Nitrogen uptake at various fertilization levels and cutting frequencies of Lolium species
¹Jõgeva Plant Breeding Institute, Aamisepa 1, 48309 Jõgeva, Estonia;e-mail: email@example.com
²Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences,Kreutzwaldi 5, 51014 Tartu, Estonia; e-mail: firstname.lastname@example.org
A field trial was carried out in 1999–2000 to identify optimal combinations of compound fertilizer rates and defoliation frequencies in perennial ryegrass cv. Raidi (diploid) and Raite (tetraploid) and Italian ryegrass cv. Talvike (tetraploid), to enable the nitrogen (N) requirements of dairy cows to be met. The study aimed at estimating the N utilization in the swards subjected to 6 cycles of simulated grazing or cutting 4 times for silage. N application rates were changed from 0–500 kg ha-1 by 100 kg in the former and from 0–400 by 80 kg ha-1 in the latter harvest regime. Increasing the rate of fertilizer increased the N concentrations and yields. Applying N 300 to ryegrasses defoliated at tillering to stem elongation stage allowed assuring minimum N content in the forage dry matter (2.2%) while at N 500 the upper level (2.7%) was exceeded. The ryegrass plants took up less N than was applied with the compound fertilizer. Increasing the defoliation frequency of grass had a positive effect on N content of the forage, but had inconsistent or no effect on improving N uptake from fertilizer and soil. Perennial ryegrass cultivars were more efficient than Italian ryegrass in taking up N from the soil and fertilizer at simulated grazing. Cutting 4 times a year at moderate to high fertilizer rate applications did not reveal a distinct superiority in N absorption of a particular cultivar, but Italian ryegrass had the best N uptake potential from N deficient soil.