Live Herbage Research Articles

Trees in silvopastoral systems reduce legume proportion with no consequence for internal N resorption efficiency

AbstractIn legume-based grasslands, legumes supply the sward with nitrogen (N) from biological N2-fixation. Previous studies in silvopastoral systems have emphasized that legume proportions decline near trees which would cause spatial variation in the N supply and the concentration of N in the harvested herbage of grass swards between trees. In natural ecosystems, it was shown that the N resorption efficiency (NRE) was increased by nutrient limitation, hence, near trees where legumes are scarce. Therefore, we tested the hypothesis that the NRE is increased near trees and compensates for the loss of legumes with respect to N concentration in live herbage. Two vegetation compositions consisting of legume-based grass swards were analysed across positions between tree lines in an alley cropping system established 5 years prior to this study. Legume proportion declined up to 45% towards the tree line, and also N concentration in live and dead herbage but on average only declined by 15%. As a consequence of a reduced N concentration and also herbage mass close to trees, the N yield decreased by up to 50%. Despite the loss of legumes near trees, the NRE was unaffected by the tree line irrespective of vegetation composition. Further, the results indicate that internal N cycling of managed grass swards in silvopastoral grassland with short defoliation intervals between harvests is of lesser relevance than in unmanaged ecosystems. Legume proportions control the N concentrations of live and dead herbage irrespective of tree shading in silvopastoral systems.

Impacts of cutting frequency and position to tree line on herbage accumulation in silvopastoral grassland reveal potential for grassland conservation based on land use and cover information

AbstractIn agricultural grassland, high herbage utilisation efficiency (HEFF), which is the proportion of gross live‐green herbage production that is utilised before entering senescence, is ensured by frequent defoliation. The decision upon which defoliation frequency to apply depends on the farming intensity. Assuming a reduced total herbage accumulation near trees in silvopastoral systems, frequent defoliations with high HEFF become less worthwhile—at least in specific spatial configurations. This makes an extensive management near trees an interesting option because it promotes other grassland‐related ecosystem services such as biodiversity. The present study first analysed the interaction between defoliation frequency and position to trees on the total, dead and live herbage accumulation and the HEFF at two silvopastoral sites with short‐rotation coppices in Germany. In addition, the total grassland–tree interface in Germany was assessed from land use and land cover maps of Germany based on satellite data to approximate the potential of grassland extensification near trees. The total herbage accumulation near trees declined by up to 41% but the HEFF was not affected by the position. Consequently, any intensification is not paid‐off by adequate productivity and herbage quality in terms of HEFF and tree‐related losses in herbage accumulation are expected up to a distance of 4.5–6 m. Applying a 4.5 m border on satellite data, we found that up to 4.4% (approximately 2200 km2) of the total grassland area in Germany is at a tree interface and potentially suitable for extensification. These findings indicate substantial potential for biodiversity conservation in grasslands with low trade‐off for high‐quality yield.

Nutrient Pools in Bermudagrass Swards Fertilized at Different Nitrogen Levels

Nitrogen (N) fertilization affects grassland herbage accumulation and nutritive value, but its effect on the distribution of nutrients among soil and plant nutrient pools is less understood. This 2‐yr study determined the effect of N fertilization levels of rotationally stocked ‘Tifton 85’ bermudagrass (Cynodon spp.) pastures on nutrient concentration and content in soil (top 20 cm), live root‐rhizome mass, live herbage mass, and aboveground plant litter pools. Treatments were 50, 150, and 250 kg N ha−1 yr−1. Greater N fertilization increased N concentration in all plant nutrient pools and potassium (K) concentration in live herbage and plant litter, but plant‐pool phosphorus (P) concentrations changed little across N levels. With increasing N fertilization, live herbage (118–159 kg ha−1) and plant litter (8–14 kg ha−1) K pools increased linearly, but the Mehlich‐1 extractable soil K pool decreased linearly (182–139 kg ha−1); live herbage (50–92 kg ha−1), plant litter (30–49 kg ha−1), and root rhizome (63–95 kg ha−1) N pools also increased with increasing N fertilization. The proportion of K in various pools was affected more by N fertilization than were proportions of N, P, or carbon. Soil was the dominant pool for all nutrients, with the exception of K in pastures fertilized at the greatest N level. Increasing N fertilization increased the proportion of K and N contained in plant pools and decreased the proportion in soil. Although N fertilization affected quantity and proportion of nutrients in pools in Tifton 85 pastures, changes occurred to a limited extent, with the exception of plant and soil K pools.

The effect of peri-conceptual grazing of live pasture on fetal numbers in unsynchronised ewes

Methods of increasing the number of lambs born per ewe that avoid the use of pharmaceutical methods of oestrus synchronisation but which require a short period of increased nutrition are desirable. Four separate experiments evaluated whether peri-conceptual grazing of lucerne, compared with senescent herbage or other live herbage, increased fetal numbers in unsynchronised ewes. Merino ewes that grazed lucerne pasture for 7 days before joining and for the first 7 days of a 5–6-week joining produced up to 21 extra (P < 0.05) fetuses per 100 ewes joined, compared with ewes grazing cereal stubble with minimal live herbage (Experiment 2). In Experiments 1, 3 and 4, Merino or First Cross ewes grazing either cereal stubbles or phalaris pasture with as little as 200 kg DM/ha of live herbage produced a similar (P > 0.05) number of fetuses per ewe joined as those grazing on lucerne, either because this quantity of live feed was sufficient to increase fetal numbers, or because, for Experiment 3, First Cross ewes may not have responded at the commencement of the breeding season. It is concluded that grazing live pasture for 7 days before joining and for the first 7 days of joining during the breeding season can substantially increase fetal numbers in unsynchronised ewes compared with ewes grazing stubbles containing no live herbage. The response appears to occur on a range of plant species, and a small quantity of live herbage can elicit a response. Grazing lucerne in the peri-conceptual period did not increase (P > 0.05) the proportion of non-pregnant ewes. Further studies are required to determine how early in the breeding season ewes with a distinct breeding season will respond to nutritional manipulation.

Short-term grazing of lucerne and chicory increases ovulation rate in synchronised Merino ewes

This study evaluated the ability of short-term grazing of live = green pasture to increase ovulation rate during late summer when annual pasture is generally dead and of low quality. Ovulation rates, measured by the number of corpora lutea, were compared between 4 nutritional treatments: senesced phalaris ( Phalaris aquatica), phalaris plus 500 g lupin grain per day, lucerne ( Medicago sativa) or chicory ( Chicorum intybus) pastures. The study used 100 Merino ewes per treatment, divided between 2 replicates. The experiment was repeated in 3 years; February 2006, and January 2007 and 2008. Oestrus was synchronised and the ewes grazed the pastures for 9 days prior to ovulation at times corresponding to days 8–17 of the cycle in 2006, and days 6–14 in 2007 and 2008. The proportion of ewes producing multiple ovulations was higher ( P < 0.05) in the lucerne and chicory (0.36, 0.38) than the phalaris (0.27), and intermediate in the lupin (0.33) treatment. Regression analysis showed that the proportion of ewes with multiple ovulations increased with the quantity of live herbage ( P < 0.04). Responses were achieved even at low levels of live herbage with 90% of the maximum proportion of multiples occurring at 350 kg DM/ha. It is concluded that providing short-term grazing of live chicory or lucerne to ewes can increase ovulation rates relative to ewes grazing senesced phalaris and to levels similar to those achieved by lupin grain supplementation.

Species Contribution to Seasonal Productivity of a Mixed Pasture under Two Sward Grazing Height Regimes

Mixed pastures often include tall and short plant species that respond differently to grazing intensity. We evaluated the effect of two rotational grazing height regimes on species productivity and availability to animals. We compared tall and short grazing height regimes within current recommendations in a Pennsylvania pasture dominated by orchardgrass (Dactylis glomerata L.) and Kentucky bluegrass (Poa pratensis L.) and grazed by cow–calf (Bos taurus) pairs. Orchardgrass height defined grazing regimes. Tall pastures were grazed from 27 cm down to 7 cm and short pastures from 20 to 5 cm from April 1998 to May 2000. Before each grazing period, herbage was sampled at grazing regime residual heights of 7 or 5 cm (herbage harvested) and at ground level (herbage mass). Species harvest index (HI) was calculated as the ratio of herbage harvested over live herbage mass to compare herbage availability among species and grazing regimes. In tall vs. short pastures, there was 50% more herbage harvested at each grazing event and 23% more total herbage harvested over the 2.3‐yr experiment. Higher production was mainly due to orchardgrass (51% more herbage harvested in tall vs. short pastures) and tall legumes. Herbage harvested decreased during dry, warm periods independent of season, with bluegrass decreasing most. Orchardgrass HI was highest, quackgrass (Elytrigia repens L.) and bluegrass HIs were intermediate, and white clover (Trifolium repens L.) HI was lowest. Small differences in grazing height recommendations had significant effects. Tall grazing heights increased productivity and favored tall‐growing species that had higher harvest indices.

Seasonal Dynamics of Prairie Sandreed Rhizome Development

Multiple generations of rhizome-connected tillers stabilize soils and produce measurable amounts of herbage on sandy rangeland throughout the world. However, little is known about the dynamics of rhizome development in these clonal plant species. Seasonal relationships between foliar characteristics and rhizomes of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were examined on sands range sites at 30-day intervals from May through September 1989 and 1990 at the University of Nebraska, Panhandle Experimental Range near Scottsbluff. Quadrats were excavated each year from two, 5 x 5 Latin Square macroplots in each of 2 grazing histories, long-term rest or current-year deferment. Under dry conditions in 1989, a 65% reduction in the length of new rhizomes during July preceded a 64% reduction in live tillers in August. After which, rhizome length and live tiller density were unchanged and mean tiller weight increased during September. When average precipitation occurred in 1990, a 25% reduction in live tillers and concurrent increases in new rhizome length and mean tiller weight occurred during July. Rhizome bud densities increased throughout the growing season at different but predictable rates (R2 greater than or equal to 0.95) for grazing histories, regardless of precipitation. Length of new rhizomes was highly correlated (R2 = 0.91) with live herbage throughout the growing season. Measurable increases in total rhizome length did not occur until live herbage of prairie sandreed exceeded a threshold of about 50 g m(-2). Maximum increase in length of new rhizomes per unit of live herbage was about 10 cm g(-1) near 100 g m(-2). Given its dependence on vegetative reproduction and relatively high palatability to beef cattle, periodic or repeated years of full growing season deferment may be the only reliable method of obtaining measurable increases in prairie sandreed populations. DOI:10.2458/azu_jrm_v55i2_reece

Seasonal dynamics of prairie sandreed rhizome development

Multiple generations of rhizome-connected tillers stabilize soils and produce measurable amounts of herbage on sandy rangeland throughout the world. However, little is known about the dynamics of rhizome development in these clonal plant species. Seasonal relationships between foliar characteristics and rhizomes of prairie sandreed [Calamovilfa longifolia (Hook) Scribn.] were examined on sands range sites at 30-day intervals from May through September 1989 and 1990 at the University of Nebraska, Panhandle Experimental Range near Scottsbluff. Quadrats were excavated each year from two, 5 x 5 Latin Square macroplots in each of 2 grazing histories, long-term rest or current-year deferment. Under dry conditions in 1989, a 65% reduction in the length of new rhizomes during July preceded a 64% reduction in live tillers in August. After which, rhizome length and live tiller density were unchanged and mean tiller weight increased during September. When average precipitation occurred in 1990, a 25% reduction in live tillers and concurrent increases in new rhizome length and mean tiller weight occurred during July. Rhizome bud densities increased throughout the growing season at different but predictable rates (R2 greater than or equal to 0.95) for grazing histories, regardless of precipitation. Length of new rhizomes was highly correlated (R2 = 0.91) with live herbage throughout the growing season. Measurable increases in total rhizome length did not occur until live herbage of prairie sandreed exceeded a threshold of about 50 g m(-2). Maximum increase in length of new rhizomes per unit of live herbage was about 10 cm g(-1) near 100 g m(-2). Given its dependence on vegetative reproduction and relatively high palatability to beef cattle, periodic or repeated years of full growing season deferment may be the only reliable method of obtaining measurable increases in prairie sandreed populations.

Effect of Defoliation Intensity on Regrowth of Tallgrass Prairie

Grazing trials were conducted in north and south-central Oklahoma throughout the growing season of 1989 and 1990 in an attempt to explain live herbage accumulation rate of tallgrass prairie as a function of live residual herbage level. A 1-2 day grazing period on 8 treatment paddocks began 26 May (Trial 1), 7 July (Trial 2), and 18 August (Trial 3) of each year. Two replicate paddocks per trial were subjected to stocking densities of 7,600, 15,200,22,700, and 30,300 kg animal weight ha-1. Live herbage was measured immediately after grazing to determine live residual herbage level and 2,4,6, and 8 weeks after grazing to determine live herbage accumulation. Live herbage accumulation rate was determined as the first derivative with respect to day after grazing day of polynomial regression equations fit to live herbage accumulation data. Maximum live herbage accumulation rate decreased as season progressed but the time required to reach maximum live herbage accumulation rate was not dependent upon season. Live residual herbage level was a significant parameter in equations describing live herbage accumulation rate in 6 of 9 trials.

The Constituent Differential Method for Determining Live and Dead Herbage

Determination of live and dead herbage fractions from mixed herbage samples requires hand separation or specialized laboratory procedures. The constituent differential method is designed to determine the relative proportion of live and dead components in a mixture based on the difference in dry matter concentration between the components. Our objective was to evaluate several characteristics of the constituent differential method under field conditions in tallgrass and mixed grass vegetation. Estimation of live standing crop by this method is most sensitive to the dry matter content of the total mixture and the dead component but becomes less sensitive as the difference between these variables increases. Time-of-day was not usually associated with dry matter content of the herbage components if sampling began after the herbage was thoroughly dry to the touch. Suggested sample sizes in large experimental units for estimating dry matter content are 40-50 samples for herbage mixtures, 10 samples for live herbage, and 5 samples for dead herbage. In 4 field trials the average value for percent live herbage determined by hand separation and the constituent differential method differed by 1.6 percentage units, which was nonsignificant P>0.10). The constituent differential method is a relatively rapid and accurate method for determining live and dead herbage fractions.

Plant Responses to Stocking Rate in a Subtropical Grass‐Legume Pasture

Abstract‘Florida’ carpon desmodium [Desmodium heterocarpon (L.) DC] is a persistent legume under grazing but is often difficult to establish. Aeschynomene (Aeschynomene americana L.) and, especially, phasey bean [Macroptilium lathyroides (L.) Urb.] establish more reliably. Overseeding a mixture of these legumes in bahiagrass (Paspalum notatum Flugge) pastures could provide the quality forage and N input of legumes initially from the rapidly establishing species and for extended periods from the persistent carpon desmodium. The objective of this study was to evaluate the potential of such mixtures. Effects of stocking rate and grazing season on botanical composition, herbage availability, and herbage nutritive value were evaluated on a Pomona fine sand (sandy, siliceous, hyperthermic Ultic Haplaquod). Following overseeding of legumes in March 1987, pastures were grazed at three stocking rates in summer 1987 and in spring and summer 1988. Carpon desmodium increased from less than 1% at the start of grazing in 1987 to over 7% of the live herbage in 1988. Combined percentage of aeschynomene plus phasey bean decreased during 1987 from more than 4 to 1.6%. Carpon desmodium percentage was highest (P &lt; 0.10) at the intermediate stocking rate, while percentage of other legumes was not affected by stocking rate. Herbage mass decreased linearly with increases in stocking rate in both summer grazing seasons. Leaf/stem ratio and nutritive value of legume leaf and stem were not affected by stocking rate but decreased with time during each grazing season. The short‐lived legumes, aeschynomene and phasey bean, provided high quality forage during the establishment period of carpon desmodium but contributed negligibly during the second year.

Quality and Botanical Composition of Cattle Diets under Rotational and Continuous Grazing Treatments

Proponents of rotational grazing claim that individual animal performance in a properly managed rotational grazing (RG) treatment will be equal to or greater than that in other, less intensively managed treatments even when rate of stocking in the RG treatment is much greater. The objective of this study was to examine the effect of a heavily stocked RG treatment, at 2 stock densities, on quality and botanical composition of cattle diets. The control treatment was a moderately stocked, continuously grazed pasture. Diets were collected from all treatments on 8 dates over a 22-month period using esophageally fistulated steers. Only minor differences occurred among treatments in dietary crude protein (CP), organic matter digestibility (OMD), and botanical composition. Diet quality and species composition of diets were closely correlated with quality and availability of live herbage, which varied more among trials than among treatments. Quality and composition of diets collected during the first and last day of grazing in the RG paddocks were not different. These data support the hypothesis that installing rotational grazing at a high stocking rate does not lower diet quality and would not be expected to be a factor affecting individual animal performance.

STUBBLE MANAGEMENT OF HAY AFTERMATH

Possible management strategies for areas of stubble left after hay had been harvested from a ryegrass/white clover pasture were studied in a trial on an irrigated Wakanui silt loam at Lincoln College, Canterbury. Following a hay crop cut in late December, the stubble was either trimmed to 2 cm (920 kg DM/ha) or left intact at 8-12 cm (2200 kg DM/ha) and spelled for either four or eight weeks. Subsequent regrowth herbage yield, botanical composition and digestibility were measured. The highest live herbage mass of 5380 kg DM/ha resulted from leaving the stubble intact and cutting the regrowth at four weekly intervals. The other treatments gave herbage masses from 4120 kg DM/ha to 4350 kg DM/ha but did not significantly differ from one another. However while 1220 and 1650 kg DM/ha of dead material was present in the "stubble intact" treatments, only 470 and 880 kg DM/ha occurred where the stubble was trimmed to 2 cm. The amount of dead material was the main determinant of overall digestibility, as the digestibility of the green herbage was similar (79-80%) for all treatments. As a result of differing amounts of dead material therefore, the herbage mass from trimmed stubble was from 4 to 10% higher in digestibility than that from the stubble left intact treatment. Clover proportion was high throughout the treatments, ranging from 50% in the long spelled treatment to 70% in the short spelled treatment. The results of this trial suggest that hay stubble should be left intact but regrowth should be closely defoliated after four weeks to maximise production and return the sward to a leafy state as quickly as possible.

Interrelationships between net primary production, ground-storey condition and grazing capacity of the Acacia aneura rangelands of semi-arid Australia

A simulation model which estimates the net primary production of the ground-storey component of the extensively grazed Acacia aneaura rangelands of semi-arid Queensland, Australia, was applied to the assessment of grazing capacity. The method described represents an alternative approach to the traditional method used by land administrators. Historic climatic records for a continuous period of 25 years were analyzed for one centre. Annual live herbage biomass production fluctuated widely in relation to both climate and grund-storey condition class. Herbage biomass carryover from year to year decreased significantly as the level of herbage utilization through animal consumption increased. At a conservative level of use, herbage biomass carryover provided an important reserve to supplement the smaller amount of live biomass produced in low rainfall years. Consequently, grazing capacity was related to the total herbage biomass available to the grazing animal at the end of each summer growing period. There were only small changes in the mean value of end-of-summer peak herbage biomass crop and sheep carrying capacity over the excellent to good ground-storey condition classes. However, there was a pronounced decline in these values as condition class decreased from moderate to poor. The implications of this method assessing grazing capacity for semi-arid rangeland management and administration are discussed.

Influence of Grazing on Crude Protein Content of Blue Grama

Highlight: Grazing intensities of light, moderate, and heavy by cattle did not affect the protein content of blue grama herbage in northeastern Colorado. Crude protein content of live herbage changed with phenological development and with season, but no change occurred in dead herbage. During the early vegetative growth period, a high of 18% crude protein occurred in the plant tissues. Additional precipitation during the growing season did not appear to affect the content of protein in herbage.

Dynamics of Blue Grama within a Shortgrass Ecosystem

Highlight: The dynamics of standing crop for live, dead, and litter compartments of blue grama were studied for 2 years to formulate equations useful for predicting growth rates over 2-week intervals. During the period of rapid vegetative growth, 54% of the variation in rates of changes for live herbage was accounted for by the amount of live herbage present at a given time. During the declining period, the amount of live herbage, leaf moisture, and air temperature accounted for 58% of the variation in net changes. The transfer rate from live to dead herbage was 0.22% of the live herbage per day during the growing season, while litter accumulated from the dead herbage at a rate of 0.31%o per day. This transfer rate became 0.0867o per day during the non-growing season. Litter decomposed during the growing season at a rate of 0. 35% per day.