Effects Of Nitrogen Application Rates And Frequencies On Nitrogen Metabolism And Turf Characteristics Of Three Native Dichondra Repens Forst

The experiment was in two-factors completely randomized design, where the annual nitrogen application rates (N) were designed as5g/m2,12.5g/m2and20g/m2(N1, N2, N3, a non-nitrogen fertilizer as control), the annual nitrogen application frequencies (T) were designed as1times,2times and4times (T1, T2, T4). Effects of different nitrogen application rates and frequencies on root characteristics, nitrogen uptake, accumulation, metabolism and turf characteristics of three wild Dichondra repens among growth period (April-October) were studied through pot experiments. The purpose was to seek optimal nitrogen application rate and frequency, providing a scientific basis for afforested management of wild Dichondra repens. The results showed as follows:1. The root biomass, total absorption area and active absorption area were improved with the rates of nitrogen application increased (except N3T1). Increasing the nitrogen application frequencies at the same application rate could make the above indicators maintaining a high level among recession period. The variation of specific surface area was not obvious by nitrogen application treatment.2. The root biomass, total absorption area, active absorption area and specific surface area had good relativity with the nitrogen accumulation, by highly significant positive correlation (P<0.01). The active absorption area played a dominant role in absorbing and accumulating nitrogen among exuberant growth period; and the root biomass, total absorption area and specific surface area had a closer relationship with nitrogen absorption and accumulation among recession period.3. Different treatment could affect the nitrogen accumulation of wild Dichondra repens among growth period, but could not affect the general trend of accumulation. In May-August, wild Dichondra repens demanded large amount of nitrogen; while in autumn, nitrogen topdressing could avoid the nitrogen accumulation declining sharply among recession period and the plant aging prematurely, but also conducive to accumulating nitrogen among wintering period. The nitrogen accumulation of different organs was leaf>stem>root, with the nitrogen accumulating most in leaf, but the nitrogen transported into root and stem among recession period, high nitrogen rate promoted to the transportation of nitrogen to overground part. Of three tested materials, the nitrogen accumulation (mean value) of root, stem and leaf of GD200503and SD200303under treatment N3T2had the largest increasing range; but the nitrogen accumulation (mean value) of root, stem and leaf of SD200310had largest increasing range under treatment N3T4.4. The nitrogen application increased NO3--N content, NR activity, GS-GOGAT activity and SP content of leaf, promoting nitrogen reduction and assimilation. In addition to treatment N3T1, the NO3--N content, NR activity, GS-GOGAT activity and SP content of leaf were improved with more rates of nitrogen application, increasing nitrogen application frequencies could delay the weakening of the nitrogen metabolism among recession period, and extend the function period of leave. Of three tested materials (GD200503, SD200303and SD200310), the NO3--N content and NR activity (mean value) of leaf under treatment N3T2had the largest increasing range, while the GS-GOGAT activity and SP content of leaf (mean value) under treatment N3T4had the largest increasing range.5. There was significant positive correlation between nitrogen metabolism indicators and turf quality (P<0.01), the correlation coefficient between nitrogen accumulation and turf quality was r=0.764, and the correlation coefficient of remaining indicators were r>0.9, indicating that improved nitrogen metabolism could be effective to improve the quality of wild Dichondra repens.6. The turf had higher color score, better density and uniformity (except N3T1) under the treatment of high nitrogen application, but the prolonged affect of turf green period was best under the treatment of middle nitrogen application. Increasing nitrogen application frequencies could reduce turf growth fluctuations and maintain the ornamental more durable. The turf texture of GD200503and SD200310had no significant difference (P>0.05); but the turf texture rating of SD200303were reduced under some treatments, because the score of CK was higher, the corresponding score would be lower while leaf area increasing in a smaller magnitude.7. Based on the integrated analysis, the turf quality was the best under treatment N3T4, the second was N3T2. Of three tested materials, the effects of nitrogen application on turf quality of SD200310were greatest, with an increase of24.73%, followed by GD200503of17.22%, the minimal impact was SD200303, just of11.16%.