Response of Stipa bungeana and Pennisetum flaccidum to urine of sheep in steppe grassland of north-western China
Urine [12·3 g nitrogen (N) L−1], collected from native Tan sheep in rangeland of the Loess Plateau in north-western China, was applied to vegetation patches dominated by Stipa bungeana (C3 grass) or Pennisetum flaccidum, (C4 grass) at either 0, 1·0, 2·0 or 4·0 L urine m−2 in early-, mid-, or late-growing season, and herbage mass and tiller number per sample recorded, allowing calculation of the respective contributions of increases in tiller weight and tiller density to the response from N in urine. Such records were made three times in the growing season of application of urine, and at the end of the following growing season. Responses to urine were of the order of 1 and 5 kg herbage DM kg−1 N applied for S. bungeana and P. flaccidum, respectively. Except for early-season application, responses of S. bungeana were mainly expressed in the season following urine application whereas responses of P. flaccidum tended to be expressed within the year of urine application, although with a residual response in the following year. The general pattern was for a tiller density-mediated response in the period immediately after application, followed later by a tiller weight-mediated response. Taken together with other recent research, S. bungeana can be considered a stress-tolerating species with a limited response to N application and P. flaccidum an opportunist species able to capitalize on increased N supply.
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