PO 18. Compare and contrast the following approaches for making fertilizer recommendation

Soil buildup and maintenance recommendations aim to evaluate soil nutrient levels, alter these levels via fertilization and/or crop removal until they are at an optimal level, and then maintain that level.  Fertilization is heavy and quick, increasing soil test values rapidly over a few years, and then the subsequent maintenance fertilizer applications are made to crop removal levels.

The buildup part of the recommendation is determined by the expected crop response to the added nutrients.  Fertilizer recommendations are made using an index, which predicts yield response ased on soil test levels and different application rates.  The maintenance part of the recommendation is based on replacing the amount of nutrient expected to be removed by the crop.  This should keep the soil test level from falling below optimum between soil tests.  When the soil test reaches a level where crop removal will not reduce the soil test level to below optimum, no additional nutrients are added.  The crop is allowed to draw the nutrient levels down into the optimum range.  While this method is fairly simple, it ignores non-agronomic losses of nutrients (leaching, volatilization, etc) and requires knowledge of crop nutrient content.

Below is an example of soil buildup and maintenance recommendations.  Soils are classified as either fertile or not, which influences the amount of nutrients added.