Plant Nutrition :: Mineral Nutrition


Progress during the Nineteenth Century

Theodre de Saussure discoveries demonstrated that plants absorbed O2 and liberated carbon dioxide (CO2), the central process of respiration. In addition, he found that plants absorb CO2 and release O­2 in the presence of light; however, plants died when kept in a CO2-free environment. He concluded that the soil furnishes only a small fraction of the nutrients needed by plants, but he demonstrated that it does supply both ash (calcium (Ca), magnesium (Mg), potassium (K) and other minerals) and nitrogen (N). the plants generate potash spontaneously and that the plant root does not behave as a filter and the membranes are selectively permeable, allowing for a more rapid uptake of water than of salts. The differential absorption of salts and the inconstancy of plant composition varies with soil, plant age and plant part.

Sir Humphyr Davy in his publication “The elements of Agrl. Chemistry (1813)” stated that although plants received some carbon from the air, most was taken in through the roots. During the nineteenth to the early twentieth century, much progress was made in the understanding of plant nutrition and crop fertilization. Jean Baptiste Boussingault (1802-1882), a French chemist who was considered the father of field-plot technique maintained a balance sheet that showed how much of the various plant nutrient elements came from rain, soil and air; analyzed the composition of his crops during various stages of growth According to him the best rotation was the one that produced the largest amount of organic matter in addition to that added in the manure.

Justus Von Liebig (1803-1873), a German chemist, suggested that the C in plants comes from any source other than CO2. He stated that

  1. Most of the carbon in plants comes from the CO2 of the atmosphere.
  2. Hydrogen and O2 came from water.
  3. The alkaline metals are needed for the neutralization of acids formed by plants as a result of their metabolic activities.
  4. Phosphorus (P) is necessary for seed formation.
  5. Plants absorb everything indiscriminately from the soil but excrete from their roots those materials that are nonessential.

He believed that the ammonium (NH4+) form of N was the one absorbed and that plants might obtain this compound from soil, manure or air.

The “Law of the minimum” according to Liebig 1862, Father of Agricultural Chemistry states that” Every field contains a maximum of one or more and a minimum of one or more nutrients. With this minimum, be it lime, potash, nitrogen, phosphoric acid, magnesia or any other nutrient, the yields stand in direct relation. It is the factor that governs and controls yields. Should this minimum be limiting? Yield will remain the same and be no greater even though the amount of potash, silica, phosphoric acid, etc. … be increased a hundred fold.”

Later in 1843, J.B. Lawes and J.H. Gilbert settled the following points from their experiments at Rothamsted, England.

  1. Crops require both P and K, but the composition of the plant ash is no measure of the amounts of these constituents required by the plant.
  2. Non-legume crops require N. without this element, no growth will be obtained, regardless of the quantities of P and K present. The amount of ammonia (NH3) contributed by the atmosphere is insufficient for the needs of crops.
  3. Soil fertility can be maintained for some years by chemical fertilizers.
  4. The beneficial effect of fallow lies in the increase in available N compounds in the soil.

The problem of soil and plant N remained unsolved. Several workers had observed the unusual behaviour of legumes. In some instances they grew well without added N, whereas in others no growth was obtained. Non-legumes always failed to grow when there was insufficient soil N.

The French bacteriologists  Schloessing and Muntz, in 1878, found that the production of NO3- could be stopped by adding chloroform and that it could be started again by adding a little fresh sewage water. They concluded that nitrification was the result of bacterial action.

These experimental results were applied to soils by Robert Warrington of England. He showed that nitrification could be stopped by carbon disulfide and chloroform and that it could be started again by adding a small amount of unsterilized soil. He also demonstrated that the reaction was a two-step phenomenon, the NH3 first being converted to nitrites and the nitrites subsequently to nitrates.

In 1886, two German scientists, Hellriegel and Wilfarth, concluded that bacteria in the nodules attached to legume roots assimilated gaseous N from the atmosphere and converted it to a form used by higher plants. This was the first specific information regarding N fixation by legumes. It was M.W. Beijerinck, who isolated Bacillus radicicola, the organism responsible for N fixation.

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