Productivity, botanical composition and insect population of seven dryland pasture species in Canterbury after eight years

Abstract

The annual and seasonal water use efficiency of six pasture combinations were calculated from the ‘MaxClover’ grazing experiment at Lincoln University, Canterbury. Pastures had been established for seven years and were grazed by best mangement practises for each species combination. Measurements from this study are from individual plots of six replicates of cocksfoot (CF)/Subterranean clover (Sub), CF/Balansa clover (Bal), CF/White clover (Wc), CF/Caucasian clover (Cc), ryegrass (RG)/Wc and lucerne (Luc). Dry matter measurements of yield, botanical composition and herbage quality were assessed from 1 July 2009 to 30 June 2010. Lucerne had the highest total annual yield of 12880 kg DM/ha/y, followed by CF/Sub at 9460 kg DM/ha/y. All other pastures produced 6600 to 8360 kg DM/ha/y. Soil water measurements showed that all pastures had a plant available water content of 316 ± 24 mm. All pastures used 655 ± 22 mm/y of water. Lucerne had the highest annual water use efficiency (WUE) of 23 kg DM/ha/mm/y. The annual WUE of CF/Sub was 16 kg DM/ha/y and the lowest was 11 kg DM/ha/mm/y from RG/Wc and CF/Wc pastures. The CF/Sub and CF/Bal pastures had the highest total annual legume (sown and volunteer white clover) content of all grass based pastures at 18%. Because of yield differences CF/Sub had the highest annual nitrogen yield of 216 kg N/ha of the grass based pastures although it was less than half that from lucerne (462 kg N/ha). RG/Wc pastures had the highest proportion of weeds which represented 62% of total dry matter in Year 8 (2009/10). For dryland farmers spring is the crucial period for production before growth slows when soil water becomes limiting. For the spring period (1/7/2009 to 29/1/2010) lucerne produced 11120 kg DM/ha, which was the highest yield of all pastures follwed by CF/Sub (1/7/2009 to 16/11/2009) which produced 6020 kg DM/ha. When dry matter production was regressed against thermal time, CF/Sub pastures grew at 5.7 ± 0.08 kg DM/° Cd between 1/7/2009 and 16/11/2009 compared with lucerne which grew at 4.2 ± 0.46 kg DM/° Cd between 1/7/2009 and 29/1/2010 which was an extra 74 days of linear spring growth. WUE during the initial period for lucerne (1/7/09 to 29/1/10) was 22.3 ± 0.5 kg DM/ha/mm (R2=1.00). The CF/Sub pastures produced 20 ± 1.5 kg DM/ha/mm (R2=0.98) from 1/7/09 to 16/11/09 from 306 mm of water used. The lowest WUE was 11.7 ± 0.21 kg DM/ha/mm by CF/Wc pastures. Insect pests within CF/Sub, CF/Wc, RG/Wc and lucerne pastures were quantified in winter. Pests included Argentine stem weevil, clover root weevil, Sitona weevil and grass grub. Argentine stem weevil populations were highest in CF/Sub pastures (63 weevils m⁻²) whereas clover root weevil populations were highest in CF/Wc (5 weevils m⁻²). Grass grub was present in all grass based pastures and was the highest in RG/Wc with 208 grubs m⁻². Present pest levels were not at damaging thresholds. Based on the results from this research, dryland farmers should maximize the use and potential of lucerne on farm and sow cocksfoot as the main grass species due to persistence and insect tolerance compared with perennial ryegrass. Subterranean clover should be the main companion legume within cocksfoot pastures. Increased legume content ensures scarce water is used more efficiently because N deficiency in the grass is alleviated.