Effect of nitrogen fertilizer application on growth, biomass production and N‐uptake of torpedograss (<i>Panicum repens</i> L.)

Abstract

A glasshouse study was conducted to evaluate the effects of different rates (0, 50, 100, 200 and 400 kg ha −1 ) of nitrogen (N) fertilizer application on the growth, biomass production and N‐uptake efficiency of torpedograss. The growth responses of torpedograss to the N application were significant throughout the observation periods. Torpedograss grown for 60 days obtained the highest total biomass of 23.0 g plant −1 with an application of 200 kg ha −1 N, followed by 20.4 g plant −1 with an application of 100 kg ha −1 N; when it was grown for 90 days a significantly higher biomass of 102.3–106.0 g plant −1 was obtained with the 200–400 kg ha −1 N than the biomass (68.0 g plant −1 ) obtained with the fertilizer applied at a lower rate. When the torpedograss was grown for 130 days the highest biomass was 230.0 g plant −1 with the 400 kg ha −1 N application, followed by a biomass of 150.0 g plant −1 with the 200 kg ha −1 N application, but the above‐ground shoot in all treatments was over mature for animal food. The ratio of the above‐ground shoot to the underground part increased with the increase in N application up to 400 kg ha −1 during the 90 days after planting (DAP), but the above‐ground shoot biomass was the same with the 200 and 400 kg ha −1 N. The agronomic efficiency of the N application decreased to 5–38 with the increase in N application to 400 kg ha −1 , which was less than half the agronomic efficiency with the 200 kg ha −1 N. The agronomic efficiency of N was very low (5–22) during the 60 DAP, which indicated that the N application would not be economically viable in this period for torpedograss as a pasture, and short‐duration plants could be cultivated in torpedograss‐infested fields to minimize weed‐crop competition. The nitrogen concentration (%) in the torpedograss increased with the increase in N application, but N‐uptake efficiency was the opposite and the value was very low with the 400 kg ha −1 N. The above results lead us to conclude that the N application rate of 200 kg ha −1 is the most effective for torpedograss growth.