Nitrogen release from soils

Table 9-7. Fraction (Average Percent) of Fertilizer Nitrogen Released from Soils as N20... 

The amount of nitrogen released from soils of similar type is usually closely related to the amount of nitrogen or organic matter in the soil. This is illustrated in Fig. 14.1 taken... 

L. S. Brophy and G. H. Heichel, Nitrogen release from root of alfalfa and soybean grown in sand culture. Plant and Soil 116 11 (1989). 

Palm, C. A. and Sanchez, P. A. 1991. Nitrogen release from the leaves of some tropical legumes as affected by their lignin and polyphenolic contents. Soil Biol. Biochem. 23 83-88. 

CDU in pure form is a white powder. It is made slowly available to the soil solution by nature of its limited solubihty in water. Once in the soil solution, nitrogen from CDU is made available to the plant through a combination of hydrolysis and microbial decomposition. As with any CRE which is dependent on microbial action, the mineralization of CDU is temperature dependent. Product particle size has a significant effect on CDU nitrogen release rate. Smaller particles mineralize more rapidly because of the larger surface contact with the soil solution and the microbial environment. The rate of nitrogen release is also affected by pH because CDU degrades more rapidly in acidic soils. 

Although these studies utilizing Incorporated debris are valuable because they show the potential for allelochemlcals to be released from plant litter, they suffer from a disadvantage. The amount of debris added and Its carbon to nitrogen ratio might lead to alterations In nutrient contents In the soil as the result of proliferation or shifts In populations of micro-organisms. Thus, a control In which a material of similar C/N ratio but lacking allelochemlcals needs to be Included for such studies to be conclusive. The above studies did not Include such controls and thus are not definitive. 

In the vineyard, nitrogen must be fixed into the soil naturally. This is done by planting leguminous crops such as clovers or beans between the vines. These plants have bacteria living on their roots that fix nitrogen from the air. When the plants are dead, they are ploughed in, decay and release nitrogen into the soil. At some wineries, commercial crops such as strawberries are rotated in, which add to the profitability of the vineyard. 

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