Pasture Regrowth Research Articles

Is animal saliva a prominent factor in pasture regrowth?

Over a period spanning more than 100 years, a substantial amount of research has been undertaken to determine the impact that grazing ungulates have on grassland production systems globally, as they are the primary source of feed for these animals. Productivity of these lands, however, is highly dependent on a variety of factors such as quality and quantity of the forage, regrowth rates, and grazing rates. Expected regrowth rate of pasture, may be more influenced by animals than originally thought, as the direct effect of saliva deposition on plants on both the above and belowground biomass of plants remains relatively unclear. Though research is evident on grazing impacts on pasture, those which have utilised saliva have often found contradictory results, or do not discuss the mechanisms behind the responses in pasture observed. As such, we believe though it is a miniscule aspect of the entire grazing picture, investigating the effect of saliva in further detail may highlight gaps apparent in current research, such as what compounds are evident in saliva, and what those individual components functions are in plants, or what result may occur when applied on to plants. This review discusses what is currently known about animal saliva, the impact on pasture, and the greater practical applications of this knowledge for graziers.

Productive characteristics and structure of Paiaguás grass pasture fertilized with wood ash in the Brazilian Cerrado

The use of wood ash as a fertilizer is a practice that helps in the management of soil fertility. Our objective was to evaluate the potential use of wood ash on structural and productive characteristics of paiaguás grass (Urochloa brizantha) pasture. The experiment was carried out at the Federal University of Rondonópolis, Brazilian Cerrado. Treatments were five wood ash doses: 0, 8, 16, 24, and 32 t ha-1 and two application strategies (wood ash incorporated into the soil and wood ash not-incorporated). Wood ash doses significantly affected (p<0.05) the evaluated response variables. Forage yield ranged from (mean ± standard error) 6.98±0.34 to 8.99±0.53 t DM ha-1. The highest productivity (11.10±0.46 t DM ha-1) was obtained at a wood ash rate of 24 t ha-1. The leaf area index was also higher (9.39±1.02) in the 24 t ha-1 wood ash dose. On the other hand, the leaf/stem ratio decreased with the application rate of wood ash and varied from 1.41±0.05 to 1.09±0.07 in the absence of wood ash (dose 0) and at the highest dose, respectively. In general, wood ash positively influenced (p<0.05) the structural characteristics and yield of U. brizantha cv. Paiaguás. Wood ash doses that provided the highest crop yield were between 16 and 24 t ha-1. The incorporation of wood ash into the soil increased pasture regrowth time. Therefore, it is recommended to apply wood ash superficially in established pastures.

Humate application alters microbiota–mineral interactions and assists in pasture dieback recovery

Pasture dieback is a rapidly expanding decaying pasture syndrome that affects millions of hectares of agricultural land in Queensland, Australia, making it useless for the cattle industry and decimating farmers’ income and welfare. Since the syndrome was first identified in the early 1990s, farmers and agronomists have tried various methods for pasture recovery, including slashing, burning, ploughing and resowing grass, fertilising, destocking, and overstocking. In most cases, after a minimal initial improvement, the grass reverts to dieback within a few weeks. Here, we present an application of potassium humate, a well-known plant growth stimulator, as a possible long-term recovery option. Humate was applied once at the rate of 12 ml per m2. Humate application did not alter the alpha or beta diversity of soil bacterial communities, nor did it change the mineral profile in the soil. However, humate application altered soil microbiota–mineral temporal interactions and introduced subtle changes in the microbial community that could assist pasture recovery. A single humate application increased paddock plant biomass significantly up to 20 weeks post-application. Eleven months after the single application, the paddock was grazed to the ground by the cattle just before the rainfall season. After pasture regrowth, the humate-treated plots significantly improved root morphometric indicators for both grass and dicots and increased the ratio of grass/weeds by 27.6% compared to the water-treated control. While this treatment will not resolve the dieback syndrome, our results invite more research to optimise the use of humate for maximum economic benefit in paddock use under pasture dieback syndrome conditions.

Managing Forbs Preferred by Greater Sage-Grouse and Soil Moisture in Mesic Meadows with Short-Duration Grazing

Mesic meadows provide valuable water and forage resources for wildlife and livestock in the arid western United States. Greater sage-grouse (Centrocercus urophasianus), a species of conservation concern, rely on these habitats because they support forb species of high importance to broods during late brood rearing. Because mesic meadows comprise a small fraction of the landscape, identifying grazing strategies compatible with maintenance and production of mesic resources is vital to balancing livestock production with suitable conditions for sage-grouse. We evaluated relationships between short-duration grazing treatments and habitat components important to sage-grouse in mesic meadows. In 2019 and 2020, we implemented short-duration (16 d) grazing treatments that varied by season (Early: early June; Late: early August) and intensity (control: 0%, moderate: 30−40%, high: 70−80% relative use). We evaluated cover and biomass percentages of high importance forbs (HIF), soil moisture, and noxious weed cover before and after grazing and again after pasture regrowth (Early: ≈13 wk, Late: ≈6 wk). Short-duration treatments did not reduce HIF cover or biomass. Early-season (P = 0.018) and high-intensity (P = 0.04) grazing increased HIF cover during the pregrazing sample period from 2019 to 2020, suggesting positive effects of these treatments on HIF cover during the pregrazing sample period. Postgrazing HIF cover and biomass percentages remained similar across treatments. Percentages of HIF biomass after regrowth were greater (P = 0.04) in early-season than late-season treatments in 2020. Seasonal declines in soil moisture from pregrazing to regrowth sample periods were greater (P < 0.001) in early-season treatments than late-season treatments but not associated with grazing intensity (P = 0.60). Cover of noxious weeds remained unchanged under short-duration treatments. Our study emphasizes the potential of early-season, high-intensity grazing to increase HIF cover and biomass for brood-rearing sage-grouse in mesic meadows over short time intervals.

Voisin Rational Grazing as a Sustainable Alternative for Livestock Production.

Simple SummaryTo meet current global food supply challenges, researchers and technicians are searching for alternative livestock systems that promote highly sustainable animal productivity and farm profitability, while having a positive environmental footprint. In this narrative review, we highlight one such system, Voisin Rational Grazing (VRG). VRG is a regenerative livestock farming system proposed by French scientist Andre Voisin in the 1950s and further developed in Brazil in the 1970s. VRG has been applied in many countries with vastly different ecosystems. Like other regenerative systems, VRG provides a range of ecosystem services, including negative net carbon emission, reduced soil erosion, and increased biodiversity. Because VRG is also focused on animal performance, farmers applying VRG are more resilient against the adversities confronting farmers practicing more conventional farming systems. VRG requires a paradigm shift from the farmers and thus its uptake may be hindered if there is not enough support within the community. Here, we provide a comprehensive overview of VRG, along with its benefits and constraints.Current livestock practices do not meet current real-world social and environmental requirements, pushing farmers away from rural areas and only sustaining high productivity through the overuse of fossil fuels, causing numerous environmental side effects. In this narrative review, we explore how the Voisin Rational Grazing (VRG) system responds to this problem. VRG is an agroecological system based on four principles that maximise pasture growth and ruminant intake, while, at the same time, maintaining system sustainability. It applies a wide range of regenerative agricultural practices, such as the use of multispecies swards combined with agroforestry. Planning allows grazing to take place when pastures reach their optimal resting period, thus promoting vigorous pasture regrowth. Moreover, paddocks are designed in a way that allow animals to have free access to water and shade, improving overall animal welfare. In combination, these practices result in increased soil C uptake and soil health, boost water retention, and protect water quality. VRG may be used to provide ecosystem services that mitigate some of the current global challenges and create opportunities for farmers to apply greener practices and become more resilient. It can be said that VRG practitioners are part of the initiatives that are rethinking modern livestock agriculture. Its main challenges, however, arise from social constraints. More specifically, local incentives and initiatives that encourage farmers to take an interest in the ecological processes involved in livestock farming are still lacking. Little research has been conducted to validate the empirical evidence of VRG benefits on animal performance or to overcome VRG limitations.

Field indicators of leaf nutritive value for perennial ryegrass and tall fescue pastures under different growing and management conditions

AbstractField indicators of forage nutritive value could help farmers with rapid management decisions to optimize timing and intensity of grazing and meet objectives regarding animal nutrition. The objective of this research was to evaluate the likely relationships among leaf blade nutritive value, herbage mass and leaf stage of pasture regrowth under different growing seasons and residual sward heights. Experiments were performed on perennial ryegrass (Lolium perenne L.) and tall fescue (Festuca arundinacea Schreb.) pastures during spring and summer of 2016. In both pastures, three residual sward height treatments (3, 6 and 12 cm) were imposed on plots arranged in a split plot design, replicated in three blocks. Sward plots were harvested 5–6 times at intervals spaced 7–10 days apart to measure herbage mass, plant morphology, neutral detergent fibre (NDF), and the 24‐hr in vitro digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. Pastures showed strong (R2: .62 to .70), but variable, negative relationships between NDFD and herbage mass that varied with the rate at which pasture grew in each season of experimentation. Although there was a consistent NDFD decline as leaf stage of regrowth progressed (R2: .75 to .97), the NDFD also decreased as residual sward height increased, most notably in tall fescue. Additionally, findings indicate that the greater leaf length plasticity of tall fescue compared to residual sward heights may offer opportunities to manage both post‐ and pre‐grazing targets to achieve tall fescue forages with a similar high nutritive value as perennial ryegrass. However, the evaluation of this hypothesis at the farm level and its impacts on animal intake and performance warrants further careful investigations.

Defoliation dynamics, pasture intake and milk production of dairy cows grazing lucerne pastures in a partial mixed-ration system

The effect of lucerne pasture allocation on defoliation dynamics, pasture intake and animal production was investigated in a subtropical partial mixed-ration dairy system. The study took place at the Gatton Research Dairy, south-eastern Queensland, with a 28-day adaptation period followed by an 8-day treatment period during November and December 2016. Twenty-four multiparous Holstein Friesian dairy cows were offered 11 kg of dry matter (DM)/cow.day as partial mixed-ration dairy system, and four levels of daily pasture allocation measured to 5-cm residual pasture height (averaging 30.6, 20.5, 15.1 and 10.9 kg DM/cow.day). Cows with lower allocations were forced to graze further down the vertical plane and pasture intake and milk yield significantly (P &amp;lt; 0.001) declined. Cows grazed the top grazing stratum (TGS) across 80% of the pasture area before re-grazing another area of the paddock, regardless of the allocation level. Pasture intake (kg DM/ha) of the TGS was at least 2.9 times higher than that of the lower strata, regardless of allocation level. Therefore, the decline in pasture intake is explained by the transition from grazing the TGS to grazing lower strata. When the horizontal utilisation of the TGS approached 100%, the proportion of ungrazed, uncontaminated pasture approached 0% of the area, and intake and milk production declined. Grazing management strategies for lucerne should allocate pasture to lactating dairy cows to achieve horizontal utilisations approaching 0% for proportion of ungrazed, uncontaminated pasture to maximise intake and production. Secondary grazing herds or mechanical methods should be used to remove residual pasture to the ideal height for pasture regrowth.

Effects of grazing intensity and supplementation strategies on Tifton 85 production and on sheep performance

This study evaluated the structural and production characteristics of Tifton 85 (Cynodon spp.) pastures and the performance of lambs under different residual leaf area index (rLAI) and supplementation strategies in tropical conditions. Treatments were the factorial combination of 4- rLAI (0.8; 1.4; 2.0 and 2.6) and 2-supplementation strategies with four replicates in a randomized complete block design. The study was divided into two periods in southeastern Brazil: one in the rainy season and the other in the dry season. Lambs grazed under rotational stocking management and they grazed for 4 days in each pasture while pasture regrowth period was determined by the 95% light interception requirement. In the two evaluated periods the resting period and herbage accumulation decreased linearly and herbage allowance increased linearly with increasing rLAI. The chemical composition and digestibility were affected by rLAI only in the dry season. The dietary supplementation in the rainy season promoted increase of the gain per area but in the dry season the types of supplements did not promote changes in the animals performance. In the rainy season Tifton 85 pastures in rotational stocking can be managed with rLAI between 2.0 and 2.6 with approximately 18 days of regrowth period, and in the dry season with rLAI between 1.4 and 2.0 equivalent to the pasture regrowth period from 58–65 days.

Estimation of spatial and temporal variability of pasture growth and digestibility in grazing rotations coupling unmanned aerial vehicle (UAV) with crop simulation models.

Systematic monitoring of pasture quantity and quality is important to match the herd forage demand (pasture removal by grazing or harvest) to the supply of forage with adequate nutritive value. The aim of this research was to monitor, assess and manage changes in pasture growth, morphology and digestibility by integrating information from an Unmanned Aerial Vehicle (UAV) and two process-based models. The first model, Systems Approach to Land Use Sustainability (SALUS), is a process-based crop growth model used to predict pasture regrowth based on soil, climate, and management data. The second model, Morphogenetic and Digestibility of Pasture (MDP), uses paddock-scale values of herbage mass as input to predict leaf morphogenesis and forage nutritive value. Two field experiments were carried out on tall fescue- and ryegrass-based pastures under rotational grazing with lactating dairy cattle. The first experiment was conducted at plot scale and was used to calibrate the UAV and to test models. The second experiment was conducted at field scale and was used to test the UAV’s ability to predict pasture biomass under grazing rotation. The Normalized Difference Vegetation Index (NDVI) calculated from the UAV’s multispectral reflectance (n = 72) was strongly correlated (p < 0.001) to plot measurements of pasture biomass (R2 = 0.80) within the range of ~226 and 4208 kg DM ha-1. Moreover, there was no difference (root mean square error, RMSE < 500 kg DM ha-1) between biomass estimations by the UAV (1971±350 kg ha-1) and two conventional methods used as control, the C-Dax proximal sensor (2073±636 kg ha-1) and ruler (2017±530 kg ha-1). The UAV approach was capable of mapping at high resolution (6 cm) the spatial variability of pasture (16 ha). The integrated UAV-modeling approach properly predicted spatial and temporal changes in pasture biomass (RMSE = 509 kg DM ha-1, CCC = 0.94), leaf length (RMSE = 6.2 cm, CCC = 0.62), leaf stage (RMSE = 0.7 leaves, CCC = 0.65), neutral detergent fiber (RMSE = 3%, CCC = 0.71), digestibility of neutral detergent fiber (RMSE = 8%, CCC = 0.92) and digestibility of dry matter (RMSE = 5%, CCC = 0.93) with reasonable precision and accuracy. These findings therefore suggest potential for the present UAV-modeling approach for use as decision support tool to allocate animals based on spatially and temporally explicit predictions of pasture biomass and nutritive value.

Modeling the Nutritive Value of Defoliated Tall Fescue Pastures Based on Leaf Morphogenesis

Core Ideas The leaf morphogenetic‐based model predicted the pasture nutritive value variance generated by in an ad hoc experiment. Variation in fiber digestibility with the age and length of leaves is the main driver for declines in pasture digestibility of vegetative regrowth. The morphogenetic approach was designed to enable its potential integration with some of the available pasture growth models. The model provided mechanistic understanding and predictions that allow for the exploration of new management strategies. The leaf morphogenesis of plants is the most important determinant of the nutritive value dynamics in vegetative pasture regrowth. The aim of this study was to develop a simulation model of the pasture nutritive value dynamics based on a morphogenetic approach that takes into account the effects of leaf age and leaf length on forage digestibility in relation to defoliation management. The model was developed and evaluated with detailed data from two independent experiments (Exp. 1 and Exp. 2, respectively) on tall fescue [Lolium arundinaceum (Schreb.) Darbysh.], including descriptions of morphogenesis, neutral detergent fiber (NDF) and digestibility of NDF (NDFD) and dry matter (DMD) of leaf blades. The model precisely and accurately simulated the forage digestibility dynamics of pasture regrowth observed under different residual pasture heights in Exp. 2. The main calculated statistics for NDF, NDFD, and DMD were root mean square deviation &lt; 4% points, R2 ≥ 0.92, concordance correlation coefficient ≥ 0.86 and bias correlation factor ≥ 0.89. The evaluated model was used to investigate the responses of forage nutritive value to several combinations of residual pasture heights (2–15 cm) and defoliation intervals (one to five leaves per tiller). This study highlights the inclusion of the NDFD trait associated to leaf morphogenesis as a mechanistic way to improve predictions of DMD dynamics in vegetative regrowth under different defoliation managements.

Pasture condition and milk production by grazing dairy cows as affected by daily herbage-allowance restriction

Daily herbage allowance is recognised as the main tool to control pasture utilisation and milk production per cow. The aim of the present study was to evaluate the long-term effects of daily herbage allowance (DHA) on pasture characteristics and milk production of dairy cows. Forty-four dairy cows were randomly assigned to one of four treatments in a 2 × 2 factorial design by considering two levels of DHA (20 and 30 kg DM/cow.day) and two types of supplements (high-moisture maize and maize silage) over a 77-day period. Pre- and post-grazing herbage masses, vertical distribution of herbage mass, species density, botanical and chemical composition, sward depletion and changes in morphological components of the pasture were measured. The effect of DHA on soil compaction was evaluated on the basis of the penetration resistance. Milk production and composition levels, bodyweights and body condition scores were recorded. Post-grazing residual declined as the level of DHA decreased, while grazing efficiency increased from 39.8% to 44.8%. We found no effects of DHA on any pasture characteristics, pasture regrowth or soil compaction. Low-DHA conditions induced a faster sward-height reduction, while the herbage mass remained unaffected. Individual milk production decreased with DHA. However, milk outputs per hectare increased by 2772 L/ha. Milk composition, bodyweight and body condition score were not affected by DHA. The results showed that DHA restriction decreases milk production per cow while increasing both herbage utilisation and milk production per hectare, without affecting long-term pasture condition.

Strategic grazing management towards sustainable intensification at tropical pasture-based dairy systems

Agricultural systems are responsible for environmental impacts that can be mitigated through the adoption of more sustainable principles. Our objective was to investigate the influence of two pre-grazing targets (95% and maximum canopy light interception during pasture regrowth; LI95% and LIMax, respectively) on sward structure and herbage nutritive value of elephant grass cv. Cameroon, and dry matter intake (DMI), milk yield, stocking rate, enteric methane (CH4) emissions by Holstein × Jersey dairy cows. We hypothesized that grazing strategies modifying the sward structure of elephant grass (Pennisetum purpureum Schum.) improves nutritive value of herbage, increasing DMI and reducing intensity of enteric CH4 emissions, providing environmental and productivity benefits to tropical pasture-based dairy systems. Results indicated that pre-sward surface height was greater for LIMax (≈135 cm) than LI95% (≈100 cm) and can be used as a reliable field guide for monitoring sward structure. Grazing management based on LI95% criteria improved herbage nutritive value and grazing efficiency, allowing greater DMI, milk yield and stocking rate by dairy cows. Daily enteric CH4 emission was not affected; however, cows grazing elephant grass at LI95% were more efficient and emitted 21% less CH4/kg of milk yield and 18% less CH4/kg of DMI. The 51% increase in milk yield per hectare overcame the 29% increase in enteric CH4 emissions per hectare in LI95% grazing management. Thereby the same resource allocation resulted in a 16% mitigation of the main greenhouse gas from pasture-based dairy systems. Overall, strategic grazing management is an environmental friendly practice that improves use efficiency of allocated resources through optimization of processes evolving plant, ruminant and their interface, and enhances milk production efficiency of tropical pasture-based systems.

Low spatial and inter-annual variability of evaporation from a year-round intensively grazed temperate pasture system

Ecosystem scale measurements of evaporation (E) from intensively managed pasture systems are important for informing water resource decision making and validation of hydrologic models and remote sensing methods. We measured E from a year round intensively grazed temperate pasture system in New Zealand using the eddy covariance method for three years (2012⿿2014). Evaporation varied by less than 3% both spatially (770⿿783mm) and temporally (759⿿776mm) at an annual scale. The low spatial and temporal variation largely occurred because E was strongly controlled by net radiation (r2=0.81, p<0.01, daytime, half-hourly), which did not vary much between sites and years. However, E was strongly limited when volumetric moisture content (VMC) declined below permanent wilting point causing a strong reduction in the decoupling coefficient and an increase in the Bowen ratio. Grazing events appeared to have no effect on E during autumn and winter but reduced E by up to 5% during summer and spring while complete removal of vegetation during autumn herbicide application reduced E by ⿼30%. This implied that over the pasture regrowth period soil water evaporation (ES) could provide up to 70% of E relative to a vegetated site (during autumn) and, given that grazing events removed about 60% of leaf area, these findings suggest ES was likely able to compensate for decreased transpiration post-grazing. Agreement between measured E (EEC) and FAO-56 reference crop E (Eo) was good when soil moisture limitation was not occurring. However, during periods of soil moisture limitation Eo exceeded EEC and a correction factor was needed. We trialled the water stress coefficient (Ks) and a simple three bin VMC correction factor (KVMC) and found the KVMC approach worked better at a daily and monthly scale while both approaches worked well at an annual scale.

Effect of residual leaf area index on spatial components of Tifton 85 pastures and ingestive behaviour of sheep

This study compared the effect of residual leaf area index (rLAI) on the spatial distribution of morphological components of Tifton 85 (Cynodon spp.) pastures and the ingestive behaviour of grazing sheep. Also, it was investigated whether any specific correlation could be found between pasture structural characteristics and sheep ingestive behaviour. Four rLAI treatments (0.8; 1.4; 2.0 and 2.6) with four replications were evaluated per period. Sheep grazed under rotational stocking management and they grazed for 4 days in each pasture while pasture regrowth period was determined by the 95% light interception requirement. Pasture structure was evaluated using inclined point-quadrat, LAI estimates, light interception and leaf : stem ratio. The 2.6 rLAI yielded the highest proportion of dead material in the lower canopy. In the post-grazing period the proportion of leaves increased with increasing rLAI, especially on the canopy surface during the rainy season. In the pre-grazing average pasture height ranged between 19 and 26 cm with dead material and stem observed up to the canopy surface in the dry season. The animals grazed longer on the last day (89.72%) compared with the first day (80.25%) in the dry season. However, they spent less time (11.45%) ruminating in the dry season compared with the rainy season (15.38%), regardless of the grazing day. Grazing time decreased and rumination time increased as rLAI increased. Sheep grazing time correlated negatively with pasture height, before and after grazing. The sheep tend to graze longer on Tifton 85 pastures when rLAI was lower and forage supply was possibly less as on the last grazing day and in the dry season.

Produção de forragem, composição química e morfogênese de Brachiaria brizantha cv. Marandu em diferentes idades de corte

The effects of plant age (14, 21, 28, 35 and 42 days) on dry matter (DM) yield, morphogenetic characteristics and regrowth of Brachiariabrizantha cv. Marandu were evaluated in a cutting trial carried out at Vilhena, Rondônia. The experiment was conducted in a clayey Red-Yellow Latosol with low fertility. DM yields and the leaf area index (LAI) increased consistently with growth stage, however, nitrogen, phosphorus, calcium, magnesium and potassium contents, absolute and relative growth rates, and leaf elongation rate decreased as plant age. Maximum DM yield and LAI were obtained, respectively, at 38.6 and 37.8 days. Apical meristem removing percentage increased with plant age. Aftermath regrowth showed close negative correlation with survival of apical meristems. These data suggest that grazing or cutting at 35 to 42 days were optimal for obtain maximum yields of rich forage and better pasture regrowth.

Regular estimates of paddock pasture mass can improve profitability on New Zealand dairy farms

Paddock selection is an important component of grazing management and is based on either some estimate of pasture mass (cover) or the interval since last grazing for each paddock. Obtaining estimates of cover to guide grazing management can be a time consuming task. A value proposition could assist farmers in deciding whether to invest resources in obtaining such information. A farm-scale simulation exercise was designed to estimate the effect of three levels of knowledge of individual paddock cover on profitability: 1) "perfect knowledge", where cover per paddock is known with perfect accuracy, 2) "imperfect knowledge", where cover per paddock is estimated with an average error of 15%, 3) "low knowledge", where cover is not known, and paddocks are selected based on longest time since last grazing. Grazing management based on imperfect knowledge increased farm operating profit by approximately $385/ha compared with low knowledge, while perfect knowledge added a further $140/ha. The main driver of these results is the level of accuracy in daily feed allocation, which increases with improving knowledge of pasture availability. This allows feed supply and demand to be better matched, resulting in less incidence of under- and over-feeding, higher milk production, and more optimal post-grazing residuals to maximise pasture regrowth. Keywords: modelling, paddock selection, pasture cover

Interaction between plant physiology and pasture feeding value: a review

Plant–animal interactions impact on all elements of pasture and animal performance in grazing systems. The quality of pastures for animals can be described in terms of feeding value (FV), which is a combination of feed nutritive value (NV) and voluntary intake. There are numerous complex interactions between plant physiology and pasture FV and NV. This review focuses on these interactions in four key areas (plant growth strategies, phenological development, pasture regrowth, and response to environmental stress), extracting key principles and illustrating how plant breeding or management may be used to manipulate such interactions to improve FV. The FV is low in pastures with native species that have evolved in nutrient-poor environments, especially if there are greater proportions of C4 than C3 species in the sward. Reproductive development of grasses and long grazing intervals (which affect stage of regrowth) reduce the proportion of leaf and increase stem or dead matter content in the sward. This is exacerbated by environmental stresses such as warmer temperatures and water deficit. Management decisions provide a means of manipulating many of these interactions to improve the FV of pasture, especially by improving soil nutrient status, using irrigation where possible, introducing exotic perennial pasture species such as perennial ryegrass, phalaris and tall fescue, linking the timing of grazing to stage of regrowth, and carefully managing post-grazing residual sward state. Likewise, plant breeding has focused on altering the flowering date of grasses, reducing aftermath heading, and reducing lignification within the plant to improve the FV of pasture for livestock.

Partitioning Soil Respiration during Pasture Regrowth

ABSTRACTUnderstanding the regulation of net ecosystem exchange and soil C sequestration within pasture systems requires knowledge of its component fluxes, including photosynthetic uptake and respiratory loss. However, little information is available on the partitioning of soil respiration (RS) between its heterotrophic respiration (RH) and rhizosphere respiration (RR) components for perennial cool‐season pasture species. The purpose of this study was to use stable C isotopes to examine the effects of regrowth after defoliation on the components of soil respiration for grassland plots planted as an orchardgrass (Dactylis glomerata L.)–white clover (Trifolium repens L.) mixture but dominated by orchardgrass (90 to 100% of harvested biomass). Respiration components were quantified during the first 3 wk following defoliation at the beginning of July in 2010 and 2011. In 2010, RS, RH, and RR were all lowest 1 d after cutting (DAC). Both RS and RH significantly increased by 8 DAC but no further increase occurred over the next 2 wk. In contrast, RR continued to increase throughout the regrowth period. In 2011, RS did not differ among harvests and averaged across dates was less than in 2010. During the 2011 regrowth period RH increased slightly whereas RR did not change significantly. The rhizosphere contribution (RC) to RS averaged 0.49, increasing from 0.35 to 0.56 during regrowth in 2010 but decreasing from 0.62 to 0.43 in 2011. Differences among years in respiration responses during regrowth were possibly due to a combination of factors including resource limitations, soil moisture stress, and differences in soil temperature.

Produtividade e composição estrutural de aveia e azevém submetidos a épocas de corte e adubação nitrogenada

A atividade leiteira é fundamental para a pequena propriedade do sudoeste do Paraná. Este estudo teve como objetivo avaliar o efeito de épocas de corte de pastagem de aveia e azevém, com e sem adubação nitrogenada, sobre a produção de matéria seca e a qualidade da pastagem. O experimento foi conduzido em Pato Branco, PR, num delineamento de blocos ao acaso, com parcelas subdivididas e quatro repetições. Nas parcelas, fez-se uso de adubação nitrogenada de cobertura (0 e 100 Kg de N ha-1), na forma de ureia, e, nas subparcelas, foram avaliadas três épocas de corte de pastagem de aveia e azevém (30, 45 e 60 dias após a emergência). A aplicação de nitrogênio proporcionou um acúmulo de massa de 1133 Kg de MS ha-1, aos 45 dias após a emergência, próximo daquele considerado ideal para início de pastejo. O primeiro corte nessa época, combinado com o uso de nitrogênio, também favoreceu a capacidade de rebrota da pastagem, pois 30 dias após esse corte, o acúmulo de massa alcançou 2398 Kg de MS ha- 1. A adubação nitrogenada aumentou a quantidade de folhas de aveia na pastagem, fato que contribuiu para que o teor de proteína bruta fosse de 27%, indicando alta qualidade do material.

Componentes da biomassa pré-pastejo e pós-pastejo de capim-tanzânia sob lotação rotativa com quatro níveis de suplementação concentrada

Avaliaram-se as características estruturais do capim-tanzânia pastejado por ovinos sob lotação rotativa com quatro níveis de suplementação concentrada (NS) (0,0; 0,6; 1,2 e 1,8% PV), em delineamento de parcelas subdivididas, em que as parcelas foram os níveis de suplementação e os ciclos de pastejo (CP), as subparcelas, com quatro repetições. Estimaram-se as produções de massa seca de forragem total (MSFT), forragem morta (MSFM), forragem verde (MSFV), lâmina foliar verde (MSLV) e colmo verde (MSCV), a altura (ALT) e o número de folhas/perfilho (F/P); as relações folha/colmo (F/C) e material vivo/morto (MV/MM) no pré e pós-pastejo; a densidade populacional de perfilhos (DPP); e o índice de área foliar (IAFres). Não foram observados efeitos dos NS e nem dos ciclos para as variáveis F/P, MSFM, MSFV, MV/MM, MSLV e MSCV. Para a variável ALT, observaram-se diferenças do ciclo 4 em relação aos demais. A MSFT foi afetada pelos NS, de modo que o pasto com ovinos sob suplementação a 0,6% PV foi semelhante aos dos NS de 0,0 e 1,8% PV, porém foi superior ao do NS de 1,2% PV. Foi observado efeito dos NS sobre a MSFTres e MSFMres no nível de 0,6% PV, sendo superior ao do nível de 1,2% PV, porém semelhante aos demais. Para MSFVres observou-se efeito quadrático dos NS, porém não houve efeito dos CP. Para a relação MV/MMres, não foram observadas diferenças entre NS e nem entre CP. Observou-se efeito quadrático dos NS sobre a MSLVres, o IAFres e a MSCVres. Houve aumento linear na F/C com o aumento do NS. Quanto à DPP, não foi observada diferença entre NS. Os níveis crescentes de suplementação não comprometeram o vigor da rebrotação da pastagem, em razão da manutenção dos componentes da biomassa dentro de níveis aceitáveis.