The effect of catch crops on sulphate leaching and availability of S in the succeeding crop

Summary

Sulphate leaching losses may reduce the long-term possibility of maintaining the S supply of crops in low input farming systems. The ability of catch crops (Italian ryegrass [Lolium multiflorum Lam], winter rape [Brassica napus L.] and fodder radish [Raphanus sativus L.]) to reduce soil sulphate concentrations in autumn and make it available to a succeeding crop was investigated in a field experiment on sandy loam soil. All catch crops reduced soil sulphate concentrations in the autumn compared to bare soil. Especially the cruciferous catch crops had the ability to deplete efficiently soil sulphate levels and thus, reduce the sulphate leaching potential. The S uptake in aboveground catch crop was 8, 22 and 36 kg S ha-1 for ryegrass, winter rape and fodder radish, respectively. In the following spring, sulphate levels of the autumn bare soil were low in the top 0.5 m and a peak of sulphate was found at 0.75-1 m depth. In contrast, where a fodder radish catch crop had been grown, high sulphate levels were present in the top 0.5 m but only small amounts of sulphate were found at 0.5-1.5 m depth. The release of S to barley (Hordeum vulgare L.) were investigated in pot experiments after incorporation of the catch crops Cichorium intybus L., Medicago falcate L., Anthyllis vulneraria L., Trifolium pratense L., Oenothéra biénnis L., Pastinak sativa L., Rumex acetósa L., Sanguisórba minor Scop., Lupinus angustifólius L., Brassica napus L., Lolium multiflorum Lam and Raphanus sativus L. The S mineralisation rates were highest for cruciferous crops and lowest for legumes and differences were partly explained by the C/S-ratio (r2=0,49) that varied from 48 to 265. This study showed that catch crops have a high potential for reducing sulphate leaching and may be used to synchronise S availability with plant demand in a crop rotation.