Effects of cattle dung from farms with different feeding strategies on germination and initial root growth of cress ( Lepidium sativum L.)

Abstract

Cattle dung from four farms with different feeding strategies was used in a bioassay to determine phytotoxicity. The first farm was an extensive organic farm (ORGE) with young steers grazing on a highly biodiverse sward. Second, an intensive organic farm (ORGI) was included with dairy cattle grazing on a grass/clover sward during daytime and fed low-protein forages indoors. Next, dung from an integrated farm (INT) was used where the feeding strategy aimed at high dung quality by including straw in the diet. Finally, dung from a conventional farm (CONV) was used where fertilised grazed grass was the main component of the diet. The effect of water extracts of dung on seed germination and primary root growth of cress ( Lepidium sativum L.) was measured. Relative seed germination (RSG), relative root growth (RRG) and germination index (GI, the product of RSG and RRG) were related to different dung characteristics (electrical conductivity, total N, NH 4 + and heavy metals) to explain possible differences in phytotoxicity. Both seed germination and root growth decreased with increasing concentration of the water extracts of dung and significant differences were found between the dungs. Stimulating effects on root growth were found at 1 and 3% concentrations. The RSG after 24 h (RSG-24) showed significant differences at the 30% concentration and was best correlated with water-extractable Cu, which was highest in dung from CONV. The highest inverse correlation with RRG and GI at the 10% concentration was detected for EC and total N, whereas at the 30% concentration total N showed the highest inverse correlation. The order of total N in dung was CONV>INT>ORGI>ORGE. Levels of NH 4 +, Cd and Zn were below critical phytotoxic values. Prediction of RSG-24, RRG and GI was not improved when chemical dung characteristics were combined in a multiple linear regression analysis. It is concluded that dung from farms with different feeding strategies can vary considerably in phytotoxicity, ORGE performing best in the cress bioassay. INT appeared to result in lower inhibition of primary root growth at the 10% concentration, indicating a reduced phytotoxicity of the dung compared to CONV.