302 NATURE AND PROPERTIES OF SOILS 



decomposition of soil organic matter to decrease. There is 

 usually a more active fixation of nitrogen in grass lands than 

 in cultivated lands, but this nitrogen becomes available very 

 slowly. 



Different soils and climatic conditions necessitate varied 

 methods of manuring for grass. Farm manures may well be 

 applied to meadows in all situations, while the use of available 

 nitrogen in commercial fertilizers is generally profitable. 



Most of the leguminous crops are deep-rooted and are vigo- 

 rous "feeders." Their ability to take nitrogen from the air 

 makes the use of that fertilizer constituent unnecessary ex- 

 cept in a few instances, such as young alfalfa on poor soil, 

 where a small application of nitrate of soda is usually bene- 

 ficial. Phosphoric acid and often lime are the substances most 

 beneficial to legumes on most soils. 



Many crops will utilize very large quantities of nutrients 

 if they are in a form in which they can be used. Phosphates 

 and nitrogen are the substances generally required, the latter 

 especially by beets and carrots. In growing vegetables the 

 object is to produce a rapid growth of leaves and stalks rather 

 than seeds, and often this growth is made very early in the 

 season. As a consequence a soluble form of nitrogen is very 

 desirable. Farm manure should also have a prominent part 

 in the treatment, as it keeps the soil in a mechanical condition 

 favorable to the retention of moisture, which vegetables re- 

 quire in large amounts, and it also supplies needed fertility. 

 The very intensive method of culture employed in the produc- 

 tion of vegetables necessitates the use of much greater quan- 

 tities of manures than are used for field crops, and the great 

 value of the product justifies the practice. 



160. Quantities of nutrients removed by crops. — The 

 utilization of nutrient substances by crops is a constant source 

 of loss of fertility to agricultural soils. In a state of nature 

 the loss in this way is comparatively small, as the native vege- 

 tation falls on the ground, and in the process of decomposi- 



