White clover (Trifolium repens) is, due to nitrogen (N) fixation, important to the N dynamics of several northern temperate agroecosystems. This study aimed at monitoring growth and death of major white clover plant organs to assess their potential contribution to within-season N input and risk of off-season N losses.
White clover ('Snowy') was studied in a plot and root window experiment in southeast Norway (60 degrees 42'N, 10 degrees 51'E). Leaves, stolons and roots were tagged for lifespan measurement in harvested and unharvested stands during two experimental years. The availability of soil inorganic N was measured by plant root simulator (PRS) probes.
The longevity of leaves and petioles ranged from 21 to 86 d (mean = 59 d), of main stolon sections from 111 to over 677 d (mean = 411 d) and of roots from 27 to 621 d (mean = 290 d). About 60 % of the leaves produced had turned over by the end of the growing season and another 30 % had died or disappeared by the subsequent spring. Harvesting reduced the longevity of stolons and increased plant fragmentation, but did not decrease leaf or root lifespan or increase soil N availability. From the plant organ turnover data, it was estimated that the gross N input to the soil-plant system from white clover in pure stand during two growing seasons corresponded to a 2.5-fold increase over the total N in harvestable shoots.
The short lifespan and poor over-wintering of leaves showed their potential importance as a nitrogen source in the soil-plant ecosystem but also their potential contribution to the risk of off-season N losses.