But more important than any of the above-mentioned conditions is the nature of the crop itself. Our knowledge of the requirements of the different farm crops is still very imperfect. A very wide experience, however, of the effect of different manures on different crops, has conclusively proved that their manurial requirements differ very considerably. The subject is complicated by other considerations, such as the nature of the soil, &c.; but notwithstanding this fact, certain points seem to be pretty well established. In seeking to understand the respective requirements of the different crops for different fertilisers, two important considerations must be borne in mind. These are--(1) _the quantities of the three fertilising ingredients--nitrogen, phosphoric acid, and potash--which different crops remove from the soil;_ and (2) _the different power crops possess of assimilating these ingredients._ _Amounts of Fertilising Ingredients removed from the Soil by different Crops._ The most convenient way of instituting a comparison between the requirements of the different crops in this respect is by calculating the amount, in pounds, of nitrogen, phosphoric acid, and potash, which average amounts of the different crops remove per acre. The following table shows this for the common crops:-- FERTILISING INGREDIENTS REMOVED FROM SOIL. ----------------------------+-----------+------------+---------- | Nitrogen. | Phosphoric | Potash. | | Acid. | ----------------------------+-----------+------------+---------- Mangels {Root, 22 tons | 87 | 36.4 | 222.8 {Leaf | 51 | 16.5 | 77.9 |-----------|------------|---------- Total crop | 138 | 52.9 | 300.7 |-----------+------------+---------- Turnips {Root, 17 tons | 63 | 22.4 | 108.6 {Leaf | 49 | 10.7 | 40.2 |-----------+------------+---------- Total crop | 112 | 33.1 | 148.8 |-----------+------------+---------- Beans {Grain, 30 bushels | 77 | 22.8 | 24.3 {Straw | 29 | 6.3 | 42.8 |-----------+------------+---------- Total crop | 106 | 29.1 | 67.1 |-----------+------------+---------- Red clover hay, 2 tons | 102 | 24.9 | 83.4 |-----------+------------+---------- Swedes {Root, 14 tons | 70 | 16.9 | 63.3 {Leaf | 28 | 4.8 | 16.4 |-----------+------------+---------- Total crop | 98 | 21.7 | 79.7