52 BULLETIN 355, U. S. DEPARTMENT OF AGRICULTURE. 
to stock and the manure returned to the soil, very little potassium 
need be purchased except on farms located on marsh soils. 
EXERCISES, LESSON VII. 
Materials required. — Sodium nitrate, muriate of potash, sulphate of potash, kainit, 
acid phosphate, rock phosphate, bone meal, and of as many other fertilizer salts as 
possible; four 3-gallon crocks; ^ bushel of moist sand or loam; a handful of corn; a 
small teaspoon, a tablespoon; two or three cups. 
Solubility of fertilizer materials (Ref. No. 4, p. 240). — Place a teaspoonful of sodium 
nitrate in a cup and fill the cup two-thirds 'full of water. Stir for a few minutes. 
What happens to the fertilizer? When is a fertilizer considered soluble? Try the 
same test on muriate of potash, sulphate of potash, kainit, acid phosphate, rock 
phosphate, and bone meal. 
Fertilizer material in hill versus broadcast application. — Fill four 3-gallon crocks with 
moist clay or silt loam soil and treat as follows: 
(a) In the center make a hole about 2 inches deep and place in it three kernels of 
corn. On top of the corn place a tablespoonful of muriate of potash or any one of the 
other potash fertilizers; cover and water when necessary. 
(b) Repeat as in (a), but place the tablespoonful of the same kind of fertilizer 
2 inches deep and 3 inches away from the corn kernels. Cover and water when 
necessary. 
(c) Repeat as in (a), but use only a small teaspoonful of the same kind of fertilizer. 
(d) Determine the area of soil surface in this crock and apply as much muriate of 
potash as is equivalent to a 400-pound application per acre. Mix the fertilizer thor- 
oughly with the top 4 inches of soil and plant three kernels of corn 2 inches deep. 
Give all the crocks the same care and note carefully the effect of the different treat- 
ments upon the growth of the corn. 
(e) A small teaspoonful of potash fertilizer weighs one-fourth of an ounce. Calcu- 
late the amount of fertilizer required per acre if each hill were treated as in crocks (a) 
and (c), the corn being planted in hills 3| feet each way. 
(f) Similar tests may be made, using phosphate materials or mixed materials. 
What conclusions may be drawn from the results of these tests? 
PROBLEMS. 
1. An acre of dry sand or sandy soil 8 inches deep weighs in round numbers 2,500,000 
pounds; a clay or silt loam, 2,000,000 pounds; and a peat, 350,000 pounds. How 
many times heavier is sand than peat? 
2. A productive silt loam analyzed 0.11 per cent phosphorus. How many pounds 
of this element are contained in an acre 8 inches deep? 
3. A 75-bushel corn crop removes from an acre approximately 16 pounds of phos- 
phorus. How many such crops of corn can be supplied by the total amount of phos- 
phorus in an acre 8 inches of that fertile silt loam? 
4. A certain clay loam contains 0.049 per cent phosphorus. How many more pounds 
of this element are contained in an acre 8 inches of the fertile silt loam than in this 
clay loam? 
5. How many 75-bushel corn crops will the phosphorus in an acre 8 inches of the 
clay loam supply? Is any soil able to produce a 75-bushel corn crop every year until 
the soil supply of phosphorus is entirely exhausted? Explain. (Ref. No. 5, pp. 
107, 108.) 
6. A silt loam soil was cropped almost continuously for 63 years. It is now in a 
badly exhausted condition and analyzes only 0.04 per cent phosphorus. A sample 
of this same soil which was never cropped contained 0.074 per cent phosphorus. 
