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Organic fertilizer → Particulate organic carbon

A clear tendency, not consistent

83 %

of 6 studies with a clear result report a significant increase

+50 %

typical change (3 studies with numbers)

studies · 8 findings

Count each study by

6 studies · 8 findings

What the studies show

5 of 6 studies report a significant increase (83 %, 95 % confidence interval 44–97 %).

By the direction of each study’s results, significant or not: 6 of 6 studies with a direction point up (100 %, 95 % confidence interval 61–100 %; sign test p = 0.031).

↑ 5 increase
↓ 0 decrease
= 1 no effect

How large: typically +50 % (middle half +26 % to +66 %), from 3 studies with numbers
Basis: 6 studies, 8 findings; 0 entered by hand, 6 read by the library

6 findings on relative measures (shares, stratification ratios, values per unit) or on fractions and other compartments are not counted in this answer.

Every study counts once, however many findings it reports: one with 40 sampling dates does not outvote ten others. A study with a significant increase and decrease (say at different depths) counts as "both". A first synthesis for orientation, not a substitute for a systematic review.

Where the studies are

goes up
stays the same
goes down
both ways

Through the soil profile

Each layer on its own: a study that reports the topsoil and the subsoil counts in both. Choose a layer to see what goes with it.

goes up
stays the same
goes down
both ways

What makes a difference

The conditions whose levels differ most clearly, each with the outcome that differs most between its levels of at least 10 study layers. Choose a layer in the profile to see them for that layer alone, or a level here to filter by it.

Testing every condition on every study layer…

Along the conditions

Testing every condition on every study layer…