Note 24 — Chapter VIII
Reading edition
In order to yield a crop of twenty-five bushels per acre the soil must supply 110 lbs. of nitrogen, 45 lbs. of phosphoric acid, 30.5 lbs. of lime, 14.5 lbs. of magnesia, and 142 lbs. of potash; these are approximately the mineral elements taken out of the soil with each crop, and it is needless to say that they must be replaced or the grain will starve for want of nutrient substances.