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The Legumes

Categories: ORGANIC MATTER

Any plant that grows and rots in the soil adds to the

productive power of the land if lime is present, but plants differ in

value as makers of humus. There are only ten essential constituents of

plant-food, and the soil contains only four that concern us because the

others are always present in abundance. If lime has been applied to

give to the soil a condition friendly to plant life, we are concerned

with three consti
uents only, viz. nitrogen, phosphoric acid, and

potash. The last two are minerals and cannot come from the air. They

must be drawn from original stores in the soil or be obtained from

outside sources in the form of fertilizers. The nitrogen is in the air

in abundance, but plants cannot draw directly from this store in any

appreciable amount. The soil supply is usually light because nitrogen

is unstable in character and has escaped from all agricultural land in

vast amounts during past ages.



Profitable farming is based upon the great fact that we have one class

of plants which can use bacteria to work over the nitrogen of the air

into a form available for their use, and the store of nitrogen thus

gained can be added to the soil's supply for future crops. These

plants, known as legumes, embrace the clovers, alfalfa, the vetches,

peas, beans, and many others of less value. They provide not only the

organic matter so much needed by all thin soils, but at the same time

they are the means of adding to the soil large amounts of the one

element of plant-food that is most costly, most unstable, and most

deficient in poor soils. Their ability to secure nitrogen for their own

growth in poor land also is a prime consideration in their selection

for soil improvement, assuring a supply of organic matter where

otherwise partial failure would occur.



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