Phosphorus sorption isotherms were constructed for soils which varied in mineralogy, texture, and past history of phosphate fertilization. Equilibrating conditions were: 25C, 0.01M CaCl2, and 6 days. Effects of heavy phosphate fertilization of soils with high phosphate sorption capacities were evident in phosphate sorption isotherms 10 years later. The sorption curves were used as a basis for fertilizing soils in pots so that phosphate in soil solutions varied from about 0.01 to 1.8 ppm P. Millet (Pennesitum typhoides, var. Gahi‐1), was grown for 4 weeks. Yields approached 95% maximum when phosphate in soil solutions was adjusted to 0.2 ppm. The phosphate concentrations at which near maximum yields were attained were little influenced by soil texture or past fertilizer treatments, but absolute yields of millet growing in the sandy Norfolk soil (low phosphate buffering capacity) was greatest if the soil had been previously phosphate fertilized.

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Several methods for evaluating the sulfur status of soils were compared. Among chemical procedures used, water and phosphate extractions gave the best agreement with sulfur A values and total sulfur uptake by alfalfa from Nebraska soils. Water was an inefficient extractant of sulfate from a Hawaiian Latosol. Calcium phosphate solution was a more convenient extractant than KH 2 PO 4 for both Nebraska and Hawaii soils.

Calcium silicate slag increased sugar yields 12 tons/hectare in a field where phosphate extractable soil silicon and trichloroacetic acid (TCA) extractable silicon of sugar cane (Saccharum officinarum) leaf sheaths were about 20 ppm. Large amounts of P or lime did not alleviate leaf freckle whereas slag did so to a marked degree. Acid solutions of phosphate, sulfate, acetate, and water can be used successfully as extractants for soil silicon. The general order for extractable silicon from soils developed on basalt and alluvium was: Humic Ferruginous Latosol < Humic Latosol < Low Humic Latosol < Dark Magnesium clay. This is also the order of decreasing weathering for these soils as indicated by total soil silicon and occurrence of secondary minerals. Leaf sheath silicon (TCA extractable) was especially well correlated with log extractable soil silicon (r = 0.97 for water extraction). Irrigation waters may contain much silicon and contribute greatly to the supply of extractable soil silicon and to plant silicon.

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