Item

A comparison of Caucasian and white clovers in temperate pastures

Black, Alistair
Date
2004
Type
Thesis
Fields of Research
Abstract
A series of three main experiments aimed to define the place of Caucasian clover (Trifolium ambiguum M. Bieb) with respect to white clover (T. repens L.) in temperate New Zealand pastures. Experiment 1 used sheep liveweight gain (LWG) on Caucasian clover-ryegrass (Lolium perenne L.) (CC-RG) and white clover-ryegrass (WC-RG) pastures to assess the relative clover performance under high (High-F: Olsen P 20 µg/ml, sulphate-S 12 µg/g) and low (Low-F: Olsen P 11 µg/ml, sulphate-S 7 µg/g) soil fertility conditions. Mean annual sheep LWG on CC-RG was 1178 kg/ha at High-F and 1069 kg/ha at Low-F, and both treatments exceeded WC-RG by ~9% LWG on CC-RG averaged 141 g/head/d compared with 129 g/head/d on WC-RG. The greater sheep LWG per hectare was attributed to the higher mean clover content (20%) for CC-RG than WC-RG (10%) pastures of similar nutritive value. Dry matter (DM) production and nitrogen (N) yield (DM production x % N) from CC-RG and WC-RG pastures was used to assess the relative seasonal clover performance under High-F and Low-F conditions. In High-F, total N accumulation rates (grass plus clover) for CC-RG were 0.5-0.7 kg N/ha/d higher than WC-RG from October to February, due to double the rate of N accumulation by Caucasian clover. Similarly in Low-F clover N accumulation rates were 50-120% greater in CC-RG than WC-RG. In High-F spring clover production rates increased by 3.2 kg DM/ha/°C for Caucasian clover compared with 1.3 kg DM/ha/°C for white clover as 100 mm soil temperature increased from 6 to 15 DC. In autumn, DM production of Caucasian clover decreased more than white clover as soil temperatures dropped from 16 to 8 DC. In High-F, annual total and clover DM yields from CC-RG were 17.5 and 4.4 t/ha, respectively, compared with 16.2 and 2.1 t/ha from WC-RG. Both pastures produced ~15.6 t/ha of total DM at Low-F, but clover DM was greater for CC-RG at 3.9 t/ha than WC-RG at 2.2 t/ha. Thus, Caucasian clover production was greater than white clover during spring and summer with the greatest advantage under High-F conditions. In Experiment 2 the DM production and water use efficiency (WUE) of each species were compared under full irrigation and dryland (non-irrigated) conditions. In their third year, sown monocultures of Caucasian clover produced 11.9 t DM/ha when irrigated and 9.3 t DM/ha under dryland conditions. Both of these treatments exceeded white clover by ~2.5 t DM/ha due to ~23 kg DM/ha/d higher production rates for Caucasian clover during spring and summer. Specifically, production rates of irrigated treatments increased by 11 kg DM/ha/°C for Caucasian clover compared with 8 kg DM/ha/°C for white clover as mean daily air temperature increased from 8 to 16 °C. In late summer/autumn production rates of Caucasian clover decreased more than white clover when air temperature dropped from 16 to 9 °C. Both species had similar water use under irrigated (~913 mm) and dryland (~740 mrn) conditions. This gave mean WUE values of ~13 and 9 kg DM/mm of water for dryland Caucasian and white clovers, respectively. Growth (leaf photosynthesis rate) and development (leaf appearance rate on a shoot apex) responses of each species to temperature and water status were also measured in Experiment 2. Leaf photosynthesis rates were ~6 µmol C0₂/m²/s higher for Caucasian than for white clover irrespective of measured air temperatures (7-28 °C) and soil water from 1.00-0.39 of water holding capacity (WHC; 580 mm to 1.7 m depth). Both clovers had similar ranges of optimum temperature (21-25 °C) and soil water (1.00-0.86 of WHC) for leaf photosynthesis. Equally the phyllochron was similar between the two species (126 °Cd), but the higher base temperature (Tb) for Caucasian (5 °C) than white (1 °C) clover would mean Caucasian clover is slower to recover to canopy closure post-grazing. Experiment 2 highlighted the potential of Caucasian clover to increase spring and summer clover production, in combination or as the sale legume species in both irrigated and dryland grass/clover pastures. Experiment 3 evaluated the impact of spring and autumn sowing and ryegrass seeding rate on the establishment of Caucasian and white clovers. In spring of the second year, white clover content was >15% when sown with 3-12 kg/ha of ryegrass on 24 September (SD1), 9 November (SD2), or 4 February (SD3), but less than 9% when sown on 31 March (SD4). Caucasian clover never exceeded 9% in any treatment. Sowing on SD1-3 with 3-12 kg/ha of ryegrass gave the most successful establishment of white clover but only Caucasian clover sown alone in spring produced an adequate legume content in the following spring. Growth and development characteristics responsible for slow establishment of Caucasian clover were identified in a controlled environment study. A Tb of <4°C was found for all three species. The thermal time (Tt) requirement for 75% germination was lower for Caucasian (46 °Cd) and white (40 °Cd) clovers than ryegrass (76 °Cd). All three species required ~112 °Cd for 50% emergence and ~214 °Cd for first leaf appearance. The phyllochron for primary stem leaves was slower for Caucasian (109 °Cd) than white (94 °Cd) clover and ryegrass (101 °Cd). Axillary leaves and tillers of ryegrass first appeared after 373 °Cd compared with 440 °Cd for axillary leaves and 532 °Cd for stolons of white clover. In contrast, axillary leaves of Caucasian clover first appeared after 990 °Cd and crown shoots first appeared after 1180 °Cd. Consequently, white clover and ryegrass plants had more leaves (~15.2 /plant) and faster shoot relative growth rates (~0.062 mg/mg/d) than Caucasian clover (5.l/plant and 0.049 mg/mg/d, respectively). Small differences in root/shoot ratio between species were considered to be a minor contributor to slow establishment of Caucasian clover. Slow establishment of Caucasian clover was explained by its delayed axillary leaf and shoot development, and resultant slow relative growth rate compared with white clover and ryegrass. Successful Caucasian clover establishment in fertile soils is therefore most likely to occur in the absence of competition from either ryegrass or white clover.