Trends in herbage yields over the last century on the Rothamsted Long-term Continuous Hay Experiment

Abstract

S U M M A R YYields from five of the plots on the Park Grass Continuous Hay experiment at Rothamsted, started in 1856, were examined to see if any long-term trends could be detected over the last 100 years. Three of the plots examined are unfertilized; two receive inorganic nutrients every year; all are harvested twice a year. In 1959 the harvesting procedure was changed: yields for the periods before and after this change were examined separately and together. On none of the three unfertilized plots was the slope of the regression of total yield (i.e. first and second cuts combined) on time significantly (P < 005) different from zero in either the 1891-1958 or 1960-1992 periods. On both the fertilized plots, there were significant declines in yield with time over the 1960-92 period, assuming that the effects of autocorrelation are sufficiently small to be ignored; there were no consistent changes between 1891 and 1958. There were some significant trends on the five plots when the two cuts were considered separately.A linear regression model was fitted to the data in an attempt to separate the effects of meteorological variables (rainfall and sunshine hours over selected parts of the year) on total yield from possible long-term effects brought about, for example, by the increasing concentration of CO 2 in the atmosphere. On four of the five plots this model accounted for between 12 and 21 % of the yield variance in the pre-1959 period and between 45 and 63 % after 1960. On the fifth plot, which received the highest level of N, the model accounted for 29 % of the variance in the first period but only for 16% in the second period. When a linear trend with time was included in the model, this was not significant on any of the plots over the entire 1891-1992 period, although some significant trends appeared when the two periods were considered separately. The model was also fitted with the atmospheric CO 2 concentration in place of the linear trend with time: again there were no consistent trends.Neither changes in the concentration of CO 2 in the atmosphere over the last century nor increasing inputs of combined N in rainfall or in dry deposition have had any detectable effects on yield in these plots.

Pasture production from a long-term fertiliser trial under irrigation

“…This difference in production is similar that measured at the long-term Park Grass continuous hay experiment (Jenkinson et al 1994) where production on the non-fertilised plots was only 40Á50% of that measured on the fertilised plots, despite the nutrient cycling under grazing that occurred at Winchmore but not Park Grass. This clearly shows the benefit of continuing fertiliser applications and the change in sward to lower producing/lowfertility pasture species (e.g.…”

“…Such annual fluctuations have been noted in other long-term experiments (e.g. the Park Grass continuous hay experiment; Jenkinson et al 1994) where they have been attributed in part to changes in annual climatic (rainfall) conditions (Silvertown et al 1994). Some of the variance in our annual yields could be similarly explained by insufficient water for irrigation in dry years, such as 1954 (Rickard & McBride 1987).…”

Dynamic responses of African ecosystem carbon cycling to climate change

“…Like other ecosystem models, the CEVSA model describes the effects of atmospheric CO 2 on photosynthesis and stomatal conductance based on the currently available results from controlled experiments in which annual plants or tree seedlings are normally used to test the plant responses to elevated atmospheric CO 2 ; however natural vegetation and big trees may respond differently (Korner 1995, Bazzaz 1996. The CO 2 fertilization at the ecosystem level may be smaller than that at the individual plant level (Norby et al 1992, Jenkinson et al 1994, Bazzaz 1996. Early increases in plant photosynthesis and growth due to elevated atmospheric CO 2 may disappear as plant growth becomes limited by other environmental factors, such as nutrient supply (McGuire et al 1995, Bazzaz 1996.…”

Nitrogen deposition and its contribution to nitrogen cycling and associated soil processes

“…Annual yields from the long-term experiments at Rothamsted, measured for up to 154 yr, show no detectable effects from the increases in atmospheric N or carbon dioxide concentration (Jenkinson et al, 1994). However, clear and well documented effects of N and soil acidification on the species number and composition of the Park Grass Experiment can be observed.…”