Effects of soil disturbance, seed rate, nitrogen fertilizer and subsequent cutting treatment on establishment of Bromus inermis seedlings on degraded steppe grassland in China

Establishment of seedlings of Bromus inermis, a native grass species of China, into a degraded steppe grassland was studied in an experiment with a factorial combination of different soil disturbance (control and harrowing), cutting post-sowing (control and cutting), nitrogen (N) fertilizer application (0 and 100 kg KNO3 hm(-2)) and seed rate (400, 800 and 1200 seeds m(-2)) treatments. Seedling emergence and survival rates, and plant performance, were followed over 2 years. Seedling emergence was increased by soil disturbance (harrowing). Cutting post-sowing and N fertilizer application did not increase seedling emergence. Seedling survival rates at the end of first growing season were strongly influenced by harrowing and the use of higher seed rates. Seedling height was higher in the harrowing and the N fertilizer application treatments and at the higher seed rates. Seedling survival rates in the second growing season were low but much higher with harrowing than the other treatments. Soil disturbance by harrowing may have increased contact between seed and soil, and reduced competition from established plants. It is concluded that, for the restoration of degraded semi-arid grassland in China by re-seeding, soil surface disturbance is necessary for successful seedling establishment, and modest seeding rates should be used to control costs.