Epsilon Archive for Student Projects

Abstract

Catch crops are an important component of cropping systems in Sweden and other Scandinavian countries, but may contribute to phosphorus (P) losses after freezingthawing
cycles (FTCs). Eight existing and new catch crop species in Swedish farming were grown in a greenhouse to study potential P uptake and P release from shoots,
roots and whole plants after FTCs. The catch crop species were structurator (Raphanus sativus L. var. longipinnatus), white mustard (Sinapis alba L.), oilseed radish (Raphanus sativus var. oleiferus.), phacelia (Phacelia tanacetifolia L.), red clover (Trifolium pratense L.), chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and cocksfoot (Dactylis glomerata L).

The largest uptake of total P (TP) was found in phacelia and oilseed radish (~17 kg TP ha-1), which also had the largest biomass (approx. 8 t DM ha-1). Red clover had the smallest biomass (1.26 t DM ha-1) and uptake of P (4.4 t TP ha-1) and was excluded from the P release experiment due to its poor growth. Concentrations of TP ranged from 0.25 to 0.35% in shoots and 0.08 to 0.36% in roots. In general,
concentrations increased with increasing root specific surface area or volume (except phacelia), but decreased with increasing ratio of root specific surface area to volume.

Roots contributed 23-57% of the total biomass and 15-49% of the P content in the crops. To examine P release, fresh shoot and root samples were exposed to different combinations of freezing thawing treatments (FTTs) and P was extracted with distilled water from these and from untreated controls. Shoot and root samples were dried and milled and total-P concentrations were determined.

Compared with the control, all freezing-thawing treatments caused significant release of P from both shoots and roots of every species, with the most P being released at the first extraction after freezing-thawing. The rate of P release then declined with extraction number and after four extractions it reached the pre-treatment level. In general, shoots of all species except grasses released more P than the roots, while grasses had similar release from both parts. The shoots of the here catch crops were affected most by continuous freezing thawing cycles (CFT-Cs) and
discontinuous freezing thawing cycles (DFT-Cs) treatments and less by a single, longlasting freezing and thawing (SFT-C), whereas roots were evenly affected by all
FTTs.

Potential losses of P from the plant materials were consistent with the concentrations of P in the plants. On average for shoots and roots, structurator, white
mustard and oilseed radish had the largest release of P among all species, mainly because of high release of P from the shoots, whereas chicory and phacelia had the lowest P release owing to low P release from the roots. The ranking of P amounts released calculated on an areal basis did not differ substantially from the ranking calculated on a concentration basis.

Chicory and phacelia were the best species in terms of P retention in this study. However, the results need to be validated in lysimeter or field studies under more realistic conditions.