to be studied under varying agro-ecologies in western Uttar Pradesh, India.