Search

In parts of the upper North Island, farmers frequently report perennial ryegrass (Lolium perenne L.) pastures failing within 3 or 4 years post-sowing. This appears to be related to interactions between several factors: climatic (drier, hotter summers), biotic (insect pest), soil (texture, water-holding capacity) and grazing management factors that vary spatially and temporally. The efficacy of three management interventions for recovering ryegrass populations and production in runout pasture was assessed in an experiment initiated in 2018/19 in central Waikato. Treatments were a long-spring rotation (LSR), a longer grazing deferral during late spring and summer (pasture deferral, PD) and under-sowing with perennial ryegrass (US), each applied to pastures of four ryegrass cultivars. In the year after the treatments were implemented, the yield of ryegrass in PD was 2.4 t DM/ha greater than for the control (7-year-old pasture), and ryegrass tiller populations initially doubled but later declined. Yields in US and LSR were intermediate but not significantly different from the control. Ground score changes responded more positively to PD compared with the other treatments. Relative to the baseline prior to initiation of the study, tiller populations increased for PD and US but declined for control and LSR. There were no interactions between management treatment and cultivar for any of the variables measured. Pasture deferral shows promise as an intervention for recovering failing ryegrass pastures through natural reseeding. However, the longevity of the benefits observed here has yet to be determined.

Recent years have seen a decline in herbage production and tiller populations in New Zealand's perennial ryegrass (Lolium perenne) dairy pastures. One hypothesis is that modern genotypes are less suited to the warmer, drier weather experienced under changing climate patterns. In this study, a combination of long‐term trial data (2011–2017) and a process‐based pasture model (BASGRA) was used to explore the causes and possible mitigation of the observed production and population loss at three sites (dryland sites in Northland and Waikato and an irrigated site in Canterbury). Bayesian calibration was used to identify the model parameter sets that were consistent with the trial data and to identify differences in plant morphology and responses between sites. The model successfully simulated the observed differences in tiller numbers between the dryland sites, where populations and production declined rapidly after the second year and the irrigated site where populations and production were maintained. Analysis of the model calibrations along with preliminary scenario simulations suggests that increased tiller mortality associated with drought was the main cause of persistence failure at the dryland sites and that decreasing grazing pressure or breeding for tolerance to higher temperatures may not be successful in preventing this.

Pasture persistence can be defined several ways, but a key outcome for farmers is that the yield advantage of a new pasture compared to the pasture it replaced persists for several years after sowing. The concept of persistence of the yield advantage can also be applied to genetic evaluation of cultivars in species such as perennial ryegrass to determine the true value of pasture renewal and cultivar selection. We analysed 8 years of yield and tiller density data from pastures sown to four perennial ryegrass cultivars representing different functional types at two locations, Waikato (non-irrigated) and Canterbury (irrigated). ‘Grasslands Nui’ SE (Nui) was designated as the baseline cultivar. A significant yield advantage over Nui was observed for two cultivars (Alto AR37 and Halo AR37). Peak yield advantage occurred 4 or 5 years post-sowing, then declined by approximately 50% and became nonsignificant by Year 8. The pattern was very similar at both locations. Tiller density data indicated a shift in sward structure over time consistent with size-density trade-offs in the diploid cultivar Alto AR37 but not in the tetraploid cultivar Halo AR37. The implications for economic evaluation systems such as the DairyNZ Forage Value Index are discussed.

The aim of the study was to determine if existing technologies could reduce nitrate leaching by 50%; while maintaining high levels of milk production and profitability. One farmlet, typical of the ...

Poor persistence in perennial ryegrass has been identified as a major limitation to pasture productivity, particularly in the upper North Island. Persistence can best be defined as the continuity of forage yield relative to a cultivar’s potential. Though there is limited evidence of differences in persistence between cultivars, there is interest in including persistence in the DairyNZ Forage Value Index. This requires an agronomically robust metric of persistence, measured over a suitable time frame and connected to economic value. Five candidates are evaluated: plant populations, tiller populations, basal cover, ground score and annual dry matter yield. Scarcity of long-term data is a major limitation to development of performance values for persistence, and must be addressed. The four abundance-based measures also lack a clear connection to economic values, from the limited data available. A persistence metric is proposed, that relates medium-term dry matter yield to short-term dry matter yield, for which perennial ryegrass functional type and cultivar differences are demonstrated.

This experiment, implemented at a Southland site representative of the lower South Island, New Zealand, and monitored for three full years from 2012/2013 to 2015/2016, was one of four throughout New Zealand that investigated the yield and nutritive value rankings of perennial ryegrass cultivars sown with or without white clover and with high (225 kg N/ha/annum) or low (50 kg N/ha/annum) application rates of nitrogen fertiliser. High inputs of nitrogen (N) fertiliser increased annual total dry matter (DM) yields and seasonal yield in 12 out of 18 measurement occasions. Adding white clover increased both annual dry matter yield and seasonal yield in 7 out of 18 measurement occasions. An interaction between clover and N input occurred on 10 occasions. Over time, the low N minus clover treatment became progressively lower yielding compared with the other three treatments. Ryegrass cultivar by clover interactions occurred in the latter half of the experiment. When analysed using ryegrass characteristic...

Combining several cultivars within species in seed mixtures is often advocated as a means for improving crop or pasture performance. Herbage accumulation (HA) of perennial ryegrass-white clover pastures sown with a single cultivar representing different functional types of perennial ryegrass was compared with the HA of cultivar mixtures over three years in two contrasting environments (Waikato, dryland; Canterbury, irrigated) under dairy cattle grazing. Functional types were: mid-season flowering diploid, late-season diploid, and late-season tetraploid. Mixture treatments (n = 4 at each site) included all binary combinations plus the three-way combination. Mixture HA and the mean HA of the constituent cultivars did not differ for any of the mixture combinations in either environment, apart from winter in Waikato where the mid-diploid plus tetraploid mix out-yielded the mean of the individual cultivars and tended to increase total annual HA. The total annual HA of the mixtures was between 1.0 and 2.3 t DM/ha/year less than the HA of the highest-yielding individual cultivar included in the mixture in six of the eight mixture-environment combinations. While some benefits of mixtures for controlling grazing outcomes were observed, sowing individual high-performing cultivars is a better overall strategy than mixing cultivars to cover a spectrum of traits.

Bite placement plays an important role in determining the mean weight of bites removed from a patch, and hence intake rate. This paper describes a video and acoustic methodology to map the sequential placement of bites on the sward surface. The methodology was evaluated for dairy heifers grazing small (0.34 m 2 ) patches of alfalfa ( Medicago sativa L.) to three levels of depletion (6, 18 and 30 bites). Grazing was recorded by a single video camera positioned 0.9 m in front of the animal and on average 1.67 m above the ground. Acoustic monitoring enabled the precise timing of biting jaw movements (bite or chew-bite). For each bite, a single video frame showing the position of the animal's head in the sward canopy was selected at the point in time corresponding to bite severance. Custom image-processing software was used to extract the image (apparent) coordinates of the tip of the muzzle, which was then converted geometrically to world (true) coordinates on the sward surface. A fixed displacement of 8 cm was applied to the world coordinates in order to determine the bite centre. The pattern of grazing impact across the sward surface was predicted by assuming a radius of impact around each bite centre. This pattern was compared with the measured status (grazed or un-grazed) of the herbage beneath each cell of a grid placed over the patch after grazing. Bite placement on the sward surface, as defined by the bite-centre coordinates, followed a progressing, side-to-side pathway. The median distance between the centres of consecutive bites was 12.1 cm, and was significantly less than expected by random bite placement. The orientation of consecutive bite pairs differed significantly from random, consistent with the side-to-side pathway of bite placement. Nevertheless, based on nearest neighbour analysis, the overall pattern of bite spacing on the surface of the sward did not differ significantly from random. These results suggest that the observed declining trend in mean effective bite area with increasing depletion ( P = 0.06) derived from inefficient exploitation of the sward surface. The assumption of a radius of impact of 6 cm revealed a broad correspondence between the measured and predicted patterns of grazing impact across the sward surface. Discrepancies most likely reflected sweeping actions of the tongue during bite formation, lateral head movements during bite severance and simplifying assumptions required by the single-camera approach. The results indicate that the methodology is potentially useful for investigating the rules governing bite placement in the horizontal plane.

Resistance de structure du couvert vegetal et effort de prelevement des bouchees chez les ruminants au pâturage. Face a l'heterogeneite de la ressource en abondance, en valeur nutritive et en repartition, les ruminants au pâturage doivent prendre des decisions complexes pour rechercher et recolter les fourrages necessaires a leurs besoins. Certaines de ces decisions affectent la la masse de la bouchee et donc, l'ajustement de l'ingestion en terme de profondeur et de surface de la bouchee, ainsi que de force de prelevement. Ces decisions sont prises en relation avec 1' heterogeneite de la structure du couvert vegetal. Nombre de relations ont ete mises en evidence liant l'adaptation de la mecanique de la bouchee aux variations de la hauteur et de la densite du couvert vegetal de fourrages temperes pour des animaux de differentes tailles corporelles. En revanche, les grandes variations de resistance des vegetaux, qui resultent des arrangements verticaux et horizontaux des organes morphologiques de la plante (feuille, gaine et tige), ont des effets variables sur la mecanique de la bouchee. De plus, seuls des progres limites ont ete accomplis pour quantifier les forces de prelevement des bouchees impliquees au pâturage, les liens entre les organes morphologiques de la plante et leurs effets sur les forces de prelevement, ainsi que l'interaction avec le format des animaux. Dans cet article, nous discutons les differentes hypotheses qui ont ete proposees pour expliquer la regulation de la profondeur des bouchees, et nous proposons des elements pour leur acceptation ou leur rejet. Nous exposons les lacunes qui subsistent pour comprendre les mecanismes des forces de prelevement a travers differentes especes animales de formats distincts et nous soulignons le besoin de differencier deux concepts: la force de prelevement et l'effort de prelevement.