Biomass production and phosphorus retention by catch crops on clayey soils in southern and central Sweden

Catch crops are a potential option to reduce phosphorus (P) losses, but little is known about their establishment success and capacity to retain P on clayey soils in regions with short autumns, e.g. Sweden. This study screened biomass production and P retention by eight catch crop species: the perennials chicory (Cichorium intybus L.), cocksfoot (Dactylis glomerata L.), perennial ryegrass (Lolium perenne L.) and red clover (Trifolium pratense L.) and the annuals phacelia (Phacelia tanacetifolia L.), white mustard (Sinapis alba L.), oilseed radish (Raphanus sativus L. oleiformis) and white radish (R. longipinnatus). The catch crops were grown at six field sites, where the perennial species were under-sown with barley and the annual species were after-sown following barley harvest. Biomass production, P content in above-ground and below-ground plant parts and content of available P in the soil were determined in autumn and survival rate of the catch crops in the following spring. Biomass production and P retention in autumn both differed significantly between species (p < 0.0001), and were greatly affected by site-specific conditions and time of sowing, which differed between experiments. Growth of catch crops can also be suppressed by low precipitation. Content of P in roots varied substantially between species, a factor which must be considered in species comparisons. The under-sown species produced more or equivalent amounts of biomass, retained more or equivalent amounts of P in autumn and survived better over winter than the after-sown species. Thus under-sown catch crops generally seem more suitable as catch crops for P.