Herbage Nitrogen Research Articles

Maintaining scattered trees to boost carbon stock in temperate pastures does not compromise overall pasture quality for the livestock

Scattered trees in wood-pastures represent outstanding conservation value by providing microhabitats for a variety of organisms. They also diversify ecosystem services by creating shade for livestock, and capturing and storing carbon. However, trees in wood-pastures are declining Europe-wide and an appropriate legal environment to maintain them is mostly lacking. Here we looked beyond the well-documented beneficial effects of trees and assessed potential ecosystem disservices, which may drive the controversial appreciation of trees. In a grazing exclusion experiment, we assessed the effect of trees on herbage production in wood-pastures from semi-arid continental to humid montane areas in the temperate deciduous forest ecoregion, and found that trees have a suppressive effect throughout the year, although herbage nutritive value, as indicated by herbage nitrogen content, seems to be improved in spring. When we up-scaled the local ecosystem disservice on herbage yield to entire wood-pastures, the loss remained below 3%, which is lower than reported gains in livestock production due to free access to shade. Thus, the motivation for the under-appreciation of trees by land managers and decision makers may lie in that trees suppress herbage production, but the importance of this effects is offset by the magnitude of the beneficial services of trees. We recommend current wood-pasture stakeholders to revisit their attitude towards scattered trees and encourage tree planting campaigns and tree-based climate mitigation strategies to consider the protection of trees in wood-pastures and the establishment of young ones in currently open pastures up to traditionally low tree cover proportions, as livestock production is unlikely to be compromised by this action.

Meta-analyses comparing the nutritional composition of perennial ryegrass (Lolium perenne) and plantain (Plantago lanceolata) pastures

Studies comparing livestock responses to diets containing plantain with traditional ryegrass/clover diets suggest differences in the nutritional composition between the species might explain some of the variation in results. To explore this theory, a meta-analysis was performed to compare the nutritional composition of plantain and perennial ryegrass pastures, and define key differences between the species. Standardised effect sizes (plantain vs ryegrass pastures), expressed as correlation coefficients (r) with values from -1 to +1, and treatment means from 34 studies were determined using a weighted random effects model. Pastures containing plantain had lesser herbage dry matter content than ryegrass pastures across all seasons (mean 13.4 vs. 19.4%, P<0.001; r<-0.65). Structural fibre content was consistently smaller (mean 32.1 vs. 43.4% DM), but non-structural fibre content larger in plantain compared with ryegrass pastures (large effect sizes of r>0.70). There was no difference in total herbage nitrogen concentration (g/100 g DM; r<0.03). However, plantain pastures contained less soluble and degradable nitrogen compared with ryegrass pastures (r<-0.78). Herbage digestibility did not differ significantly between pastures (r=-0.13; P=0.168). Generally, the effect of plantain on nutritional composition was consistent across seasons. Experiments and models investigating the effects of pasture mixes on environmental nitrogen losses ought to include detailed nitrogen and carbohydrate fractions data for accurate interpretation and prediction.

ZnO nanoparticles and zeolite influence soil nutrient availability but do not affect herbage nitrogen uptake from biogas slurry

Recently, there is a growing interest among agriculturists to use nanotechnology for the development of nutrient-use efficient fertilizers. However, its sustainable use for the synthesis of mineral or organic nano-fertilizers requires a thoughtful of the mechanism as well as the fate of nutrients and their interaction with soil-plant systems. Therefore, the aim of current study was to investigate the mixing of three different application rates of zinc oxide nanoparticles (ZNPs: 1.4, 2.8 and 3.6 mg kg−1 soil) as well as zeolite (141, 282 and 423 mg kg−1 soil) with biogas slurry (AS) on soil nutrient availability and herbage nitrogen (N) and zinc (Zn) uptake in a standard pot experiment. We found that both ZNPs and zeolite significantly increased mineral N content in soil compared to AS alone (P < 0.05). On the other hand, plant available phosphorus or potassium and microbial biomass carbon (C) in the soil were neither significantly affected by any application rate of ZNPs nor zeolite mixed AS. Soil microbial biomass N was significantly higher in second and third application rates of both ZNPs and zeolite amended AS treatments compared to AS alone. However, this increment in mineral N did not influence shoot uptake and herbage apparent recovery of this nutrient from AS. Similarly, co-mixing of both ZNPs and zeolite in AS did not influence shoot N uptake but Zn uptake was significantly higher in this treatment compared to AS alone. Therefore, this combination would be considered for improving crop Zn uptake under such fertilizer management regimes.

Sorghum–Sudangrass Responses to Nitrogen and Tillage following Polyphenol‐Containing Legumes, Alfalfa, Reed Canarygrass, and Kale

Core Ideas Low concentrations of polyphenols in forage legumes had no impact on sorghum–sudangrass production. Sorghum–sudangrass dry matter yield and N uptake were related to herbage N yield from prior forages. Tillage enhanced sorghum–sudangrass production especially after reed canarygrass. Adjusting fertilizer N based on crop sequence and tillage practices avoids soil nitrate buildup. The collective effects of protein‐binding polyphenols (PBP), preceding forage type, tillage, and fertilizer N on soil nitrate production, N uptake, and dry matter yield (DMY) of N‐demanding crops such as sorghum–sudangrass [SS, Sorghum bicolor (L.) Moench × S. sudanese Piper] are poorly understood. These factors and response variables were evaluated in Wisconsin by growing SS for 2 yr with two harvests yr−1 using no‐tillage or conventional‐tillage and fertilizer N rates of 0, 33, 67, 112, or 220 kg N ha−1 harvest−1 following 1‐yr stands of birdsfoot trefoil (Lotus corniculatus L.) containing condensed tannins (CT), o‐quinone producing red clover (Trifolium pratense L.), alfalfa (Medicago sativa L.), reed canarygrass (Phalaris arundinacea L.), and kale (Brassica oleracea L.). Herbage PBP was associated with reduced in vitro soil NO3–N accumulation, whereas herbage nitrogen yield (NY) primarily affected in situ soil NO3–N accretion and N uptake and DMY of SS. The DMY of first‐year sorghum–sudangrass (SS1) following legumes exceeded that following kale in both tillage systems, but rotational benefits of grass equaled legumes when conventional tillage was used. To maximize net return, SS1 required 75 kg N ha−1 harvest−1 following legumes and 125 kg N ha−1 harvest−1 following nonlegumes. Depending on tillage system and harvest, SS2 required 50 to 130 kg N ha−1 harvest−1 to maximize net return. To optimize DMY and profitability of SS following short‐term forages, producers should grow legumes to maximize NY before SS production, use conventional tillage following reed canarygrass, and adjust N rates according to crop sequence and tillage practices.

Studies on the Utilization of Pasture Herbage Nitrogen by Rumen Microorganisms : 2. Effects of Carbohydrate and Lipid Material on the Microbial Utilization of Rumen Ammonia in vitro

Studies on the Utilization of Pasture Herbage Nitrogen by Rumen Microorganisms : 2. Effects of Carbohydrate and Lipid Material on the Microbial Utilization of Rumen Ammonia in vitro

0640 The effect of defoliation severity during late autumn–winter on herbage production, regrowth, and nitrogen uptake

0640 The effect of defoliation severity during late autumn–winter on herbage production, regrowth, and nitrogen uptake

Effect of increased concentrate allotment before evening grazing on herbage intake, nitrogen utilization and rumen fermentation in dairy cows grazed on perennial ryegrass pasture.

Two experiments were conducted to elucidate the effect of increased concentrate allotment before evening grazing on herbage intake, nitrogen utilization and rumen fermentation in dairy cows. In experiment 1, nine lactating cows were grazed in the morning and evening sessions (2.5 h each). The cows were allocated to treatments of three concentrate allotment levels before the evening grazing session by altering proportions to daily total offered; 25%, 50% and 75%. Daily herbage dry matter intake quadratically decreased with increasing the concentrate allotment levels (P < 0.05). Nitrogen utilization was similar among treatments. To investigate diurnal changes in rumen fermentation, a second experiment was conducted where six ruminally cannulated non-lactating dairy cows grazed in the morning and evening sessions (3 h each) were subjected to the same treatments as experiment 1. Total volatile fatty acid concentration in the rumen linearly increased with increasing the concentrate allotment levels throughout the pre-evening grazing session to the post-morning grazing session (P < 0.01). The results indicate that dairy cows reduce daily herbage intake but do not alter nitrogen utilization with increasing concentrate allotment before evening grazing. © 2016 Japanese Society of Animal Science.

Improving ryegrass‐clover pasture dry matter yield and urea efficiency with gibberellic acid

The effects of spraying gibberellic acid (GA3) at 20 or 30 g ha(-1), with or without application of urea, on pasture dry matter (DM) yield, herbage nitrogen (N) concentration and feed quality were investigated in 2011 and 2012 for managed pastoral systems in New Zealand across a range of sites, in both autumn and spring. On the Waikato site (autumn and spring, 2012), and at all five sites in 2011, liquid urea applied with GA3 at 20 or 30 g ha(-1) consistently produced significantly higher pasture shoot DM yield, relative to liquid urea alone. Application of GA3 alone reduced feed quality by lowering metabolizable energy, crude protein and organic matter digestibility values. However, a reduced feed quality was not observed when GA3 was applied together with liquid urea. Liquid urea applied with GA3 also reduced total N and nitrate-N concentration in herbage, relative to liquid urea applied alone. Application of GA3 together with liquid urea provides an opportunity for the strategic use of urea to meet both production and environmental goals.

Dry matter accumulation and nutritive value of winter forage crops sown in Canterbury on different dates

Supplementary forage crops are used in New Zealand to overcome feed shortages during winter and early spring. The objective of this study was to maximize annual dry matter (DM) yield by optimizing sowing and harvest dates. Forage crop options include faba bean, oats and Italian ryegrass. These were sown on five dates in the autumn and winter of 2008 and on three sowing dates in the autumn of 2009. The maximum total DM ranged from 4420 to 26,310 kg ha−1 across all species and sowing dates for both seasons. Oats yielded the highest maximum total DM in both years. The quality analysis showed oats sown in early March and harvested at the end of August attained herbage metabolisable energy (ME) of 11.5 MJ kg−1 DM and high total ME per ha which was suitable for the lactation of dairy cows. Thus, oats was the beneficial alternative forage crop for farmers to choose. Faba bean had lowest maximum total DM yield compared with oats and Italian ryegrass in the first season; however, faba bean had higher maximum total DM compared with Italian ryegrass but lower than oats and faba bean-oat intercrop in the second season. Faba bean sown from early March to mid-April and harvested at the end of November attained a herbage nitrogen (N) content of more than 2.4% and had the highest total N uptake per ha compared with oats and Italian ryegrass at 2.4% of herbage N.

Soil pH and earthworms affect herbage nitrogen recovery from solid cattle manure in production grassland

Long term use of inorganic fertilisers and reduced organic matter inputs have contributed to acidification of agricultural soils. This strongly affects the soil dwelling fauna and nutrient mineralisation. Organic fertilisers such as solid cattle manure (SCM) resurge as an option to overcome this acidification problem and to provide the required blend of essential macro- and micronutrients for plant growth. We assessed the effects of earthworm density (400 or 700 m−2) at two levels of soil pH (ambient and increased), with or without application of solid cattle manure (SCM), on herbage nitrogen (N) uptake, and CO2 and N2O emissions over a period of 134 days using undisturbed soil cores from an acid peat grassland in a mesocosm experiment. Liming proved to be beneficial for earthworm performance and grassland productivity. A higher soil pH and earthworm density resulted in a higher soil biological activity measured as soil respiration. The combined application of lime and earthworms increased herbage apparent N recovery from SCM by 83% compared to SCM only. In the manured treatments, herbage N uptake was positively correlated with earthworm density (R2 = 0.92). N2O emissions increased by 37% when SCM was applied compared to the unfertilised control. Following SCM application, the cumulative increase in herbage N uptake was almost ten times greater than the measured total N2O losses. No relationship was observed between earthworm density and level of N2O emission. N mineralisation and herbage N uptake from SCM in acidic peat grasslands were greatly stimulated by the combined increase in soil pH and earthworm density. This stimulated the activity of soil biota, resulting in an increased herbage N recovery from the applied SCM.

Herbage Nitrogen, Fiber, and In Vitro Disappearance of Three Great Plains Grasses during Establishment

ABSTRACTNative warm‐season grasses have the potential to provide summer grazing because of their adaptation and persistence. Little nutritive value information is available, however, on the effects of maturity and soil amendments for native North American warm‐season grasses during establishment. Multiflower false rhodesgrass (Chloris pluriflora E. Fourn.), pink pappusgrass (Pappophorum bicolor E. Fourn.), and plains bristlegrass [Setaria vulpiseta (Lam.) Roem. &amp; Schult.] were harvested monthly during the first 2 yr after establishment on a Windthorst sandy loam soil and fertilized with 0 or 67 kg N and P ha−1 yr−1 Spring application of fertilizer resulted in early season herbage N concentrations 58 to 79% greater (p ≤ 0.10) than unfertilized herbage and maintained N concentrations (p ≤ 0.10) above the 11.2 g kg−1 considered minimum for cattle maintenance through September for most entries. Multiflower false rhodesgrass had the least (p ≤ 0.10) fiber and greatest N and in vitro organic matter disappearance (IVOMD). During Year 1 and early in Year 2, IVOMD was sometimes greater (p ≤ 0.10) when goat rumen liquid was used compared to steer liquid. This relationship was nullified or even reversed as plants matured in Year 2, indicating that donor species of rumen liquid should be considered when interpreting IVOMD results for native warm‐season grasses.

Fertiliser management for higher productivity of established lucerne pasture

Lucerne (Medicago sativa L.), a deep-rooted perennial legume forage, is a significant part of pastures, and is also grown in rotation with wheat to improve the yield and protein content of grains. Adequate supply of key nutrients is one of the important factors in higher productivity and sustainability of lucerne pastures. However, farmers mostly overlook the importance of nutrient management of established lucerne pastures, resulting in poor persistence, low productivity and weed invasion. The aim of this on-farm field study was to investigate the effects of the combined use of P, K, S and Zn and different sources of Zn on herbage yield, crude protein, nutrient composition, nitrogen fixation, weed invasion and persistence of an established (2 years old) stand of ‘Aurora’ lucerne pasture. A randomised block design was used to test ten fertiliser treatments. The combined use of P, K, S and Zn significantly (P<0.05) increased herbage yield (139% increase) over 2 years, nitrogen fixation, leaf-to-stem ratio, crude protein, nutrient composition (P, K, Ca, S, Zn concentrations), persistence and groundcover, and also led to significant weed suppression (weed biomass decreased from 53 to 69%). Of the three forms of zinc tested, zinc sulphate and zinc-coated single superphosphate proved superior to zinc oxide. The results suggest that nutrient management is essential for improved persistence, reduced weed invasion and higher sustainable productivity of established lucerne pastures, which is important for livestock production systems and overall profitability of farming systems.

Validation of a canopy photosynthesis model for cocksfoot pastures grown under different light regimes

Daily net canopy photosynthesis (P n) was predicted for cocksfoot (Dactylis glomerata L.) canopies grown under different light regimes by integration of a leaf photosynthesis model developed for the light-saturated photosynthetic rate (P max), photosynthetic efficiency (α) and the degree of curvature (θ) of the leaf light–response curve. When shade was the only limiting factor, the maximum P n (P nmax) was predicted to decrease approximately linearly from 33.4 g CO2 m−2 d−1 to zero as photosynthetic photon flux density (PPFD) fell from full sunlight (1800 μmol m−2 s−1 PPFD) to 10% of this in a fluctuating light regime. It was also predicted that at 50% transmissivity P nmax was higher for a continuous light regime (10.4 g CO2 m−2 d−1) than for a fluctuating light regime with the same intensity (8.4 g CO2 m−2 d−1). The canopy photosynthesis model was then used to predict dry matter (DM) production for cocksfoot field grown pastures under a diverse range of temperature, herbage nitrogen content and water status conditions in fluctuating light regimes. This prediction required inclusion of leaf area index and leaf canopy angle from field measurements. The model explained about 85% of the variation in observed cocksfoot DM production for a range from 6 to 118 kg DM ha−1 d−1. The proposed model improves understanding of pasture growth prediction through integration of relationships between shade limitations in fluctuating light regimes and other environmental factors that affect the canopy photosynthetic rate of cocksfoot pastures in silvopastoral systems.

Nitrogen Effects on Herbage Nitrogen Use and Nutritive Value in a Meadow and Loblolly Pine Alley

ABSTRACTHerbage response to N is poorly understood in alley cropping systems. Our objective was to determine site specific effects of N on herbage N use and nutritive value in separate experiments conducted in a meadow and a loblolly pine (Pinus taeda L.) alley (995 trees ha−1) near Booneville, AR. Tall fescue (Festuca arundinacea Schreb.) was the predominant herbage species. Fertilizer N was broadcast as split‐applications at six rates (100 kg ha−1 increments from 0 to 500 kg ha−1 yr−1). The proportion of total herbage as tall fescue was favored at rates ≥ 200 kg N ha−1, but these rates increased concentrations of herbage NO3−–N in the pine alley to potentially harmful levels for grazing ruminants (&gt;2300 μg NO3−–N g−1). Cumulative herbage N use efficiency (CNUE) was 23 and 10 kg dry weight per kilogram supplied N for the meadow and pine alley, respectively. Cumulative N acquisition efficiency (CNAE), not cumulative N conversion efficiency (CNCE), appeared to be the primary driver of low CNUE in the pine alley. The apparent increase in crude protein (CP) in pine alley vs. meadow herbage appeared to be a mechanistic response to decreased specific leaf weight. Only maintenance levels (≤100 kg ha−1) of N fertilization should be applied to pine alley herbage given the low CNUE, and risk of NO3−–N toxicity to ruminant livestock at higher N rates.

Effects of variation in shade level, shade duration and light quality on perennial pastures

Two experiments examining the effect of artificial shade on pasture net herbage accumulation (NHA), botanical composition and soil characteristics were conducted between 1994 and 1999 at Whatawhata Research Centre. Both experiments included a range of shade levels (0–94%) and shade durations (3–12 months per year). Experiment 1 also included a light quality treatment, incorporating a range in the red:far red ratio (0.49–1.00). All three shading factors decreased annual NHA, with the most influential being the level of shade, which accounted for 68% of the variation and reduced NHA by 20–80% compared with open pasture. The second most influential factor was shade duration, which accounted for only 6% of the variation in NHA. Shading also led to changes in pasture botanical composition, most notably a decline in legume content in both experiments. There was no evidence that hairy pasture species (grasses or legumes) had any advantage over glabrous species under shade. At shade levels >60%, herbage nitrogen concentrations were elevated by 0.2 percentage points on a per unit dry weight basis, although reduced pasture NHA under higher shading meant lower demand for soil nitrogen. Potential nitrogen mineralisation measurements also indicated that nitrogen cycling is likely to be reduced under shading.

Nitrogen Use Efficiency and Herbage Production of an Established Grass Sward in Relation to Moisture and Nitrogen Fertilization

ABSTRACT Herbage growth and nitrogen (N) use efficiency in grazed or mown grasslands are generally low, associated mostly with poor response to fertilizer N. The aim of the present investigation was to examine the short-term response of grass to fertilizer N with respect to herbage yield and nitrogen use efficiency (NUE) in order to provide a better basis for improving the efficient use of fertilizer N in grassland ecosystems. Both NO3 − and NH4 + sources of N were applied to an established grass sward with three moisture levels, i.e., natural conditions (63% water-filled pore space, WFPS), near field capacity level (71% WFPS), and slightly wetter than field capacity (84% WFPS). Herbage yield, i.e., dry matter (DM), N uptake, N recovery efficiency, yield efficiency, and physiological efficiency were determined over a 7–28 d period. Addition of N fertilizers significantly increased the herbage yield and N uptake of grass sward over that of the control. In the plots where NO3 −−N was added as the N source, DM yield was between 1760–1870 kg ha−1, N recovery efficiency was between 24%–43%, and yield and physiological efficiency were in the range of 2.1–3.2 and 6.4–8.8 kg DM kg− 1 N, respectively. In NH4 +−N added plots, the DM yield was between 3190–3700 kg ha− 1, N recovery efficiency was between 39%–48% while yield and physiological efficiency were in the range of 3.5–5.6 and 9.0–11.6 kg DM kg− 1 N, respectively. Results indicated that total DM yield, N uptake, and NUE depend on the source of N and the level of moisture in the field. Assimilation of N is also affected by the stage of plant development after N fertilization. About 50%–54% of applied N was recovered in the initial 14 and 21 d after fertilizer application and thereafter translocation of N slowed. A fall in herbage production and minimal response to N fertilizer has been observed at 84% WFPS, while the maximum herbage yield and N recovery efficiency was recorded in soil near or below field capacity. The grass sward with added NH4 +−N produced a larger yield and had higher NUE relative to the sward with NO3 −−N. Results confirm that applied N was not utilized efficiently by grass sward and a decrease in N uptake and its utilization seem to be the key factors responsible for the poor herbage productivity often observed in pastoral agriculture. These results suggest that both moisture and N source have a substantial effect on herbage yield and N utilization by plants and therefore should be considered for efficient management of N fertilization and recommendations for grass sward.

Herbage Nitrogen Recovery in a Meadow and Loblolly Pine Alley

Herbage in conventional pasture and agroforestry systems is managed for microclimate and spatial differences inherent to these systems, but managers have scarce data on which to base their decisions. Our objective was to measure herbage N fertilizer recovery at two sites, an unshaded meadow and a shaded alley in 10‐yr‐old loblolly pine (Pinus taeda L.). The test was conducted on a Leadvale silt loam soil (fine‐silty, siliceous, semiactive, thermic Typic Fragiudult) near Booneville, AR, in 2002 and 2003, with tall fescue (Festuca arundinacea Schreb.) the predominant herbage species. Fertilizer N was broadcast as split‐applications at six rates (100 kg ha−1 increments from 0 to 500 kg ha−1 yr−1). The meadow and pine alleys had sufficient herbage yield for rotational livestock production. Cumulative herbage yield (CHY) in the meadow was much more responsive to added N than pine alley herbage, but average cumulative fertilizer N (CFN) recoveries were only 38% and 12%, respectively. A shallow fragipan, low available soil P (≤ 6 μg g−1), depletion of soil water in July to September (both sites), and low solar irradiance (pine alley) were likely contributors to low fertilizer N recovery and herbage productivity. Because of poor herbage yield response and substantial accumulation of soil mineral N (62 to 237 kg ha−1) in pine alleys fertilized with ≥200 kg N ha−1 yr−1, only maintenance levels of fertilizer N ( ≤ 100 kg ha−1) should be applied to similar sites. For these same reasons, yearly applications of fertilizer N &gt; 300 kg ha−1 yr−1 are not recommended for meadows similar to the study site.

A canopy photosynthesis model to predict the dry matter production of cocksfoot pastures under varying temperature, nitrogen and water regimes

AbstractDaily net canopy photosynthesis (Pn) of cocksfoot (Dactylis glomerata L.) was predicted for combinations of temperature, herbage nitrogen (N) concentration and water status from the integration of models of leaf photosynthesis of the light‐saturated photosynthetic rate (Pmax), photosynthetic efficiency (α) and the degree of curvature (θ) of leaf light‐response curves. The effect on Pn, maximum Pn (Pn max) and the optimum leaf area index (LAI at Pn max) was examined when any one of these factors was limiting. The ranges that gave the optimum values of Pn (Pn max = 30·8–33·5 g CO2m−2 d−1) for temperature (19–22°C) and N concentration (40–50 g N kg−1 DM) were smaller than those for net leaf photosynthesis. Also, Pn fell to 0 at a lower level of water stress (pre‐dawn leaf water potential, ψlp = −12·5 bar) than for Pmax. The canopy photosynthesis model was then used to compare predicted and measured dry matter (DM) production for cocksfoot pastures grown under a diverse range of environmental conditions with field data from New Zealand and Argentina. To predict DM production leaf area index and leaf canopy angle were included from field measurements. The model explained about 0·85 of the variation in cocksfoot DM production for the range of 6·5–134 kg DM ha−1 d−1. The canopy model overestimated the DM production by 0·10 which indicates that a further Pmax function for leaves of different ages and a partitioning sub‐model may be needed to improve predictions of DM production.

The use of herbage nitrogen status to optimize herbage composition and intake and to minimize nitrogen excretion: an assessment of grazing management flexibility for dairy cows

AbstractA framework for managing rotationally grazed pastures for dairy cattle which enables the cows’ energy and protein requirements to be met while simultaneously limiting the amount of N excreted in order to reduce N losses is described. The first objective is achieved by ensuring that lamina mass and the N concentration of herbage do not limit herbage intake or feeding value. The second objective is achieved by limiting N fertilizer supply or increasing the interval between defoliations to reduce the N concentration of herbage. Lower and upper thresholds for the N concentration of herbage and lamina mass were estimated from published data. The method is illustrated using two vegetative regrowths (beginning and end of spring) in a cutting experiment with two fertilizer treatments, 0 or 120 kg N ha−1 (−N and +N), and early or late cutting. Decreasing N supply led to a reduction in grazing management flexibility, i.e. the defoliation interval ranges which were compatible with the required sward characteristics (minimum lamina mass and N concentration of lamina) for herbage intake and to meet the protein requirements of dairy cows. Aiming for the upper threshold N concentration of herbage increased the minimum interval between defoliations only for the +N treatments. Nevertheless, grazing management flexibility remained the highest for the +N treatments.

An integrated model for predicting maximum net photosynthetic rate of cocksfoot (Dactylis glomerata) leaves in silvopastoral systems

Net light-saturated photosynthetic rate (Amax) of field grown cocksfoot (Dactylis glomerata L.) leaves in a radiata pine (Pinus radiata D. Don) silvopastoral system (Canterbury, New Zealand) was measured at different times under severe shade (85–95 µmol m–2 s–1 photosynthetic photon flux density, PPFD) and in full sunlight (1900 µmol m–2 s–1 PPFD). The aim was to integrate individual functions for Amax against air temperature (2 to 37 oC), water status, expressed as pre-dawn leaf water potential (ψlp) (-0.01 to −1.6 MPa), herbage nitrogen (N) (1.5 to 5.9%), regrowth duration (20 to 60 days) and time under shade (1 to 180 min) into a multiplicative model. The highest Amax value obtained was 27.4 µmol CO2 m–2 s–1 in non-limiting conditions with full sunlight. This value was defined as standardised dimensionless Amaxs = 1 for comparison of factor effects. The canopy temperature of the cocksfoot sward was up to 7.4 oC cooler than air temperature for plants under shade. Therefore, canopy temperature was used to predict Amax. The only interaction was between time under severe shade (5% of the open PPFD) and water stress (ψlp = −0.4 to −1.3 MPa) and this was included in the model. Validation of this model indicated 78% of the variation in Amax could be accounted for using these five factors by the addition of the interaction function. This model could be used to assist the prediction of pasture growth in silvopastoral systems through incorporation into a canopy photosynthesis model.