Grazed Dairy Pasture Research Articles

Modelling nitrous oxide emissions from dairy-grazed pastures

Soil N2O emissions were measured during four seasons from two highly productive grass-clover dairy pastures to assess the influences of soil moisture, temperature, availability of N (NH 4 + and NO 3 – ) and soluble C on N2O emissions, and to use the emission data to validate and refine a simulation model (DNDC). The soils at these pasture sites (Karapoti fine sandy loam, and Tokomaru silt loam) differed in texture and drainage characteristics. Emission peaks for N2O coincided with rainfall events and high soil moisture content. Large inherent variations in N2O fluxes were observed throughout the year in both the ungrazed (control) and grazed pastures. Fluxes averaged 4.3 and 5.0 g N2O/ha/day for the two ungrazed sites. The N2O fluxes from the grazed sites were much higher than for the ungrazed sites, averaging 26.4 g N2O/ha/day for the fine sandy loam soil, and 32.0 g N2O/ha/day for the silt loam soil. Our results showed that excretal and fertiliser-N input, and water-filled pore space (WFPS) were the variables that most strongly regulated N2O fluxes. The DNDC model was modified to include the effects of day length on pasture growth, and of excretal-N inputs from grazing animals; the value of the WFPS threshold was also modified. The modified model ‘NZ-DNDC’ simulated effectively most of the WFPS and N2O emission pulses and trends from both the ungrazed and grazed pastures. The modified model fairly reproduced the real variability in underlying processes regulating N2O emissions and could be suitable for simulating N2O emissions from a range of New Zealand grazed pastures. The NZ-DNDC estimates of total yearly emissions of N2O from the grazed and ungrazed sites of both farms were within the uncertainty range of the measured emissions. The measured emissions changed with changes in soil moisture resulting from rainfall and were about 20% higher in the poorly drained silt loam soil than in the well-drained sandy loam soil. The model accounts for these climatic variations in rainfall, and was also able to pick up differences in emissions resulting from differences in soil texture.

Dung decomposition in temperate dairy pastures. II. Contribution to plant-available soil phosphorus

Changes in dung and soil inorganic and organic P pools were measured in an experiment investigating the effects of dung on soil properties in 2 grazed dairy pasture systems (low and high input). Total dung P and bicarbonate-extractable P pools were measured in decomposing pads and compared with the changes in inorganic and organic bicarbonate-extractable soil P, P sorption, and microbial P flush of soils beneath dung pads and control 'pads' where nothing was applied. Bicarbonate-extractable total P in the dung pads declined to the same level in both systems by the last sample date. Organic P comprised a similar proportion (36%) of the bicarbonate-extractable total P pool in dung from both low and high input systems. However, the transformations of dung P were different in each system, with the bicarbonate-extractable total P in the low input dung increasing by 25% before declining, and a greater decrease in percentage bicarbonate-extractable organic P in this system.Bicarbonate-extractable soil organic P did not vary under dung pads despite the large increases in Olsen and Colwell P observed. Soil Olsen P trends observed in the low and high input systems indicate a potential for leaching losses of P in high input systems compared with low. This increase in soil Olsen P was not due to decreased P sorption as dung did not reduce the sorption capacity of the soil. Microbial soil P increased under dung pads only after 60 days in this experiment. Neither the organic P nor microbial P pools contributed significantly to soil labile P pools in these temperate dairy pasture systems. The transformations of P thought to occur during the decomposition of dung are discussed.

Mitigation of nitrous oxide emissions in spray‐irrigated grazed grassland by treating the soil with dicyandiamide, a nitrification inhibitor

Abstract. Nitrous oxide (N2O) from animal excreta in grazed pasture systems makes up a significant component (c. 10%) of New Zealand's total greenhouse gas inventory. We report an effective method to decrease N2O emissions from animal urine patches by treating the soil with the nitrification inhibitor dicyandiamide (DCD), in a simulated grazed dairy pasture system under spray irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). By treating the soil with DCD, N2O emissions were decreased by 76% following urine application in the autumn, from 26.7 kg N2O‐N ha−1 without DCD to an average of 6.4 kg N2O‐N ha−1 with DCD over the 6‐month experimental period. N2O flux was decreased by 78% following urine application in the spring, from 18 kg N2O‐N ha−1 without DCD to 3.9 kg N2O‐N ha−1 with the application of DCD over the 3‐month period. A single application of DCD immediately after urine was sufficient to effectively mitigate N2O emissions from the urine. The results showed that repeated applications of DCD after urine application, or mixing DCD with urine, offered no advantage over a single application of DCD immediately after urine deposition.

Using constructed wetlands to treat subsurface drainage from intensively grazed dairy pastures in New Zealand

Performance data, during the start-up period, are presented for constructed wetlands treating subsurface drainage from dairy pastures in Waikato (rain-fed) and Northland (irrigated), North Island, New Zealand. The wetlands comprised an estimated 1 and 2% of the drained catchment areas, respectively. Nitrate concentrations were high in the drainage inflows at both sites (medians 10 g m(-3) at Waikato and 6.5 g m(-3) at Northland), but organic N was also an important form of N at Waikato (37% of TN). Comparison of wetland inflow and outflow nutrient concentrations showed overall nutrient reductions during passage through the wetlands for NO3-N (34 and 94% for medians, respectively), TN (56 and 33%, respectively), and DRP (80%, Northland only). Median NH4-N (both sites) and DRP (Waikato) concentrations showed apparent increases between the wetland inlets and outlets. However, a mass balance calculated for the 3 month preliminary monitoring periods showed substantial mass removal of DRP (80%) and all measured forms of N (NO3-N 78%, NH4-N 41%, Org-N 99.8% and TN 96%) in the Waikato wetland. Monitoring of these systems needs to be continued through a range of seasons and years to fully assess their long-term performance.

Hot-water extractable carbon in soils: a sensitive measurement for determining impacts of fertilisation, grazing and cultivation

Using pre-established trial sites on allophanic soils, we investigated the impacts of long to medium-term pastoral management practices, such as fertilisation and grazing intensity, on a range of soil biological and biochemical properties; hot water-extractable C (HWC), water-soluble C (WSC), hot-water extractable total carbohydrates, microbial biomass-C and N and mineralisable N. These properties were examined for their usefulness as soil quality indicators responding to changes in the rhizosphere caused by management practices. Adjacent cropping, market garden and native bush sites located on similar soil types were included to determine the changes in soil biological and biochemical properties resulting from changes in land use. The seasonal variability of HWC and its relationship with other labile fractions of soil organic matter was also examined. Microbial biomass-C, mineralisable N and extractable total carbohydrates showed promise in differentiating treatment and land use effects. However, HWC was one of the most sensitive and consistent indicators examined at 52 different sites. The impact of different land uses on the amounts of HWC in the same soil type was far greater than that was observed for the soil organic carbon. The average values of HWC for soil under different land use were: native (4000 μg C g −1 soil), sheep/beef pastures (3400), dairy pastures (3000), cropping (1000) and market gardening soils (850). HWC was also sensitive to differences within an ecosystem, e.g. effects of grazing intensities and effects of N or P fertilisers on pastures. The sheep and beef/cattle grazed pastures always had higher amounts of HWC than the intensively grazed dairy pastures. Nitrogen fertiliser application (200 and 400 kg N ha −1 yr −1) over the previous 5 yr had significant ( P<0.001) negative impacts on HWC and other soil microbial properties. In contrast, long-term application of P fertilisers had a significant ( P<0.001) positive effect on the HWC levels in pastoral soils. In the case of long-term P trials, HWC increased even though no increase in the total soil carbon pool was detected. HWC was positively correlated with soil microbial biomass-C ( R 2=0.84), microbial nitrogen ( R 2=0.72), mineralisable N ( R 2=0.86), and total carbohydrates ( R 2=0.88). All these correlations were significant at P<0.001 level of significance. The HWC was also positively correlated with WSC and total organic C. However, these correlations were poorer than those found for other soil parameters. Most of these measurements have been actively promoted as key indicators of soil quality. Given the strong correlations between HWC and other biochemical measurements, HWC could be used as an integrated measure of soil quality. When HWC is extracted, other pools of labile nutrients are also extracted along with C. Therefore it is suggested that decline in HWC would also indicate a decline in other labile organic pools of nutrients such as nitrogen, sulphur and phosphorus. About 40–50% of the C in the HWC extract was present as carbohydrates.

The use of a nitrification inhibitor, dicyandiamide (DCD), to decrease nitrate leaching and nitrous oxide emissions in a simulated grazed and irrigated grassland

Abstract. In grazed dairy pasture systems, a major source of NO3– leached and N2O emitted is the N returned in the urine from the grazing animal. The objective of this study was to use lysimeters to measure directly the effectiveness of a nitrification inhibitor, dicyandiamide (DCD), in decreasing NO3– leaching and N2O emissions from urine patches in a grazed dairy pasture under irrigation. The soil was a free‐draining Lismore stony silt loam (Udic Haplustept loamy skeletal) and the pasture was a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). The use of DCD decreased NO3–‐N leaching by 76% for the urine N applied in the autumn, and by 42% for urine N applied in the spring, giving an annual average reduction of 59%. This would reduce the NO3–‐N leaching loss in a grazed paddock from 118 to 46 kg N ha–1 yr–1. The NO3–‐N concentration in the drainage water would be reduced accordingly from 19.7 to 7.7 mg N L–1, with the latter being below the drinking water guideline of 11.3 mg N L–1. Total N2O emissions following two urine applications were reduced from 46 kg N2O‐N ha–1 without DCD to 8.5 kg N2O‐N with DCD, representing an 82% reduction. In addition to the environmental benefits, the use of DCD also increased herbage production by more than 30%, from 11 to 15 t ha–1 yr–1. The use of DCD therefore has the potential to make dairy farming more environmentally sustainable by reducing NO3– leaching and N2O emissions.

A lysimeter study of the fate of 15N‐labelled nitrogen in cow urine with or without farm dairy effluent in a grazed dairy pasture soil under flood irrigation

Nitrate (NO 3 – ) leaching from cow urine patches is considered to be a major contributor to the overall NO 3 – leaching loss in grazed dairy pastures. Farm dairy effluent (DE) is usually applied to grazed pastures to recycle nutrients. The objective of this study was to determine the fate of cow urine nitrogen (N), labelled with 15N, applied to soil monolith lysimeters with or without DE application. The soil was a Templeton fine sandy loam (Haplustepts), and the pasture was perennial ryegrass (Lolium perenne) and white clover (Trifolium repens). Cow urine was applied in the autumn at 1000 kg N ha–1 either alone or with DE (400 kg N ha–1 yr–1 split into four applications). The lysimeters were flood irrigated. One year after application, 6.4–9.1% of the 15N‐labelled urine N was lost by leaching, 29.3–38.8% was removed in the cut pasture, 45.7–47.5% remained in the soil and plant roots, and <2% was lost by volatilisation. The application of DE plus urine significantly increased pasture yield and pasture N offtake above those in the Urine alone treatment, but reduced the percentage recovery of the 15N‐labelled urine N in the pasture top compared with the Urine alone treatment. The amount of N unaccounted for was slightly higher in the Urine + DE (13.9%) treatment than in the Urine alone treatment (5.3%), probably due to increased denitrification as a result of organic carbon inputs from the DE. The urine N application significantly suppressed the clover component of the pasture, and this has implications for N budgeting on grazed dairy pastures. The amount of 15N lost by leaching from the Urine alone treatment confirms that this is a major contributor to the overall effect of dairying on drainage water quality.

The long-term impact of nitrogen fertiliser on perennial ryegrass tiller and white clover growing point densities in grazed dairy pastures in south-western Victoria

A 3-year grazing experiment determined the impact of multiple applications of different rates of nitrogen (N) fertiliser, applied over autumn and winter in 1997, 1998, and 1999, on perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) tiller and growing point densities (stolon apices with at least 2 nodes). Annual pasture dry matter (DM) yields were also monitored. Four treatments were replicated 3 times in a randomised block design and included: 0 N (A); 3 applications of 25 kg N/ha (B); 3 applications of 50 kg N/ha (C); and 3 applications of 75 kg N/ha (D). Urea (46% N) was the N source. Grazing of treatment plots occurred at a pre-grazing herbage mass of 2200–2500 kg DM/ha.Over 3 years, N applications consistently increased annual pasture DM yields by 0.9–3.3 t/ha when a total of 75–225 kg N/ha was applied annually.Generally, treatments B, C, and D resulted in higher perennial ryegrass tiller densities than treatment A. An exception occurred from July 1998 in Year 2 to July 1999 in Year 3, when all perennial ryegrass densities were similar. Nitrogen fertiliser generally produced no consistent effect on white clover growing point density, with the exception of July–December in Year 2 when treatments B, C, and D resulted in lower growing point densities than treatment A. Clover growing point density decreased over the trial period irrespective of treatment. There were no N fertiliser effects on 'other' grasses and broadleaved weeds. 'Other' grasses (mainly winter grass, Poa annua) did, however, peak in density (up to 2500 tillers/m2) from July to September each year.Seasonally, the peak perennial ryegrass tiller density was similar each year and occurred during late winter–early spring (5450 tillers/m2 in July 1997; 6200 tillers/m2 in August 1998; 5400 tillers/m2 in July 1999). This was followed by a trough over midsummer (800 tillers/m2 in January 1998; 725 tillers/m2 in January 1999). White clover growing point density declined over 3 years. During this decline there were peaks in June 1997 (2650 growing points/m2), November 1997 (1600 growing points/m2), June 1998 (1250 growing points/m2), April 1999 (1050 growing points/m2), and November 1999 (850 growing points/m2). Troughs occurred in January 1998 (530 growing points/m2) and February 1999 (380 growing points/m2).It is concluded that although increasing applications of N increased annual pasture DM yields and generally increased perennial ryegrass tiller densities, with little effect on clover growing point densities, there is little to suggest that N fertiliser alone would enhance the persistence of these pasture species. Persistence is likely to be influenced by a combination of factors including grazing management and climatic effects, rather than N fertiliser alone.

Soil dwelling macro-invertebrates in intensively grazed dairy pastures in Pennsylvania, New York and Vermont

This study estimates the relative contributions of environment and farm management strategies in influencing soil faunal assemblages and attempts to identify the species with potential to affect sustainability of intensive grazing management systems in the north-eastern USA. It arises because of the change from confinement feeding of dairy cattle, consequent upon concerns about negative environmental effects, the rising costs for machinery and housing, and reduced profit margins, together with the absence of data from which the consequences of such change on the soil fauna may be predicted. Macro-invertebrates were sampled in soil from seventy-eight grazed pastures on twenty-one dairy farms in Pennsylvania, USA, in the spring of 1994. On five of these farms, macro-invertebrates were sampled (four pastures per farm) in the spring, summer and autumn seasons of 1994, 1995 and 1996. In 1997, macro-invertebrates were sampled in soil during spring, summer and autumn from (four pastures per farm) on three farms in New York, and during spring and summer on three farms in Vermont. Species richness ranged from two to twelve species (mean 6·4) per pasture site in Pennsylvania and five to eighteen species (mean 10·7) in New York and Vermont. The communities were dominated at most sites by earthworms. Earthworms were correlated with soil basal and substrate-induced respiration/carbon ratio, and soil moisture, but were negatively correlated with cows per hectare and herbage biomass in Pennsylvania. Sitona larvae were recorded at nineteen of the twenty-one farms during the spring of 1994 across Pennsylvania and occurred at populations >5 m−2 in 68% of the sampled pastures. Sitona larvae were less abundant in New York and Vermont. Elaterid larvae comprised a complex of seven species of which Aeolus melillus (Say) and Melanotus communis (Gyllenhal) comprised 35% and 39%, respectively, of the elaterids collected in Pennsylvania. Agriotes mancus (Say) and Ctenicera destructor (Brown) comprised 41% and 26%, respectively, of four species collected in New York and Vermont. Scarabaeid larvae, comprising a complex of eight species, were detected at only 27% of the seventy-eight pastures sampled in spring 1994 in Pennsylvania. Five species were collected in ten of the twelve New York pastures and four species in nine of the twelve Vermont pastures. Populations of scarabaeid larvae averaged <25 m−2 in all three states, except in three Pennsylvania pastures in spring 1994. Detrended canonical correspondence analysis (DCCA) showed pasture standing biomass, legume diversity, pre-winter stubble height, white clover pasture content, and soil phosphorus levels influenced numbers of invertebrate species more than climatic factors, such as temperature, rainfall, altitude, latitude and seasonal water table. DCCA also showed most pastures to be close to the average of environmental factors. The extremely low density of herbivorous macro-invertebrates in soil and the absence of pest outbreaks may indicate a stable soil ecosystem.

White clover growth patterns during the grazing season in a rotationally grazed dairy pasture in New York

White clover (Trifolium repens L.) is an important stoloniferous pasture legume in the Great Lakes region of the United States, but it often has limited persistence. Researchers in New Zealand and Wales have found that in spring, compared with other seasons, white clover plants have reduced branching complexity and have the fewest buds that produce leaves. They therefore suggested that in spring the plants are most vulnerable to grazing and climatic stress.Because of severe winter and cool, wet spring weather in New York State, it was hypothesized that white clover plants would also be of low branching complexity, smaller and have low axillary bud activity in spring compared with later in the grazing season. To test this, growth of white clover was monitored in an orchard grass (Dactylis glomerata L.)/white clover pasture in New York that was rotationally grazed with dairy cows during the 1993 and 1994 grazing seasons.Three sets of plants were sampled. The first set consisted of forty random plants sampled before each grazing event. Stolon branching order, number of each stolon branching type and area the plant occupied were determined. Approximately each month before one grazing event, a separate set of 32 random plants was measured in the field to determine the area they occupied; these plants were then removed to the laboratory for the measurement of stolon order, number of each stolon type, stolon lengths, total number of growing points, number of taproots and adventitious roots, root position and above‐ground dry matter. Once a month, 12 additional plants were removed to measure axillary bud activity at each node.Leaf development from nodes tended to increase from spring to summer. However, the stolon branching order of white clover plants was not simpler in spring compared with summer or autumn. In 1994 during and after a dry and hot period, white clover plants were smaller, of lower stolon branching order and had fewer roots. Climate and associated soil organism activity appear to explain the different white clover growth patterns observed in New York and New Zealand. Severe winters in New York limit earthworm activity and stolon burial, which is important in contributing to stolon/plant breakdown in New Zealand. During the years of this study in New York, a hot and dry period had the most negative effect on the growth pattern of white clover.

High phosphorus supply increases persistence and growth of white clover in grazed dairy pastures during dry summer conditions

Measurements of pasture appearance, white clover leaf and stolon mass, stolon water potential, and percentage clover cover in the sward were made for grazed dairy pastures at Ellinbank, West Gippsland, Victoria, during the hot, dry month of February 1997. The perennial ryegrass–white clover-based pastures were in rotationally grazed paddocks from a large farmlet experiment and had received different levels of phosphorus fertiliser (0 or 280 kg P/ha over an 18-month period), and were being grazed with 2 or 3 cows/ha for the no-phosphorus, or 3 or 4 cows for the high-phosphorus paddocks. Further measurements of white clover composition in the pasture swards were made in April, following autumn rain. There were marked differences in white clover (i.e. more yellow, flaccid and desiccated plants with fewer leaves) and pasture appearance (higher frequency of patchy, weedy, poorly utilised areas) in the no-phosphorus, compared with the high-phosphorus treated pastures with the same stocking rate of 3 cows/ha. Also, the high-phosphorus paddocks had a greater white clover percentage than the low-phosphorus paddocks in February with mean percentages of 13.8 and 7.8% respectively. Following rains in March and April, the mean percentage clover cover in high-phosphorus paddocks had increased substantially by 30 April 1997 to 30.6% whereas there was a small improvement in mean clover content in the low-phosphorus paddocks (12.3%). The white clover plants in the high-phosphorus paddocks had heavier stolons, larger leaves and, for the medium stocking rate (3 cows/ha), they appeared to have more leaves per cm of stolon. The findings support previous studies which have highlighted how high-phosphorus application rates can improve the performance of repeatedly defoliated white clover plants during dry periods.

Annual nitrogen fixation in grazed dairy pastures in south-western Victoria

Amounts of biologically fixed nitrogen (kg N/ha) were determined in grazed dairy pastures in 3 different areas of south-western Victoria over 12 months between October 1995 and 1996 using measurements of pasture growth, botanical composition, and the 15N natural abundance of white clover (Trifolium repens) and non-legume components. Estimates of the amounts of N fixed, based on N in clover shoots, were similar in each pasture (11, 16, and 18 kg N/ha.year), despite different environmental and management conditions. These on-farm determinations were low compared with experimental studies on N fixation by white clover undertaken in New Zealand (224–291 kg N/ha.year) and elsewhere in Australia (44–135 kg N/ha). Low fixation levels were attributed to low pasture yields (average 8.2 t dry matter (DM)/ha.year) and poor legume content in the swards (average 8%). Despite this, most of the white clover N was derived from atmospheric N2 (65%), and therefore, N fixation could potentially be playing an important role in the N economy of milk production on these farms.

Effect of high rates of nitrogen fertiliser on white clover growth, morphology, and nitrogen fixation activity in grazed dairy pasture in northern New Zealand

Abstract Nitrogen (N) fertiliser was applied to dairy pastures at nominal rates of 0, 200, or 400 kg N/ha per year on farmlets stocked at 3.24 (LS) or 4.53 (HS) Friesian cows/ha from June 1993 to June 1995. By June 1995, clover contents on farmlets LS200 and LS400 were 10.6 and 2.2%, respectively, compared with 16.8%onfarmletLS0. Most loss of clover on farmlets LS200 and LS400 occurred during the first 6 months of the trial when slow early‐spring growth of clover combined with high N responses put clover at a competitive disadvantage. N had a smaller effect on clover content under the high stocking rate because of improved utilisation of N‐boosted pasture. By June 1995, there was little difference in clover content between farmlets HS0 (15.4%) and HS200 (14.9) although clover content was lower on farmlet HS400 at 6.8%. The decrease in clover content under N fertiliser on the low‐stocked farmlets was confirmed by the decrease in clover plant density and stolon biomass. N fixation activity was consistently higher under no N fertiliser than on either of the low‐stocked farmlets which received N. Application of 400 kg N/ha per year had a significant (P < 0.05) effect on clover plant morphology but plants on farmlet LS200 were no different to those on farmlet LS0. Plants on farmlet LS400 had lower stolon length and stolon dry weight (DW), developed fewer axillary buds, and therefore had fewer stolons. Although total leaf DW and number of leaves/plant were lower on farmlet LS400, values for number of leaves/stolon and individual leaf DW were not significantly different. There were no significant differences between populations in either root number/plant or root DW/plant.

Effect of high rates of nitrogen fertiliser on perennial ryegrass growth and morphology in grazed dairy pasture in northern New Zealand

Abstract Nitrogen (N) fertiliser was applied to dairy pastures at rates of 0,200, or 400 kg N/ha per year on farmlets stocked at 3.24 (LS) or 4.53 (HS) Friesian cows/ha from June 1993 to June 1995. Annual net herbage accumulation increased 22 and 23% on farmlets LS200 and HS200 respectively, and 37 and 24% on farmlets LS400 and HS400. Most of the extra herbage was perennial ryegrass. Ryegrass contents (% total dry matter (DM)) were 71 and 76% on farmlets LS200 and LS400 respectively compared with 61% on farmlet LS0. Ryegrass tiller densities were also higher on farmlets LS200 and LS400 (6295 and 6673 tillers/ m2 respectively) than on farmlet LS0 (4072 tillers/ m2). On all farmlets there was a post‐flowering (January‐February) increase in tiller density although this increase was enhanced by N. N application also increased tiller number/plant (3.37, 4.10, and 4.26 tillers/plant on farmlets LS0, LS200, and LS400 respectively). The greater leaf number and leaf dry weight (DW)/plant on farmlets LS200 and LS400 was connected to the increased tiller number/plant, although DW/leaf was also significantly (P < 0.05) greater under N. There was no N effect on leaf sheath or basal stem, but DW/ tiller was significantly (P < 0.05) greater. Ryegrass plants formed two types of internodal stolon: I(v) associated with vegetative growth throughout the year; and I(r) associated with reproductive growth and only formed during November—January. N had no effect on I(v) formation but 35 and 34% of plants formed I(r) on farmlets LS200 and LS400 respectively compared with 22% on farmlet LS0. It is suggested the positive effects of N on tiller number and DW/plant together with the post‐flowering increase in tillering may improve persistence of perennial ryegrass in intensively grazed dairy pastures.

Nitrogen losses from grazed dairy pasture, as affected by nitrogen fertiliser application

Abstract Inputs and losses of nitrogen (N) were determined in dairy farmlets receiving nominally 0, 200 or 400 kg N/ha/yr as urea at Dairying Research Corporation No. 2 dairy, Hamilton. In year 1, N, fixation by white clover was estimated by r5N dilution at 212, 165 and 74 kg N/ha/yr in the 0, 200 and 400 N treatments respectively. Removal of N in milk was 76, 89 and 92 kg N/ha in the 0, 200 and 400 N farmlets respectively. Loss of N into the air by denitrification was low (6-15 kg N/ha/yr), and increased with N application. Ammonia loss into the air was estimated by micrometeorological mass balance at 15, 45 and 63 kg Nlhalyr in the 0, 200 and 400 N treatments respectively. Most of the increase in ammonia loss was attributed to direct loss after fertiliser application. Leaching of nitrate was estimated using ceramic cup samplers at 1 m soil depth, in conjunction with lysimeters, to be 74, 101 and 204 kg NlhaJyr during the second winter when rainfall and drainage (55@-620 mm) were relatively high. Nitrate-N concentrations in leachates increased gradually over time in the 400 N treatment to an average of 37 mg/l during the second winter, whereas the corresponding values for the 0 and 200 N treatments were 12 and 18 mg/l. Preliminary measurements of groundwater suggest that :ihe nitrate-N concentration is increasing under the 400 N farmlet relative to the other two farmlets. Thus, the 400 N treatment had a major effect by greatly reducing N, fixation and increasing N losses, whereas the 200 N treatment had relatively little effect on N, fixation or on nitrate leaching. However, these results refer to the first 18 months of the trial and further measurements are required over time to determine the longer-term effects of these treatments, particularly on nitrate levels in groundwater. Keywords: ammonia loss, dairying, denitrification, groundwater, leaching, nitrogen fertiliser, N, fixation

Growth and persistence of perennial ryegrass and white clover direct-drilled into a paspalum-dominant dairy pasture treated with glyphosate

Abstract Paspalum-dominant pastures suffer from poor winter/spring herbage production, which can be corrected by direct-drilling cool-season-active species such as ryegrass. The growth and persistence of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.) direct-drilled into a paspalum (Paspalum dilatatum Poir.)-dominant, rotationally grazed dairy pasture, and their effects on production, were studied over 5 years. Treatments were original pasture (control) and herbicide treatment with 0, 0.72, 1.44, and 2.16 kg a.i./ha of glyphosate (Roundup® herbicide, 36% glyphosate) before direct-drilling. Observations on tagged ryegrass and white clover plants found establishment plant numbers for ryegrass were 74% higher (788 plants/m2) in herbicide-treated than in untreated areas (452 plants/m2). Half of all tagged ryegrass plants disappeared in the first year after which losses were much reduced. The establishment and survival of tagged white clover plants were poor. Paspalum gradually re-infested the herbicide-treated areas and by the end of the fourth year had reached pretreatment levels of 30–40% of dry matter (DM). Application of glyphosate before drilling produced a 38% increase in winter/spring herbage accumulation in the first year, but this advantage declined and was non-significant by the end of the fourth year.

Mass balance modelling of potassium losses from grazed dairy pasture

Abstract A simple mass balance model was used to estimate the annual losses of potassium (K) from three dairy farms. The results showed that while the amount lost from each farm varied, 74–92% of the losses were directly caused by the grazing dairy cow through product removal from the farm, excreta transfer to unproductive areas, and preferential flow of urine K through the soil to beyond the effective plant rooting depth. A net loss of K leads to reductions in soil K, and for one of the farms (on an organic soil with a low total soil K content) it was possible to show that the predictions of K losses made by the model were comparable with actual changes in soil K status. The K losses per stock unit (su) estimated by this model for the three farms ranged from 3.4 to 4.7 kg K/su and contrasted with a loss of 4.0 kg K/su in the model used by the Ministry of Agriculture and Fisheries (MAF) for predicting K fertiliser requirements. Refinements to the MAF model are suggested for calculating the animal loss factor.

Use of potassium bromide solutions to simulate dairy cow urine flow and retention in pasture soils

Abstract A series of field experiments determined the amount of dairy cow urine that moved preferentially via a network of soil macropores beyond the 15 cm depth of soil following a urination event onto pasture. Urination events were simulated using potassium bromide solutions and the amount of bromide that was retained within the top 15 cm of the soil profile was measured. The experiments were carried out on seven different soil types, four of which were sampled in two different seasons. Results showed that between 52 and 106% of the applied bromide was retained in the top 15 cm depth of soil, therefore between 0 and 46% of the “urine” was lost beyond this depth as a result of preferential flow. In general, the amount of urine that was lost was more dependent on the physical conditions of the soil surface (e.g., water-repellent or compacted soil surface, irregular surface microtopography, and macropore distribution) than the soil chemical and mineral characteristics or moisture content. These results indicate that preferential flow of urine could result in significant losses of the urine potassium, nitrogen, and sulphur from grazed dairy pastures.

Losses of potassium from grazed dairy pastures

A simple model was used to estimate losses of potassium (K) which occur from a Mid- Canterbury dairy farm. Analysis of the results shows the role of the dairy cow in causing losses of K from the farm. The results from this study could be used to refine the estimates of animalinduced losses of K in the model used by MAF Technology to predict fertiliser recommendations. Such refinements include the incorporation of information on the time that cows spend off the pasture (in the dairy shed, raceway and on feedpads) and the amount of K lost from urinations. The study suggests that savings in K fertiliser requirements through reduced losses from dairy farms are best achieved by minimising the time that dairy cows spend off the pasture and avoiding excessive K concentrations in herbage through heavy rates of K fertiliser. Keywords potassium, model, potassium cycling, potassium losses, dairy cattle