Pasture Dry Matter Production Research Articles

Lowering the water solubility of phosphorus fertilisers impacts leaching, plant growth and residual soil phosphorus

Context Leaching of phosphorus (P) from water soluble agricultural fertilisers applied to sandy soil can adversely impact downstream water quality. Less soluble fertilisers may reduce P leaching and increase production. However, repeated application of low water soluble P (LWSP) fertiliser with high citrate soluble P (CSP) has potential to increase P leaching and P accumulation. Methods We examined the effect of LWSP fertilisers (single superphosphate, SSP; fertilisers low in water soluble P, WSP) on leaching losses in soil with low P retention/low P status; with/without bauxite residue amendment and with/without plants. Key results On low P retentive soils with a low P status, P leaching was reduced by reducing the WSP of fertiliser. Plants and soil amendment reduced P leaching further, but P loss remained proportional to WSP applied. Under field conditions, a subset of LWSP fertilisers greatly increased pasture dry matter production and increased soil test P values. Soil test P increases were positively correlated to fertiliser citrate soluble P content. Soils already containing at least 80% of the required plant available P did not require a WSP fertiliser to provide early season P. Conclusions LWSP fertilisers and soil amendment have potential to reduce P leaching in low P retentive soils. Fertiliser formulations targeting reduced WSP and high CSP require attention. Implications LWSP fertilisers may increase soil P residues reducing future P needs; however, ongoing soil testing is required for assessment of soil P accumulation, requirements and leaching potential.

Productivity, changes and resilience in New Zealand grassland agriculture over the last three decades

This paper discusses key changes in New Zealand pastoral agriculture over the last three decades at the national scale, and how these have influenced the performance of grasslands, animal productivity, and the resilience of pastoral livestock systems. It assesses the positive and negative impacts of land-use change, changes in pasture production and supplementary feeding and dry matter (DM) consumed, and the key management practices implemented by farmers to enhance farm system resilience. It also notes environmental and other policy changes and examines how sectors and Government have started to respond. The largest estimated increase in DM consumed by livestock from 1990 to 2018 was from increased supplementary feed in the dairy sector. The largest estimated decline in DM production was due to pasture-land conversion to planted forests, followed by weed and pest impacts. In 2018, the dairy sector consumed the most DM at an estimated 25.0M t/yr, followed by sheep at 16.6M t/yr and beef at 10.1M t/yr. The total consumed DM in 2018 was 51.9 M t/yr which corresponds well with the independently estimated national pasture DM production of 64M t/yr. The environmental impacts of managements to enhance resilience in DM availability are becoming evident and future regulations may limit the extent some of these practices can expand.

The effect of fertilizer nitrogen input to grass-clover swards and calving date on the productivity of pasture-based dairy production

The objective of this systems-scale study was to investigate grazing season timeframes on pasture and milk production and on milk processability of dairy systems with compact spring-calving dairy cows grazing white clover (Trifolium repens L.) based grassland. Fifty-four primiparous and multiparous Holstein-Friesian dairy cows were used in a one-factor study with 3 systems (n = 18) and repeated over 2 yr (2008/09 and 2009/10). The 3 systems were: early spring calving with annual fertilizer N input of 100 kg·ha-1 applied in spring (ES100N; 2.1 cows·ha-1; grazing February to November), early spring calving without fertilizer N (ES0N; 1.6 cows·ha-1; grazing February to November) and late spring calving without fertilizer N (LS0N; 1.53 cows·ha-1; grazing April to January). Annual pasture production was affected by an interaction between grazing system and year: Mean annual pasture yields for 2008 and 2009 were ES100N; 10.35 and 9.88, ES0N; 8.88 and 8.63, LS0N; 9.18 and 10.31 t of dry matter (DM)·ha-1 (SEM 0.39). LS0N had higher pasture DM yield in 2009 due to higher clover DM production and biological N fixation compared with the other systems. Clover stolon and root mass in the following February was correlated with stolon and root mass in the previous November with 64% of stolon mass present on LS0N in February (R2 = 0.84). There were no detectable differences in per-lactation milk yield (6,335 kg·cow-1), fat, protein and lactose yields (271, 226, 297 kg·cow-1, respectively), cow liveweight (585 kg) or body condition score (3.02). Although winter grazing favored subsequent clover DM production, biological N fixation and pasture DM production, delaying calving date in spring and extending lactation into the following winter led to inefficient use of this pasture by the grazing herd and lowered the quality of late-lactation milk for processing purposes. Hence, a mean calving date in mid- to late-February is recommended for zero-fertilizer N input clover-based grassland.

Irrigation Scheduling with Soil Gas Diffusivity as a Decision Tool to Mitigate N2O Emissions from a Urine-Affected Pasture

Pastures require year-round access to water and in some locations rely on irrigation during dry periods. Currently, there is a dearth of knowledge about the potential for using irrigation to mitigate N2O emissions. This study aimed to mitigate N2O losses from intensely managed pastures by adjusting irrigation frequency using soil gas diffusivity (Dp/Do) thresholds. Two irrigation regimes were compared; a standard irrigation treatment based on farmer practice (15 mm applied every 3 days) versus an optimised irrigation treatment where irrigation was applied when soil Dp/Do was ≈0.033 (equivalent to 50% of plant available water). Cow urine was applied at a rate of 700 kg N ha−1 to simulate a ruminant urine deposition event. In addition to N2O fluxes, soil moisture content was monitored hourly, Dp/Do was modelled, and pasture dry matter production was measured. Standard irrigation practices resulted in higher (p = 0.09) cumulative N2O emissions than the optimised irrigation treatment. Pasture growth rates under treatments did not differ. Denitrification during re-wetting events (irrigation and rain) contributed to soil N2O emissions. These results warrant further modelling of irrigation management as a mitigation option for N2O emissions from pasture soils, based on Dp/Do thresholds, rainfall, plant water demands and evapotranspiration.

Simulated seasonal responses of grazed dairy pastures to nitrogen fertilizer in SE Australia: N loss and recovery

Evidence from farm level studies indicates that there is potential to improve nitrogen (N) fertilizer efficiency of Australian dairy farms. Increasing N fertilizer application rates to drive pasture dry matter production beyond an agronomic or economical optimum has the potential to result in detrimental environmental outcomes. Our study, using the biophysical whole-farm systems model DairyMod, modelled a range of N fertilizer rates on total N loss for five dairy sites through south-eastern Australia, using 18 years of historical climate. Nitrogen accumulation in plant biomass and soil N accumulation within and below the rootzone were estimated. Total N loss, in the form of volatilization, leaching, runoff and denitrification lost to the environment were also estimated. The reduction in N fertilizer inputs required to achieve 90% of relative yield (Y90), relative to maximum pasture production (Ymax), was > 50% across all sites and seasons. The associated reduction in total N loss when fertilizer was reduced from Ymax to Y90, varied between 34% and 74%, depending on site and season. Nitrogen recovery (proportion of N recovered in biomass relative to N fertilizer applied) exceeded 100% with lower N fertilizer rates (< 30 kg N ha-1 month-1) for most sites and seasons. Demand for N was high during spring due to high pasture growth and this was supported via N mineralization and legacy N build-up in winter. Nitrate leaching risk was highest in winter for the four temperate sites and autumn at the subtropical site. This study demonstrated the benefits of developing site and seasonal-specific N fertilizer best management practice guidelines that are both economical and environmentally beneficial. When considering whether to add more fertilizer, the value of additional pasture production needs to be weighed up against environmental N losses and the cost of additional N fertilizer to achieve this. The relationship between seasonal soil and climatic conditions and N loss and recovery were also examined for one rainfed site. As this study does not consider the externalities associated with N loss, recommendations need to be considered and amended in the context of location specificity and seasonal climatic conditions.

Grazing Preference of Dairy Cows and Pasture Productivity for Different Cultivars of Perennial Ryegrass under Contrasting Managements.

Simple SummaryIncreasing soluble sugars in pasture species can lead to an improved nutrient use efficiency in the rumen and a greater digestibility of forage, which in turn might increase pasture intake. However, this improvement in nutritional value must not be at the expense of pasture productivity; the amount of nutrients harvested is a relevant factor in ruminant grazing systems’ efficiency. Therefore, we tested four different cultivars of perennial ryegrass (two selected for greater soluble sugar content and two standard cultivars) submitted to two contrasting managements (one aimed at improving sugar content and one with the opposite intended effect) for their effects on pasture productivity (by cutting herbage every time the plots reached the target number of leaves per tiller, i.e., two or three) and the grazing preference of dairy cows (six cows grazed for up to 5 hours, in an experimental area with three plots for each of the eight treatments) in spring, summer and autumn. We found that high sugar grasses had lower annual dry matter productivity and no preference was shown by cows, although the agronomic management aimed at reducing sugar concentration enhanced crude protein concentration and increased the herbage harvested (greater preference) in the three seasons, and the time spent grazing in autumn.The objective of this study was to evaluate the pasture performance of different cultivars of perennial ryegrass, two “high sugar” and two standard cultivars, under two contrasting agronomic managements (aimed at either decreasing or increasing water soluble carbohydrates concentration), and their effects on the grazing preference of dairy cows. Eight treatments arising from the factorial combination of four cultivars and two managements were randomly applied to 31-m2 plots in three blocks. Pasture dry matter production and growth rate were measured for one year. Three grazing assessments were performed to establish the grazing preferences of six dairy cows in spring, summer and autumn. High sugar cultivars produced less dry matter per hectare than the standard cultivars. Cows consumed more grass and harvested a greater proportion of the pasture under the agronomic management aimed at decreasing sugar concentration, i.e., with a greater nitrogen fertilization rate and under a more frequent defoliation regime, which could be explained by the greater crude protein concentration achieved under this management. The results suggest that the genetic selection for greater levels of sugars was at the expense of herbage yield, and that cows preferred to graze herbage with a greater crude protein level instead of a greater sugar concentration.

Dairy cow breed interacts with stocking rate in temperate pasture-based dairy production systems

Economic optimum stocking rates for grazing dairy systems have been defined by accounting for the pasture production potential of the farm [t of dry matter (DM)/ha], the amount of feed imported from outside the farm (t of DM/ha), and the size of the cow (kg). These variables were combined into the comparative stocking rate [CSR; kg of body weight (BW)/t of feed DM available] measure. However, CSR assumes no effect of cow genetics beyond BW, and there is increasing evidence of within-breed differences in residual feed intake and between-breed differences in the gross efficiency with which cows use metabolizable energy for milk production. A multiyear production system experiment was established to determine whether Jersey (J) and Holstein-Friesian (HF) breeds performed similarly at the same CSR. Fifty-nine J cows and 51 HF cows were randomly allocated to 1 of 2 CSR in a 2 × 2 factorial arrangement; systems were designed to have a CSR of either 80 or 100 kg of BW/t of feed DM (J-CSR80, J-CSR100, HF-CSR80, and HF-CSR100 treatment groups). Data were analyzed for consistency of farmlet response over years using ANOVA procedures, with year and farmlet as fixed effects and the interaction of farmlet with year as a random effect. The collated biological data and financial data extracted from a national economic database were used to model the financial performance for the different breed and CSR treatments. On average, annual and individual season pasture DM production was greater for the J farmlets and was less in the CSR100 treatment; however, the effect of CSR was primarily driven by a large decline in pasture DM production in the HF-CSR100 treatment (breed × CSR interaction). This interaction in feed availability resulted in a breed × CSR interaction for the per-cow and per-hectare milk production variables, with HF cows producing more milk and milk components per cow in the CSR80 treatment but the same amount as the J cows in the CSR100 treatment. On a per-hectare basis, HF cows produced the same amount of 4% fat-corrected milk and lactose as J cows in the CSR80 treatment, but less fat; at CSR100, J cows produced more 4% fat-corrected milk, fat, and protein per hectare than HF cows. Our results support a greater gross efficiency for use of metabolizable energy by the J cow; 11% less total metabolizable energy was required to produce 1 kg of fat and protein at a system level. Economic modeling indicated that profitability of both breeds was less at CSR100, but the decline in profitability with increasing stocking rate was much greater in the HF breed. Holstein-Friesian cows were more profitable at CSR80 but were less profitable at CSR100.

Modelling of lucerne (Medicago sativa L.) for livestock production in diverse environments

Several models exist to predict lucerne (Medicago sativa L.) dry matter production; however, most do not adequately represent the ecophysiology of the species to predict daily growth rates across the range of environments in which it is grown. Since it was developed in the late 1990s, the GRAZPLAN pasture growth model has not been updated to reflect modern genotypes and has not been widely validated across the range of climates and farming systems in which lucerne is grown in modern times. Therefore, the capacity of GRAZPLAN to predict lucerne growth and development was assessed. This was done by re-estimating values for some key parameters based on information in the scientific literature. The improved GRAZPLAN model was also assessed for its capacity to reflect differences in the growth and physiology of lucerne genotypes with different winter activity. Modifications were made to GRAZPLAN to improve its capacity to reflect changes in phenology due to environmental triggers such as short photoperiods, declining low temperatures, defoliation and water stress. Changes were also made to the parameter governing the effect of vapour pressure on the biomass-transpiration ratio and therefore biomass accumulation. Other developments included the representation of root development and partitioning of canopy structure, notably the ratio leaf : stem dry matter. Data from replicated field experiments across Australia were identified for model validation. These data were broadly representative of the range of climate zones, soil types and farming systems in which lucerne is used for livestock grazing. Validation of predicted lucerne growth rates was comprehensive owing to plentiful data. Across a range of climate zones, soils and farming systems, there was an overall improvement in the capacity to simulate pasture dry matter production, with a reduction in the mean prediction error of 0.33 and the root-mean-square deviation of 9.6 kg/ha.day. Validation of other parts of the model was restricted because information relating to plant roots, soil water, plant morphology and phenology was limited. This study has highlighted the predictive power, versatility and robust nature of GRAZPLAN to predict the growth, development and nutritive value of perennial species such as lucerne.

Phosphate fertiliser application effects on seasonally dry hill country pasture and soil

ABSTRACTA grazed trial established in 1980 evaluated the effects of superphosphate fertiliser application on pasture growth on Easy (10°–20° slope) and Steep (30°–40° slope) land in the Waikato, North Island, New Zealand. Continuous and rotational grazing showed no effects on pasture responses to fertiliser. Mean annual pasture dry matter (DM) production ranged from 11,275 to 14,155 kg DM ha−1 on Easy, and 6413 to 7480 kg DM ha−1 on Steep slopes through the range of 10–100 kg ha−1 yr−1 of phosphate (P) fertiliser rates. Initial fertiliser effects on Olsen P tests were in the 0–3 cm depth only, and in the 7–15 cm soil depth only in the 100 kg ha−1 yr−1 treatment by year 4. Near maximum (97%) annual production, derived from relative yield analysis, was obtained at 0–7 cm depth soil tests of 30 on Easy slopes and at 12 on Steep slopes. Results from this trial are directly relevant to the variable fertiliser rate aerial application technology currently being developed.

Effect of stocking rate on pasture and sheep production in winter and spring lambing systems

A 2-year study was conducted to quantify the effect of stocking rate on pasture and sheep production in winter and spring lambing systems. Pastures were set-stocked with ewes and their winter-born single lambs at low (20 ewes + lamb ha?1), medium (28 ewes + lamb ha?1), and high (36 ewes + lamb ha?1) stocking rates in spring 2012 and by ewes and their spring-born lambs at low (16 ewes + lamb ha?1), medium (24 ewes + lamb ha?1), and high (32 ewes + lamb ha?1) stocking rates in spring 2013. Annual pasture dry matter production ranged from 8.9 to 10.2 t ha?1 but was not affected by the spring stocking rates. The average live weight gains of the winter-born lambs were 73 and 10 g head?1 day?1 for low and medium stocking rates, respectively, while the lambs at the high stocking rate lost 10 g head?1 day?1 in spring 2012. The spring-born lambs grew at 245, 189, and 133 g head?1 day?1 for low, medium, and high stocking rates, respectively, in spring 2013. High stocking rates did not have any negative effects on the pasture production or botanical composition but they resulted in poor sheep performance, particularly in the winter lambing system.

Dry matter and sheep production of four dryland tall fescue-clover pastures 4-6 years after establishment

Effects of tall fescue cultivar ('Advance' and 'Flecha') and clover species (white and subterranean (sub) clovers) combinations on pasture dry matter (DM) and sheep production were assessed in years four (2011/12), five (2012/13) and six (2013/14) after establishment in dryland, Canterbury. 'Advance' pastures yielded less total herbage than 'Flecha' pastures (13.9 cf. 16.5 t DM/ha) but more fescue (8.6 cf. 5.9 t DM/ha) and 2.1 t DM/ha clover in year four, 13.5 t DM/ha total herbage with more fescue (8.0 cf. 4.1 t DM/ha) and 1.9 t DM/ha clover in year five, and 11.7 t DM/ha total herbage, 5.4 t DM/ha fescue and 0.8 t DM/ha clover in year six. Sub clover pastures yielded more total, fescue and clover herbage (16.9, 8.8 and 3.2 t DM/ha) than white clover pastures (13.5, 5.7 and 1.0 t DM/ha) in year four, more fescue in year five (7.2 cf. 4.9 t DM/ha), and more clover in year six (1.2 cf. 0.3 t DM/ha). Sheep liveweight gain was greater for sub than white clover pastures in year four (939 cf. 431 kg/ha) and five (697 cf. 481 kg/ha) and 689 kg/ha in year six. Therefore, sub clover and 'Advance' were generally more productive than white clover and 'Flecha', but both fescues showed similar persistence after 6 years. Keywords: cultivar, Festuca arundinacea, grass-clover mixtures, liveweight gain, Trifolium subterraneum, Trifolium repens

The economic significance of maintaining pasture production at its peak value

Persistence of pasture is considered an important trait by many farmers using pasture-based systems. Despite this, pasture persistence is generally poorly defined. This study includes an analysis of changes in farm operating profits (OP) when pasture persistence is improved. Persistence was defined as either a 1-year increase in years at peak dry matter (DM) production or a reduction in the rate of decline in annual pasture DM production after the year that peak production occurred (duration of pasture life), both resulting in a 1-year delay in pasture renovation. Changes in OP for these definitions of pasture persistence were modelled for two dairy farms in temperate regions of Australia (Terang in south-western Victoria and Elliott in Tasmania). An increase in duration of peak DM production on the basis of economic theory increased OP more than an increase in duration of pasture life. Increases in OP for a 1-year increase in peak DM production were AU$165 ha–1 for Terang and $202 ha–1 for Elliott. This compared with $21 ha–1 for Terang and $15 ha–1 for Elliott for a 1-year increase in the duration of pasture life. Therefore, farmers and plant breeders could place more emphasis on improving the duration of time that pasture plants achieve peak DM production than improving pasture persistence at the end of the pasture plant’s lifetime, to increase annual OP.

Progress in developing perennial wheats for grain and grazing

Dual-purpose cereals have been important for increasing the flexibility and profitability of mixed farming enterprises in southern Australia, providing winter feed when pasture dry matter production is low, and then recovering to produce grain. A perennial dual-purpose cereal could confer additional economic and environmental benefits. We establish that, at the end of a second growth season, selected perennial cereals were able to achieve up to 10-fold greater below-ground biomass than a resown annual wheat. We review and expand the data on available, diverse, perennial, wheat-derived germplasm, confirming that perenniality is achievable but that further improvements are essential through targeted breeding. Although not yet commercially deployable, the grain yields and dry matter production of the best performing lines approach the benchmarks predicted to achieve profitability. On reviewing the genomic composition of the most promising wheat-derived perennials, we conclude that the best near-term prospect of a productive breeding program for a perennial, wheat-derived cereal will utilise a diploid, perennial donor species, and the most promising one thus far is Thinopyrum elongatum. Furthermore, the breeding should be aimed at complete wheat–Th. elongatum amphiploids, a hybrid synthetic crop analogous to triticale. We advocate the generation of many primary amphiploids involving a diversity of Th. elongatum accessions and a diversity of adapted annual wheat cultivars. Primary perennial amphiploids would be inter-crossed and advanced with heavy, early-generation selection for traits such as semi-dwarf plant height, non-shattering heads, large seed size and good self-fertility, followed by later generation selection for robust perenniality, days to flowering, grain yield, forage yield, stability of grain yield across seasons, and disease resistance.

Effect of pre-grazing herbage mass on dairy cow performance, grass dry matter production and output from perennial ryegrass (Lolium perenne L.) pastures

A grazing study was undertaken to examine the effect of maintaining three levels of pre-grazing herbage mass (HM) on dairy cow performance, grass dry matter (DM) production and output from perennial ryegrass (Lolium perenne L.) pastures. Cows were randomly assigned to one of three pre-grazing HM treatments: 1150 – Low HM (L), 1400 – Medium HM (M) or 2000 kg DM/ha – High HM (H). Herbage accumulation under grazing was lowest (P<0.01) on the L treatment and cows grazing the L pastures required more grass silage supplementation during the grazing season (+73 kg DM/cow) to overcome pasture deficits due to lower pasture growth rates (P<0.05). Treatment did not affect daily milk production or pasture intake, although cows grazing the L pastures had to graze a greater daily area (P<0.01) and increase grazing time (P<0.05) to compensate for a lower pre-grazing HM (P<0.01). The results indicate that, while pre-grazing HM did not influence daily milk yield per cow, adapting the practise of grazing low HM (1150 kg DM/ha) pasture reduces pasture DM production and at a system level may increase the requirement for imported feed.

Time of sowing and the presence of a cover-crop determine the productivity and persistence of perennial pastures in mixed farming systems

Incorporation of perennial pastures into cropping rotations can improve whole-farm productivity, profitability and sustainability of mixed farming systems in southern Australia. However, success in establishing perennial pastures depends on choice of species, time of sowing, method of establishment, seasonal conditions, and whether sowing is under a cover-crop. Field experiments were sown from 2008 to 2010 to determine effects of sowing time and the presence of a cover-crop on the performance of four perennial pasture species, lucerne (Medicago sativa L.), chicory (Cichorium intybus L.), phalaris (Phalaris aquatica L.) and cocksfoot (Dactylis glomerata L.), at Yerong Creek, New South Wales (NSW). Results showed that lucerne was the most productive pasture, followed by chicory and phalaris, with cocksfoot being the poorest performer. Under favourable seasonal conditions, lucerne and chicory pastures produced 29.3 and 25.0 t ha–1 of total dry matter (DM), comprising 71% and 52%, respectively, of sown perennial species in the sward in their second growing season, when sown in autumn. Spring-sown pastures produced 24.6 and 18.3 t ha–1 of total DM in the second season, with 55% and 47% of sown species in the sward being lucerne and chicory, respectively. However, spring-sown pastures contained a very low proportion of subterranean clover (Trifolium subterraneum L.) in the sward in the first 2 years, despite efforts to broadcast seeds at the break of season in the following year. It is recommended that non-legume perennial species, such as chicory and phalaris, be sown in autumn with companion annual legumes until methods are developed and tested to establish annual legumes reliably in spring. However, lucerne can be established in autumn or spring because it can fix its own nitrogen and is not reliant on a companion legume. Cocksfoot cv. Kasbah, in general, appears less suitable than the other perennial species for this medium-rainfall environment in southern NSW. Our study showed that pastures sown without a cover-crop had the most reliable establishment, whereas pastures sown with a cover-crop in a dry year had poor establishment or total failure, as well as a significant reduction of grain yield from the cover-crop. In a wet year, pastures established satisfactorily under a cover-crop; however, growth of the cover-crop still suppressed pasture DM production in subsequent years. Research is under way to model our data to determine the likely financial implications of establishing perennial pastures under cover-crops.

Identification and testing of early indicators for N leaching from urine patches

Nitrogen leaching from urine patches has been identified as a major source of nitrogen loss under intensive grazing dairy farming. Leaching is notoriously variable, influenced by management, soil type, year-to-year variation in climate and timing and rate of urine depositions. To identify early indicators for the risk of N leaching from urine patches for potential usage in a precision management system, we used the simulation model APSIM (Agricultural Production Systems SIMulator) to produce an extensive N leaching dataset for the Waikato region of New Zealand. In total, nearly forty thousand simulation runs with different combinations of soil type and urine deposition times, in 33 different years, were done. The risk forecasting indicators were chosen based on their practicality: being readily measured on farm (soil water content, temperature and pasture growth) or that could be centrally supplied to farms (such as actual and forecast weather data). The thresholds of the early indicators that are used to forecast a period for high risk of N leaching were determined via classification and regression tree analysis. The most informative factors were soil temperature, pasture dry matter production, and average soil water content in the top soil over the two weeks prior to the urine N application event. Rainfall and air temperature for the two weeks following urine deposition were also important to fine-tune the predictions. The identified early indicators were then tested for their potential to predict the risk of N leaching in two typical soils from the Waikato region in New Zealand. The accuracy of the predictions varied with the number of indicators, the soil type and the risk level, and the number of correct predictions ranged from about 45 to over 90%. Further expansion and fine-tuning of the indicators and the development of a practical N risk tool based on these indicators is needed.

Vulnerability of pastoral farming in Hawke's Bay to future climate change: Development of a pre‐screening (bottom‐up) methodology

AbstractAlthough future climate change will significantly affect New Zealand's climate, how regional climates will be changed remains highly uncertain. As a consequence, pre‐screening sensitivity analysis is recommended for climate‐sensitive activities. A ‘bottom‐up’ approach intended to serve this purpose in the context of non‐irrigated pasture is developed and demonstrated in the Hawke's Bay context. This is achieved using a simple daily water balance model to simulate near‐surface hydrological processes and empirical relationships between transpiration and pasture dry matter production. The Hawke's Bay case study indicates that the methodology has merit and is worthwhile pursuing nationally (with refinements).

Effects of stocking rate and closing date on subterranean clover populations and dry matter production in dryland sheep pastures

The effect of stocking rate (8.3 [low] and 13.9 [high] ewes+twin lambs/ha) and time of closing in the spring on subterranean clover morphology, phenology, seedling population and the subsequent clover and pasture dry matter production were monitored over 2 years in a cocksfoot-subterranean clover pasture. Mean subterranean clover seedling populations (per m2), measured in autumn 2007, after grazing treatments in the previous spring, were greater (P<0.05) at the low (2850±267) compared with the high (2500±217) stocking rate and with the earlier closing dates (P<0.05) (3850±398, 2950±242, 2100±126 and 1700±152 at 2, 4, 6 and 8 weeks after the first flower, respectively). Seedling populations measured in 2008, after grazing treatments in the second spring, were lower at both stocking rates (1290±89 at low and 1190±70 at high) and at each closing date (1470±84, 1320±84 and 940±66 at 3, 5 and 8 weeks after the first flower, respectively). The effect of stocking rate and closing dates in spring on pasture and clover production in the following autumn was proportional to seedling numbers in both years. Clover production in the following spring was unaffected by stocking rate or closing date in the previous year at the relatively high seedling populations generated by the treatments.

Response of intensively grazed ryegrass dairy pastures to fertiliser phosphorus and potassium

Intensively grazed, rain-fed dairy pastures on the predominantly sandy soils in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise >90% ryegrass (annual ryegrass, Lolium rigidum Gaud. and Italian ryegrass, L. multiflorum Lam.). To maximise pasture use for milk production, the pastures are rotationally grazed by starting grazing when ryegrass plants have 3 leaves per tiller, and fertiliser nitrogen (N) and sulfur (S), in the ratio of 3–4 N and 1S, need to be applied after each grazing for profitable pasture dry matter (DM) production. In addition, farmers usually also apply low levels of phosphorus (P) and potassium (K) fertiliser to these pastures after each grazing, despite Colwell soil test P usually being well above critical values for pasture production, and fertilizer K being only required for clover in the traditional clover (Trifolium subterraneum L.) ryegrass pastures of the region. In field experiments undertaken May 2006–June 2010 on intensively grazed ryegrass dairy pastures in the region, no significant ryegrass DM responses to applied fertiliser P or K were obtained, regardless of level or method of P or K application. When no P was applied, soil test P declined gradually, by between 4.4 and 7.1 mg/kg per year, and remained above the critical value for the soils at 2 sites, but declined below the critical value for soil at a third site. Critical soil test P is located near the maximum yield plateau in the flat part of the relationship between yield and soil test P, particularly when, as appropriate for dairy production, the critical value is for 95% of the maximum pasture DM yield. Consequently, when no P is applied and soil test P decreases, significant pasture DM yield decreases will only occur when soil test P approaches the steeper part of the relationship, which can take some time. In addition, as occurs on farms, faeces deposited by cows while grazing supplied P to pasture even when no fertiliser P was applied. Soil K testing proved unreliable for indicating the need for fertiliser K applications to pasture in the next growing season because many soil samples collected within and between urine patches contained elevated levels of K deposited by cows while grazing. We conclude fertiliser P should only be applied to intensively grazed ryegrass dairy pastures when soil testing indicates it is required. Further research is required to assess if plant K testing is an alternative, but urine patches may also pose a problem for plant testing.

Recovery of pasture production and soil properties on soil slip scars in erodible siltstone hill country, Wairarapa, New Zealand

Landslide scars previously dated (1977, 1961 and 1941) and sampled in 1984 for pasture production and topsoil characteristics were re-sampled. Pasture dry matter (DM) production and selected soil properties were re-measured on the same scars and uneroded control sites for 2 years, beginning in 2007. The results show that after a further 25 years of recovery, no significant increase in pasture production had occurred on the 1941 and 1961 slip scars. Average DM pasture production on eroded sites increased from 63 to 78% of pasture production levels on uneroded sites, but improvement was restricted to the youngest 1977 slip scars, where DM production increased from 20 to 80% of uneroded levels. Regression analysis revealed that maximum pasture recovery occurred within about 20 years of landsliding and further recovery beyond 80% of uneroded level was unlikely. The recovery of pasture production on slip scars follows similar recovery to soil physical (e.g. soil depth, particle density, bulk density) and chemical properties (e.g. total C, total N). Topsoil depths on eroded sites were roughly a third of topsoil depths on uneroded sites, indicating reduced profile available water capacity on eroded soils. This research was unable to determine if total C would recover to uneroded levels because of the high variability in total C at eroded sites. However, given that uneroded soils were formed under native forest (over a long period of time) and that new soils are forming under pasture (over a short period of time), it is unlikely that total C will recover to uneroded soil levels. This research verifies the conclusion of the previous work carried out in 1984 that it is unlikely pasture production on slip scars will return to production levels on uneroded sites in human timescales. The sustainability of pastoral agriculture on steeper slopes in soft-rock hill country is increasingly under threat from the progressive reduction of pasture production from cumulative erosion.