However, the nutrient level of organic materials is lower, rate of release is slower, and levels of minerals may vary and are not balanced. The information below will help you interpret differences in nutrient content and relative availability of organic materials. Fruits and vegetables often have high nitrogen demands, and it can be difficult to provide sufficient nitrogen from an organic source throughout the growing season of the crop. In addition, availability of nitrogen late in the season can make perennial plants such as raspberries and apples susceptible to winter injury. It is a challenge to provide plants with a readily available organic nitrogen source early in the growing season, yet have it less available in late summer.
Much variability exists in the composition of similar organic materials.
For example, manure with straw will have a different nitrogen composition than pure manure, and the rate of nitrogen release may be slower because of the higher amount of carbon in the straw. The table below lists the approximate composition of various organic materials, and the nitrogen, potassium and phosphorus that can be provided from them. Knott's Handbook for Vegetable Growers. 6 2.5 1.7 Slow Med.