Abstract:
Variation in the level of nitrate nutrition is known to affect plant growth. Typically, increased nitrate application increases shoot growth, at least up to certain limits. (See for example Figure 1.). The effects of different nitrate levels on root growth are less well known.
Turner (1922) carried out early research into the effects of mineral nutrition on the root growth of barley seedlings. His three treatments ranged from a very low level of nitrate, (approximately 1.8 mEq/litre), through a roughly "normal" level, (approximately 9 mEq/litre), to a very high level, (approximately 18 mE1/litre). In treatments of longer than three weeks duration, increased nitrate decreased root dry weight, and increased the shoot/root ratio, although for shorter periods the "normal" nitrate treatment produced the greatest root dry weight. Turner also investigated the effects of various nitrate levels on excised roots, and on seedlings with plumules and endosperm removed. His results with this material showed that, so long as carbohydrate was supplied, increased nitrate levels increased root growth. This led him to propose that the effect of nitrate on root growth of intact plants might he indirect, perhaps involving a modification of distribution and utilisation of carbohydrate within the plant.
