104 AGRONOMY 



lack of another ; a sufficient amount of each must be present. 

 Often supplying a single lacking element in the soil will more 

 than double the returns from the crop. 



Elements that may be lacking. Soils are seldom deficient in 

 sulphur, iron, or magnesium, and calcium is usually abundant 

 enough, though it may sometimes be lacking even in soils de- 

 rived from the weathering of limestone rocks, because it is 

 easily dissolved and carried off by the water. Phosphorus, nitro- 

 gen, and potash, however, belong to a different category. They 

 are seldom abundant in any soil and are so rapidly removed 

 by crops that the lack of one of them is usually the cause of 

 a decreased yield. Soils may be analyzed by the chemist and 

 the exact amount of each mineral constituent determined, but 

 there are various ways of making the plants themselves tell 

 what essential element is lacking. One of the best methods 

 of determining this is to make ten plots, side by side, in soil 

 as nearly uniform as possible, and add to each plot a different 

 fertilizer or combination of fertilizers containing the elements 

 likely to be lacking. The usual arrangement is as follows : 



Plot 1. Nitrogen as nitrate of soda at the rate of 160 Ib. to the acre, or 

 dried blood at the rate of 700 Ib. to the acre. 



Plot 2. Potash as muriate of potash at the rate of 80 Ib. to the acre, or 

 potassium sulphate at the rate of 200 Ib. to the acre. 



Plot 3. Phosphorus as acid phosphate at the rate of 320 Ib. to the acre, 

 or bone meal at the rate of 200 Ib. to the acre. 



Plot 4. Calcium as lime at the rate of 40 bu. to the acre. 



Plot 5. Nothing. This plot serves as a check for comparison. 



Plot 6. Nitrogen and potash in the proportions given above. 



Plot 7. Nitrogen and phosphorus in the proportions given above. 



Plot 8. Potash and phosphorus in the proportions given above. 



Plot 9. Potash, phosphorus, and nitrogen in proportions as above. 



Plot 10. Same as Plot 9 with the addition of lime. 



The crops to be tested should be sown across all the plots, and 

 will soon show which element is deficient by a more thrifty 

 growth in the plot containing this element. It is desirable that 



