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The Broadbalk experiment - Farm study on organic-inorganic debate
Read more on - Polity | Economy | Schemes | S&T | Environment
- A long running study: The planet’s most famous 4.5 hectares (ha) field is in Hertfordshire county of southern England, under continuous scientific experiments for the past 178 years, making it the world’s oldest and longest running study. The research was started by agricultural scientist John Bennet Lawes and chemist Joseph Henry Gilbert (under the Rothamsted Research institution in the autumn of 1843), when the first crop of wheat was sown on a field named Broadbalk.
- Each year: Every year since then, researchers from the institute have sown winter wheat on all or some parts of the field to compare crop yields, when grown using inorganic fertilisers with those when grown using organic or farmyard manure (FYM). A patch that receives no fertiliser or manure inputs is also maintained for control treatment.
- Goal of the study: The aim of the "Broadbalk experiment" is to test the effects of different organic and inorganic fertilisers on soil fertility and study the optimum nutrition requirements to improve crop yield. The research took shape by growing the same crop each year on the same land, a practice considered bad farming in the 19th century; Lawes and Gilbert had realised this was the best way to learn about the individual crop nutrient requirements.
- Details: Under Broadbalk experiment, the land was divided into 19 strips of wheat field, each 300 metres long and 6 m wide. To test the benefits of different combinations, some strips received inorganic fertilisers, some organic and some others a combination of both. One strip was left received neither of these. Modifications were made over the years.
- Wheat was grown continuously till 1968, when the strips were further divided into sections, with 10 of them growing the crop in rotation after a twoyear break. On six sections, wheat was grown in two different threecourse rotations with oats and beans.
- In 1978, one of the six sections reverted to continuous wheat; potatoes, oats, maize and beans were grown under a five-course rotation with wheat on the remaining five sections.
- These experiments were not envisioned to be long-term initially, but Lawes and Gilbert later thought more useful information could be gained by continuing them over many growing seasons. And they were not wrong.
- Learning: After 175 years of study, scientists found that yields from the section where wheat was grown with a two-year break, were higher (2 tonnes per ha) than from sections where wheat was grown continuously. The effects of soil-borne pests and diseases are minimised in case the field gets a two-year break.
- Use of soil nutrition - In the 1860s, the average yield of continuous wheat treated with organic manure was 2.35 tonnes per ha; yield from strips treated with inorganic fertilisers — phosphorus (P), potassium (K), magnesium (Mg), nitrogen (N) — was 2.85 tonnes per ha. Between 1890 and 1940, the field strips treated with both combinations resulted in almost similar yields.
- Between 1950 and 2019, the average yield with fertilisers was 4.9 tonnes per ha, while the average for fym was 4.8 tonnes. But research showed that the use of organic manure had increased the soil organic matter content on some plots. It also had beneficial effects on many soil properties, including fertility, structure and water holding capacity. This can make the soil more easily workable and decrease the energy required to plough it.
- Soil has the ability to act as a sink for methane. Such benefits may not require large increase in soil organic matter.
- A comparison of recent yield between 2016 and 2018 of both continuous and rotational wheat plots shows that the higher the amount of nitrogen, the greater is the yield.
- This was observed by comparing plots that received only fym, those that received different amounts of N fertiliser (N1 to N6 with N1 having lowest amount of nitrogen and N6 the highest) and those that received same amounts of P, K and Mg. The highest average yield was was in wheat treated with N6 fertiliser, grown in both continuous and rotational manner.
- The finding shows that there is little benefit for farmers using fertiliser with such high levels of nitrogen. Also, since most of the nitrogen gets converted to nitrate, any residue not retained in soil may convert to nitrous oxide, a greenhouse gas that leaks when water drains through the soil.
- Organic matter in soil: Hundred years from the start, it was found that the amount of organic carbon (C) in topsoil (0-23 centimetres) in FYM-treated plots was more than double of that in fertiliser-treated plots. Long-term changes in the total percentage of nitrogen concentration in the topsoil where winter wheat was grown in most years since 1843 were also tested.
- Indian experiment: India has also been conducting its own long-term experiments, especially related to fertiliser and nutrient management. Long-term fertiliser experiments are being carried out at 17 Indian Council of Agricultural Research (ICAR) centres since 1970 to study changes in soil quality, crop productivity and sustainability. It is not possible to sustain productivity without external supply of nutrients. The research has led to the development of integrated plant nutrient supply and management strategies for improving soil fertility, enhancing and sustaining productivity of intensive cropping systems — rice-wheat, rice-rice, maize-wheat, finger millet-maize, soybean-wheat and groundnut-wheat — in major soil groups of India.
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