Concentrations of soil potassium after long-term organic dairy production

Loes,-A-K; Ogaard,-A-F

Norwegian Centre for Ecological Agriculture (NORS<O>K), N-6630 Tingvoll,
Norway. E-Mail: anne.k.loes@norsok.no

Abstract
On five long-term organic dairy farms located in the southern part of Norway, aiming at self-sufficiency with nutrients, soil concentrations of ammonium-acetate lactate extractable potassium (K-AL) and acid-soluble K was measured twice in topsoil (0-20 cm) and subsoil (20-40 cm) over periods of 6-14 years.

Organic management had occurred for >9 years at the second sampling. On average there were most probably field level K-deficits. Even so, topsoil K-AL concentrations were medium high (65-155 mg K kg-1 soil), and did not decrease during the study period. However, for three farms, topsoil K-AL was approaching a minimum level determined by soil texture, where further decrease is slow.

Subsoil K-AL concentrations were generally low (<65). The soils were mostly light-textured, and reserves of K-releasing soil minerals (illite) were low, never exceeding 6% of the mineral particles <2 mm diameter.

Topsoil acid -soluble K concentrations were low (<300 mg K kg-1 soil) on two farms, medium (300-800) on three farms and decreased significantly on one farm. Cation -exchange capacity increased on two farms. This may indicate increased amount of expanded clay minerals caused by K-depletion.

On self-sufficient organic dairy farms, purchased nutrients will be required by low soil nutrient reserves to avoid seriously decreased yields and quality of crops.

 

Source
International-Journal-of-Agricultural-Sustainability. 2003; 1(1): 14-29

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Posted July 2007