Short-term effects of soil amendment with dairy sludge on yield, botanical composition, mineral nutrition and arbuscular mycorrhization in a mixed sward

Resumo

A field study was carried out to evalúate the short-term effects of increasing dairy sludge application rates on yield, botanical composition and nutrient content of the first regrowth of a grass-white clover sward. Arbuscular mycorrhizal (AM) root colonization and forage phosphorus concentration were also analyzed five months after dairy sludge addition. The cultivated soil was a Humic Cambisol which was limed, NPK-fertilized and sown with a mixture of perennial ryegrass, cocksfoot and white clover. After a silage cut made in June 1997, four dairy sludge rates were applied: 0, 80, 160 and 240 m3 ha1. Increased rates of the sludge resulted in higher DM yields of the first regrowth. Soil fertilization with 240 m3 ha-1 sludge favoured grass growth and competition, while decreased clover proportion (6.5%) in the sward. Higher percentages of clover (20%) were found when 80 or 160 m3 ha-1 of dairy sludge were applied. Concentrations of N, P and K were greater in forage from sludge-added plots than in the control. There were no differences between sludge treatments. AM root colonization slightly decreased on adding any of the sludge rates to the sward compared with control, which was related to higher P concentration in forage. Results indicated that optimal dose was 80 m3 ha1, which yielded only 30% less than the highest sludge rate and best favoured competition of clover against grass.