An introduction to agriculture . PHOSPHORUSPOT CULTURE POTASSIUM In the above jars, nitrogen is evidently the plant food needed most.—Courtesy of the Iowa State Department of Public Instruction lizers, to supply these three important raw plant foods to the soil. Nitrogen.— Nitrogen is a gas. It forms four-fifthsof the air we breathe, the other part being mostly plant gets all its nitrogen through its roots in theform of a soluble compound called a nitrate. There aretwo sources of nitrogen in the soil. The principal oneis the organic matter which the soil contains. Theother is the ai
An introduction to agriculture . PHOSPHORUSPOT CULTURE POTASSIUM In the above jars, nitrogen is evidently the plant food needed most.—Courtesy of the Iowa State Department of Public Instruction lizers, to supply these three important raw plant foods to the soil. Nitrogen.— Nitrogen is a gas. It forms four-fifthsof the air we breathe, the other part being mostly plant gets all its nitrogen through its roots in theform of a soluble compound called a nitrate. There aretwo sources of nitrogen in the soil. The principal oneis the organic matter which the soil contains. Theother is the air in the soil. The compound of nitrogen, 50 AN INTRODUCTION TO AGRICULTUEE called a nitrate, which the roots of a plant take up, ismade in the soil by the good bacteria, from the organicmatter and from the nitrogen in the soil air. Legumes are always rich in nitrogen. When theydecay in the soil, the nitrogen they contain is left in aform which is readily changed back into a nitrate. Thisis partly the reason why crops like cl
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