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 p eriod of time. It can provide a favorable nitrogen (N) concentration for ro ot growth, especially at the early stage of plant development. The objectiv e of this study was to determine the interactions of urea or controlled-rel ease urea granules with barley roots and the resultant N uptake by plants. Two experiments (Experiment I and Experiment II) with treatments of Nil, no n-coated urea, Coated I and Coated II (Coated I and Coated II are controlle d-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 on e granule of urea or controlled-release urea were placed in a pot (5.2-cm h eight 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. Ro ots and fertilizer interaction were visually examined and photographed. In Experiment II, root samples both around the fertilizer granule and away fro m 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 s oil were determined. In Experiment I, at the 28-day sampling roots prolifer ated around the controlled-release urea granule but not around the urea gra nule. Shoot N uptake since the 28 days was higher with controlled-release u rea than with urea because of the root proliferation. In Experiment II, roo t dry mass and N content around the granule was higher with controlled-rele ase urea than with urea. In the controlled-release urea treatments, root ma ss 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 th e roots in the same plant, i.e., the roots being accessed to the N source i ncreased growth of the other roots with no access to the source. Because on ly a small portion of roots was involved in N uptake in the controlled-rele ase urea treatments, the intensity of N uptake per unit of root mass was mu ch higher with controlled-release urea as compared to urea. In conclusion, root growth was enhanced around controlled-release urea granule, and that p ortion of roots around the fertilizer granule played a major role in absorb ing N. In addition, a stimulus relationship existed between roots grown aro und the granule and those grown away from the granule.