16 FERTILIZERS 



Applications of nitrate are helpful but not lasting 

 unless applied in organic forms, capable of making 

 humus. (86) (96). 



DRAINAGE. 



21. Citrus soils must be well drained. The top 

 soil may be free from gravel for a considerable depth 

 as long as it does not hold free water. The "mesa" 

 or "bench" soils of California, usually situated 

 near the foot hills, are ideal in this regard. Figure 2 

 is a photograph of a stream bank, running through 

 a "mesa." The top soil, free from rock, is here 

 about 5 feet deep, below which there is excellent 

 drainage. 



HARD PANS. 



22. Occasionally the best situation and soil for 

 fruit culture is underlaid at a few feet with an im- 

 pervious strata, so that orchards soon show lack of 

 vigor. These "hard pans" may be at the very sur- 

 face or at any depth below. Blasting with powder 

 or dynamite to break up the fixed condition is effec- 

 tive, but must be repeated from time to time. Per- 

 haps the best remedy where water is sufficient, is to 

 prepare it long before planting trees, by raising a 

 one or two year old stand of alfalfa, the roots of 

 which penetrate hard soils to a considerable depth. 

 Though the orchard is already established, alfalfa 

 might be grown in alternate spaces between the 

 tree rows for two years, then ploughed under and 

 the remaining spaces planted for the next two years. 



" Hard pans" are usually deficient in nitrogen, but 

 may be well supplied with the other plant foods, 

 and especially with lime and iron. The latter gives a 

 very noticeable deep red tint to the orange. 



