44 



MISC. PUBLICATION 3 6 9, U. S. DEFT. OF AGRICULTURE 



expressed as milligram equivalents, and the terms of the equation are 

 multiplied by 100 to avoid fractions, Thomas obtains his expression 

 for the NPK unit, and the properties of this expression are such that 

 "for each simultaneous value of N, P, and K there is one point and 

 only one on an equilateral triangle each of whose sides equals 100 

 [units]." 



SECTION A 



FERTILIZER PER 

 PLOT 



.6 LB. N AS 

 SODIUM NITRATE 



SECTION B 



FERTILIZER PER 

 PLOT 



1.0 LB. P 2 s AS 



SUPER PHOSPHATE 



SECTION C 



FERTILIZER PER 

 PLOT 



0.8 LB. K 2 AS 



POTASSIUM CHLORIDE 



YIELD, 155 LB. 

 PER PLOT 



SECTION D 



FERTILIZER PER 

 PLOT 



0.6 LB. N 

 1.0 LB.P 2 0j 



YIELD ,124 LB. 

 PER PLOT 



SECTION E 



FERTILIZER PER 

 PLOT 



06 LB. N 

 0.8 LB. K a 



YIELD. 163 LB. 

 PER PLOT 



SECTION F 



FERTILIZER PER 

 PLOT 



1.0 LB. P a s 



0.8 LB.KgO 



YIELD , 148 LB. 

 PER. PLOT 



SECTION G 



FERTILIZER PER 

 PLOT 



0.6 LB. N 

 1.0 LB. P;,0j 

 0.8 LB. K 2 



YIELD, 162 LB. 

 PER PLOT 



7? 



MONTH 7 7 8 8 7 8 8 7 8 (TT J 8 ~ 7 1 8 5" 7 7 5 B~ 7 7 8 8" 



DAY 9 29 9 24 9 29 9 24 9 29 9 24 9 29 9 24 9 29 9 24 9 29 9 24 9 29 9 24 



DATE SAMPLED 



Figure 2. — Influence of different fertilizer treatments on the nitrogen, phosphoric 

 acid, and potash content of potato leaves at different stages of growth. (From 

 Thomas, 560.) 



Thomas assumes that a fertilizer may modify the composition of a 

 plant by (1) "an increase in the sum, (N + P 2 5 +K 2 0), i. e., in the 

 intensity of nutrition, or (2) a change in the composition of the 

 NPK-unit, or (3) a change in both (1) and (2) simultaneously." 



His data, plotted in figure 2, when analyzed on the NPK-unit basis 

 show that compared to a balanced fertilizer: 



(1) The omission of nitrogen from the complete fertilizer has increased the 

 potash and phosphoric acid in the NPK-unit of the leaf throughout the whole 

 period, resulting in decreased yields. 



(2) The omission of potash from the complete mixture has increased the nitrogen 

 and the phosphoric acid in the NPK-unit, resulting in decreased yields. 



(3) The omission of phosphorus has increased the potash in the NPK-unit of 

 the leaf at the expense of the nitrogen, resulting in a slight increase in yield. 



(4) The omission of both phosphorus and potash has increased the nitrogen 

 in the NPK-unit, resulting in considerably decreased yields. 



(5) The omission of both nitrogen and potash has increased the nitrogen and 

 the phosphorus in the NPK-unit, with considerable reduction in yields. 



(6) The omission of both nitrogen and phosphorus has resulted in increasing 

 the potash in the NPK-unit, resulting in decreased yields. 



McCool and Weldon (866) in 1928 noted that 36 days after planting, 

 the phosphorus content of the juice of barley plants had increased 

 with both phosphorus and potassium fertilization. After 90 days, 

 however, a lower phosphorus content of the juice of both leaves and 



