Heavy metal content and yielding of Italian ryegrass cultivated in the soil intensively fertilized with municipal sewage sludges

The paper contains results of yielding and heavy metal content in Italian ryegrass cultivated in the fourth year of investigations conducted to determine the effect of two sewage sludges and manure applied once (in the first year of the experiment) and four times in the 1st to 4th year of the experiment. A experimental design comprised 8 treatments in 4 replications. Treatment 1 was the control (without fertilization), whereas on treatment 2 exclusively mineral fertilizers were applied. In the first year of the experiment organic fertilization (two different sewage sludges and farmyard manure) were applied on treatments 3-8, whereas in the second, third and fourth year only on variants 6-8. It was done so to make possible checking the residual effect and the effect of cumulated doses of applied organic materials in the subsequent years. Over the next three years of the experiment, the soil in variants 3-5, which was not enriched with organic materials, received mineral fertilization. On the basis of obtained results it was found that four-year sewage sludges and manure fertilization positively affected the amount and quality of Italian ryegrass yield. Total yields obtained on treatments fertilized with organic materials were statistically significantly higher (by about 20%) than the yields obtained on the treatments receiving mineral fertilizers, and twice bigger as compared with the yield from the control variant. Heavy metals contents in tops of Italian ryegrass on treatments with mineral fertilizers (2-5) was significantly higher as compared with the variants receiving organic materials. In the case of cadmium difference reached up to 100%. Contents of the analyzed heavy metals in Italian ryegrass samples, except cadmium, did not exceed values critical for plants destined for animal feed