Detection of historical changes in pasture growth and attribution to climate change

Abstract

Few studies consider historical trends in biological systems in relation to changes in climate. These detection and attribution studies are particularly challenging in agricultural systems where other factors (such as management) are changing over time. Here we consider changes in pasture yield (net herbage accumulation [NHA]) over the period 1960−2004 in a dataset from a trial in New Zealand where management (grazing protocol and fertiliser application) was constant over time. We used 2 approaches: a statistical approach looking for trends in, and correlations between, NHA and climate variables and a process-based modelling approach where combinations of variables were held constant at their starting values or allowed to change with time enabling us to isolate the impact of individual factors. There was a significant positive trend for NHA in spring over the period and positive trends in rainfall and atmospheric CO 2 concentration; soil nitrogen (N) also increased over time. The statistical approach was useful for identifying trends but was unable to resolve the driving variables. Modelling identified CO 2 , soil properties and their interaction as the most influential variables. The calculated impact of CO 2 was a 0.21% increase in NHA ppm CO 2 −1 ; this compares to a value of 0.19% from a FACE (free air carbon dioxide enrichment) experiment with a similar type of management and pattern of pasture production. The results instill confidence in experimental estimates of the CO 2 fertilisation effect, particularly at low levels of CO 2 enrichment, and provide evidence that climate change impacts are already in progress. KEY WORDS: CO 2 fertilisation effect · ApSim · GrasslandResale or republication not permitted without written consent of the publisher FREE REE ACCESS CCESS

Summer growth rates and annual yields of perennial ryegrass (Lolium perenne L.) in the Upper North Island are expected to decline as a result of climate change

“…While the Southland site in Lieffering (2016) experienced an increase in annual yields into the future, it should be noted that negative daily pasture growth rates were excluded from their calculations, which could result in an overestimation of pasture yields. An increase in annual yields was also calculated by Newton et al (2014); however, this was for the period 1960-2004 and is in line with the 1980, 1990 and 2010 annual yield predictions presented here.…”

“…Improved winter growth rates could potentially be taken advantage of by farmers by moving to a winter milking schedule (Chikazhe et al, 2017). Several studies (Newton et al, 2014;Lieffering 2016;Ausseil et al, 2019) predicted higher growth rates in spring under climate change, but this was not corroborated in the current study. Their findings could have been due to the inclusion of other pasture species in their models, compensating for perennial ryegrass when growth rates were low.…”