MAINTENANCE OF FERTILITY

The important factors in maintaining or increasing the fertility of the soil are: 

The mechanical operations of tillage, especially with reference to the control of soil water.

The application of manures and fertilizers, especially with reference to maintaining a supply of humus and plant food.

Methods or systems of cropping the soil, with reference to economizing fertility.

CHAPTER XVII

SOIL WATER

The more important tillage tools and tillage operations we studied in Chapters XI and XII.  They will be noticed here only in connection with their influence over soil water, for in the regulation of this important factor in soil fertility the other conditions of fertility are also very largely controlled.

IMPORTANCE OF SOIL WATER

“Of all the factors influencing the growth of plants, water is beyond doubt the most important,” and the maintaining of the proper amount of soil water is one of the most important problems of the thinking farmer in controlling the fertility of his soil.

NECESSITY OF SOIL WATER

The decay of mineral and organic matter in the soil, and the consequent setting free of plant food, can take place only in the presence of moisture.  The plant food in barn manures and crops plowed under for green moisture, can be made available only when there is sufficient moisture in the soil to permit breaking down and decomposition.

The presence of moisture in the soil is necessary for the process of nitrification to take place.

Soil moisture is necessary to dissolve plant food.  Plant roots can absorb food from the soil only when it is in solution, and it seems to be necessary that a large quantity of water pass through the plant tissues to furnish the supply of mineral elements required by growth.

Moisture is necessary to build plant tissues.  The quantity of water entering into the structure of growing plants varies from sixty to as high as ninety-five per cent, of their total weight.

During the periods of active growth there is a constant giving off of moisture by the foliage of plants and this must be made good by water taken from the soil by their roots.

In a series of experiments at the University of Wisconsin Agricultural Experiment Station, it was found that in raising oats, every ton of dry matter grown required 522.4 tons of water to produce it; for every ton of dry matter of corn there were required 309.8 tons of water; a ton of dry red clover requires 452.8 tons of water to grow it.  At the Cornell University Agricultural Experiment Station, a yield of potatoes at the rate of 450 bushels per acre represented a water requirement of 1310.75 tons of water.