Benefits Are Limited with High Nitrogen Fertiliser Rates in Kikuyu-Ryegrass Pasture Systems

Nitrogen (N) fertiliser is applied to pastures in dairy farming systems to ensure productivity, but it is an expensive input that could be damaging to the environment if used excessively. In the southern Cape region of South Africa, N fertilisation guidelines for pastures were developed under conditions different to current management practices, yet dairy producers still base fertiliser programmes on these outdated guidelines. This study aimed to determine the efficiencies of N fertilisation. Various N fertiliser rates (0, 20, 40, 60 and 80 kg ha−1 applied after grazing), as well as a variable rate according to the nitrate concentration in the soil water solution, were assessed on a grazed pasture. Dairy cows returned to a pasture approximately 11 times per year. Pasture production showed a minimal response to fertilisation within each season. The most responsive parameters to fertilisation were the herbage crude protein content, soil mineral N content and urease activity. Reduced microbial activity was observed when more than 40 kg N ha−1 was applied. When considering the soil total mineral N content, N is used inefficiently at rates above 40 kg N ha−1. The results are indicative of an N saturated system that provides a rationale for reducing N fertiliser rates.

Dairy soil bacterial responses to nitrogen application in simulated Italian ryegrass and white clover pasture

Through clearing and use of fertilizer and legumes, areas of southwestern Australia's unique coastal sand plains can support relatively low-cost dairies. However, the ancient, highly weathered nature of the soils in this region makes the dairies susceptible to a range of threats, including nutrient leaching and erosion. Despite this, Western Australian dairy cows typically produce up to 5,500 L of milk per head annually supported by inorganic nitrogen (N) fertilizer (commonly 50:50 urea and ammonium sulfate) at rates up to <320 kg of N/ha per year. Where hotspots exist (up to 2,000 kg of N/ha per year), total N exceeds pasture requirements. We investigated plant and soil bacteria responses to N fertilizer rates consistent with Australian legislated production practices on dairy farms for pure and mixed swards of white clover (Trifolium repens) and Italian ryegrass (Lolium multiflorum) in a long-term pasture experiment in controlled glasshouse conditions. Although the soil bacterial community structure at phylum level was similar for white clover and Italian ryegrass, relative abundances of specific subgroups of bacteria differed among plant species according to the N fertilizer regimen. Marked increases in relative abundance of some bacterial phyla and subphyla indicated potential inhibition of N cycling, especially for N hotspots in soil. Ammonium concentration in soil was less correlated with dominance of some N-cycling bacterial phyla than was nitrate concentration. Changes in bacterial community structure related to altered nutrient cycling highlight the potential for considering this area of research in policy assessment frameworks related to nutrient loads in dairy soils, especially for N.

More milk from forage: Milk production, blood metabolites, and forage intake of dairy cows grazing pasture mixtures and spatially adjacent monocultures

There is interest in the reincorporation of legumes and forbs into pasture-based dairy production systems as a means of increasing milk production through addressing the nutritive value limitations of grass pastures. The experiments reported in this paper were undertaken to evaluate milk production, blood metabolite concentrations, and forage intake levels of cows grazing either pasture mixtures or spatially adjacent monocultures containing perennial ryegrass (Lolium perenne), white clover (Trifolium repens), and plantain (Plantago lanceolata) compared with cows grazing monocultures of perennial ryegrass. Four replicate herds, each containing 4 spring-calving, cross-bred dairy cows, grazed 4 different forage treatments over the periods of early, mid, and late lactation. Forage treatments were perennial ryegrass monoculture (PRG), a mixture of white clover and plantain (CPM), a mixture of perennial ryegrass, white clover, and plantain (RCPM), and spatially adjacent monocultures (SAM) of perennial ryegrass, white clover, and plantain. Milk volume, milk composition, blood fatty acids, blood β-hydroxybutyrate, blood urea N concentrations, live weight change, and estimated forage intake were monitored over a 5-d response period occurring after acclimation to each of the forage treatments. The acclimation period for the early, mid, and late lactation experiments were 13, 13, and 10 d, respectively. Milk yield (volume and milk protein) increased for cows grazing the RCPM and SAM in the early lactation experiment compared with cows grazing the PRG, whereas in the mid lactation experiment, milk fat increased for the cows grazing the RCPM and SAM when compared with the PRG treatments. Improvements in milk production from grazing the RCPM and SAM treatments are attributed to improved nutritive value (particularly lower neutral detergent fiber concentrations) and a potential increase in forage intake. Pasture mixtures or SAM containing plantain and white clover could be a strategy for alleviating the nutritive limitations of perennial ryegrass monocultures, leading to an increase in milk production for spring calving dairy cows during early and mid lactation.

Simple versus diverse pastures: opportunities and challenges in dairy systems

For Australian and New Zealand dairy farms, the primary source of home-grown feed comes from grazed perennial pastures. The high utilisation of perennial pasture is a key factor in the low cost of production of Australian and New Zealand dairy systems and, hence, in their ability to maintain international competiveness. The major pasture species used are perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.), normally grown in a simple binary mixture. As pasture production has been further driven by increasing use of nitrogen fertiliser and irrigation, farms are getting closer to their economic optimum level of pasture utilisation. Increasing inputs and intensification have also increased scrutiny on the environmental footprint of dairy production. Increasing the diversity of pasture species within dairy swards presents opportunities to further increase pasture utilisation through additional forage production, extending the growing season, improving forage nutritive characteristics and, ultimately, increasing milk production per cow and/or per hectare. Diverse pastures also present an opportunity to mitigate some of the environmental consequences associated with intensive pasture-based dairy systems. A consistent finding of experiments investigating diverse pastures is that their benefits are due to the attributes of the additional species, rather than increasing the number of species per se. Therefore, the species that are best suited for inclusion into dairy pastures will be situation specific. Furthermore, the presence of additional species will generally require modification to the management of dairy pastures, particularly around nitrogen fertiliser and grazing, to ensure that the additional species remain productive and persistent.

Fatty acid profile differs between organic and conventionally produced cow milk independent of season or milking time

Differing amounts of fresh forage and concentrates fed, and level of input contributes to the differences reported in fatty acid (FA) composition of organic and conventionally produced cow milk. In many previous studies designed to investigate this phenomenon, comparisons were made between grazed organic cows and housed conventional cows. In the present study, we have investigated differences between organic and conventional milk produced using year-round pasture grazing, as practiced in New Zealand. The FA composition was determined in milk sampled at morning and evening milking in both spring and autumn. Samples were taken from 45 cows from the Massey University organic herd and compared with 50 cows from the corresponding conventional herd grazed and managed similarly at the same location. Forty-three out of 51 analyzed FA were influenced by season, whereas 28 were different between production systems. In addition, one-half were also different due to time of milking. Levels of linoleic acid and α-linolenic acid were higher in organic milk, whereas conjugated linoleic acid (CLA) and vaccenic acid were higher in conventional milk. The first 3 FA (linoleic acid, α-linolenic acid, and CLA) were more abundant in milk harvested during autumn, and the CLA concentration was also significantly influenced by time of milking. Our results confirm reports that the FA profile is affected by season and time of milking, and we also showed an effect due to the production system, when both sets of cows were kept continuously on pasture, even after taking milking time and seasonal effect into account.

Nutritive value of herbage from mountain hay meadow managed under traditional and intensive harvest systems as affected by nitrogen fertilisation and time of cutting

The aim of this study was to investigate the influence of harvest season and nitrogen (N) fertilisation on chemical composition and digestibility of the herbage harvested from a mountain meadow (of the vegetation type Arrhenatheretalia). Four rates of N fertiliser (0, 60, 120 and 180 kg N/ha per year in a single spring application of calcium ammonium nitrate) were compared in field-replicated plots. The experiment lasted 7 years. During the first 3 years each plot was harvested twice per year (June and September) according to a traditional harvest system, whereas in the last 3 years (after a transitional year) each plot was harvested three times per year (spring, summer and autumn) following a more intensive harvest system. In both harvest systems, herbage collected in the first cut (early or late June) had higher fibre contents and lower digestibility (P < 0.001) than herbage collected in the regrowth. N fertiliser increased significantly (P < 0.001) the annual yield of herbage in the 2-harvest system, but did not affect (P > 0.10) herbage yield in the 3-cuts system. N fertiliser changed the botanical composition of herbage and promoted grass growth, resulting in increased (P < 0.05) fibre content and decreased (P < 0.05) digestibility and rate of degradation of herbage, these effects being variable in the different harvest seasons. Our results suggest that the more intensive management system without N fertilisation could be considered a suitable practice for the management of these botanically complex mountain meadows. These results may contribute to design fertilisation and management practices of mountain hay meadows to optimise their productivity and sustainability.

Quantifying pasture dry matter responses to applications of potassium fertiliser for an intensively grazed, rain-fed dairy pasture in south-western Australia with or without adequate nitrogen fertiliser

Rain-fed dairy pastures on sandy soils common in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise the annual species subterranean clover (Trifolium subterraneum L.) and annual and Italian ryegrass (Lolium rigidum Gaud. and L. multiflorum Lam.). In wet years, clover becomes potassium (K) deficient and shows large dry matter (DM) responses to applied fertiliser K due to leaching of K in soil by rainfall. In contrast, ryegrass rarely shows DM responses to applied K. Many dairy pastures in the region are now intensively grazed to maximise pasture use for milk production, and nitrogen (N) fertiliser is applied after each grazing. It is not known if frequent applications of fertiliser N to these pastures changes pasture DM responses to applied K. Therefore, a long-term (2002–07) field experiment was undertaken on an intensively grazed dairy pasture in the region to quantify pasture DM responses to applied fertiliser K with or without applications of adequate fertiliser N (141–200 kg N/ha per year). Soil samples (top 10 cm of soil) were collected from each plot of the experiment each February to measure soil test K by the standard Colwell sodium bicarbonate procedure used for both K and phosphorus soil testing in the region. When no N was applied, pasture comprised ~70% (dry weight basis) clover and 25% ryegrass, compared with ~70% ryegrass and 25% clover when adequate N was applied. Significant linear responses of pasture DM to applied K occurred in 3 of the 6 years of the experiment only when no N was applied and clover dominated the pasture. The largest response varied from ~1.7 to 2.0 t/ha DM consumed by dairy cows at all grazings in each year, giving a K response efficiency of between 8 and 10 kg DM/ha per kg K/ha applied. Significant pasture DM responses to applied N occurred at all grazings in each year, with ~2–3 t/ha extra DM consumed by dairy cows at all grazings in each year being produced when a total of 141–200 kg N/ha was applied per year, giving an N response efficiency of ~7–19 kg DM/ha per kg N/ha applied. Soil test K values were very variable, attributed to varying proportions of soil samples per plot collected between and within cow urine patches, containing much K, arbitrarily deposited on experimental plots during grazing. Soil test K values were not significantly affected by the rates of K applied per year. A re-evaluation of results from the major soil K test study conducted for pastures in the region confirm that ryegrass rarely showed DM responses to applied K, and that for clover, soil K testing poorly predicted the likelihood of K deficiency in the next growing season.