Shortly after the 2017 business merger, Dow- DuPont announced a write-down if its assets including goodwill of $4.6 billion. Read more about it below.

QUESTION: How do you think this write-down might impact share price and investor decisions? What are the implications for assessment of fair values at acquisition?

DowDuPont, the chemicals group formed in a $130bn merger last year, has announced a $4.6billion (bn) non-cash write-down and warned it had been forced to reduce its long-term forecasts of revenues and profitability in its agriculture division, which it plans to spin off as a separate company next year.

In regulatory filings after the market closed on Thursday, the company said it planned to write off about $4.5bn in goodwill and $100million in other assets from its balance sheet, reflecting a recognition it was over-optimistic about the outlook at the time that the merger of Dow Chemical with DuPont closed in August last year.

It put part of the blame on pressures on farmers' incomes caused by falling commodity prices and high grain inventories, which it said would result in "shifts to lower technologies and pricing pressure".

The division includes a seeds business, which supplies crops including corn and soya beans, and a crop- protection business making chemicals including herbicides and insecticides.

DowDuPont shares, which dropped 1.7 per cent during the trading day on Thursday, were down a further 2.1 per cent at $57.33 after hours.

Laurence Alexander, an analyst at Jefferies who has a "buy" rating on the company's shares, described the write-down in a note as "mostly if not entirely a mark-to-market of known conditions in the seed and crop-protection chemical markets".

DowDuPont said the goodwill on its balance sheet had been built up by the accounting treatment of the deal that created the company, which meant that its reporting units "became more susceptible to impairment for any decline in fair value since the merger".

Cash flow projections drawn up during strategic business reviews in the third quarter of this year concluded that "events and circumstances that have developed during 2018" would mean that long- term revenues and profits would be lower than had been believed at the time of the merger, the company said.

In particular, it blamed lower growth in sales and margins in North America and Latin America, linked to a reduction in planted area, an expected unfavourable shift to soya beans from corn in Latin America, delays in expected product registrations and unfavourable currency impacts related to the Brazilian real, as well as the pressure on farm incomes.

DowDuPont described those circumstances as "a triggering event" that required it to perform an impairment analysis of the goodwill and intangible assets in the agriculture division.

Later on Thursday evening, about three hours after its initial filing, the company issued another statement "in response to market activity", stressing that the impairment was non-cash and "reflects the effect of previously reported market conditions". It added that the write-down would have no impact on the previously announced financial guidance for its agriculture division for 2018.

DowDuPont previously said it expected its agriculture division to report flat net sales and a "mid-single digits" per cent increase in operating earnings before interest, tax, depreciation and amortisation for 2018.

Corteva Agriscience, as the business will be called when it is spun out as a separate company, will hold an investor day setting out the details of its view of the outlook on November 8. The spin-off is scheduled for June 1 2019.