Plant and Soil

Gessa, C.; Deiana, S.

doi: 10.1007/BF00012801pmid: N/A

The transfer of nutrients from the soil to root cells is mediated by a mucilaginous interface composed predominantly of polysaccharides which are characterized by a fibrillar structure. A network of Ca-polygalacturonate was formed on garlic roots. This artificial network was compared with naturally formed mucilage structures using transmission (TEM) and scanning electron microscopy (SEM). The synthetic Ca-polygalacturonate could serve as a model for the study of the ionic transfer in the soil-root interface.

Latif, M.; Mehuys, G.; Mackenzie, A.; Alli, I.; Faris, M.

doi: 10.1007/BF00012802pmid: N/A

The effect of intercropped legumes and three N fertilizer rates in a continuous maize (Zea mays L.) cropping system on the physical properties of two soils were investigated for three years. The legumes, being a mixture of alfalfa, clover and hairy vetch, had a significant cumulative effect on some physical properties of both soil. The lowest stability and smallest mean weight diameter of soil aggregates were associated with monoculture maize plots. Aggregate size and stability were not affected by N fertilization at any of the rates of 0, 70, and 140 kg ha-1 in intercropped plots, except that aggregate stability was actually reduced by N fertilization in one soil, the Ste. Rosalie clay. In maize plots in both soils, stability and size of soil aggregates were significantly increased with increased added N. Intercropped legumes significantly decreased dry bulk density and soil penetration resistance. Added N had no measurable influence on these compaction factors. Soil water properties were not significantly affected by either intercropping or N fertilization. Positive effects noted on soil aggregation and other physical properties in intercropped plots are the result of enhanced root activity, or incorporation of legumes as green manure, or both. Improvement of soil structure in maize plots associated with increasing N application was the result of increased maize-root residues.

Megharaj, M.; Pearson, H.; Venkateswarlu, K.

doi: 10.1007/BF00012803pmid: N/A

Phenol and three nitrophenols (o-nitrophenol, m-nitrophenol, p-nitrophenol), commonly occurring pollutants in natural eco-systems, were tested for their toxic effects on soil isolates of Chlorella vulgaris and Scenedesmus bijugatus, growing under phototrophic, photoheterotrophic and heterotrophic conditions. The toxicity criteria included cell number, chlorophyll, total protein and carbohydrate content, 14CO2 uptake and in vivo nitrate reductase activity. Both C. vulgaris and S. bijugatus were sensitive to the pollutants when the cultures were grown under phototrophic or heterotrophic conditions. However, the toxicity was found reversed or alleviated upon photoheterotrophic growth of the cultures. Transmission electron microscope studies revealed various cytological abnormalities in C. vulgaris in the presence of phenolics at algistatic levels.

Li, C.; Massicote, H.; Moore, L.

doi: 10.1007/BF00012804pmid: N/A

Nitrogenase activities, measured by acetylene reduction, were detected under microaerophilic field conditions in Douglas-fir tuberculate ectomycorrhizae. Tuberculate ectomycorrhizae consist of densely packed clusters of ectomycorrhizal rootlets enclosed in a supplementary fungal peridium-like layer. Nitrogenase activity was primarily in the external layer and was greatly enhanced with added sucrose. The bacterium isolated, a nitrogen-fixing, spore-forming Bacillus sp., is an aerobe but requires anaerobic conditions for nitrogenase activity. Respiration in the tuberculate complex by the fungus, roots, and associated mycorrhizosphere microbes probably contributes to maintaining a microaerophilic niche where nitrogen fixation can take place. Water extracts of peridium or mycorrhizal root tips enhanced nitrogenase activity of this associative Bacillus sp., thereby indicating a close nutritional relationship between this bacterium and the tuberculate mycorrhizae. Thiamine more significantly enhanced bacterial nitrogenase activity than biotin; no activity was detected with p-aminobenzoic acid. Even though the levels ofnitrogenase activities in the tubercles in situ were low, as measured by the present methods, they may indicate a significant contribution to the nitrogen dynamics of these nitrogen-limited Douglas-fir forests over a long-term period.

Conner, R.; Carefoot, J.; Bole, J.; Kozub, G.

doi: 10.1007/BF00012805pmid: N/A

Agronomic studies were conducted to examine the effect of fertilizer N on black point incidence in Fielder soft white spring wheat (Triticum aestivum L. em Thell.). Black point incidence rose with increases in the amount of N supplied either as fertilizer applied during the growing season in irrigation water or as soil N, specifically nitrate, from fertilizer N application in previous years. A comparison of four different irrigation regimes demonstrated that black point incidence was highest under frequent irrigation (irrigate to field capacity at 75% available moisture) and lowest under conventional irrigation (irrigate to field capacity at 50% available soil moisture). In each irrigation regime, disease incidence increased as N rates were raised from 0 to 120 kg ha-1. A residual fertilizer-N study demonstrated in 1985 and 1986 that black point incidence generally rose with increasing levels of nitrogen from either preplant applications in the spring or soil nitrate from the previous year. However, additions of fertilizer N were shown to slightly reduce black point incidence at soil nitrate levels above 150 kg ha-1. A two-year fertilizer N study demonstrated that in treatments receiving the same amount (90 kg ha-1) of fertilizer N, the amount broadcast as a preplant treatment versus the amount applied in irrigation water in a fertigation treatment had no effect on black point incidence, but all fertilized treatments had significantly higher levels of disease than the unfertilized check.

Gahoonia, Tara; Nielsen, Niels

doi: 10.1007/BF00012806pmid: N/A

A method to control the rhizosphere pH of plants under controlled nutritional conditions is suggested. An earlier developed method for plant growth in soilless culture according to the principle of regeneration and pH control by adjusting the percentage of total N supplied as NH4-N in the maintenance solution was applied to control rhizosphere pH in connection with a recently developed plant-growing technique. Using this technique, thin soil layers (0.2 mm) at different proximity to a root mat can be sliced from a soil column and analyzed.

Badraoui, Mohammed; Bloom, Paul; Delmaki, Abdelfattah

doi: 10.1007/BF00012807pmid: N/A

Intensive cropping of Italian ryegrass (Lolium multiforum L.) in pots was used to assess the contribution of non-exchangeable K to plant uptake. The soils used were: two soils high in mica (illite) developed on recent alluvium plus two smectitic (beidellitic) soils and a soil of mixed mineralogy rich in mica. Four K treatments were used (0, 28.6, 143, and 286 mg kg-1 soil) with 8 successive monthly cuttings. A response of plant K uptake to added K was observed in all soils. Both 1.0 M NH40Ac and 0.2 M CaCl2 extractable K were depleted to a minimum level specific for each soil. The minima were lower in the old upland soils compared to the young alluvial soils. Uptake of K by Italian ryegrass induced K release from the non-exchangeable K to replenish the plant available pool of K ions. The release of mica interlayer K in the alluvial and in the high K smectitic soil supplied sufficient K to plants even under intensive cropping. The rate of mobilization of interlayer K was low in the smectitic soil with lower K. The lowest release rate was in the old high mica soil. Iron coatings may have inhibited mobilization of interlayer K. The rates of mobilization cannot be predicted from mineralogical and K-extraction data only. The rates of K uptake and the rates of K release by ryegrass under intensive cropping are potential values which can be used for modelling K availability to plants in the soils studied.

Kirkegaard, J.; So, H.; Troedson, R.

doi: 10.1007/BF00012808pmid: N/A

The effect of soil strength on the growth of pigeonpea radicles and seedlings was investigated in cores of three clay soils prepared at different water contents and bulk densities in the laboratory.

Pal, Samir

doi: 10.1007/BF00012809pmid: N/A

Properties of soil humic acids (HAs) due to incorporation of plant materials (berseem and wheat) were studied in black, laterite and red soil representing the soil orders vertisol, ultisol and alfisol, respectively. Incorporation of plant material was found to reduce the carbon content, but to increase the nitrogen content of soil HAs, irrespective of soil type. The total-N/available-N ratio of soil was found to be a determining factor for the variation in nitrogen content of soil HAs due to incorporation of plant materials. Cation exchange capacity (CEC) and optical density of soil HAs decreased, whereas coagulation threshold, absorption in different infrared regions, buffering beyond pH 7.0, and reduced viscosity increased due to addition of plant material. The amount of proton released and the drop in the initial pH of soil HAs after addition of different metal ions indicated formation of mono-, dihydroxy-metal-HA complexes which were unstable at pH 8.0 and above.

Ross, D.; Speir, T.; Cowling, J.; Feltham, C.

doi: 10.1007/BF00012810pmid: N/A

The recovery of soil biochemical properties under grazed, grass-clover pasture, after simulated lignite mining, was studied over a 5-year period in a mesic Typic Dystrochrept soil at Waimumu, Southland, New Zealand. The restoration procedures involved four replacement treatments, after A, B, and C horizon materials had been separately removed, from all except the control, and stockpiled for 2–3 weeks. In each replacement treatment, the effects of ripping to 1.8 m depth, mole drainage, and the use of fertilizer nitrogen were also investigated.