Nutrient removal with the harvest

Removal of a nutrient

R = M × c × 10

Content is published in kilograms per decitonne, that is per 100 kg; the factor of 10 converts the result to grams. Twenty kilograms of tomatoes at 0.30 kg N per 100 kg give 60 g of nitrogen.

Source of the content values

Basisdaten für die Düngung und Nährstoffflüsse of the Bavarian State Research Center for Agriculture, tables 1a (main crops), 1c (vegetables) and 1d (medicinal and aromatic plants). These data serve as the basis for determining fertiliser requirements under the German fertiliser ordinance. Content is given for four nutrients with the harvested plant part named: "washed carrots, root" and "bunched carrots, root with leaf" are separate rows with different figures.

Independent cross-check

The British guide AHDB RB209 gives phosphate and potash removal per tonne of fresh produce for six of the same crops. Across the five crops they share, the two national guides differ by no more than forty per cent. The agrochemical literature notes that removal per unit of produce varies by a factor of one and a half or more with soil, climate, cultivar, yield, fertilisation and irrigation; the divergence lies within that variability.

The result is a lower bound

Removal is computed from recorded mass. The mass field on a harvest entry is optional, and a harvest never entered in the journal is not visible to the application at all. The result is therefore stated as "at least", with the number of weighed entries given against the total.

Coverage

Thirty-five of the catalogue's forty-nine crops. Nine green manures do not arise: they are incorporated into the bed, and removal is zero by definition. Fruit and berry crops are covered by group rows: one for pome fruit, one for stone fruit, one for currants and similar berries; within a group the source does not distinguish species, and this is stated beside the figure. Blackberry, gooseberry and honeyberry are not covered at all: the neighbouring group row does not name them, and the reason is stated separately from "the harvest was not weighed".

Removal is not an application rate

The figures shown state what left the bed. Converting removal into a fertiliser dose requires the soil's nutrient supply, established by analysis; both guides used make that step through soil indices unavailable to the application. The fertiliser estimate remains a separate calculation and does not take removal into account.