CURRENT PROGRAMME HIGHLIGHTS

Nitrogen cycling

Much current work on nitrogen (N) extends the application of our expertise, gained in research into agricultural systems, to natural and semi-natural ecosystems. Research on the role of dissolved organic nitrogen (DON) in agricultural soils has expanded into a study of DON across all UK land use types. Our Global Nitrogen Enrichment (GANE), projects have shown links between extractable and dissolved organic N and broad classes of vegetation cover. Amounts decrease in the order grassland > woodland > arable land; land use also affects the composition of extractable and dissolved organic N, but in unexpected ways that are still being unravelled. Seasonal changes are surprisingly small. Our GANE project studying the impact of deposited N on Svalbard in the Arctic, made in collaboration with the University of Nottingham, has shown that N is moving into local waters as well as into the mosses and willows growing on the island.

We have constructed a model of the impacts of atmospheric nitrogen on woodland plant species, using data from the Environmental Change Network (ECN). The model runs from weather data and predicts total wet and dry deposition and changes in ground cover vegetation. It works well for deciduous woodland in NW Europe.

Sulphur supply to crops

The area of crops deficient in sulphur is increasing due to decreased atmospheric deposition. Sulphur deficiency symptoms in wheat were observed in the Broadbalk Experiment in the 2001/02 season, for the first time in its >150 year history, two years after sulphur fertiliser was withheld from Plot 14. Wheat yield was reduced on average by 1 t/ha. We are investigating novel diagnostic methods that can be used to identify sulphur deficient crops. New research will also focus on the sulphur nutrition of barley and the influence of sulphur on malting quality.

Sulphur deficiency symptoms on the Broadbalk Experiment, Plot 14

We have used stable S isotope ratio (³⁴S/³²S) to identify sources of sulphur entering soil-plant systems. We are also using highly enriched stable isotopes ¹³C, ¹⁵N and ³⁴S to investigate sulphur fluxes and interactions between C, N and S. Our ultimate aim is to develop a sulphur cycling model that is fully integrated with the existing C and N models, which can be used to help fertiliser recommendations.

Stable S isotope ratio of wheat from the Broadbalk control plot mirrors UK SO2 emissions over the last 150 years.

Recent papers on sulphur nutrition

Knights JS, Zhao FJ, Spiro B and McGrath SP. 2000. Long-term effects of land use and fertilizer treatments on sulfur cycling. Journal Environmental Quality 29: 1867-1874.
Blake-Kalff MMA, Hawkesford MJ, Zhao FJ and McGrath SP. 2000. Diagnosing sulfur deficiency in field-grown oilseed rape (Brassica napus L.) and wheat (Triticum aestivum L.). Plant and Soil 225: 95-107.
Zhao FJ, Knights JS, Hu ZY and McGrath SP. 2003. Stable sulfur isotope ratio indicates long-term changes in sulfur deposition in the Broadbalk experiment since 1845. Journal of Environmental Quality 32: 33-39.

Lupin production

It has long been recognised that lupin seeds are an excellent source of protein in livestock diets. Previous attempts to produce lupin seeds in the UK had been unsuccessful. Over the last 12 years a programme of research based at Rothamsted has studied the agronomic and physiological barriers to lupin production in the UK, in collaboration with the lupin breeding team at INRA Lusignan, France. The focus was autumn sown cultivars of white lupin (Lupinus albus) because of their high yield potential but the work has equal relevance to spring sown cultivars (L. albus, L. angustifolius and L. luteus).

Genetic restriction of the extent of the branching in each plant (often referred to as determinacy) provided the basis for more detailed agronomic experimentation to minimise plant losses and seed yield variation in the best cultivars. Models of plant development derived from the research are used in conjunction with the results of that experimentation to make site-specific agronomy recommendations. This principally involves calculating a sowing window and seed rate to optimise the distribution of light in the crop canopy.

As of harvest 2002, approximately 6,000 ha of lupins are grown in the UK. There is sufficient acid and neutral land in the UK to increase the area to 130,000 ha. Several UK seed companies and agronomists are developing their preferred cultivars (autumn and spring sown) and Rothamsted provides unbiased information to all.

A field of autumn sown white lupins in mid May.

Optimising farm systems for profitability and minimum environmental impact

The Broadbalk Experiment is 160 years old in summer 2003 and continues to be of relevance to agricultural research. The graph of yield against time for some of the plots shows clearly the value of fertilizers and manures in increasing yields, and also how herbicides and fungicides have increased yield potential. Best yields of wheat ever recorded, of > 11 t ha^-1, were obtained in 2002. Generally optimum fertiliser applications and generous quantities of manure give equal yields, albeit at the cost of much larger losses from the manure. However, for the years 1980-1995 there was a period when farmyard manure (FYM) outyielded fertilisers. The benefits to yields of manure are even greater for spring barley grown on Hoosfield. Research to date suggests the cause to be a more constant N supply. We are collaborating with colleagues in ADAS to better understand the benefits of manure for crops and soil and so improve its utilisation.

The Coates Farm Study shows how, even under Best Management Practice and efficient farming, large amounts of nitrate can be leached to waters from the thin soil over limestone in wet years. Typical Cotswold farm practices such as grazing stubble turnips and applying manure to forage maize are effective economically but can leave large amounts of N at risk of loss in wet weather.

The MEASURES model shows the complex interactions between all components of a farm system - labour, machinery, cropping, sprays and fertilisers, weather, yield and environmental impact. The model allows farm systems to be optimised for all of these. Applying it to Nitrate Vulnerable Zones (NVZs) suggests that NVZ policies will have little impact on nitrate leaching as farmers optimise their system within the rules. However, 'win-win' solutions are possible. MEASURES predicts that persuading farmers to increase the value they put on manure saves them money and reduces environmental impact. We hope to add biodiversity to the model in the near future - the environmental impact of farming that resonates most with the public.

Options for soil management that reduce greenhouse gas (GHG) emissions are being investigated in a BBSRC-funded project with Edinburgh University and the Royal Agricultural College. Fluxes of carbon dioxide, methane and nitrous oxide above a range of land uses are being measured at three sites around the UK using Eddy Covariance for carbon dioxide and sealed chambers for all three gases. Data will be used to test model predictions that, for example, changing from ploughing to minimum tillage would decrease carbon dioxide fluxes but increase nitrous oxide fluxes.

Eddy Covariance Equipment

RothLime

Rothamsted Lime Requirement Model (RothLime) (New: October 2002)

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