... accumulation of nitrogen.aOptimum or sufficient values for maximum yield or for healthy growth of plants will varywith species, age, and nutrition of plant, position of organ on plant, portion of plant ... generation of indices (87 ,88 ).2.4 NITROGEN IN SOILS2.4.1 FORMS OF NITROGEN IN SOILSThe total nitrogen of the Earth is about 1.67 ϫ1023g (89 ,90). Stevenson (89 ,90) reported that about 98% of the ... mid- 180 0s, as it was shown that crop yields rose as a result of fertilization of soil. Using lab-oratory methods of de Saussure, Boussingault (1), in field research of 183 8, developed balances of carbon,...