Dry matter production and water use of dryland cocksfoot/lupin and lucerne pastures in the third year after establishment

Cocksfoot (Dactylis glomerata) is a preferred grass option for dryland pastures on high country farms in the South Island of New Zealand. However, increasing the productivity of cocksfoot based pastures with legumes is difficult due to the harsh environment and difficulty to apply fertiliser. Russell lupin, or perennial lupin (Lupinus polyphyllus) has been identified as a potential legume option due to its ability to tolerate low fertile and acidic soils, cold winters and hot, dry summers in extensive high country grasslands. However, the productivity and water use of cocksfoot/lupin pastures is not well understood. The aim of this study was to compare the dry matter (DM) production and water use of cocksfoot/lupin pastures compared with a standard pure lucerne (Medicago sativa) pasture under dryland conditions. The two pasture types were sown in December 2013 at Lincoln University and in this study they were compared during their third year after establishment. During the first and second years after establishment, lucerne produced more DM than cocksfoot/lupin, and the lupin content halved each year such that the cocksfoot dominated the cocksfoot/lupin pasture after 2.5 years. In attempt to increase the legume content of cocksfoot/lupin pasture, a mixture of two cultivars of subterranean clover (Trifolium subterraneum) (Denmark and Narrikup) were oversown in autumn 2017. Six 0.13 ha paddocks of each pasture type were rotationally grazed by young sheep and not irrigated. In the third year after establishment (11 July 2016 to 29 June 2017), lucerne produced 10,617 kg DM/ha compared with 6,433 kg DM/ha for cocksfoot/lupin. The lucerne yield contained 97% lucerne, 0.2% voluntary white clover and 3.2% weed, whereas the cocksfoot/lupin yield contained 86% cocksfoot, 12% lupin, 0.05% sub clover, 1.2% voluntary white clover and 0.8% weed. Sub clover content averaged 2% in the cocksfoot/lupin pasture during the first grazing rotation in the following spring (3 August to 14 September 2017), with 28% of this Denmark and 72% Narrikp. Nitrogen yield in the herbage was 223 kg N/ha for lucerne compared with 87 kg N/ha for cocksfoot/lupin. Pasture growth rates for lucerne and cocksfoot/lupin were 2.06 and 1.21 kg DM/Cd from 11 July to 17 August, then 6.36 and 3.94 kg DM/Cd to 13 December and then 1.75 and 0.88 kg DM/Cd to 29 June. Water use was 503 mm for lucerne and 498 mm for cocksfoot/lupin. Water use efficiency for iii lucerne and cocksfoot/lupin was 6.35 and 3.40 kg DM/ha/mm from 11 July to 17 August, then 23.33 and 16.30 kg DM/ha/mm to 13 December and then 16.46 and 7.50 kg DM/ha/mm to 29 June. Leaf area index, which was quantified pre-grazing in each paddock from 2 March to 22 May, was 2.0 for lucerne, 2.8 for cocksfoot and 1.5 for lupin. Overall the results suggest that the lucerne pasture was able to produce more DM than the cocksfoot/lupin pasture due to a faster pasture growth particularly in spring. This faster growth rate which lead to a higher water use efficiency, deeper access to soil moisture during summer, and possibly a higher LAI which could have resulted in increased light interception. These attributes make lucerne an attractive option for dryland pastures in areas of the South Island high country where soil fertility is unsuitable for lucerne. By comparison, lupin did not persist and Denmark and Narrikup were established from oversowing in the cocksfoot-dominant pasture.