Broadbalk

This site was most likely occupied since Roman times. The land, and the house Rothamsted Manor has passed from family to family since the 13th century, and in 1623 the site was under arable cultivation. John Bennet had inherited the Manor, and when he passed in 1783, his nephew Sir John Bennet Lawes (1814-1900) inherited it. It was Lawes who founded Rothamsted as a research station, and with his scientific collaborator Sir Joseph Henry Gilbert (1817-1901), they established 9 experiments there of which one is the Broadbalk Wheat experiment. It began in 1843, to understand how application of plant nutrients in either fertilizers or manures, affect crop nutrition and yield as this had not been studied systematically previously.

At the same time, Lawes and Gilbert established the Rothamsted Sample Archive where they stored samples from all of Rothamsted’s long-term experiments. Over the years, more crop and soil samples were stored there, including samples from other experiments around the world. It now contains more than 300,000 samples. The Electronic Rothamsted Archive complements the archive by storing digital data which has been updated continuously to hold an increasing amount of data.

Over the decades, changes have been made to this experiment which has included new technology for maintaining and collecting samples, and changes to the plots based on evolving priorities in a new century.

‍ ‍

Phase 1 1852-1925

19 strip plots were set up across the field, being 300 m in length is and either 6 m or 4 m in width (Figure 1).

‍Nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg) and farm yard manure (FYM) were all applied in different forms (e.g. potassium chloride or potassium sulphate) and, for N, in differing amounts (see Table 1, pg 9 in MacDonald, A.J. [eds.] 2018. Guide to the Classical and other Long-term experiments, Datasets and Sample Archive. Rothamsted Research for details).

‍Weeds were dealt with by hand-hoeing, and the plots were ploughed by animals (initially by oxen, then horses).

‍A number of different wheat cultivars were grown in this phase, including Red Rostock, Red Club, Squarehead’s Master, and Red Standard.

‍Phase 2 1926-1967

‍Changes to the set up included- Five Sections (I-V) established. Because increased weed problems had caused hand-hoeing to become impractical, bare fallowing was incorporated on one Section in any one year to allow the land to recover and to store organic matter, and also to control weeds.

Red Standard and Squarehead’s Master were the wheat cultivars used in this phase.

1950s- Chalk was first introduced to maintain the pH.

1964- Herbicides were used for the first time.

1968- The forms, amounts and combinations of treatments (N, P, K, FYM) across the strips were changed (see Table 1, pg 9 MacDonald, 2018).

‍Phase 3 from 1968

‍Changes to the set up included-The old 5 Sections (I-V) were each split in two to create 10 Sections (Sections 0-9) established so that the yield of wheat grown continuously can be compared to that grown in rotation after a break.

‍Sections 2, 3, 4, 5 and 7 are currently in a 5-year crop rotation (wheat-wheat-oats-wheat-beans) with every phase of the rotation present in any one year. Crops that have previously been part of the rotation include potatoes, maize, and a bare fallow (no crop).

‍Long-strawed wheat cultivars were replaced by modern short-strawed higher-yielding winter wheat cultivars. The following wheat cultivars were used in this phase: Capelle Desprez, Flanders, Brimstone, Apollo, Hereward, Crusoe, and Zyatt (the current variety).

‍Higher application rates of N were introduced to some plots in 1968 and again in the 1980s.

‍See Extended Experimental Design and Treatments for further historical changes.‍‍ ‍

Over the decades, the measurements and data that were collected included crop yields, crop grain and straw samples for chemical analyses, soil samples for chemical analyses, and meteorological data.

‍Results and innovation have driven Broadbalk’s evolution from crop production to sustainability of the whole agricultural system

Food security is highly dependent on crop yield and sustainability, which are affected by soil fertility (Johnston and Poulton 2018). While this experiment was set up to look at how nutrients affected crops, key historical developments led to results that bought the focus on soil fertility and therefore sustainability. A good example of this is when Lawes discovered that inorganic fertilisers (with the right amount of nitrogen) gave the same yield as 35t ha-1 of farmyard manure (FYM). He subsequently realised that farmers would not have enough FYM to apply to the field, and therefore, fertilisers were sufficient to maintain crop production. However, stable isotope analysis (Johnston and Poulton, 2018) revealed that ~25% of the nitrogen from fertiliser is lost by leaching or denitrification, which is currently an environmental issue.

‍Figure 2 illustrates how Broadbalk’s key developments such as herbicide application and weed management have affected crop yield, which led to widespread adoption. The suggestion that farmers rotate crops is based on results that wheat grown in rotation after a 2- year break have larger yields than if grown continuously. Crop rotation is also known to be environmentally sustainable.

‍Over the decades, the results have shown how important it is to maintain such long-term experiments where in this case they lead to balancing crop production while also ensuring sustainability.

‍Increased fertiliser use and a change in the crop cultivar has exacerbated the threat of weeds today

‍While weeds pose a threat to crop productivity, the usefulness of chemicals is decreasing as weeds develop herbicide resistance. Herbicides were introduced to Broadbalk in 1968, but one strip: (Section 8, Figure 1) had no application. This provided a unique opportunity to compare how different the crop yields were between plots that had herbicide applied and those which did not (Section 8).

‍Even though changes in crop management and the environment can affect weeds, the question that Storkey et al (2021) asked was: To what extent has crop yield changed due to factors other than the herbicide application? By looking at spatial and temporal trends in the crop yields across the strips, they found that it was a combination of increased nitrogen fertiliser, and a change in crop cultivar (short straw was grown from 1968) that showed the biggest difference in crop yields between the strips that had herbicide applied, and Section 8.

‍Moreover, as an increasing amount of nitrogen fertiliser is added, this changes the weed composition; species become less diverse, dominated by nitrogen-loving species, and more competitive. In effect, the weeds become more of a threat, and Storkey et al (2021) suggest altering the sowing date to decrease weed pressure and reduce weed competitiveness.

With the right fertiliser, nitrogen can be used efficiently as a nutrient, and emissions can by minimised

When the pollutant nitrous oxide (N₂O) is emitted from agricultural soils, it indicates that nitrogen is not being used very efficiently as a nutrient (nutrient use efficiency) so reducing it is important for food sustainability, and climate mitigation (N₂O has a global warming potential about 300 times greater than that of carbon dioxide).

Neal et al 2023 describe a theory that soil is an extended composite phenotype which shows the interplay between different factors, such asorganic matter input and nutrient use efficiency. By identifying the link between these two factors, their aim is to therefore reduce N₂O emissions. Soil samples were taken to examine its structure, chemistry and microbial genetics.

Neal et al 2023 found that applying farmyard manure (which has higher organic matter) directly to soils is related to less N₂O emissions, and that microbial genes associated with nitrogen metabolism were in abundance. This indicates that organic matter affects the expression of the microbial genes that control nitrogen metabolism. The organic matter from the manure also helps to create better soil structure, reducing the risk of waterlogging and anaerobic conditions (which can lead to N₂O production through denitrification).

Therefore, by using the right amount of organic matter input, nutrient use efficiency can be achieved and less N₂O can be emitted.

Dr Andy Gregory

Tel: +44 (0) 1582 938 482

Email: andy.gregory@rothamsted.ac.uk

Ainsdale Dune Slacks, Aston Rowant, Buxton, Colt Park Meadows, Denmark Farm, Elan Valley Meadows, Glen Finglas, Hillsborough LTS, Loughgall, Moor House Grazing Plots, Nash’s Field, Newborough Warren, North Wyke Farm Platform, North Wyke (Rowden Plots), Park Grass, Palace Leas, Pound Hill, Pwllpeiran/Brignant, Raisbeck & Pentwyn, Somerford Mead, Tulloch, Wardlow, Wicken Fen, Wytham (Gibson/RainDrop)

‍ ‍

Budworth Common, Colt Park Meadows, Culardoch, Elan Valley Meadows, Glas Maol, Hillsborough LTS, Llyn Brianne, Moorco, Nash’s Field, Newborough Warren, North Wyke Farm Platform, North Wyke (Rowden Plots), Park Grass, Pwllpeiran, Raisbeck & Pentwyn, Ruabon Moor, Tadham & Tealham Moor, Thursley Common, Wardlow, Whim Bog

‍ ‍

Ainsdale Dune Slacks, Aston Rowant, Bamford Edge, BIFoR-FACE, Buxton, Colt Park Meadows, Denmark Farm, Hordron Edge, Little Budworth Common, Moorco, Moor House Grazing Plots, Moor House Hard Hill, Nash’s Field, North Wyke Farm Platform, North Wyke (Rowden Plots), Park Grass, Palace Leas, Peatland-ES-UK, Somerford Mead, Thursley Common, Wardlow, Wicken Fen, Wytham, (Gibson/RainDrop)