Nitrogen extraction from soil

Iindau and Spalding [21] have studied the effects of 2 M potassium chloride extractant ratios of between 1 1 to 1 10 on nitrate recovery in nitrate and nitrite extractions from soil. Preliminary data indicated that concentrations of extractable nitrate and nitrogen isotopic values were influenced by the volume of extractant. The 1 1 extractions showed decreasing nitrogen isotope values with increasing nitrate levels, whereas in the 1 10 extractions these values were independent of each other. Incomplete extraction occurred for the 1 1 ratios. The ratio required for maximal recovery was not determined. 

We first deal with humic substances extracted from soils formed under different climates because climate, as will be shown later, has a profound effect on the types and concentrations of nitrogen compounds present in humic substances. 

Fulvic acids extracted from soils formed under cool temperate climates (Table 3) contain similar proportions of amino acid nitrogen and amino sugar... 

Differences in the nitrogen distribution in humic substances extracted from soils developed under cool temperature and tropical climates are sum-... 

Humic matters are present in almost all natural waters. They are extracted from soil and peat. The solubility of the constituents of the soil humus depends on the type of soil, period of contact with water, pH of the water and its composition, and depending on such factors, the humic materials are present as either true or colloid solutions. In waters from peat moors the concentration of humic matters is usually tens of mg 1 . In some stationary waters as much as 500 mg 1 can be found. In waters from peat moors a low pH is typical (it can be lower than 4), high oxidation potential and the presence of iron, manganese and ammonia nitrogen (anaerobic processes). Iron and other metals are present in an organic complex form and they are difficult to remove [52, 53]. 

Plant samples are homogenized with sodium hydrogencarbonate aqueous solution to prevent decomposition of the analytes during homogenization. Imibenconazole and its primary metabolite, imibenconazole-debenzyl, are extracted from plan materials and soil with methanol. After evaporation of methanol from the extracts, the residues are extracted with dichloromethane from the residual aqueous solution. The dichloromethane phase is cleaned up on Florisil and Cig columns. Imibenconazole and imibenconazole-debenzyl are determined by gas chromatography/nitrogen-phosphorus detection (GC/NPD). 

The chemical structures of the amino acids found in soil-solids are shown in Fig. 6 [25] while the quantities of amino acids found in HS extracted from various solid phases are represented in Fig. 7 (data were collected from Ghosh and Schnitzer [37] and Schnitzer et al. [38]). High levels of amino acid nitrogen were found in HA, FA, and humin fractions, indicating incorporation of common acidic and some neutral amino acids, particularly glycine, alanine, and valine. 

Calculation. Subtract the blank titre from that of the soil extract, multiply by 700 and divide by y(see Method 5.5b.i) to give the mg kg nitrate-N, potassium chloride extractable, in the air-dry soil. Express results for oven-dry soil as in Method 5.2, Calculation (2). Sum the extractable ammonium-N and nitrate-N to obtain the total mineralizable nitrogen in the soil. 

The aroma compounds from the tropical fruits described in this chapter can be very important for consumers and industry as they are exotic and extremely pleasant however, the production of these compounds by biotechnological processes should be emphasised since the extraction from the fruits is a hard task. Many tropical soils contain less nitrogen and phosphorus, have lower capacity to absorb fertilisers, and therefore have lower conventional productive capacity, but some tropical soils have been very intensively farmed and further intensification is possible in other areas. Thus, the evaluation of a sustainable agriculture in tropical regions requires a sophisticated approach including the estimation of the risk of microbial or insect infestations. As many fruits go directly to fresh markets or to immediate processing, a continuing supply of the flavour manufacturers in the future is not completely assured. 

Greco [40] determined optimal extraction conditions for the recovery of nitrogen-containing aromatic compounds from soil. 

In addition to the previous three commercial extractors, some authors have developed custom models [78,79], adapted in most cases from a supercritical fluid extractor [25,58,80]. For example, Heemken et al. altered a Suprex SF extractor for use in ASE [81] they disconnected the syringe pump from the COj cylinder and filled it with a suitable ASE solvent. The restrictor was replaced with a stainless steel capillary tube leading into the trapping vial and an additional nitrogen pipe was installed at the inlet valve of the extraction vessel for purging after extraction. In the extraction of PAHs from soil [79], a custom extractor and commercially available equipment provided equivalent results on the other hand, in the extraction of benzene and toluene from soil [78], the former provided even better results than the latter. 

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