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  • 1
    Electronic Resource
    Electronic Resource
    Competition for N and P between wheat and wild oats (Avena sterilis L.) according to the proximity of their time of emergence (1987)
    Springer
    Plant and soil 102 (1987), S. 133-136 
    Details
    ISSN: 1573-5036
    Keywords: competition ; nitrogen ; nutrition ; phosphorus ; wheat ; wild oats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract In the cultivated wheat fields of the Mediterranean area, wild oats (Avena sterilis L.), is commonly found a weed, which competes with the wheat for soil nutrients, water and light. To study this mutual competition for N and P, a pot experiment was devised in which the planting of wheat and weed seeds, in the pots, was so arranged that the lengths of time between the emergence of each specie was different for each treatment. When the time of emergence of the wild oat coincided with that of wheat, the latter was affected in its development, productivity and total accumulation of N and P. However, the earlier the emergence of wheat was relative to that of wild oat, the greater was the suppression of the weed, with a lower total accumulation of N and lower P content in the plant. Bringing forward the emergence of either of the two species conferred advantages for the development of the earliest emerger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370914
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  • 2
    Electronic Resource
    Electronic Resource
    Nitrogen mineralization and its controlling factors in various kinds of temperate humid-zone soils (1992)
    Springer
    Plant and soil 144 (1992), S. 31-44 
    Details
    ISSN: 1573-5036
    Keywords: mineralization capacity ; nitrogen ; principal components analysis ; soil incubation ; temperate humid zone ; soils
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The N mineralization capacity of 41 temperate humid-zone soils of NW Spain was measured by aerobic incubation for 15 days at 28°C and 75% of field capacity. The main soil factors affecting organic N dynamics were identified by principal components analysis. Ammonification predominated over nitrification in almost all soils. The mean net N mineralization rate was 1.63% of the organic N content, and varied according to soil parent materials as follows: soils on basic and ultrabasic rocks 〈 soils over acid metamorphic rocks 〈 soils developed over sediments 〈 soils over acid igneous rocks 〈 soils on limestone. The N mineralization capacity was lower in natural soils than in cropped soils or pastures. The accumulation of organic matter (C and N) seems to be due to poor mineralization which was caused, in decreasing order of importance, by high exchangeable H-ion levels, high Al and Fe gel contents and, to a lesser extent (though more markedly in cropped soils), by silty clay texture and exchangeable Al ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00018842
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  • 3
    Electronic Resource
    Electronic Resource
    Salinity and fish effects on Salton Sea microecosystems: water chemistry and nutrient cycling (1998)
    Springer
    Hydrobiologia 381 (1998), S. 105-128 
    Details
    ISSN: 1573-5117
    Keywords: Microcosms ; Salton Sea ; saline lakes ; microcosms ; salinity ; ionic composition ; oxygen ; pH ; nutrients ; nitrogen ; phosphorus ; silicon ; fish ; grazing ; Oreochromis mossambicus ; Gammarus mucronatus ; Artemia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A 15 month long experiment was undertaken to document responses of the Salton Sea biota to experimentally manipulated salinity levels (30, 39, 48, 57, and 65 g l-1) in 312-liter fiberglass tanks maintained outdoors. At two salinities (39 and 57 g l-1) microcosms were set up each having one small tilapia ( Oreochromis mossambicus) in order to assess its influence on the system. To 28 tanks filled with Salton Sea water diluted to 30 g l-1, different salts (NaCl, Na2SO_4, MgSO4 · 7H2O, KCl) were added in constant proportions to produce the desired salinity levels. Salton Sea shoreline sediment was added to the bottom of each tank, and inocula of algae and invertebrates were added on several occasions. Invertebrate populations, phytoplankton, periphyton, and water chemistry were monitored at regular intervals. This article present the results concerning water chemistry and nutrient cycling. There was no apparent increase in salinity over time, though ∼ 1190 l of tapwater with a salinity of ∼ 0.65 g l-1 were added to each tank during the experiment. Ionic composition varied both among treatments and over time to some degree. Ca2 concentrations were the same at all salinities, while K1 concentrations were 〉3 times greater at the highest salinity than at the lowest. pH showed little consistent variation among salinities until the last few months when it was higher by ∼ 0.4 units at the two higher salinities than at the lower ones; it was unaffected by fish. Absolute oxygen concentrations were negatively correlated with salinity, and occasionally depressed by the presence of fish. PO3-4, dissolved organic phosphorus, and particulate phosphorus concentrations were often reduced by 30–80% at 65 g l-1 relative to lower salinities and by the presence of fish. Early in the experiment NO2-3 concentrations were 〉2 times higher at 57 and 65 g l-1 than at lower salinities, but otherwise effects of salinity on dissolved forms of nitrogen were not marked; particulate nitrogen was much lower at 65 g l-1 than at other salinities and also was reduced by up to 90% by the presence of fish. Silica concentrations increased over time at all salinities, but, relative to those at lower salinities, were reduced by 60–90% at 65 g l-1 by abundant periphytic diatoms. The TN:TP ratio (molar basis) was 24–30 initially and 35–110 at the end of the experiment; it was positively correlated with salinity and the presence of fish. Mechanisms accounting for the above patterns involve principally the biological activities of phytoplankton and periphyton, as modified by grazing by Artemia franciscana and Gammarus mucronatus, and the feeding and metabolic activities of the tilapia. The large reduction in water column TN and TP levels brought about by the fast-growing, phyto- and zooplanktivorous tilapia suggest that amelioration of the Salton Sea's hypereutrophic state might be assisted by a large scale, sustained yield fish harvesting operation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1003227624686
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  • 4
    Electronic Resource
    Electronic Resource
    Environment, seed rate, and N rate influence on yield of winter barley (1993)
    Springer
    Nutrient cycling in agroecosystems 34 (1993), S. 59-65 
    Details
    ISSN: 1573-0867
    Keywords: Barley ; environment ; nitrogen ; seeding rate ; yield ; yield components
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This study was conducted to determine the effects of rainfall and temperature during the growing season, seed rate, and N rate on grain yield and yield components of winter barley (Hordeum vulgare L.) on a Typic Haploxeralf soil in Santa Olalla (Toledo), Spain in 1986/7, 1987/8, and 1988/9. Two experiments were conducted each year using the 6-rowed variety ‘Barbarrosa’ and the 2-rowed variety ‘Reinette’. Both experiments used seed rates of 80, 160, and 240 kg ha−1 as whole plot treatments, and N rates of 0, 40, 80, 120, and 160 kg ha−1 as subplots. Responses to N depended on both the quantity and distribution of rainfall during the growing season, and temperature during grain fill. In the high rainfall, moderate grain-fill temperature year, increasing the N rate from 0 to 160 kg ha−1 increased grain yields (by 2.3 t ha−1), straw yields and the harvest index while maintaining the kernel weight for both varieties. In the low rainfall, high grain-fill temperature year, N rate had little influence on grain yield, but increased the straw yield, which reduced the harvest index, and also decreased kernel weight. Seed rate had no influence on grain yields even though wide variation in N rates, rainfall and temperatures occurred in the three-year study. Results from this study indicated that strategies to reduce (or avoid) water/high temperature stress during grain fill are necessary to assure more uniform yield responses to N application across years. However, decisions about seed rate can be made independently for conditions similar to those in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00749961
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  • 5
    Electronic Resource
    Electronic Resource
    Nutrient enrichment of Cabo Frio (Brasil) sea water for phytoplankton mass production (1984)
    Springer
    Hydrobiologia 111 (1984), S. 49-56 
    Details
    ISSN: 1573-5117
    Keywords: nutrient enrichment ; yield coefficient ; nitrogen ; phosphorus ; mass culturing ; phytoplankton ; sea water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Natural phytoplankton of Cabo Frio area was grown in 42 m-deep artificially upwelled seawater enriched with increasing concentrations of nitrogen or phosphorus. Respective values allowing maximum biomass, maximum uptake of initial reserve and maximum yield coefficient are rather conflicting. Notwithstanding, respective values of 75 µg at 1−1 nitrogen and 5 µg at 1−1 phosphorus, and therefore N:P = 15, appeared to be the best compromise for initial nutrient levels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00007380
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison between a chemical and a biological method to determine the N mineralization potential of temperate-humid region soils (1994)
    Springer
    Plant and soil 162 (1994), S. 147-150 
    Details
    ISSN: 1573-5036
    Keywords: biological method ; chemical method ; mineralization potential ; nitrogen ; soil incubation ; temperate humid-zone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The potentially mineralizable organic N of 33 different soils was estimated by a chemical test (hot extraction with 2N KCl) and the values compared with those previously obtained by a biological method (aerobic incubation in the laboratory). On average, the organic N solubilized by the chemical procedure was significantly lower than that mineralized by a two weeks aerobic incubation for all the soils as a whole. The same was true for soils developed over acid rocks and over sediments. However, the values obtained for the soils developed over limestone and basic rocks were similar by both methods. The values obtained by both methods were not significantly correlated neither when considering all soils together nor when considering different groups according to soil management or parent material. Significant correlations between both methods were only found when the soils were separated into two groups according to their organic N content: soils with less than 400 mg N 100 g−1 soil and soils with more than 400 mg N 100 g−1 soil. The organic N solubilized by the chemical procedure was significantly correlated with the hexosamine-N content; however, it was not correlated with the factors that control the biological mineralization of the organic N, except with the soluble Al content. Therefore, the chemical extraction did not seem to address the biologically active N pool in a selective way.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01416100
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