SOIL FERTILITY

Timaru Herald, Volume CXLVIII, Issue 21821, 26 November 1940, Page 3

SOIL FERTILITY

Loss Of Plant Foods MEETING THE DRAIN There is often misunderstanding as to the loss of plant foods from the soil. Such plant foods as phosphorus and potassium (potash) are leached from the soil only slightly. They are removed when the soil is washed away and are removed by or in other crops, but only slightly by other means. Even nitrogen, when applied in its most readily soluable form, such as nitrate of soda, is not leached from the soil or lost nearly as readily or as much as formerly thought. The effects of one application arc often seen in the second, or even the third crop, after its application. Of course, soils without a compact sub-soil, Ic.se plant foods more readily than clay soils or those rich in organic matter. That is, plant foods applied in commercial fertilisers are not retained in sandy soils as long or as well as in heavier soils. That is one reason why sandy soils are often less fertile than the stiffer soils. As a chain is no stronger than its weakest link, so a soil is no more productive than its weakest plant food. Nitrogen will not take the place of phosphorus or potassium, nor will any one of these take the place, or do duty for any other to any large extent. Rotation of Crops Another basic fact in this connection is that no rotation of crops, no system of cropping or farming will add to the store of phosphorus or potassium in the soil. In fact, all systems of farming and all rotations reduce the supplies of plant food in the soil, in all crops or animals removed. Some crops and some systems of farming reduce the supplies of these two plant foods more rapidly than do others, but all have a tendency to lessen rather than increase the supplies of these plant foods in the soil. Moreover, if a soil is already, or by poor farming, becames deficient in either or both of these plant foods, they can only be put in the soil through commercial fertilisers. It must also be remembered that no matter how much of any plant food there may be in a soil, if it is not in such a form that the plant roots can get at it, it does the growing crop no good. Of course, chemical plant foods or commercial fertilisers are not the only factors in crop production, or in the making of fertile soil, but an abundant supply of available plant foods is essential to a fertile soil.