Professor Keith Goulding

Recent Research

websites:

Soil acidification in China

A study published in Science (Guo, J.H. et al., 2009, Regional Acidification in Major Chinese Croplands. Science, 327: 1008-1010.) shows that over-use of ammonium-based fertilizers in China has caused soil acidification that is 100 times greater than that associated with acid rain. This has implications for the protection of ecosystems and their biodiversity and has led to a significant rise in emissions of the harmful greenhouse gases, carbon dioxide and nitrous oxide. In addition, large amounts of nitrogen are released as ammonia which further contributes to acid rain. I have been collaborating with Chinese researchers to achieve optimal crop yields with reduced fertilizer inputs and to prevent environmental damage. In an effort to meet the food demands of a growing population, China has relied upon the use of chemical fertilizers to increase crop yields. Around 30% of the global production and use of nitrogen (N) fertilizer occurs in China and this has led to cropland soils becoming significantly more acid.

The Highfield Reversion Experiment

Plants provide the primary carbon source for soil communities, but there are few studies on the consequences of their absence over an extended period and replanting after a prolonged absence. Soil organic carbon (SOC), microbial and mesofaunal communities in the Highfield Ley-Arable Experiment at Rothamsted Research were compared. Samples were taken from an old grass sward, a section converted to arable rotation 60 years ago, and a section regularly tilled to maintain a bare fallow for the past 50 years. The diversity of the community does not appear to be influenced by treatment. In contrast, the abundance and diversity of the soil mesofauna are strongly influenced by recent plant inputs. On the fallow plot, the virtual elimination of fresh carbon inputs results in the degradation of SOC and reduction in microbial and mesofaunal numbers. However, the plot supports a species-rich and metabolically active bacterial community that is not significantly reduced in diversity compared to soil under arable cultivation or maintained as grass. Reversion – planting the fallow plots with grass or arable – is resulting in the slow return of larger organisms.

A previous BBSRC-funded project showed that the considerable variation in nitrous oxide fluxes across a fallow 1-km transect seems to be controlled by different factors at different scales. We are extending our analysis to a much broader landscape scale (10-20 km) and a range of crop and natural vegetation covers, including bioenergy crops.

Tackling greenhouse gas emissions from agriculture

Denitrification in agricultural soils is an important route for loss of fertiliser nitrogen and so impacts on farm economics but also Climate Change because nitrous oxide (N2O) is a powerful greenhouse gas. The ecology of denitrifier communities, and process controls are not fully understood. In two laboratory experiments we examined the influence on emissions and process controls of (a) different long-term fertiliser and cultivation treatments, and (b) of predicted climate change, modelled as pre-wetted or pre-dried soil. N2O emissions were much higher in soil from woodland than from the same soil growing arable crops and receiving farmyard manure, which in turn was higher than those from inorganic nitrogen-fertilised and unfertilised arable plots. The abundance of bacteria containing nirK best explained the increased emissions, associated with increasing amounts of excess available nitrogen and organic carbon content. Ratios of N2O:N2, measured under closely controlled laboratory conditions, were higher in soils which were pre-incubated under dry conditions than wet, most probably due to the mobilization of organic carbon during the pre-treatment but also because the pre-wetted soil contained far more copy numbers of nosZ genes that facilitate the reduction of N2O to N2. The experiments suggest that predicted Climate Change impacts of more variable and extreme weather patterns could increase N2O emissions and that managing soil for optimal moisture (via structure), carbon and nitrogen content will be the best way to minimise emissions.

The Royal Society meeting at which this work was presented was highlighted in BBSRC’s ‘Food Security’ blog: http://www.foodsecurity.ac.uk/blog/index.php/2011/06/