Extractable sulfur, accumulated in the lower horizons, may be unavailable to shallow-rooted crops but may be available to deep-rooted plants, except in early stages of growth. Thus cotton responded to sulfur in certain soils in Alabama, but alfalfa and sericea lespedeza did not. Seedling plants often are deficient in sulfur throughout the Southeast; as their roots extend into deeper horizons, however, the deficiencies may disappear and yields may be normal or nearly normal.

Deficiencies of sulfur may persist throughout the growing season in the Northwest an indication that subsoil accumulations of extractable sulfur do not occur there. Sufficient research has not been completed to determine how widely the pattern extends beyond the Red-Yellow Podzolic group, however.

Additions of sulfur in rainwater may be adequate for crop production in industrial areas, but they only supplement the supplies in areas of potential deficiency of sulfur.

Rainwater is said to add about 209 pounds of sulfur an acre annually near Chicago, 127 pounds near Gary, Ind., and 40 to 60 pounds near smaller industrial centers. Even the smaller additions are enough for normal crop production.

In the Southeast, in the area south of the Virginia-Kentucky border and in areas away from industry, rainwater has added only 5.4 pounds of sulfur an acre a year. In six rural areas in Nebraska, a 2-year study gave a corresponding value of 6.2 pounds an acre a year. An estimated 6 pounds of sulfur an acre a year are added in precipitation in Washington. Sulfur accretions of this amount alleviate, but do not end, deficiencies of sulfur if other supplies are inadequate.

2. These charts show how increased applications of nitrogen fertilizer to wheat in Washington increased the requirement of the crop for sulfur. On this Palouse silt loam, which is low in sulfur, application of 1 pound of sulfur per acre increased wheat yields up to 7 bushels per acre in 1954. The crop yield was reduced in 1955 when nitrogen was applied alone, but it increased it bushels per acre with both nitrogen and sulfur.

Additions of sulfur in the irrigation water may be enough to supply the total crop requirements. Western river waters contain 6 pounds to 2 thousand pounds of sulfur an acre-foot of water. The average is 50 pounds. The sulfur content of most rivers is lowest near their source and increases as the flow is supplemented with drainage water from irrigation projects. In only a very few areas in the West is sulfur fertilization of irrigated crops required for the maximum yields.

The sulfur content of well waters, though highly variable, generally is lower than that of river waters.

As to fertilizers, normal superphosphate contains about 11 percent of sulfur in the form of gypsum. Ammonium sulfate contains about 24 percent, and potassium sulfate about 16.5 percent. The average mixed fertilizer sold in the United States has about 7.5 percent.

In the Northwest, increases in yields of alfalfa from applications of superphosphate and potassium sulfate, formerly attributed to the primary constituents of those fertilizers, were found later to be largely responses to sulfur.

The equivalent of about 1.4 million tons of sulfur was applied in primary fertilizers in the United States in 1955. Additions in secondary nutrient fertilizers, liming materials, manures, and miscellaneous items (including insecticides and fungicides) brought the total close to 2 million tons that year.

That total is large, but the additions of sulfur from those sources were not uniformly distributed and perhaps were inadequate in some areas where soils were deficient and rainfall and irrigation water added little sulfur.

Fertilizers that are essentially sulfur-free have been used increasingly. Ammonium nitrate, anhydrous ammonia, urea, and ammonia solutions are examples among the nitrogen carriers.

The use of concentrated superphosphate and other phosphorus carriers with little sulfur has been expanding.

We recommend that farmers in areas of potential deficiency should have a planned program of adding sulfur instead of depending on incidental applications in ordinary fertilizer materials.

Losses of sulfur from soils are due mainly to leaching, erosion, and removal by crops.

Some sulfur is lost from soils of humid regions in drainage water. Measured losses from eight soil types in Illinois maintained in fallow ranged from 1.5 to 57 pounds of sulfur an acre a year; the average was 30 pounds. The larger losses occurred from the more permeable and more fertile soils. Annual losses from a Fayette silt loam with 10 percent slope in Wisconsin were approximately 1 pound an acre when crops were grown and 3 pounds an acre from uncropped soil.

The measurements in both States were made in lysimeters that permitted runoff and probably are fairly applicable to sloping upland soils. Earlier measurements, made in lysimeters that did not permit runoff, were considerably higher.

Sulfur losses from erosion have been estimated to average about 6 pounds an acre.

The losses may deplete soil supplies of sulfur, except perhaps in industrial and irrigated areas where accretions may exceed losses.

A balance sheet of the sulfur economy of soils and crops in the United States would appraise these additions and losses. It would be expected that soils well supplied with organic matter and occurring near industrial areas would not at present need sulfur fertilization. Requirements in such areas may change, particularly if sulfur-free fertilizers come into wide use or coal is replaced as fuel.