Novel sowing strategies to improve white clover production in mixed pastures : A dissertation submitted in partial fulfilment of the requirements for the Degree of Bachelor of Agricultural Science with Honours at Lincoln University

Abstract

The white clover (Trifolium repens) content of finely mixed ryegrass-white clover pastures is often less than 20%. As a consequence, new methods of pasture establishment and management are sought to increase white clover content. Pastures were established on 15 March 2005 at four perennial ryegrass sowing rates: 2.5, 5, 10, 20 kg/ha and using four sowing methods: standard (15 cm drill rows), spatial separation (alternating drill rows of perennial ryegrass and white clover), broadcast (seed spread on soil surface) and temporal separation (white clover sown initially, perennial ryegrass overdrilled later). White clover was sown at 3 kg/ha and chicory (Cichorium intybus) was sown at 1.5 kg/ha in all plots. Dry matter production, botanical composition, soil temperature distribution, chicory, white clover and perennial ryegrass morphology and extent of clover grazing were assessed. From January - September 2006, total dry matter production was greater in temporal treatments (4665 kg DM/ha) than spatial (3102 kg DM/ha), standard (2801 kg DM/ha) and broadcast (3300 kg DM/ha) treatments. The temporal treatment also had a higher average white clover percentage (12%) than spatial (5%), standard (5%) and broadcast (7%) treatments. Dry matter production was similar for all rye grass sowing rates, but white clover percentage was higher in 2.5 kg/ha treatments (8%) than in 5 kg/ha (7%), 10 kg/ha (7%) and 20 kg/ha (6%) treatments. White clover plants between ryegrass drill rows in the spatial sowing treatment had higher total stolon length, leaf dry weight, tap root weight and tap root diameter, and more primary and secondary stolons and total growing points than those located in ryegrass drill rows in standard and spatial sowing treatments. Moreover, there was a greater population of these plants between ryegrass drill rows in spatial plots, and chicory plants in these locations had larger basal diameters. During an autumn grazmg event, a greater proportion of white clover leaves were grazed for plants located between ryegrass drill rows in spatial treatments than in ryegrass drill rows in spatial and standard treatments. Results from this trial show that the temporal sowing method led to increased dry matter production and white clover content in pasture but there was no difference between standard, spatial or broadcast sowing methods. It appears that spatial separation, while minimising competition between ryegrass and white clover and chicory, it also allowed sheep to show greater selection for clover. The results also show that sowing rates of ryegrass are commonly too high, with no losses in production shown from lower sowing rates (e.g. less than 10 kg/ha).