Effect of soil compaction on photosynthesis and carbon partitioning within a maize–soil system

Soil compaction is known to affect plant growth. However, most of the information regarding the effects of this factor on carbon partitioning has been obtained on young plants while little is known about the evolution of these effects with plant age. The objective of this work was to investigate how soil compaction affects carbon assimilation, photosynthate partitioning and morphology of maize plants during vegetative growth up to tassel initiation. A pressure was applied on moist soil to obtain a bulk density of 1.45 g cm⁻³ (compacted soil (CS) treatment) while the loose soil (LS) treatment (bulk density of 1.30 g cm⁻³) was obtained by gentle vibration of soil columns. Plants were grown in a growth chamber for 3–6 weeks and carbon partitioning in the plant–soil system was evaluated using ¹⁴C pulse-labelling techniques. Soil compaction greatly hampered root elongation and delayed leaf appearance rate, thereby decreasing plant height, shoot and root dry weights and leaf area. The increase in soil bulk density decreased carbon assimilation rate especially in early growth stages. The main effect of soil compaction on assimilate partitioning occurred on carbon exudation, which increased considerably to the detriment of root carbon. Furthermore, soil microbial biomass greatly increased in CS. Two hypotheses were formulated. The first was that increasing soil resistance to root penetration induced a sink limitation in roots and this increased carbon release into the soil and resulted in a root feedback that regulated carbon assimilation rate. The second hypothesis relies on soil–plant water relations since, due to compaction, the pore size distribution has to be considered. In a compacted soil, the peak of the pore size distribution curve is shifted towards the small pore size. The volume of small pores increases and the unsaturated conductivity decreases substantially, when compared to non-compacted soil. Due to small hydraulic conductivity, the inflow into the roots is well below optimum and the plant closes stomata thus reducing carbon assimilation rate. The effects of soil compaction persisted with plant age although the difference between the two treatments, in terms of percentage, decreased at advanced growth stages, especially in the case of root parameters.     

Morphological Variability of Prosopis cineraria (L.) Druce, from the Cholistan Desert, Pakistan

Sixty-two accessions of Prosopis cineraria, collected from different areas of the Cholistan desert and from the vicinity of Islamia University, Bahawalpur during June, 2002 were evaluated for agro-morphological diversity. Data collected revealed considerable variation for pod length, pod thickness, number of seeds per pod, pod weight, 100-seed weight, seed size, number of pinnules, length of pinnae, length of the pinnulae, and breadth of the pinnulae. Accessions GD-1 and GD-2, collected from Gadhen Wala Toba, KWT-1, KWT-3, KWT-4, KWT-6, from Khokhran Wala Toba, TWT-2, TWT-7, TWT-8, from Taraway Wala Toba, CSW-2, CSW-7, CSW-8, from Chah Sulleh Wala, and IUB-5, IUB-9, from Islamia University, Bahawalpur, showed very high variation. Overall, accessions KWT-6 from Khokhran Wala Toba, and TWT-7, from Taraway Wala Toba, (both from Cholistan desert), appeared as best genotypes based on their morphological variation detected in this study.     

Multilocus variable number tandem repeat analysis (MLVA)-typing of Brucella abortus isolates of India reveals limited genetic diversity

Tropical Animal Health and Production - Multilocus variable number tandem repeat analysis (MLVA) technique has wide applications in studying phylogenies and short-term epidemiology of pathogens....     

Determination of thiamphenicol in bovine plasma by liquid chromatography

A liquid chromatographic method is described for the measurement of thiamphenicol in bovine plasma. The plasma (1 mL) is extracted with ethyl acetate. After the solvent is evaporated under a stream of nitrogen, the residue is reconstituted in methanol-water and analyzed by reverse-phase liquid chromatography with UV detection at 224 nm. The intra-day recoveries for bovine plasma spiked with 5 and 50 micrograms/mL of thiamphenicol were 102 and 101%, respectively, with coefficients of variation of 2.40 and 0.28%, respectively. The interday recoveries for the 5 and 50 micrograms/mL samples were 103 and 101%, respectively, with coefficients of variation of 3.40 and 0.94%, respectively. The sensitivity of the method allows quantitation to at least the 100 ng/mL level.     

Electrokinetic Remediation of Pentachlorophenol Contaminated Clay Soil

This paper presents a bench-scale experimental study performed to investigate the remediation of low permeable soil contaminated with pentachlorophenol (PCP) using the electrokinetic technique. A total of six electrokinetic tests were performed using kaolin soil spiked with 100 mg/kg of PCP. The first three tests were performed with an applied voltage gradient of 1 VDC/cm, where each test employed one of the three different flushing solutions: deionized water, electrolyte, or buffered electrolyte. The other three tests were performed using the same electrolyte solution, but each employed voltage gradient of 2 VDC/cm under constant and periodic application modes and constant voltage gradient with electrode liquid recirculation. The results of this study showed that PCP can be degraded in an electrokinetic system due to the direct electrochemical reduction process at the electrodes. The degradation of PCP ranged from 52% to about 78% depending on the conditions present. As the applied voltage gradient across the PCP-contaminated soil increased, the electroosmotic flow and PCP migration toward the cathode increased, resulting in higher PCP degradation by the direct reduction process. In the tests with electrolyte flushing solution, PCP degradation was about 58% and 65% under the applied voltage gradients of 1 and 2 VDC/cm, respectively. The mode of application of voltage potential across the PCP-contaminated soil showed noticeable effect on the system pH and electroosmotic flow and hence the PCP degradation. The highest PCP degradation (i.e., 78%) was in the test with constant 2 VDC/cm voltage gradient and recirculation application. Overall, this study demonstrated that electrokinetic technology has the potential to remediate PCP-contaminated clay soils by the direct reductive process. The electroosmatic flow as well as degree of PCP degradation during electrokinetics depend on the applied potential gradient and properties of the aqueous phase such as pH, ionic strength, and presence of carbonates.     

Is occluded phosphate plant‐available?

Background: The phosphate concentration of the soil solution is generally low, allowing sufficient plant nutrition only for a few days. Therefore, supply from various fractions of bound phosphate is essential to meet plant demand. It is known that plants have developed strategies to acquire phosphorus (P) from phosphates adsorbed on clay minerals or oxides, from organically bound phosphates, and from calcium phosphates. However, it is generally assumed that occluded phosphate is not plant‐available. Results: In a pot experiment, two plant species, namely maize (Zea mays L.) and white lupin (Lupinus albus L.), differing in acquisition efficiency, were used to investigate whether Al oxide‐occluded and Fe oxide‐occluded phosphates can be acquired. Artificially prepared Al oxide‐occluded phosphate or Fe oxide‐occluded phosphate, respectively, was added to a subsoil low in available phosphates. It is shown that both plant species were not able to acquire P from Al oxide‐occluded phosphate. Also, maize was incapable of using Fe oxide‐occluded phosphate. In contrast, white lupin took up significant amounts of P from Fe oxide‐occluded phosphate. Conclusion: It is concluded that the strategy to form cluster roots together with their reducing power may allow white lupin to destabilize Fe oxides that occlude phosphates and to mine the soil for this additional phosphate fraction.     

Soil and microbial biomass stoichiometry regulate soil organic carbon and nitrogen mineralization in rice-wheat rotation subjected to long-term fertilization

Journal of Soils and Sediments - Soil microbial biomass (SMB), as the source and sink of soil nutrients, and its stoichiometry play a key role in soil organic carbon (SOC) and nitrogen (N)...     

Land suitability evaluation in damghan plain for barley, using compare and conformity methods (northeast-Iran)

In this study, land suitability evaluation based on FAO guidelines on the land evaluation system has been determined for barley irrigated area of about 3400 ha in the south of plains Damghan. In order to have more reliable soil data, particularity to control the old soil map of the area, a new soil survey was carried out in the area. South soils of Damghan plain were classified based on semi detailed studies of three physiogrphy units, four map units and two order Aridisols and Entisols. Climatic Data were used from Damghan meteorological synoptic stations for climate evaluation for barley. With respect to climate and soil severe limitations in the study area, the results of map units as the assessment methods include the storie, square root and the number of simple constraints were the same as N2 with permanent unsuitable.     

Growth and ion uptake of four Brassica species as affected by Na/Ca ratio in saline sand culture

The influence of supplemental Ca² in saline nutrient solutions on germination, growth, and ion uptake of four Brassica species, B. campestris L., B. carinata, A.Br., B. juncea (L.) Czern. and Coss., and B. napus L. was studied in sand culture. The addition of 11.25 mM CaC1² to nutrient solution containing 225 mM NaC1 improved percentage of germination of B. napus and B. juncea, but had no significant effect on the germination speed of the four species. There was no significant effect of additional amount of Ca² in the saline medium (150 mM NaC1) on the shoot biomass and seed yield of B. carinata and B. campestris. By contrast, shoot dry matter of B. napus and B. juncea increased significantly with the increased in Ca² concentration of the growth medium, but their seed yield remained unaffected. Decreased Ca² concentrations of the saline growth medium reduced percent oil content in B. carinata, B. juncea, and B. campestris. Increasing Na/Ca ratio of the external medium affected ion uptake differently in different species. In B. carinata, a relatively salt-tolerant species, the concentrations of Na⁺ and K⁺ in the shoots remained unaffected, but the C1 concentration was reduced linearly with the increase in external Na/Ca ratios. Root K⁺ and Ca²⁺ of the species decreased with the decrease in Ca²⁺ supply. In B. campestris increasing Na/Ca ratios of the saline medium had no effect on the concentrations of Na⁺, C1, and Ca²⁺ in the shoots and Na⁺, C1, and K⁺ in the roots. Only shoot K⁺ and root Ca²⁺ decreased consistently. In the highly salt-sensitive species, B. napus, the shoot Na⁺ was reduced by the addition of Ca²⁺ in the salt treatment, whereas the C1 and Ca²⁺ uptake was promoted by supplemental Ca²⁺. The root K⁺ concentrations decreased with the increase in Na/Ca. In B. juncea, which was similar to B. napus in biomass production, high Ca²⁺ concentration in the salt treatment reduced the shoot Na⁺ and root C1 concentrations and promoted the K⁺ uptake. Shoot Na/Ca and Na/K ratios were increased in B. napus and B. juncea at the highest Na/Ca ratio of the growth medium. Shoot K⁺ selectivity, S^K,Na (determined as molar ratio of K: Na in tissue to molar ratio of K:Na in external medium) of all species remained unaffected except for B. juncea in which it decreased significantly at the highest Na/Ca ratio. The root K⁺ selectivity increased in B. carinata.     

Trait phenotyping and SSR markers characterization of wheat (Triticum aestivum L.) germplasm for breeding early maturing wheat’s for Western-Himalayas

Genetic Resources and Crop Evolution - The study involved evaluation of 96 wheat genotypes for early maturity and related traits and molecular characterization of trait specific candidate genotypes...