Agronomic potential of Lupinus polyphyllus L. for dryland Merino properties in the Mackenzie Basin : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University
This research examined the potential of Lupinus polyphyllus L. (also known in New Zealand as perennial lupin and Russell lupin) as a productive pasture component for high-country pastures. To do this, a combination of on-farm studies, controlled field experiments and glasshouse experiments were carried out. Throughout the thesis, lucerne (Medicago sativa L.) was used as a control. The use of perennial lupin as a suitable feed for a commercial Merino ewe flock was evaluated in an on-farm study at Sawdon Station, Lake Tekapo. The performance of ewes and lambs grazing a lupin-based pasture was compared with a control flock that was predominantly grazing lucerne. The lupin pasture grew rapidly during the spring period and average pasture cover increased by about 4500 kg of dry matter (DM)/ha under a stocking rate of 15-17 stock units/ha. At tailing in December 2012 and 2013, lambing averaged 111% and ewes averaged 58 kg for the lupin pasture, and 105% and 62 kg for the control flock, while lambs averaged 19 kg for both mobs. At weaning in February 2013, ewes and lambs on the lupin pasture averaged 58 kg and 28 kg compared with 63 kg and 31 kg for the control flock, respectively. During autumn, ewes on the lupin pasture gained 3.8 kg compared with 5.5 kg for the control flock before mating in May. In September, the ewes were shorn and wool averaged 4.62 kg/ewe for the lupin mob and 4.92 kg/ewe for the control flock, with a mean fibre diameter of 18.5 µm. A selection of L. polyphyllus samples were subjected to wet chemistry analyses, which was later used to calibrate a near infrared spectroscopy analyser and predict the nutritional composition of lupin material. Lupin lamina was consistently high in metabolisable energy (11.3-12.6 MJME/kg DM) and crude protein (24-33%) throughout the growing season. Under controlled experimental conditions at Lincoln University, sheep liveweight gain from a dryland mixed cocksfoot (Dactylis glomerata L.)-lupin pasture was 810 kg/ha compared with 1227 kg/ha from dryland lucerne over a 15-month period. This difference was primarily driven by the amount of palatable feed consumed by the sheep, which was 7330 kg DM/ha for cocksfoot-lupin compared with 10,922 kg DM/ha for lucerne. The abundance of lupin in the mixed pasture declined from 40% of the total herbage offered, during the first autumn after sowing (March to May, 2014), to 22% of total herbage offered in the first full growth season (August 2014 to May 2015). This meant that at least 60% of the diet of these sheep was comprised of cocksfoot. In late spring/summer, the growth rate of cocksfoot-lupin pastures slowed to 20 kg DM/ha/day compared with 43 kg DM/ha/day for lucerne. Despite these differences in feed consumption and pasture composition, the feed conversion efficiency of sheep liveweight gain was the same for both pasture types and averaged 131 g of liveweight gain/kg of DM consumed from August 2014 to May 2015. The greater sheep liveweight gain and total feed consumed on lucerne compared with cocksfoot-lupin was associated with a greater DM yield through improved water-use efficiency for lucerne. During the 2014/2015 growth season, the cocksfoot-lupin pasture produced 6612 kg DM/ha compared with 8122 kg DM/ha for lucerne before a soil moisture deficit started to limit pasture growth in summer 2014/15. To produce this yield, lucerne used 404 mm of water whereas cocksfoot-lupin used 360 mm of water. This equated to a water use efficiency of 20.9 kg DM/ha/mm for lucerne and 18.6 kg DM/ha/mm for cocksfoot-lupin. The ‘Monteith framework’ was successfully applied to both pasture types and provided an accurate description of water extraction patterns to a depth of 165 cm. Lucerne extracted an additional 53 mm of moisture than cocksfoot-lupin from the soil profile between 55 and 155 cm. These results helped to explain the superior sheep liveweight gain on lucerne. Lupinus polyphyllus plants were heavily nodulated at 10 field sites sampled across the South Island. Twenty-two bacterial isolates formed functional nodules on L. polyphyllus, which indicated that rhizobia, capacble of nodulating L. polyphyllus, were present across a wide range of sites in the South Island. Gene sequences identified all 22 isolates and the Group G commercial inoculant as Bradyrhizobium sp. Eleven isolates and the Group G inoculant were tested for their effectiveness on growth of L. polyphyllus under glasshouse and field conditions. Plants were grown in a high-country soil under glasshouse conditions and all plants nodulated regardless of inoculum treatment. However, plant growth was variable and further quantification was required. Field studies showed that inoculation was beneficial for the growth of L. polyphyllus seedlings under high-country conditions. Therefore, despite the presence of effective rhizobia throughout the South Island, inoculation is recommended for newly established stands. Both L. polyphyllus and lucerne responded to increasing levels of soil nitrate by reducing N fixation. Application of potassium nitrate at rates up to 600 kg N/ha had little effect on the growth or herbage N concentration of L. polyphyllus or lucerne. However, the proportion of N derived from soil (%Ndfs) increased consistently with fertiliser applications between 50 and 600 kg N/ha. For both species, %Ndfs was highest at a fertiliser rate of 600 kg N/ha, where %Ndfs was 62% for L. polyphyllus and 74% for lucerne. This thesis confirmed that L. polyphyllus is a suitable forage option for dryland, high-country, farmers. Rather than replacing lucerne, L. polyphyllus should be viewed as a complementary species that can considerably improve the productivity of areas of lower soil fertility. In this context, L. polyphyllus is best suited to areas that are often uneconomical to develop for traditional legumes. Farmers will need to carefully manage L. polyphyllus during establishment, with a focus on seedbed preparation and careful grazing management during the first season. However, once established, L. polyphyllus will likely remain as a persistent dryland species that will produce significant amounts of spring forage on high-country farms.
agronomy, perennial lupin, high country, plant science, Lupinus polyphyllus L., Russell lupin, dryland, high country pastures, Medicago sativa L., Mackenzie Basin, farming, ANZSRC::07 Agricultural and Veterinary Sciences, ANZSRC::0703 Crop and Pasture Production, ANZSRC::070302 Agronomy
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