Use of Stjernøy's rock powder as a slow releasing phosphorus and potassium fertilizer in white clover

Abstract

Plant availability of K and P from biotite and apatite present in the carbonatite rock formation of Stjernøy, was investigated in a pot experiment with white clover. The pot experiment consisted of nine different treatments that included apatite and biotite alone or in combination with chemical fertilizers, lime alone or in combination with PK- fertilizer and PK-fertilizer alone, all added to a low fertility sandy soil. Each treatment had four pot replicates and four subsequent herbage cuts and stolons were sampled. Dry matter yield, concentrations and uptake of K, P and other elements in the herbage and stolons was analysed. Plants were grown in an artificially lighted growth chamber in Jord laboratory, UMB, Norway. All treatments with rock application maintained high K concentration (> 25 g kg- 1DM) in the herbage. Application of rock powder with a full dose PK-fetilizer gave highest total yield (23.1 g pot-1), highest total K-uptake (769 mg pot-1), and higher uptake of Mg and Ca than rock alone. This study concludes that biotite releases K at rate that easily matches requirements by plants. On the other hand P bounded in magmatic apatite was not taken up by plant, and the presence of carbonatite reduced the availability of P present in the soil or added as soluble fertilizer in the sandy soil with low buffering ability. All plants receiving P fertilizer had significantly higher DM yield and improved K uptake compared to similar treatments without soluble P. This biotite carbonatite rock used alone as a fertilizer is not feasible for plant production. It was also found that plants easily absorbed nutrients from the applied fast-released soluble salts with no longer effect on plant availability. Further investigation needs special knowledge on mineral weathering processes and soil reactions especially enhancing P solubility for better understanding the potentiality of applied carbonatite rocks, relationship between nutrients released and plant uptake.