90 Elementary Principles of Agriculture 



126. How Legumes Enrich the Soil. By growing 

 legumes (cow-peas, alfalfa, peanuts, etc.) the farmer is 

 able to harvest a crop valuable as food for man, or feed 

 for stock. These crops are especially valuable because 

 of the large amount of nitrogenous or muscle-building 

 substances which they contain. At the same time, 

 strange as it may seem, they leave a larger quantity 

 of nitrogen in the soil than was there before the crop 

 was sown. The latter becomes available to other plants 

 by the decay of the roots. This promotes the yield 

 of the succeeding crop, as the following experiment 

 shows: The -plan of the experiment included two 

 plots, "A" and "B." On "A" clover was grown the 

 first year and barley the second. On "B" barley was 

 grown both years. The increase in yield of barley on 

 plot "A" over "B" is the measure of the manurial value 

 of the roots of the clover left in the soil by the first year's 

 crop. 



pi . Yield in Yield in 



first year second year 



A. Clover Clover Barley 69.4 bus. 



B. Barley 37.3 bus. Barley 39.1 bus. 



Increase in yield due to clover roots. .30.3 bus. per acre. 



The fixation of free nitrogen by the bacteria in the 

 root nodules of the pea family has been thoroughly 

 studied and is well established. 



127. Nitrification is the formation of nitrates or salts 

 containing nitrogen. Whenever vegetable or animal 

 remains, like guano, cottonseed meal, composts and 

 animal bodies, decay in the soil, the complex nitrogen 

 compounds are broken up, and nitrates are formed. 

 Nitrogen, which is so essential to plant life, is absorbed 

 from the soil as nitrates. The nitrogen in the cottonseed 



