A 3-yr field study in Quebec assessed effects of tillage (no-till, reduced, or conventional) × crop residues (removed or retained) on soil nitrate under corn production. Fall nitrate levels were greatest in plots without residues 1 yr after treatments began, but not thereafter. No-till and conventional tillage had similar values, but sometimes differed from reduced tillage. Key words: Nitrate, corn, no-till, reduced tillage, conventional tillage, crop residues
The possibility of nitrate adsorption in 18 samples representing 11 soil types from the lower Fraser Valley of British Columbia was examined by differential extraction, equilibration and column leaching methods. Contrary to what was expected if nitrate was adsorbed by the soil, more nitrate was extracted by water than by 2 M KCl from some of the samples. Observations in related studies of greater microbial growth in 0.1 and 1.0 than in 2.0 M KCl extracts after more than 1 wk of storage and of different equilibrium results when conducted with and without toluene supported the conclusion that microbial or enzyme activity caused the larger amount of nitrate to be extracted by water than by 2 M KCl. Both equilibration and column leaching methods measured adsorption in some of the soil samples, but the amounts in the various samples by the two methods were not always the same. The equilibration method was analytically more precise than the column leaching method because it was simpler and required fewer measurements, but the column leaching method was considered to match more closely the soil to water ratio that would occur in the field. The equilibrium method found from 0 to 34% adsorption of the nitrate when added at a concentration not exceeding 50 μg N g−1. Further work is required to develop a practical method to meaningfully quantify nitrate adsorption in soils. The presence of nitrate adsorption has important implications for the interpretation of soil nitrogen research data and should possibly be included in nitrogen simulation models. The observation of microbial or enzyme effects on extraction of nitrate from soil shows the importance of using extraction solutions (e.g., those of high salt concentration or that contain a microbial inhibitor) that eliminate that possibility. Key words: Nitrate reactions, anion adsorption, nitrogen process, microbial effect, microbial inhibition
Characteristics of the enzymes involved in the assimilation of NO3− and NH4+, in particular the nitrate and nitrite reductases, glutamine synthetase, glutamate synthase, glutamate dehydrogenase, glutamate decarboxylase, and asparagine synthetase, are described. The cellular organization of these enzymes in root and leaf tissues are assessed in view of recent research developments that utilize various tissue blotting techniques. Regulation of nitrate assimilation is analyzed at the physiological, biochemical, and molecular levels. Key words: nitrate, ammonium, assimilation, regulation.
Our study consisted of three sites, continuously cropped with grain corn and fertilized annually with N rates ranging from 0 to 336 kg ha−1. Soil NO3-N was measured to 90 cm at least twice yearly over three cropping seasons. In Ontario’s semi-humid environment, soil nitrate (NO3-N) is usually completely lost from soil profiles over the winter months by leaching and denitrification. We found this to be generally true over 3 yr on a sandy loam and on a silt loam soil. However, on a clay loam soil in 2 of 3 yr NO3-N concentrations in the spring were almost as high as those of the previous fall. Key words: Nitrate, corn, continuous cropping, retention
Nitrate, given intraruminally (0.1 g NO−3 per kg of body weight) to cattle, stimulated the capacity of the rumen microflora to degrade nitrite (NO−2) and nitrate in vitro. Threefold to fourfold increases in rates of NO−2 and NO−3 reduction were observed during NO−3 treatment. The treatment also appeared to stimulate nitropropanol degradation but this effect was less pronounced. The enhanced capacity of rumen microbes to degrade NO−2 and NO−3 was transferred to noninduced (untreated) animals housed in adjacent pens. The transfer of induced metabolism was not observed when induced animals were widely separated from the noninduced ones. This apparent transfer of microbial activities between adjacent animals may complicate studies in which treated and control animals are not separately housed. Key words: Nitrate, nitrite, nitropropanol, induction, degradation, cattle
The distribution of NO3-N in the soil, and N uptake by the crop during the first 12 yr of a long-term rotation study at Swift Current, Saskatchewan were studied. A considerable amount of NO3-N appeared to be leached beyond the rooting zone of the cereal crop in years of above average precipitation and also in some relatively dry years with heavy spring rains. Thus, leaching of NO3-N seemed to occur even under continuous wheat rotations. At all times there was considerable NO3-N situated at the 60- to 120-cm depth. In wet years N uptake by the plants reduced the amount of NO3-N located in the subsoil, but in dry years the amount of NO3-N in the subsoil remained higher throughout the growing season. The latter could result in groundwater pollution, especially if such a soil was fallowed the next year. Fall rye (Secale cereale L.) made more efficient use of mineral N than spring-sown crops. In dry years more NO3-N persisted in the root zone of N-fertilized wheat than in the root zone of unfertilized wheat, but in wet and average years there was little difference due to N application. The average rate of net NO3-N production in fallow land from spring thaw to freeze-up (166 days) was 107 kg∙ha−1. Values ranged from about 60 to 175 kg∙ha−1 with the lowest values being obtained during very dry or very wet years. The quantity of N mineralized (kg∙ha−1) between spring thaw and freeze-up was related to precipitation (mm) by the equation Nmin = 29.0 + 0.20 precipitation for the 0- to 60-cm depth (R2 = 0.65*). Key words: Nitrate leaching, N uptake, crop rotations, N mineralization rate
A laboratory based column leaching experiment was set up to study the retention of nitrate (NO3- ) and phosphate (PO43-) in three Bangladesh soils (Ghatail, Tejgaon and Sonatola) and their subsequent uptake by plants (Ipomoea aquatica). The investigation showed that the higher the clay contents, the higher was the retention of NO3- and PO43- by the soils and the lesser was their transfer into the growing plants. Again the higher the pH values in soils, the lower was the retention of NO3- and PO43- elements retained in the soils and the higher was the transfer of the elements into the growing plant. Retention of nitrate and phosphate followed the order: Ghatail>Tejgaon> Sonatola while the transfer to plant was in the order Sonatola>Tejgaon>Ghatail.
Key Words: Nitrate, Phosphate, Retention, Leaching, Plant Uptake.
DOI: 10.3329.bjsir.v43i1.858
Bangladesh J. Sci. Ind. Res. 43(1), 67-76, 2008
Retention of Nitrate and Phosphate in Soil and their Subsequent Uptake by Plants