Growth and root architecture responses of zoysiagrass to changes in fertilizer nitrate : urea ratio

Although zoysiagrass (Zoysia spp.) responds to nitrogen (N) application in the field, especially during the establishment phase, no guidelines are available for the preferred form of N for these species. A greenhouse experiment was performed to see how zoysiagrass responds to nitrate and urea as N sources. Z. japonica cv. El Toro (fast‐growing) and cv. Meyer (slow‐growing) and Z. matrella cv. Zorro (fast‐growing) and cv. Diamond (slow‐growing) were chosen for this study. Plants were clonally propagated as phytomers, established in 21 cm deep cone‐tainers filled with a sand‐based growth medium. The treatment consisted of a modified, half‐strength Hoagland's solution with five different nitrate : urea ratios (100 : 0, 75 : 25, 50 : 50, 25 : 75, 0 : 100). Plant responses were assessed in terms of biomass production (leaf, culm, roots, and total plant dry weight) and rooting characteristics (length, area, diameter, volume, tips, forks, crossings, and root volume ratio) 10 weeks after the initiation of the experiment. The differing sources of N resulted in changes in plant growth and development. The cultivars had different above and below‐ground biomass and root architecture traits. El Toro had the highest total biomass production (2.083 g plant−1 DW), while Meyer and Zorro together averaged 0.734 g plant−1 DW (65% less than El Toro). Diamond was the least productive in terms of leaf, culm, and root biomass (0.278 g plant−1 DW; 87% less than El Toro). Furthermore, above‐ and below‐ground DW production was greatest following treatment with 25 : 75 nitrate:urea, whereas 100% nitrate produced plants with the lowest DW. Zoysiagrass rooting traits were only minimally influenced by N source; as the concentration of urea increased, slight increases in root surface area and volume were observed, accompanied by a decline in the root volume ratio.