Waikato Dairy Pastures Research Articles

Response of pastures to fertiliser nitrogen on two peat soils in the Waikato region

Abstract Fertiliser nitrogen (N) response trials were conducted on Waikato dairy pastures on two contrasting peat soils: a well-developed Kaipaki peat loam and a lessdeveloped Rukuhia peat. On the well-developed site the most efficient N fertiliser rate in spring was 25 kg N/ ha with a response of 22 DM/kg N applied. However, in autumn the most efficient rates of N fertiliser were 75 and 100 kg N/ha, with an average response rate of 11 kg DM/kg N. At the less-developed site, the most efficient rates in the spring were 25 to 75 kg N/ha with an average response of 18 DM/kg N applied. In autumn, the maximum response rate of 21 kg DM/kg N was reached through application of 50 and 75 kg N/ha. Results indicate that greater yields are expected from larger applications of N fertiliser on less-developed peat. However, the environmental consequences of increased N fertiliser applications have not yet been assessed. Keywords: nitrogen fertiliser, pasture production, peat

Trade-offs between profit, production, and environmental footprint on pasture-based dairy farms in the Waikato region of New Zealand

Trade-off curves are valuable formalisms for summarising the relationship between profit and environmental outcomes for individual farming systems. This concept is extended here to incorporate production, to recognise the importance of output for promoting economic growth and retaining market access. A whole-farm model is used to evaluate relationships between profit, production, and nitrogen (N) leaching for three pasture-based dairy farms of different intensity in the Waikato region of New Zealand. Using a loafing pad reduces N leaching through preventing the deposition of urinary N on pasture. In the absence of a loafing pad, the lack of cost-effective mitigation strategies means that production and profit decrease markedly when leaching is constrained. However, the use of a loafing pad on medium- and high-intensity farms allows plans with broad diversity in production and leaching to be attained at manageable cost, given the availability of supplement. Collateral impacts of nitrogen-leaching restrictions for greenhouse gas emissions are also explored. It is highlighted that even though imported supplement and a loafing pad are important for reducing nitrogen loss from Waikato dairy pastures, reliance on storage ponds to collect effluent deposited on pads allows atmospheric escape of methane, reducing the value of restricted grazing for the simultaneous reduction of greenhouse gas emissions.

Nutritive value and production of yellow bristle grass (<i>Setaria pumila</i>) in Waikato dairy pastures validating Farmax model assumptions

Yellow bristle grass is a C4 summeractive annual weed prevalent in the upper North Island Its production and nutritive value was assessed onfarm to validate the assumptions used in a published Farmax model on the impact of yellow bristle grass The percentage ground cover of yellow bristle grass averaged 9 in a survey of 39 central Waikato dairy pastures assessed each February over 8 years Yellow bristle grass dry matter content peaked in February Herbage production of patches of yellow bristle grass was greater than patches of perennial ryegrass when assessed over one yellow bristle grass growing season Nutritive value was lower for yellow bristle grass than perennial ryegrass over two consecutive growing seasons Given the prevalence of yellow bristle grass in Waikato dairy pastures its lower nutritive value and more vigorous growth than perennial ryegrass it is likely to have a negative impact on the performance of sown pasture species Findings support the assumptions used in the Farmax model

Multiple small monthly doses of dicyandiamide (DCD) did not reduce denitrification in Waikato dairy pasture

The effectiveness of multiple small doses of the nitrification inhibitor dicyandiamide (DCD) to decrease denitrification under warm moist conditions was tested in a 1-year field trial on a grazed dairy pasture. DCD was applied approximately every 4 weeks as an aqueous spray onto ten replicate plots 3 days after rotational grazing by dairy cows. Each application was at the rate of 3 kg DCD ha−1, with a total annual application of 33 kg ha−1. Denitrification was assessed 5 days after each DCD application using the acetylene block method. At the end of the trial, the rate of degradation of DCD under summer conditions was measured. DCD significantly decreased the mean annual nitrate concentration by about 17%. Denitrification and denitrification enzyme activity were highly variable and no significant effect of DCD in decreasing denitrification was detected. In the summer month of December, DCD degraded rapidly with an estimated half-life of 5±3 days (mean and standard deviation).

Summer pasture yield variation in a central Waikato location from 1979 to 2010: implications for pasture persistence.

Three datasets spanning 31 years (1979-2010) of net herbage accumulation (HA) for Waikato dairy pastures were studied to determine between-year variability in summer HA. In addition, a dairy farm at the same location was modelled with the DairyNZ Whole Farm Model, using climate data for 15 years to predict HA, and milksolids production. Measured extremes for HA over 5 months (1st December to 30th April inclusive) were from 4.7 to 9.1 t DM/ha, with a mean of 7.0 t DM/ ha ±1.2 t DM/ha SD. Rainfall during these months had a positive impact on HA, with an extra 849 kg DM/ ha (r2=0.43, p

Endophyte effects on major insect pests in Waikato dairy pasture

A paddock-scale field trial comparing pastures of perennial ryegrass without endophyte (Nil) or infected with the selected endophytes AR1, AR37 or the standard endophyte (SE) sown with clover was monitored for insect pests over 3 years (2006-2008). Argentine stem weevil larval damage was reduced by all endophytes in each year.

Yellow bristle grass: a recent weed incursion in Waikato dairy pastures

Yellow bristle grass (Setaria pumila) is a summer growing annual grass with a C4 photosynthetic pathway. It is now becoming a serious weed in pasture where it is highly competitive with perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) and is avoided by stock when at the seed head stage. On severely infested farms, it is estimated to cause production losses in the order of $100 000/100 ha unit, mostly due to stock not grazing areas where the yellow bristle grass is seeding. Keywords: yellow bristle grass, Setaria pumila, pasture, grass weed

Sweet success? Managing yellow bristle grass (Setaria pumila) with grazing attractants in dairy pastures

Yellow bristle grass (YBG) is a summer-active grass weed which is rapidly spreading in dairy pastures in the North Island. Different grazing attractants were applied to Waikato dairy pastures at the end of January and February. Cows responded to attractants containing molasses (foliar applied or pellets), but not to coarse agricultural salt or sugar. There was less pasture dry matter, less YBG cover and more bare ground in the pellets treatment. Keywords: Setaria pumila, yellow bristle grass, grazing attractants, molasses, salt, sugar

Modelling factors affecting reproductive development of perennial ryegrass in Waikato dairy pastures

A mechanistic model was developed to identify biological processes responsible for differences in reproductive tillering between 'Ellett' and 'Grasslands Ruanui' perennial ryegrass cultivars. In the model, a field perennial ryegrass tiller population was represented with six compartments: vegetative, emerging reproductive, mature reproductive and dead tillers (three compartments). The biological processes driving the transfer of tillers from one compartment to another were: conversion of vegetative tillers to reproductive tillers, maturation of emerging reproductive tillers, senescence of mature reproductive tillers, and death of reproductive tillers due to grazing. The model was used to analyse data from Waikato dairy pastures. This enabled some of the effects of irrigation, nitrogen, cultivar and season (weather) on the biological processes to be identified. During spring and early summer, the proportion of reproductive tillers in 'Ellett' pastures was always higher than in 'Grasslands Ruanui', regardless of treatment and year. The model explained this difference by a higher conversion rate of 'Ellett' vegetative tillers to reproductive tillers, and suggested that conversion rate is the key process determining reproductive development in perennial ryegrass. Opportunities to control reproductive tillering are discussed. Keywords: flowering, Lolium perenne, perennial ryegrass, reproductive development

Performance of white clover cultivars and breeding lines in rotationally grazed Waikato dairy pasture, New Zealand

The performance of 30 white clover breeding lines, including some already released cultivars, was measured over four years (1 June 1993 to 31 May 1997) in mixed pasture under rotational grazing by dairy cows, in the Waikato region of New Zealand. All the white clovers persisted throughout the trial but parameters measured (visual scoring of vigour, clover yield, and clover %) showed that the performance of most lines and cultivars fell in the final season due mainly to cooler than normal growing conditions in late winter‐summer and a dry spring‐summer. ‘Grasslands Pitau’ was, overall, the top white clover cultivar but showed a significant drop in performance during the dry 1996/97 year. Six other lines, including a newly released cultivar, ‘Kopu II, were in the group of top performing white clovers characterised by high visual scores, clover yields, and clover % in the 1996/97 year. ‘Grasslands Kopu’, the control cultivar, performed poorly, ranking 25th overall. Results indicated that clover persistence is still a problem in dairy pastures, particularly if the climate is dry. Overall, the trial showed that persistence and drought tolerance should be a major focus of future white clover breeding programmes aimed at developing cultivars more suitable for dairy farming in New Zealand.

Effect of deferred grazing during summer on white clover content of Waikato dairy pastures, New Zealand

New Zealand dairy pastures rotationally grazed at intervals of 25 to 30 days to low residual herbage masses (<1400 kg DM ha−1) over summer often suffer white clover death. An experiment was conducted over 1994–1997 in mixed perennial ryegrass/white clover dairy pastures to examine the effects of deferred grazing, the practice of holding over pasture in situ for 50, 75, or 100 days over summer, on white clover growth compared with a more common 25‐day grazing interval. Additional pasture cover built up in 100‐day deferred (100D) plots resulted in significantly (P < 0.05) lower soil temperatures and higher soil moisture levels than in the 25D treatment. Clover stolon survival was up to 63% higher in deferred pastures than the 25D treatment. This, combined with higher clover seedling density, resulted in significantly (P< 0.05) higher clover contents in pastures following deferral compared with the 25D grazed pasture. These differences did not persist through to the following spring. Deferred grazing also resulted in small increases in total herbage accumulation but had little effect on ryegrass tiller density.

White clover growth and morphology in dairy pasture in the Waikato region of northern New Zealand

Abstract Seasonal changes in clover plant growth and structure in a Waikato dairy pasture were monitored over 1 year. Pasture plugs and clover plants separated from turves were removed from paddocks before grazing. They provided data on clover plant density, total stolon biomass, vertical distribution of stolons in the sward, and various morphological characteristics. Plant density averaged 610 plants/m2 which was higher than that recorded in a comparable study of Manawatu sheep‐grazed pastures. Stolon biomass was also greater in the dairy pasture; most of this stolon was on the soil surface (58%) whereas in sheep‐grazed pastures most was buried. The proportion of stolon within each class varied throughout the year. Clover plants fragmented during spring as was shown for Manawatu sheep pastures. Plant density therefore peaked during spring while values for plant morphological characteristics were low since most of the clover population comprised small, 1st‐order plants. Overall, clover plants in Waikato dairy pastures were larger than those in Manawatu sheep‐grazed swards. These differences probably resulted from interactions between several factors including cultivar, climate, soil type, companion species, farm management, and grazing effects.

Cyclic oscillations between a summer-annual (C4) and a winter-annual weed grass in Waikato dairy pastures

Cyclic oscillations between a summer-annual (C4) and a winter-annual weed grass in Waikato dairy pastures

White clover plant morphology in Waikato dairy pastures

Seasonal changes in white clover plant morphology were investigated in Waikato dairy pasture. Plants were classified according to the degree of branching, 2nd-order plants comprising the bulk of the population (47%) throughout the year. There was a slightly greater proportion of lst-order plants than found in similar studies on sheep-grazed swards in Manawahr. Plant fragmentation occurred in late spring, increasing the proportion of lstorder plants. A corresponding decrease in plant size was observed, with minimum values measured for most characteristics, i.e., stolon, leaf and root dry weight (DW); stolon length, and number of leaves, roots and growing points. Overall, white clover plants in Waikato dairy pastures are considerably larger than plants in Manawatu sheep pastures. The trial highlighted that because white clover plants in spring are small, they are vulnerable to mismanagement in dairy pastures, just as has been demonstrated in pasture grazed by sheep. There were, however, some significant differences in white clover plant structure in dairy pastures compared with sheep-grazed swards. Keywords: dairy pasture, morphology, plant order, plant size, seasonal variation, Trifolium repens

Porina control in Waikato dairy pasture

Porina control in Waikato dairy pasture