Nitrogen is one of the most important nutrients that plants need in order to grow adequately. Nitrates (NO3-) and ammoniacal (NH4+) ions are the main forms of nitrogen absorbed by plants. Ammonium ions are absorbed at a slower speed and converted into the nitrate form through nitrification. When nitrogen is added in insufficient or excessive amounts it can negatively affect production and productivity
· Studies have revealed two separate periods of , nitrogen absorption, the first one starting slowly after the buds have budded and extending to passage and the second one post-harvest and up to normal defoliation.
The second period of intense nitrogen absorption garnered 34% the overall requirements of the plant for the growing season.
· During the vegetative period the distribution of nitrogen within the plant was also investigated by showing the accumulation of nitrogen in the , fruits in the , leaves in the pruning wood and in the duct system which amounted to 35.8% , 31,4% , 14.4% and 18.7% respectively.
· Knowledge of uptake periods is particularly useful , but moving and distributing the added nitrogen in both periods is of particular interest.
* Determination of the amount of nitrogen to be added to each application is a more complex issue , but the finding that 60% the nitrogen reserves of the plant during the budding period come from what is added after harvesting highlights the importance of the applied post-harvest nitrogen fertilisation programme.
It was found that during the period of decline only 22% · the nitrogen content in the , plant corresponded to the amount added early in the summer (after flowering). Of this most of it is located (52%) growing vegetation and the rest in grapes (28%) and permanent parts of the plant (20%).
From the harvest period until the dormancy, the distribution of nitrogen within the plant is differentiated and shifted to its permanent parts. During this period only 6% ^ "Total nitrogen in the plant corresponds to that added in early summer , and is detected by 78".% at the roots and 22% in the other permanent parts.
The addition of nitrogen after harvesting in the previous season was also investigated. It was found that in 60% · the plant's nitrogen reserves at the start of the bud development are derived from the nitrogen absorbed during the post-harvest period and that 1⁄4 of the plant's nitrogen reserves are used until the end of the , flowering and until the end of the harvest 50% · the nitrogen reserves available at the time of the , bud development were used (Conradie 1980,1991,1992c).
Generally, three main periods of time during which nitrogen is added are used in production:
← During the development of , buds
after flowering and
after harvest.
Data collected during experimental work on the effect of application time and the amount of nitrogen added support the correctness of the above nitrogen addition times.
* Determination of the amount of nitrogen to be added to each application is a more complex issue , but the finding that 60% the nitrogen reserves of the plant during the budding period come from what is added after harvesting highlights the importance of the applied post-harvest nitrogen fertilisation programme.
Source: Bell S-J and P.A. Henschke , 2005. Implications of nitrogen nutrition for grapes , fermentation and wine. Australian Journal of Grape and Wine Research 11 , 242-295.
