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‘Crop residue can boost soil health’

Andy MacDonald, manager, Rothamsted long-term experiments, Rothamsted Research, UK, speaks to Down To Earth on key findings of the Broadbalk study on running farms

What does it take to sustain an experiment like this for almost two centuries?

Broadbalk is one of the several agricultural field experiments established by John Lawes and Henry Gilbert between 1843 and 1856. Lawes supported the experiments with funds from his fertiliser-manufacturing business and eventually established the Lawes Agricultural Trust to ensure that the experiments continued after his death.

The management of the experiments was subsequently taken over by the British government as part of their support for agricultural research and development.

Some of the experiments continue today and are supported by the UK Biotechnology and Biological Sciences Research Council (part of UK Research and Innovation) and the Lawes Agricultural Trust, under its experimental facility, the National Capabilities, for use by scientists in the UK and abroad for new agro-ecological research.

How beneficial are long-term agriculture experiments for modern agriculture?

Long-term experiments provide a unique insight into the effects of changes in land use and management on agricultural systems, because these effects occur over extended periods of time and are characterised by considerable variability. It is only by collecting data over long periods of time that clear trends become apparent.

Such data can be used to develop and test models to help understand the effects of changes on the crop/soil system. Such experiments also act as a physical demonstration of the key factors necessary to maintain food production.

What are the two or three most important findings from the research till now?

With sufficient input of fertilisers, lime and pesticides along with the use of new higher-yielding crop varieties, sustainable crop production can be achieved on the same site for generations.

However, for optimum yields, inputs of fertiliser N (nitrogen) which greatly exceed crop requirements and organic manure are not environmentally sustainable. Consequently, it is important to manage nutrient inputs, whether from mineral fertilisers or organic manures, to match crop demand as carefully as possible.

What are the key takeaways in terms of soil health?

In addition to good management of organic manures, the management of crop residues is also important. In Broadbalk, there is an indication that inputs of mineral fertilisers, especially Nitrogen and Phosphorus, have resulted in slight increases in soil organic Carbon and Nitrogen contents, perhaps due to enhanced crop growth and increased returns of crop residues in roots and stubble. These increases were associated with a decrease in the energy required to plough the soil (plough draft).

Other long-term studies have shown that straw incorporation has also resulted in small increases in soil organic carbon and soil microbial biomass. There is evidence that these increases have beneficial effects on soil physical properties including aggregate stability, water infiltration and plough draft. Consequently, the incorporation of crop residues into the soil may well have considerable benefits for soil health.

What is the best treatment for wheat yields — organic manure, inorganic fertilisers or a combination of both?

The Broadbalk experiment demonstrates that both mineral fertilisers and organic manures are beneficial for crop production. Wheat yields from plots under rotation, given farmyard manure plus mineral fertilisers or higher rates of mineral fertilisers alone, are similar.

However, the annual farmyard manure inputs used on Broadbalk greatly exceed those which can be used in current commercial practice because of limited availability of manure.

Do you think there are any lessons for a developing and densely populated country like India, where agriculture is one of the main occupations but is not lucrative enough?

The many differences between the climate and agriculture systems in Europe and India make it difficult to translate findings directly from the Rothamsted experiments. However, they demonstrate some principles common to all agricultural systems, including the importance of maintaining soil fertility and other aspect of soil health (organic matter content, pH, structure and biological activity) necessary to ensure global food security for a growing population in a changing climate.

This was first published in Down To Earth’s print edition (April 16-30, 2021)

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