292 LEGUMES AND FERTILIZERS 



good for Irish potatoes may be expressed 4-8-10, or 3-6-8. In 

 most states of this country the first number indicates the number of 

 pounds of nitrogen (not ammonia) in each hundred pounds of the 

 mixed fertilizer. The middle number refers to the amount of 

 available phosphate. The last number, to the potash. The order 

 is N-P-K. In Texas, Tennessee, and a few other states, the first 

 number refers to the phosphate the second to nitrogen, and the last 

 to potash. P-N-K. By inquiry find what the formulas mean in 

 your state. 



Home mixtures may be made to suit the conditions better than 

 ready-made preparations. For example, soils are sometimes so 

 rich in nitrogen that they will not produce good yields of Irish 

 potatoes or sweet potatoes. These soils need to be balanced in 

 their plant food by applying phosphoric acid and potash only. A 

 complete fertilizer, containing the three main plant foods, would 

 not remedy the difficulty. 



In other cases nitrogen may be the \ery thing that is lacking. 

 If so it would be best to use fertilizer that is not rich in phosphoric 

 acid and potash, but is rich in nitrogen. 



Needs of soils and crops are not very difficult to determine. 

 Crops that are expected to make much leaf growth in yielding 

 their crop need an abundance of nitrogen. This is true of lettuce, 

 cabbage, cauliflower, celery and others. 



Crops that produce seed crops or fruit require much phosphoric 

 acid. Potash adds strength to stems and vigor throughout. 



Indications of needs may be detected in the growth (Fig. 204). 

 Root crops forming too much top and not enough storage in the 

 underground parts, need less nitrogen and more potash and phos- 

 phoric acid. If the leaf growth of trees or any plants is limited or 

 not of a good deep color, the indication is lack of nitrogen. 



When crops fall down too badly in the wind, the indication is 

 for more potash. Soils that have been farmed for a long time, 

 sandy soils, and peaty soils are likely to need potash. 



If the yield of vegetables or fruits is light as compared to what it 

 should be, the soil probably needs more available phosphoric acid, 

 and perhaps some more potash. In this regard watch the toma- 

 toes, melons, cucumbers, okra, peppers, eggplant, corn, and other 

 vegetables in which the crop is the real fruit of the plant. 



Sources of Nitrogen. — In the commercial form nitrogen or 

 ammonia may be purchased as nitrate of soda, containing fifteen 

 to sixteen per cent of nitrogen, and sulfate of ammonia containing 



