The influence of ryegrass sowing rates and nitrogen fertiliser on white clover establishment : A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

Perennial ryegrass (Lolium perenne L.) pastures were sown on 19 February at four sowing rates (0, 5, 10, 20 kg/ha) with four rates of nitrogen fertiliser (0, 20, 40, 80 kgN/ha). White clover (Trifolium repens L.) was sown at 3 kg/ha in all plots. Ryegrass and white clover seedling development, herbage production, botanical composition, herbage nitrogen percentage and grazing preference of autumn sown pastures were assessed.

There was no advantage in terms of dry matter production from sowing greater than 10 kg/ha. Total dry matter from at 10 kg/ha was 3600 kgDM/ha from 19/02/04 until 09/09/04. In September (203 DAS) there was no difference in ryegrass plant population numbers in the 10 and 20 kg/ha rates and sowing at 5 kg/ha gave the highest clover populations with 127 plants/m² compared with 55/m² at 20 kg/ha. Sowing at 5 kg/ha gave highest white clover content within the sward; 9.8% (24 April, 36 DAS), declining to 1.6% at 20 kg/ha and 5.7% (9 September) declining to 2.7%. There was no difference in weed suppression between 5 and 20 kg/ha sowing rates at all harvest.

At 41 DAS white clover shoot and root weights were 25% greater in ryegrass pastures sown at 10 kg/ha or less. By spring shoot and root weights in the 5 and 10 kg/ha pastures were 180% and 380% greater than 20 kg/ha treatments. In September clover plants had an average of 8.5 trifoliate leaves/plant in 5 and 10 kg/ha pastures, compared with 2.6 trifoliate leaves in the 20 kg/ha pastures. Clover seedlings sown in the 0 kg/ha plots averaged 11.4 trifoliate leaves/plant.

Pastures sown at 5 kg/ha and 10 kg/ha contained had an overall average nitrogen content of 4.3%, compared with 4.0% for 20 kg/ha pastures. This may have influenced grazing preference. Pastures sown at 10 kg/ha were utilised (>75%) more than 20 kg/ha pastures (<60%). There were larges patches of un-grazed material (up to 20%) and up to 53% of leaf material on offer was left un-grazed in 20 kg/ha pastures.

There was no response to nitrogen in this field experiment. There is a need for more work to be done in this area as the vigour of grass seedlings is strongly influenced by soil nitrogen. On sites of low nitrogen fertility clovers are able to thrive relative to grass seedlings due to their ability to fix atmospheric nitrogen. However, on higher nitrogen fertility sites rye grass is more vigorous and lower sowing rates (<10 kg/ha) are necessary to achieve satisfactory clover establishment. Results from this trial show that in autumn sown pastures there is no advantage to sowing rye grass greater than 10 kg/ha and a rate of 5 kg/ha will give improved clover establishment.