Leguminous cover crops are also the best and the cheapest source of nitrogen for the apple orchard, after they are well established. Their use may be overdone, however. Too much nitrogen results in a growth of wood at the expense of fruit buds. To avoid this it is often advisable to use non-leguminous and leguminous crops alternately, when the orchard is making a satisfactory growth. Sometimes also these two kinds of crops, as buckwheat and clover for example, may be combined with good results. When this is done one half the usual amount of seed of each should be used. EARLY PLOWING.--Many people make the common mistake of thinking that a green manure crop must be allowed to grow until late in June in order to secure the maximum amount of growth. There are several reasons why this is not good practice. In the first place cultivation is most essential in the early spring as has been pointed out. Then moisture is better conserved by plowing under the crop early and a better physical condition of the soil secured. Plowing early in the spring warms up the soil and sets plants to work more quickly. Lastly, material rots much more quickly in the early spring when moisture is more abundant, which is very important. An apple tree is as much a crop as anything grown on the farm and must be so regarded by those who would become successful orchardists. When it is not properly fed and cared for, good yields of fruit may not justly be expected. Especially is this true of an orchard which is being intercropped. But because of the fact that an apple tree is not an annual crop but the product of many years' growth, because its root system is deeper and more widely spread out than those of other crops, and because the amount of plant food removed in a crop of fruit is comparatively small, fertilization is less important than many persons would have us think. It is a fact that where orchards receive good cultivation and a liberal supply of humus commercial fertilizers give but medium results. ELEMENTS OF FERTILITY.--Three elements are necessary for the growth of apple trees, nitrogen, phosphoric acid, and potash. To these lime may be added, although its benefit is indirect rather than direct as a plant food. How badly any of these elements may be needed depends on the soil, its previous treatment, and on the system of management. By learning what are the effects of these elements on the tree and fruit we may determine under what conditions, if any, their use is advisable. Nitrogen promotes the growth of new wood and leaves, giving the latter a dark green color. In fact the color of the leaves and the amount of the wood growth are usually good indicators of the need of nitrogen. Nitrogen in excess develops over vigorous growth and prevents the maturity of wood and buds. It always has a tendency to delay the maturity of the fruit by keeping it growing late. On many varieties it tends to produce poorly colored fruits.