Nitrogen plant available

Agronomic Properties and Nutrient Release Mechanism. The conversion of UF reaction products to plant available nitrogen is a multistep process, involving dissolution and decomposition. Materials are slow to enter the soil solution by virtue of their low solubiUty. Longer polymer chain products are less soluble than shorter chains and take longer to become available to the plants. 

Once in the soil solution, urea—formaldehyde reaction products are converted to plant available nitrogen through either microbial decomposition or hydrolysis. Microbial decomposition is the primary mechanism. The carbon in the methylene urea polymers is the site of microbial activity. Environmental factors that affect soil microbial activity also affect the nitrogen availabiUty of UF products. These factors include soil temperature, moisture, pH, and aeration or oxygen availabiUty. 

Nitrogen fixation Conversion of atmospheric nitrogen into organic nitrogen compounds available to green plants a process that can be carried out only by certain strains of soil bacteria. 

The morphological and physiological dissimilarities between mycorrhizal symbi-o.ses probably determine their success and their distinct patterns in different ecosystems (92). Nitrogen (N) available to both AM and ectomycorrhizal plants should not be regarded as a single pool open to free competition. Specialization of its acquisition and utilization in a given habitat is an important feature of plant and microbial community structure, while the fact that the ability to exploit its sources (and tho.se of other limited nutrients) is not the same in all species may result in niche differentiation (93). If habitat specialization is a reflection of differences between mycorrhizal types, ectomycorrhizal and AM species could cooccur because they exploit different niches in the. same ecosystem. 

No-till methods, with more rapid replenishment of plant-available soil water, have paved the way for more intensified cropping, even to the point of eliminating summer fallow in some areas and some years. As a result, soil organic carbon and nitrogen concentrations are enhanced, especially near the soil surface (Sherrod et al, 2003). 

Nitrogen is a component of amino acids that make up proteins chlorophyll (the molecule that captures the sun s energy) enzymes and the genetic material, nucleic acids. Therefore, this nutrient is required in large amounts by all plants and forms one of three primary nutrients. Although nitrogen is available in abundance... 

The salt is produced in small amounts commercially in the United States, Israel, and Norway by the reaction of KCl with nitric acid. Though the salt is an attractive fertilizer material containing the two essential nutrients, nitrogen and potassium, in plant-available form, it is expensive to produce and thus enjoys only a limited market. 

Only organic fertilizers can be used in organic farming. To make sure that the nitrogen is available to the plants at the time of greatest need, it is important to take into account the time needed to convert the nitrogen to a form that is available to the plant (speed of action). The speed of action depends on the fertilizer, the soil conditions and the weather. Farm manures can also be used, except for blueberries. Only 10% of the total nitrogen in compost and 50% of that in cattle manure can be included in the nutrient balance in the first year. In the case of other nutrients, 100% is included. 

The N requirements of fruit trees vary within the growing season and are essentially limited to the months April to July, with a peak in June. Half of the N requirements in spring are met from the tree s own reserves. The provision of N to meet requirements is thus more a matter of timing than of quantity. Only a few N fertilizers, which are mineralized relatively quickly, are permitted in organic farming. This is why the application of N fertilizers needs to be precisely timed. Any competition from companion plants in the row of trees must be controlled in time, e.g. by mechanical tilling, so that mineralization is accelerated and the nitrogen is available for use by the trees. The N supply of an orchard should be optimized by means of N analyses. 

Column 2 of Table 1.1 shows the ratio of plant content to soil content of important ions. The hydrogen, carbon, and oxygen ratios are omitted because these ions are not derived directly from soils. The ratios are crude indices of the relative availability of soil components to plants. Calcium, sulfur, nitrogen, and potassium in soils are more available than iron and manganese. One goal of soil chemistry is to explain why ions in soils vary widely in their degree of plant availability. 

By microbial decomposition the organic bond nitrogen (—NH2-group) is transformed to the plant-available forms NH4 and at the rate of 1 to 3% armually ... 

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