170 PLANT GROWTH 



4 per cent of nitrogen, 12 per cent of phosphoric acid, and 

 4 per cent of potash are present. This is a good general pur- 

 pose proportion of elements for much of the eastern United 

 States, but many other combinations are available as well as 

 incomplete fertilizers, containing one or two elements. If a 

 large leafy plant is desired a much higher proportion of nitro- 

 gen may be used. The analysis above shows only twenty 

 pounds per hundred of available plant food, but it must be 

 remembered that part of the other eighty pounds will become 

 available gradually. 



The most successful method of fertilization over a long 

 period is the application of manure and a phosphorus fertil- 

 izer. The photograph (Plate XIII) shows the importance 

 of higher amounts of phosphorus on root growth and deep 

 color of the tops, since they improve from the smaller to the 

 larger amounts. In the lower series the influence of varying 

 amounts of nitrogen is shown. The reverse response in root 

 growth is seen; but the tops are larger with higher nitrogen. 

 The phosphorus and the manure make the most desirable 

 combination of elements for most soils. The manure is often 

 difficult to procure and to apply on the lawn, and besides 

 it has many weed seeds. The use of three pounds per one 

 hundred square feet of a complete fertilizer, in the late fall 

 and again a month before active growth begins in the spring, 

 on the lawn and the perennials will make a wonderful im- 

 provement in growth. The garden areas that are dug and 

 cultivated should have a like application before planting and 

 two more at about twenty-day intervals when hoeing. It has 

 been found that plants require large amounts of fertilizers 

 when they are making their early growth and relatively small 

 amounts as they mature. It is possible to use too much 

 fertilizer, but this happens only rarely. It must be mixed 

 with the soil, or, if put on the lawn, followed by a copious 

 watering to carry it to the soil. In this way it becomes in- 

 corporated with the soil and can be absorbed by the plant. 



