Effect of pyrite and fertilizer on rice protein quality

Protein concentration in grain increases with high fertility. Because the poor biological value of rice protein is attributed to the deficiency of essential amino acids, such as lysine and tryptophan, the effect of different levels of pyrite and fertilizer on protein quality of rice was studied. The soil was slightly saline-alkali with moderate pH and exchangeable sodium percentage. Pyrite was applied 10 d before transplanting Saket 4 to ensure complete oxidation in the experimental field. N as urea, single superphosphate, and muriate of potash were applied. Half the N and all the P and potash were applied at transplanting. The remaining N was applied 30 d after transplanting. Grain samples were harvested with a sickle and dried in an oven at 60 degrees Celsius. The samples were hand pounded to brown rice, ground to powder, and passed through a 60-mesh sieve for chemical analysis. N content in the defatted samples was determined by micro K jeldahl method; that value was multiplied by a factor of 5.95 to get protein content. Protein fractions were estimated on the basis of solubility in water (albumin), sodium chloride (globulin), ethyl alcohol (prolamin), and sodium hydroxide (glutelin). Lysine content was measured using trinitrobenzene sulfonic acid reagent. Protein fractions and lysine content were calculated as percent of grain. Protein content increased in all treatments. The highest protein content was obtained with 600 kg pyrite/ha and 120-60-60 kg NPK/ha. Fractionation revealed that the major amount of protein was in the form of glutelin (6.65%). Higher fertility slightly increased the prolamin and glutelin fractions. Lysine content decreased with increased pyrite and NPK. Protein content was positively correlated with prolamin and glutelin and negatively correlated with lysine.