Field and Laboratory Data Required to Evaluate Nitrogen Effects

In many developing countries there is a need to improve the food by increasing its protein content. The stimulation of the synthesis of proteins by the crops must be considered of primary importance in those countries. Different methods for determination of the available nitrogen and of the nitrogen uptake by plants can be defined: field, trials; plot methods; micro-plots; pot experiments; lysimeters; incubation of samples in the laboratory, and recurrent profile sampling. Advantages and disadvantages of all these methods are briefly discussed, considering whether the main transformations of nitrogen in soil and the nitrogen status could be characterized applying these methods. The most important nitrogen transformations in soil may be summed up as follows: 1. Leaching by rain, thereby distinguishing ammonia- and nitrate-nitrogen; 2. Volatilization (denitrification, disintegration of nitrites, evaporation, of NH₃); 3. Fixation of NH₄⁺, in expanding crystal-lattices of clay minerals. Finally, the situation in developing countries and in the industrialized, developed countries is compared, deriving some conclusions for the way of farming; to be recommended in connection with the nitrogen problems. (author)