FIELD CROPS 415 



guarded against is the robbing of the land. As much vegetable 

 growth should be left on the land as judicious management will per- 

 mit. Soils are not enriched by rest but by producing crops, provided 

 the crops are left on the land. Of the ten elements necessary to plant 

 growth, nitrogen, potassium, and phosphorus are the ones whose 

 application to soils produces the greatest increase in productivity. 

 Soils composed almost wholly of sand are often deficient in all three 

 of these elements. Soils containing much vegetable matter are not 

 deficient in nitrogen and usually contain sufficient phosphorus. Clay 

 soils may contain sufficient potassium and phosphorus and be de- 

 ficient in nitrogen. Such soils are made highly productive by grow- 

 ing upon them leguminous crops. 



Nitrogen can be added to the soil by applying sodium nitrate, 

 dried blood, tankage, etc., but this element can be more cheaply ob- 

 tained from the air by growing and plowing under legumes. Potas- 

 sium can be supplied in the form of potassium chloride or potassium 

 sulphate. Phosphorus can be supplied by applications of ground 

 rock phosphate or ground bone. 



If the soil is of such a nature that the application of one or a few 

 elements at a small cost will cause it to produce good corn crops, 

 these elements should be supplied ; but if the soil is little more than a 

 foundation, to which must be added a large portion of the necessary 

 plant food, corn growing should be suspended until the soil is perma- 

 nently enriched by applying large quantities of barnyard manure 

 or by liberal and continued growing and plowing under of legumi- 

 nous crops. There are many thousand acres of peaty swamp land in 

 Illinois, Indiana, and Wisconsin which, although containing all the 

 elements necessary for plant growth, are caused to produce much 

 more abundantly by applications of potassium. Such land produces 

 little or no corn without potassium, but by such an application will 

 produce good crops. 



Nitrogen, which is an essential element of plant growth and the 

 most costly ingredient of chemical fertilizers, in a free state con- 

 stitutes four-fifths of the atmosphere. By the aid of microscopic or- 

 ganisms leguminous plants, such as clovers, vetches, beans, peas, and 

 the like, extract nitrogen from the atmosphere and store it in the soil 

 in a form available to succeeding crops. This is one of nature's ways 

 of applying fertilizer, and by working in harmony with nature man 

 can hasten these processes and render poor soils fertile in a few years' 

 time and at but slight expense other than for labor. Soils enriched 

 by the growing and plowing under of leguminous plants retain their 

 fertility well, but no soil, unless it be a river bottom which is fre- 

 quently renewed by overflows, should be planted to corn year after 

 year. The fertility should be maintained and improved by crop 

 rotation and by the turning under of green crops, which can often 

 be grown the same season with the crop grown for profit. 



The plowing under of leguminous crops is here given much 

 emphasis because it is the cheapest way of permanently enriching 

 the large areas existing in almost all the States of the Union, and 

 which each year yield poor corn crops because of lack of fertility. 



