These operations when properly and thoroughly done tend to supplement the work of the plow in fitting the soil to absorb rain and in making a mulch to check loss by surface evaporation. The entire surface should be worked and the soil should be left smooth and not in ridges. Rolling cutters and spring-toothed harrows are apt to leave ridges and should have an attachment for smoothing the surface or be followed by a smoothing harrow. Cultivators used to make mulches to save water should have many narrow teeth rather than few broad ones. If a large broad-toothed tool is used to destroy grass and large weeds it should be followed by a smoother to level the ridges and thus lessen the evaporating surface. The soil should be cultivated as soon after a rain as it can be safely worked. Rolling compacts the soil and starts a quicker capillary movement of water toward the surface and a consequent loss by evaporation. When circumstances will permit, the roller should be followed by a light harrow to restore the mulch. Ridging the land tends to lessen the amount of moisture in the soil because it increases the evaporating surface. It should be practiced only on wet land or in early spring to secure greater heat. Drains placed in wet land remove free water to a lower depth and increase the depth of soil occupied by capillary water and therefore increase the body of soil available to plant roots. MANURES AND SOIL WATER Humus, as we learned in Chapter IV, has a very great and therefore important influence over the water-absorbing and water-holding powers of soils. Therefore, any of the farm practices that tend to increase or diminish the amount of humus in the soil are to be seriously considered because of the effect on the water content of the soil. For this reason the application of barn manures and green crops turned under tend to improve the water conditions of most soils. The mixing of heavy applications of coarse manures or organic matter with light sandy soils may make them so loose and open that they will lose moisture rapidly. When this practice is necessary the land should be rolled after the application of the manure. METHODS OF CROPPING AND SOIL WATER Constant tillage hastens the decay of organic matter in the soil. Hence any method or system of cropping which does not occasionally return to the soil a new supply of humus tends to weaken the powers of the soil toward water. All of the operations and practices which influence soil water also affect the other conditions necessary to root growth; namely, texture, ventilation, heat, and plant food, and those operations and practices which properly control and regulate soil water to a large degree control and regulate soil fertility. SELECTION OF CROPS WITH REFERENCE TO SOIL WATER