Abstract
Biomass production and plant species diversity in grassland in southern England was monitored before and after a change from conventional to organic farming. Our 18-year study, part of the UK's Environmental Change Network long-term monitoring programme, showed that the cessation of artificial fertiliser use on grassland after conversion to organic farming resulted in a decrease in biomass production and an increase in plant species richness. Grassland productivity decreased immediately after fertiliser application ceased, and after two years the annual total biomass production had fallen by over 50%. In the subsequent decade, total annual grassland productivity did not change significantly, and yields reached 31–66% of the levels recorded pre-management change. Plant species richness that had remained stable during the first 5 years of our study under conventional farming, increased by 300% over the following 13 years under organic farm management. We suggest that the change in productivity is due to the altered composition of species within the plots. In the first few years after the change in farming practice, high yielding, nitrogen-loving plants were outcompeted by lower yielding grasses and forbs, and these species remained in the plots in the following years. This study shows that grassland can be converted from an environment lacking in plant species diversity to a relatively species-rich pasture within 10–15 years, simply by stopping or suspending nitrogen additions. We demonstrate that the trade-off for increasing species richness is a decrease in productivity. Grassland in the UK is often not only managed from a conservation perspective, but to also produce a profitable yield. By considering the species composition and encouraging specific beneficial species such as legumes, it may be possible to improve biomass productivity and reduce the trade-off.
Highlights
In 1939 the British parliament removed covenants protecting old grasslands from ploughing restrictions (Duffey et al, 1974)
The inclusion of a random intercept term for each exclusion cage was preferred over a simple linear model, the variance associated with the random intercept term was very low (0.005)
Autocorrelation function (ACF) residual plots indicated the presence of strong temporal correlation
Summary
In 1939 the British parliament removed covenants protecting old grasslands from ploughing restrictions (Duffey et al, 1974). This, coupled with a desire for self-sufficiency, accentuated by the onset of the Second World War, marked the start of intensive agriculture in the United Kingdom This intensification substantially increased between the 1940s, when two thirds of Britain’s food was imported (Lloyd and Wibberley, 1977), and the 1980s when overproduction and subsequent detrimental effects on the environment were causing concern. Over the past 20 years three types of schemes have been introduced: Environmentally Sensitive Areas (ESAs), Countryside Stewardship (CSS) and Environmental Stewardship (ESS) The uptake of these schemes has substantially increased in the last 10 years: in 2005, 13% of the UK (Defra, 2007) was covered by AES, and by 2009 this had reached 66%, in excess of 6 million ha. In 2013 the area of land enrolled in entry level AES had risen to 7.4 million ha, compared to just under 2 million ha in 2005 (Defra, 2014)
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