Response of Sophora secundiflora to Nitrogen Form and Rate

Texas mountain laurel (Sophora secundiflora) is a native shrub tolerating drought, heat, windy conditions, and alkaline or wet soils. However, its availability is somewhat low and little information is available on nutrient requirement and other culture information. Two greenhouse experiments were conducted to quantify the responses of Texas mountain laurel to different forms and rates of nitrogen (N) fertilizer. In Expt. 1, 1-year old seedlings were treated for 194 days with three NO3:NH4 ratios at 25:75, 50:50, and 75:25 and two rates of N at 100 and 200 mg.L-1 in a factorial design. There was no interaction between the N rate and form on any growth parameters. Nitrogen form did not significantly affect shoot dry weight, root dry weight, root to-shoot ratio, or the total dry weight. There was no significant difference between N rate of 100 and 200 mg.L-1 on root dry weight, root-to-shoot ratio, or the total dry weight. The shoot dry weight of Texas mountain laurel fertilized with 100 mg.L-1 was higher compared with that of the plants fertilized at 200 mg.L-1. The reduced shoot dry weight at N of 200 mg.L-1 was the result of the higher substrate salinity. In Expt. 2, seedlings were fertilized with five N rates (50, 100, 150, 200, and 250 mg.L-1) for 203 days. Plants watered with 150, 200, and 250 mg.L-1 were taller than those fertilized with 50 mg.L-1. The shoot height of plants watered with 100 mg.L-1 was only significantly different from 50 mg.L-1. For rapid growth of Texas mountain laurel, a N rate range of, approximate to 150 mg.L-1 was recommended supplied with a combination of NO3-N and NH4-N in the ratios of 0.3 to 3.0.