SOIL NITROGEN : SUPPLY PROCESSES AND CROP REQUIREMENTS

Of all the soil elements essential for plant growth, nitrogen is the most likely to limit crop growth. Attention is focused on some of the principles affecting nitrogen availability and use which provides for maximum efficiency in the production of cereal crops. In forecasting fertilizer nitrogen needs, several use factors are collectively evaluated. Crop requirements are determined first. The kind of crop, expected yield, amount of nitrogen absorbed and used by the plants at the projected yield level. Expected yield levels depend mostly on soil properties and climatic factors. The amount of nitrogen expected from the soil and natural resources are assessed through mineralization, biological fixation, and additions from rainfall. An evaluation of all these processes are obtained by measuring the yield of a crop when no nitrogen fertilizer has been applied.