Further experiments on the acid grassSetaria sphacelata

Summary

Field trials carried out in 1963 and 1964 have confirmed the ammonia-acidity relationship in the grassSetaria sphacelata. The addition of nitrogenous fertilisers enhanced ammonia accumulation in the grass but not titratable acidity. Sand- and water-culture experiments confirmed the essentially acidic nature ofS. sphacelata and the presence of a relatively highly dissociated acid which was found to be oxalic acid. In these experiments ammonia accumulated inS. sphacelata even when nitrogen was supplied as nitrate alone. Darkening the plants for seven days during growth in the field led to a marked accumulation of ammonia inS. sphacelata particularly when covered during early growth.

From the evidence obtained it is concluded thatS. sphacelata is essentially an acid grass and that ammonia accumulation is a consequence of this. The mechanism proposed is that part of the ammonia in the plant, whether derived from direct uptake, nitrate reduction or decomposition (following darkening) of organic nitrogenous compounds, is present as ammonium oxalate. Since plant protoplasts are relatively impermeable to ions ammonium accumulates in the grass. The subsequent decline in concentration in the plant, with increasing maturity, is ascribed to the increase in structural carbohydrates and lignin (a dilution effect) and possible slow utilisation of the ammonium.