EFFECT OF N SUPPLIES ON THE PROTEIN AND AMINO-ACID CONTENTS OF SOYA FLOUR

The effect of N fertilisation on the seed yield and on the crude prote in and amino acid contents of soya was examined in a lysimeter experim ent set up on Ramann's calcareous sandy roam (CaCO3 2.1 %, humus 1.3 % , silt 28 %, poorly to moderately supplied with available P and K). Th e treatments were 0, 40, 80 and 120 kg/ha N in the form of NH4NO3, wit h 100 kg/ha P2O5 and 120 kg/ha K2O as basic fertiliser. The four N tre atments were set up in three replications using a total of 12 lysimete rs, each of which had a soil volume of 4 m(3) and a growing area of 4 m(2). The plant stand was equivalent to a density of 500 000 plants/ha and the water supply was adjusted to 70 % field water capacity. The m ajor conclusions can be summarised as follows: 1. The yield of uninocu lated soya increased parallel to the rate of N fertilisation or the N supplies of the soil. The N % and crude protein content of the seed wa s not modified to any great extent by N fertilisation, since the soil supplies were utilised in forming a yield surplus. The crude protein y ield per hectare increased with the seed yield and rose by some 70 % a s the N supplies improved. 2. As a result of the N surplus arising in the 2nd and 3rd years of the experiment the seed yield was 4-5 t/ha, t he seed N content was 6-7 %, the crude protein content was 35-40 % and the crude protein yield was 1.8 t/ha, i.e. three times that obtained in the 1st year. 3. In contrast to the results of field experiments, p robably due to the less drastic N surplus, the amino acid content did not differ significantly in the majority of cases as a function of the N supply. However, there was a significant rise in the contents of th e essential amino acids threonine (THR) and methionine (MET) and in th ose of the non-essential amino acids serine (SER) and aspartic acid (A SP). This increase was moderate, averaging 10-15 %. 4. The essential a nd non-essential amino acid contents of soya flour amounted to 10 and 15-16 g/100 g protein, respectively, giving a total value of 25-26 g/1 00 g protein. The total amino acid yield fluctuated between 226 and 37 6 kg/ha, rising roughly parallel with the seed yield. In the first yea r of the experiment the N surplus was not great enough to cause major modifications in the crude protein contents or amino acid composition.