Localized root growth in soil induced by controlled-release urea granule and barley nitrogen uptake

Controlled-release urea is a fertilizer which meters out urea over a long period of time. It can provide a favorable nitrogen (N) concentration for root growth, especially at the early stage of plant development. The objective of this study was to determine the interactions of urea or controlled-release urea granules with barley roots and the resultant N uptake by plants. Two experiments (Experiment I and Experiment II) with treatments of Nil, non-coated urea, Coated I and Coated II (Coated I and Coated II are controlled-release urea products) were conducted in a greenhouse at 23+/-5 degrees C. In both experiments, one barley (Hordeum vulgare L. cv. Duke) seed and one granule of urea or controlled release urea were placed in a pot (5.2-cm height and 8-cm diameter) containing soil low in mineral N. In Experiment I shoot and soil samples were taken at 14, 28, and 46 days after seeding. Roots and fertilizer interaction were visually examined and photographed. In Experiment II, root samples both around the fertilizer granule and away from the granule were taken only at 28 days after seeding. In both experiments, dry matter mass and total N content of shoot and root, and mineral N in soil were determined. In Experiment I, at the 28-day sampling roots proliferated around the controlled-release urea granule but not around the urea granule. Shoot N uptake since the 28 days was higher with controlled-release urea than with urea because of the root proliferation. In Experiment II, root dry mass and N content around the granule was higher with controlled-release urea than with urea. In the controlled-release urea treatments, root mass and N content away from the granule were also increased in comparison to the Nil. This shows a stimulus relationship between the two portions of the roots in the same plant, i.e., the roots being accessed to the N source increased growth of the other roots with no access to the source. Because only a small portion of roots was involved in N uptake in the controlled release urea treatments, the intensity of N uptake per unit of root mass was much higher with controlled-release urea as compared to urea. In conclusion, root growth was enhanced around controlled-release urea granule, and that portion of roots around the fertilizer granule played a major role in absorbing N. In addition, a stimulus relationship existed between roots grown around the granule and those grown away from the granule.