Plant availability of catch crop sulfur following spring incorporation

Catch crops might reduce sulfate leaching and thereby increase the overall sulfur (S)‐use efficiency in crop rotations. At two experimental sites in Denmark (a sandy loam and a coarse sand), S uptake of catch‐crop species was measured. Furthermore, net release of S following incorporation of this material (S contents 0.13%–1.03%, C:S ratios of 40–329, and lignin contents of 1%–10.8%) was investigated in a pot experiment with spring barley in sandy soil. The catch crops showed huge differences in their ability to sequester S. The best catch crops (legumes on sandy loam), sequestered 10–12 kg S ha^–1, and the poorest catch crops (ryegrass and sorrel on coarse sand) sequestered less than 3 kg S ha^–1. The S‐mineralization rates were highest for crucifers (57%–85% of total S added) and lowest for legumes (up to 46% of total S added). Differences can partly be explained by the C:S ratio, whereas no significant relationship was found with the lignin content of the incorporated catch crops. Catch crops may help to avoid S deficiency and increase synchrony between plant demand and available soil S in a crop rotation. However, the release of S will not fulfil the need of S‐demanding crops and even for cereals, the mineralization will most often only make a contribution. In the case of legume catch crops, it is advisable to use a supplemental S source.