Net primary production of a perennial grass ley (Festuca pratensis) assessed with different methods and compared with a lucerne ley (Medicago sativa).
Abstract
The aboveground production of an established F. pratensis ley in central Sweden was analysed by repeated clipping during 1982 and 1983. Standing vegetation was separated into living and dead material and surface litter was collected. Three methods were used to calculate net aboveground primary production (NAPP). Two of them accounted for death and shedding between samplings. Depending on the calculation method, annual NAPP of ash-free DM varied between 903 to 985 and 810 to 1039 g/m2 in 1982 and 1983, resp. The 2 methods which included biomass turnover gave the highest production values. The underestimation in NAPP due to decomposition of litter between samplings was evaluated by applying a decomposition constant, estimated in a separate litter-bag experiment, to the mean amount of litter present during a sampling period. It was found to be <10%. The mean daily growth rates of aboveground crop were 4.7 and 6.0 g/m2 in 1982 and 1983, resp., and max. recorded daily crop growth (22.0 g/m2) occurred in early June 1983. The study was part of a multidisciplinary ecosystem project, and estimates of belowground production and herbivore consumption were available, allowing total net primary production (NPP) to be estimated. Mean annual NPP was 1468 g/m2. NPP was underestimated as rhizodeposition was not measured. Its underestimation from neglecting death and decomposition was less severe above than belowground. The amount of OM input to the soil system via litterfall was a minor part of the NPP but a significant part of the total OM supplied to the soil OM pool during a year. A severe drought in 1983 affected the F. pratensis ley more than a concurrently grown M. sativa ley. Av. annual NPP was similar in both crops, but the amount of standing dead material was higher in the F. pratensis ley than in the M. sativa ley. The allocation belowground was similar, about 30%, but root death was higher in the F. pratensis ley.