The response of wheat tops and roots grown in a leaching environment to rates of nitrogen added as calcium nitrate or organic residues containing 1, 2 or 6% nitrogen

摘要

Wheat was grown under leaching conditions in a glasshouse in columns of a loamy sand soil to which nitrogen had been added in the form of calcium nitrate or organic materials containing 1, 2 or 6% nitrogen. All materials were added at a range of rates calculated on an elemental nitrogen basis, so that comparisons could be made between materials at the same level of nitrogen addition. The amount of mineral nitrogen in the soil profile 4 weeks after seeding increased with the addition of each of the sources except for the 1% nitrogen organic material which had no effect. Addition of calcium nitrate caused the greatest increase of mineral nitrogen, but did not result in the greatest plant growth because of less efficient nitrogen uptake associated with leaching. At 7 weeks after seeding, nitrogen stress, as indicated by the nitrogen content of the plant tops, had increased more where the 2 and 6% nitrogen organic materials were added than where calcium nitrate was added. This trend was also reflected in changes in the root to shoot ratios, and was the result of roots catching up with leaching nitrate from the calcium nitrate. In the columns treated with organic material, root profiles at 7 weeks after seeding showed enhanced growth at the surface, where mineralization of the added materials was occurring. Where calcium nitrate was added, a bulge in the root profile occurred at depth, associated with the leached nitrate.