Defoliation Intensity Research Articles

Collaborative Adaptive Rangeland Management, Multipaddock Rotational Grazing, and the Story of the Regrazed Grass Plant

Frequent, severe defoliation reduces grass production and can alter plant species composition in grasslands. Multipaddock rotational grazing has been proposed as a grazing strategy that may reduce the frequency and intensity of defoliation on palatable grass plants without altering stocking rates. Previous studies evaluated this hypothesis using small, homogeneous paddocks and nonadaptive rotation schedules and found small and inconsistent differences between continuous and rotational grazing systems. Using a stakeholder-driven collaborative adaptive management (CAM) framework, we conducted the first ranch-scale experimental investigation into tiller defoliation patterns in the context of adaptive multipaddock rotational grazing. We monitored tiller defoliation frequency and intensity in 10 paired 130-ha pastures assigned to either a collaborative adaptive multipaddock rotational grazing treatment (CARM, one livestock herd) or a season-long continuous grazing treatment (traditional rangeland management [TRM]; 10 separate herds) in shortgrass steppe. Consistent with previous studies, we observed that frequencies of grazing and regrazing on a palatable, cool-season grass (western wheatgrass, Pascopyrum smithii) were much more sensitive to stocking rate than grazing system. Under moderate stocking rates used in both CARM and TRM treatments, roughly two-thirds of western wheatgrass tillers remained ungrazed annually, regardless of grazing system. Thus, season-long rest is present in season-long continuous and rotational grazing systems. Frequencies of tiller regrazing were low (5−15%) and similar between CARM and TRM treatments. Although defoliation patterns were similar between treatments at the whole-ranch scale, CARM enhanced spatial and temporal heterogeneity in defoliation frequencies among individual pastures. Pastures grazed earlier in the season or for longer experienced more defoliation. Managers implementing adaptive, multipaddock rotational grazing could use this heightened and predictable variability to strategically manage impacts of grazing on western wheatgrass at the individual pasture scale. The CAM model enabled our team to identify and directly address key stakeholder hypotheses and resulted in coproduction of management-relevant research.

Impacts of a regional multiyear insect defoliation event on growing‐season runoff ratios and instantaneous streamflow characteristics

AbstractRepeated moderate severity forest disturbances can cause short‐ and long‐term shifts in ecosystem processes. Prior work has found that stand‐replacing disturbances (e.g., clear‐cutting) increase streamflow in temperate forests, but streamflow responses to repeated moderate severity disturbances are more equivocal. This study examined a moderate disturbance caused by an unexpected population irruption of the invasive insect Lymantria dispar (common name: gypsy moth) in 2015–2017. This irruption resulted in defoliation that was locally severe in some areas but spatially heterogeneous at a regional scale. L. dispar larvae consume leaves during the summer growing season, which effectively reduces tree leaf area and associated evapotranspiration. Our regional approach in Southern New England, USA, used data from 83 US Geological Survey (USGS) stream gages to assess whether changes in growing‐season watershed runoff ratios and instantaneous streamflow characteristics during the 2015–2017 L. dispar irruption were associated with satellite‐derived metrics of changes in forest condition (i.e., defoliation), compared to a 20‐year baseline streamflow period. We found a small, linear increase in growing‐season runoff ratio anomalies that was associated with defoliation intensity. The association between defoliation intensity and runoff ratio anomalies was magnified in less anthropogenically impacted reference watersheds. We also found that defoliation intensity was associated with larger volumes of high and medium instantaneous streamflows compared to baseline mean flow conditions. This study provided important insights into the impacts of moderate disturbance on ecohydrology in mesic temperate forests with a unique methodological approach that assessed the impacts of spatially heterogeneous and repeated moderate disturbance at a regional scale.

Forage productivity and chemical composition of Panicum maximum cv. Mombaça under defoliations intensities and frequencies

The effects of defoliation frequency (28, 35, 42 and 49 days) and defoliation intensity (30, 40 and 50 cm above the ground) on green dry matter (GDM) yield, and chemical composition of Panicum maximum cv. Mombaça were evaluated under natural field conditions at the Roraima´s savannas. Defoliation regimes affect productivity and chemical composition of grass forage. The decrease in the pasture defoliation frequency and intensity improved the accumulation of forage, however it reduces the tissue concentrations of N, P, Ca, Mg and K. Irrespective of defoliation frequencies, the highest levels of N (23.99 g kg-1), P (2.12 g kg-1), Ca (4.22 g kg-1), Mg (2.87 g kg-1) and K (21.45 g kg-1) were recorded for the defoliation intensity at 40 cm above the ground. The use of defoliation frequency around 42 days and defoliation intensity of 42,9 cm above the ground can be considered adequate for the management of pastures of P. maximum cv. Mombaça, in order to provides higher forage productivity and quality, regrowth vigor, larger efficiency of forage utilization, greater tissue renewal and canopy structure more favorable to grazing.

Predicting balsam fir mortality in boreal stands affected by spruce budworm

During spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks, stands dominated by balsam fir (Abies balsamea (L.) Mill.) suffer marked levels of mortality after consecutive years of defoliation. The balsam fir mortality rate is also influenced by such factors as stand age and forest composition. Nonetheless, the relative importance of these factors when predicting balsam fir mortality during an outbreak remains uncertain. Here we present models for predicting balsam fir mortality rates on the basis of defoliation duration and intensity, stand age, and forest composition. We found a significant increase in balsam fir mortality rates with an increased duration and intensity of defoliation. Balsam fir experienced >22% mortality after five years of continuous severe defoliation. The model identified cumulative defoliation—a commonly used measure in Canada of the sum of annual defoliation intensities experienced by a stand over a given defoliation period—as an effective index for predicting mortality. Detailed cumulative defoliation, a factor specifying the frequency of different levels of annual defoliation intensities experienced by a stand over a given defoliation period, provided even more reliable results. Mature stands experienced 5% greater mortality than immature stands, and mortality was 3% and 8% greater in pure balsam fir stands than in mixed balsam fir–spruce and mixed balsam fir–hardwood stands, respectively. The proportion of other tree species also affected the mortality prediction model. We attained 70% accuracy for our best model for predicting balsam fir mortality rate in heterogeneous mixed stands; this model included detailed cumulative defoliation, stand age, and the proportion of other species in the stand. Therefore, these factors must be included in decisions related to recovery cutting in forests affected by spruce budworm outbreaks.

Direct and Joint Effects of Genotype, Defoliation and Crop Density on the Yield of Three Inbred Maize Lines

The aim of this study was to observe direct and joint effects of three factors (genotypes, ecological environmental conditions and the applied crop density) on the level of defoliation intensity and yield. Three inbred lines (G) of maize (G1–L217RfC, G2–L335/99 and G3–L76B004) were used in the study. The trials were performed in two years (Y) (Y1 = 2016 and Y2 = 2017) and in two locations (L) (L1 and L2) under four ecological conditions of the year–location interaction (E1–E4) and in two densities (D1 and D2) (50,000 and 65,000 plants ha−1). Prior to tasselling, the following five treatments of detasseling and defoliation (T) were applied: T1—control, no leaf removal only detasseling, T2–T5—removal of tassels and top leaves (from one to four top leaves). The defoliation treatments had the most pronounced effect on the yield reduction in G1 (T1–Tn+1… T5), p < 0.05. The ecological conditions on yield variability were expressed under poor weather conditions (E3 and E4), while lower densities were less favorable for the application of defoliation treatments. The result of joint effects of factors was the lowest grain yield (896 kg/ha) in G3 in the variant E3D1 for T2 and the highest grain yield (11,389 kg/ha) in G3 in the variant E2D2 for T1. The smallest effect of the defoliation treatment was on the kernel row number (KRN).

Annual bromes decrease with increasing fall defoliation intensity

Japanese brome (Bromus japonicus Thunb.) has been introduced to four continents from its Eurasian origins and has increased during recent decades, particularly in North America. Invasion of this C3 annual grass into rangelands diminishes native plant communities and hinders livestock performance. Control methods have been developed, but have proven short-lived. Japanese brome is positively correlated with plant litter and standing dead material, suggesting management of those components could be important. Objectives for this study were to isolate and quantify the effects of litter and standing dead on Japanese brome utilizing fall defoliation with four different mowing heights (10, 6, 4, or 1 cm) compared to a non-mowed control. Research was conducted on two ecological sites (silty and claypan) with each site consisting of 25 plots (5.5 × 1.6-m). This study was conducted over 4 yr (2013–2017) and fall mowing reduced old dead mass every year except 2016, which followed a severe drought. Spring soil water was not reduced by fall defoliation. Mowing to 1 cm reduced brome biomass by 40% compared to non-mowed plots and brome production was highly dependent on Sep-Oct precipitation. Brome biomass was least in 2015 during a drought and greatest in 2017 following double the median Sep-Oct precipitation. Non-brome biomass was similar across treatments. An 11% reduction in current-year biomass was observed for mowing heights of 10, 6, and 4 cm whereas a 22% reduction was measured for the 1 cm mowing height compared to non-mowed plots. Perennial grass basal cover was similar for 10, 6, and 4 cm mowing heights and greater than that for mowing at 1 cm whereas, no differences were detected between non-mowed plots and any mowing height. Increasing fall defoliation intensity reduced annual bromes while allowing perennial grasses to persist, indicating fall mowing and possibly grazing are viable options for annual brome management.

Effect of grazing management strategies on the yield and nutritional value of Marandu grass in the semiarid of Brazil

The objective of this study was to evaluate the effects of two grazing management strategies on structural, productive and nutritional parameters of Marandu grass (Urochloa brizantha cv. Marandu). A completely randomized block design with two pasture management strategies and eight replications (blocks) was used. The grazing management strategies were: (1) low intensity rotational grazing (LI), with a pre-grazing sward height of 40 cm and a post-grazing sward height of 24 cm, i.e., a defoliation intensity of 50%; (2) High intensity rotational grazing (HI), with a pre-grazing sward height of 40 cm and a post-grazing sward height of 10 cm (±70% defoliation intensity). Pastures were sampled before and after grazing for estimation of forage mass, forage accumulation rate, structural characteristics, nutritional value and dry matter intake.The LI strategy resulted in higher dry matter production than HI before (18.33%) and after grazing (49.06%), increasing pre-grazing forage density by 13.21% (P < 0.05). The production of potentially digestible dry matter was highest (P < 0.05) in LI strategy (21.3% before and 39.6% after grazing, respectively). Higher post-grazing green forage mass (45%) increased the residual crude protein in LI. The LI management strategy increased forage mass production and can be used in Marandu grass pastures.

Photosynthetic carbon allocation to live roots increases the year following high intensity defoliation across two ecosites in a temperate mixed grassland

Livestock grazing is an important driver of the carbon (C) cycle in grasslands and could be a decisive factor determining whether grasslands are a net sink or source of C. However, short-term C dynamics in grassland ecosystems and its response to different grazing intensities remain unclear, especially under field conditions. Here we test the hypothesis that photosynthetic C allocation in the plant-soil system of grasslands is differentially affected by the intensity of grazing that occurred in the prior growing season. We studied the fate of new C assimilates, using a 13CO2 pulse-labeling technique, as they move from shoots to roots and soil in vegetation previously exposed to different defoliation (emulated grazing) intensities in two semiarid Mixed Prairie grassland ecosites having contrasting soil textures (sandy vs. loamy). Within 24 h after photosynthetic uptake, 34.5% of the labeled C was translocated out of shoots, with 21% of the labeled C found in the mineral soil. Plant communities treated with high intensity defoliation during the previous growing season had more of the newly fixed 13C translocate into live roots at both ecosites throughout the 25-day chase period, indicating a higher demand for photosynthetic C by the root system of heavily defoliated plants. Twenty-five days after labeling, 13C transfer into the top 30 cm mineral soil was consistently greater at the loamy (26% of total 13C remaining) than at the sandy ecosite (10.4% of 13C remaining). We conclude that conditioning with high intensity defoliation the prior growing season stimulated short-term C allocation to roots in these semi-arid grasslands. Although this response was independent of soil texture, more C was translocated belowground overall in the loamy ecosite. The effect of defoliation intensity and ecosite in regulating short-term C allocation in the plant-soil system in temperate grasslands should be incorporated into future models describing C cycling in grasslands when predicting C dynamics under different management strategies employing contrasting grazing intensities.

Development parameters of the latent period as a response of rubber tree resistance to South American leaf blight

ABSTRACT The major phytosanitary problem for rubber tree cultivation in Brazil is the disease known as South American leaf blight, caused by the fungus Microcyclus ulei. Its symptoms manifest in young leaves and cause intense defoliation, resulting in reduced latex production and even the death of susceptible plants. Thus, this disease consists in a constant threat to East Asian plantations. As worldwide traditional breeding programs have evolved, interspecific hybrid clones have currently been used for planting. They are more productive and show better resistance to pathogens. However, traditional breeding programs have not led to significant progress in resistance to South American leaf blight since the selection is directed to clones with complete resistance. In this pathosystem, horizontal or partial resistance (HR) and vertical or complete resistance (VR) can act simultaneously, evidencing their complexity and difficult quantification. This study aimed to: characterize the foliar lesion type in Hevea sp. X M. ulei pathosystem; verify the clonal susceptibility to pathogens; analyze the infection frequency for resistance quantification in Hevea sp. x M. ulei pathosystem, and recommend differentiating rubber tree clones to quantify M. ulei races in Brazil. The monocyclic parameters (latent period and lesion diameter) are applicable for resistance quantification in Hevea sp. x M. ulei pathosystem. Latent period had slight variation among clones. Lesion diameter had wide variation among clones and was a discriminating parameter for horizontal resistance and vertical resistance.

Does the type of silvicultural practice influence spruce budworm defoliation of seedlings?

AbstractSpruce budworm (Choristoneura fumiferana (Clem)) is the main defoliator in the boreal forest of North America, and its outbreaks have major ecological and economic consequences and represent a challenge for forest management. Numerous studies have addressed the effects of this defoliator on mature trees, whereas the effects of spruce budworm on regeneration remain elusive. Furthermore, intensive exploitation practices during the last decades have left a large area of the Canadian boreal forest in an early development stage. In this context, it becomes vital to understand those factors affecting the severity of spruce budworm‐related defoliation on regeneration. Here, we determine the defoliation severity of black spruce and balsam fir seedlings in both mature pure black spruce and black spruce–balsam fir stands subjected to two different silvicultural treatments (clear‐cutting and partial cutting). Defoliation intensity varied between stand types, silvicultural treatments, species, and height classes. Seedlings in black spruce–balsam fir stands experienced twice the defoliation of those in pure black spruce stands (black spruce seedlings 10% vs. 23%; balsam fir seedlings 29% vs. 47%, respectively). Harvesting methods also influenced seedling defoliation. Under clear‐cutting, black spruce seedlings (24%) were three times as defoliated as black spruce seedlings in partial cutting stands (8%), whereas balsam fir seedlings in clear‐cutting plots experienced twice the defoliation (42%) of balsam fir seedlings in partial cutting plots (20%). The level of defoliation also increased with seedling height. This study will help silvicultural strategies adapt to the effects of natural disturbance regimes. As the intensity and severity of defoliator outbreaks are expected to increase under climate change, these results will help guide forest management strategies to select harvesting methods that will limit the effects of defoliation on conifer regeneration.

Predominant Microbial Colonizers in the Root Endosphere and Rhizosphere of Turfgrass Systems: Pseudomonas veronii, Janthinobacterium lividum, and Pseudogymnoascus spp.

Microbes can colonize plant roots to modulate plant health and environmental fitness. Thus, using microbes to improve plant adaptation to biotic and abiotic stresses will be promising to abate the heavy reliance of management systems on synthetic chemicals and limited resource. This is particularly important for turfgrass systems because intensive management for plant available nutrients (e.g., nitrogen), water, and pest control is necessary to maintain a healthy and aesthetic landscape. However, little is known on microbial species and host compatibility in turfgrass root endosphere and rhizosphere. Here, by using marker gene high throughput sequencing approaches we demonstrated that a few bacterial and fungal species prevailed the root endosphere and rhizosphere and were of a broad host spectrum. Irrespective of turfgrass species (bermudagrass, ultradwarf bermudagrass, creeping bentgrass, and tall fescue), defoliation intensities (i.e., mowing height and frequency), turfgrass sites, and sampling time, Pseudomonas veronii was predominant in the root endosphere, constituting ∼38% of the total bacterial community, which was much higher than its presence in the bulk soil (∼0.5%) and rhizosphere (∼4.6%). By contrast, Janthinobacterium lividum and fungal species of the genus Pseudogymnoascus were more abundant in the rhizosphere, constituting ∼15 and ∼ 39% of the total bacterial and fungal community, respectively, compared to their respective presence in the bulk soil (∼ 0.1 and 5%) and root endosphere (∼ 0.8 and 0.3%). Such stark contrasts in the microbiome composition between the root endosphere, rhizosphere, and bulk soil were little influenced by turfgrass species, suggesting the broad turfgrass host compatibility of these bacterial and fungal species. Further, their dominance in respective niches were mutually unaffected, implying the possibility of developing a multiple species formula for coping turfgrass with environmental stresses. These species were likely involved in controlling pests, such as infectious nematodes and fungi, decomposing root debris, and helping turfgrass water and nutrient uptake; yet these possibilities need to be further examined.

Species-specific trade-offs between regrowth and mycorrhizas in the face of defoliation and phosphorus addition

Arbuscular mycorrhizal fungi (AMF) enhance nutrient provision in exchange for carbon. However, a shift from nutrient to carbon limitation, induced by repeated or intense defoliation, can represent a trade-off between plant regrowth and the maintenance of mycorrhiza. The combined effects of AMF, phosphorus and defoliation on growth of A gropyron elongatum (C 3 grass, low mycorrhizal responsiveness) and B rachiaria brizantha (C 4 grass, high mycorrhizal responsiveness) were explored. Each species was subjected to a manipulative experiment with AMF inoculation (non-inoculated, inoculated), soluble P supply (low, high) and defoliation (non-defoliated, 60% defoliated). In A. elongatum , at low P supply, mycorrhizal plants showed increased growth rates following defoliation without substantial changes in AMF colonization. At high P supply instead, we found a clear trade-off between regrowth and the maintenance of mycorrhiza evidenced by growth depression (biomass and tillers) and lower AMF activity (reduction of arbuscules). In contrast, in B. brizantha , defoliation effects on plant regrowth were independent from AMF at any P supply (no trade-off). This indicates that cost-benefit relationship in defoliated plants is highly context-dependent and may vary with mycorrhizal responsiveness of species. This variation of responses can play a decisive role on plant recovery in pastures and natural grasslands subjected to herbivory. • First comparative study of AMF, defoliation and P supply in C 3 and C 4 grasses. • In the C 3 grass, AMF promoted recovery from defoliation at low P supply. • Mycorrhiza and defoliation trade off in the C 3 grass at high P supply. • In the C 4 grass, mycorrhizae were beneficial at all environmental contexts. • AMF effects on the recovery from defoliation depend on P supply and plant identity.

Management of Source-Sink Balance for Maintaining Seed Vigor and Storability of Maize

Defoliation was the major factor which directly affected to maize seed yield and quality basis on source-sink relationship. Thus, the objectives were to study the effect of source-sink balance management on corn seed vigor and storability and to determine the effect of defoliation treatments on maize yield, yield components and produced seed germination traits. The experiment was arranged basis on Split-Plot in Randomized Complete Block Design with four replications. Main plot was the pattern of leave cutting with 5 levels: D1 = control, (without defoliating), D2 = complete defoliation, D3 = defoliating only under the ear, D4 = remain 2 top leaves, D5 = remain ear leaf. Sup-plot was leaf cutting dates which were C1 = 7 days after silking, C2 = 10 days after silking, C3 = 13 days after silking and C4 = 16 days after silking. Complete defoliation severely reduced ear weight, row number per ear, seed number per ear and 100 - seed weight (P<5%). Defoliation treatments had much more significantly affected on produced seed germination and seed vigor traits. Leaf defoliation intensity and leaf position affected total dry matter. Conclusion, the leaf defoliation only below ears was useful for source-sink balance management, because it promoted the seed qualities and vigor following to principle of parasitic sink elimination.

Grazing intensity as a management strategy in tropical grasses for beef cattle production: a meta-analysis

Correct pasture management associated with the adjustment of grazing intensity determines pasture persistence and the level of production per animal and per land area. The objective of this review was to examine the effect of grazing intensity in tropical pastures on the performance and productivity of beef cattle by a meta-analytical approach. The review followed a protocol developed and tested based on the PICOS strategy to formulate the guiding question: population (beef cattle), intervention (high grazing intensities), comparison (low grazing intensities), outcome (animal performance and productivity), and study design (experimental). Data were collected from papers published in the electronic databases of SCOPUS (Elsevier), Web of Science (Main collection), SpringerLink, Wiley Online Library, and Science Direct (Elsevier) by a single cross-reference search. The selected studies were considered relevant when they: (1) were primary research published in the format of a research article; (2) included grazing intensities as a management strategy; and (3) evaluated average daily gain (ADG, kg/animal per day), stocking rates (SR, animal unit (AU)/ha; AU = 450 kg), and weight gain per area (WGH, kg/ha). Thirteen manuscripts were selected due to their methodological strength for data extraction. The means under continuous stocking were 0.67 kg/animal per day for ADG, 518.12 kg/ha for WGH, and 4.19 AU/ha for SR. Under intermittent stocking, the means were 0.62 kg/animal per day for ADG, 980.18 kg/ha for WGH, and 5.10 AU/ha for SR. In tropical forages, the heights of 20 to 40 cm for pastures under continuous stocking and the defoliation intensities of 40 to 50% for those under intermittent stocking result in greater individual performance and animal productivity per land area.

Prioritized carbon allocation to storage of different functional types of species at the upper range limits is driven by different environmental drivers

The upper elevational range limit of tree species (including treeline and non-treeline species) is generally considered to result from either carbon limitation or sink limitation. Some evidence also suggests that tree line might reflect preferential carbon allocation to NSC storage at the expense of growth. How might the importance of these potential mechanisms be determined? We used an elevational gradient to examine light-saturated photosynthesis (Asat) and NSC concentrations in plant tissues of three different functional types of tree species. We also examined the effects of consecutive 4 years of in situ defoliation on growth and NSCs at the upper elevational range limit. Declining temperature with increasing elevation did not reduce Asat in any of the species. We found NSC increased with elevation in major storage tissues (e.g., roots and twigs) but not in leaves. The defoliation showed that C storage took priority over growth. Such preferential carbon allocation, directly caused by growth decline, always existed in the deciduous tree species. In the evergreen tree species, however, growth decline resulted from preferential carbon allocation to storage was only detected in 2017 and then disappeared as the intensity of defoliation increased. Our results showed that trees prioritized sustaining stores of C more highly than allocation of growth, regardless of the trees' C or sink limitations. At the cold range limits, the prioritized carbon allocation to storage in deciduous tree species was in response to low temperature stress, while in evergreen tree species, the prioritization of carbon allocation was only a transient physiological response to defoliation disturbances.

Physiological and growth responses to defoliation of older needles in Abies alba trees grown under two light regimes

In most defoliation experiments with evergreen trees, leaves are removed proportionally across all leaf age classes or only the younger ones are removed. However, it remains unclear how the ecophysiological functions of older foliage potentially differ from those of younger leaves. Hence, we conducted a field experiment with five intensities of artificial defoliation (0%, 11% needle biomass loss = all ≥ 5-year-old needles removed, 27% loss = all ≥ 4-year-old needles removed, 46% loss = all ≥ 3-year-old needles removed, and 71% loss = all ≥ 2-year-old needles removed) of Abies alba trees grown under low-light (LL, 28% of full sunlight) and high-light conditions (HL, 70%). Photosynthesis of the remaining one-year-old needles; concentrations of non-structural carbohydrates (NSCs = soluble sugars + starch), total nitrogen (N), and soluble protein (SP) in stem sapwood and one-year-old needles; and tree height and stem radial growth rates were measured. We found that growth light conditions, rather than old needle defoliation up to a needle biomass loss of 70%, significantly affected growth, photosynthetic capacity and concentrations of tissue N, SP, and NSCs, with levels of all parameters greater in HL trees than in LL tress. Defoliation-induced compensatory growth was found in HL trees only, whereas tree height growth rates tended to decrease with increasing defoliation intensity in LL trees. Our results indicate that light availability, rather than damage to older foliage, plays an important role in determining plant physiology and growth. These results from A. alba trees suggest that the resource uptake by older foliage almost balances their resource consumption, leading to the conclusion that the older needles from evergreen trees physiologically contribute less to the whole-tree carbon and nitrogen balance. Our findings also suggest that the effects of older foliage defoliation on forest survival and productivity may have been overestimated in past forest ecosystem management practices, while the physiological functions of the youngest foliage may have been underestimated.

Defoliation intensity and leaf area index recovery in defoliated swards: implications for forage accumulation

This study evaluated the leaf area index (LAI) recovery mechanisms and forage accumulation rates on the regrowth of different grass species subjected to different defoliation intensities. For that purpose, plots of Pennisetum clandestinum (kikuyugrass), Lolium multiflorum (annual ryegrass), and Avena strigosa (black oats) were defoliated from 20 to 80 % of their initial heights (25, 20, and 25 cm, respectively). At different increments in height, forage samples were collected to ground level and used to estimate tiller population density (TPD), leaf area per tiller (LA), and forage mass. From these data, we calculated the leaf area index (LAI), average leaf area index (aLAI), and average and instantaneous forage accumulation rate (FAR and IFAR, respectively). Data were plotted over time (days) to describe LAI recovery and forage accumulation rates. As the defoliation intensity increased, greater canopy heights were needed for pastures to achieve their maximum forage accumulation rates, which required longer regrowth intervals. The need for high tiller recruitment after defoliation, which delayed canopy LAI recovery, seemed to be one of the main cause. Thus, grazing management strategies that involve costly tiller recruitment could decrease both overall forage production and sward persistence over time. However, the plant ability to recover LAI after successive intense defoliations seems to be species-dependent and related to their phenotypic plasticity.

Leaf stage as a defoliation criterion for the production of high-vigour annual ryegrass seeds

Previous research demonstrated that the interval between defoliation treatments based on the leaf stage is a promising tool for the management of annual ryegrass (Lolium multiflorum L.) pasture. The use of this tool, which is based on the physiological status of the plant, could also benefit the seed production. We assessed the effects of the time of defoliation based on leaf stage on seed yield and quality of annual ryegrass cut to three residual stubble heights (RSH) (50%, 25% and 0% of plant height pre-defoliation) and a second defoliation applied to certain treatments based on the leaf stage of the plant regrowth (two or three leaves per tiller). Higher defoliation intensities (lower RSH) increased the amount of harvested forage to 4.0 t DM ha–1. Moderate defoliation (50%) undertaken at the 3-leaf stage combined with intense defoliation (25% and 0%) at the 2-leaf stage resulted in the highest seed yields (1.8 t ha–1). However, lower RSH reduced mean seed weight and physiological seed quality, which was also associated with lower seed starch and protein content. Accelerated ageing (AA) tests were used to compare seed vigour between treatments. A second defoliation at the 3-leaf stage plus intense defoliation (RSH 0%) resulted in seed lots with a high rate of lipid peroxidation after the AA test, followed by lower catalase activity, germination, and seedling growth. The combination of a second defoliation at the 3-leaf stage and the retention of higher RSH (50%) promoted a greater proportion of leaf blades in the stubble, with a strong positive correlation with seed production and vigour. Antioxidant enzyme activity after the AA test is an important marker of annual ryegrass seed quality.

Effect of Vine Cuttingon Multiplication Ratio and Yield of Three Orange-fleshed Sweetpotato (&amp;lt;i&amp;gt;Ipomoea batatas&amp;lt;/i&amp;gt; (L) Lam) Varieties in South Eastern Nigeria

A major constraint to sweetpotato production in Nigeria is the lack of clean and sufficient quantities of vine cutting at the time of planting in May or June. Inorder to obtain planting materials, farmers subject sweetpotato to vine harvest at various times but there is dearth of information on the effect of the level or intensity of defoliation on the crop. In this study, the response of three orange-fleshed sweetpotato varieties to cutting regimes in 2014 and 2015 cropping seasons in a tropical ultisol of South eastern Nigeria was evaluated. In each year, the experiment was laid out as 3 x 4 factorial arranged in randomized complete block design with three replications. Treatments comprised all combinations of three orange-fleshed sweetpotato varieties (Umuspo 1, Umuspo 3 and Ex-Igbariam) and four cutting regimes (6, 10 and 14 weeks after planting [WAP], 8 and 12 WAP, 10 and 14 WAP and no-cutting). Cutting regimes did not influence fresh shoot biomass in both year but cutting at 10 and 14 WAP significantly increased multiplication ratio compared to no-cutting or other cutting schedules. Storage root yield was, however, significantly higher with no-cutting than with the 4 weekly cuts, regardless of cutting dates. In all situations, Umuspo 1 produced significantly higher multiplication ratio and higher top and storage root yields than other varieties. Conversely, Umuspo 3 produced higher carotene yield at 10 and 14 WAP cutting compared to other varieties and cutting regimes.

Grazing strategies for resilience of ryegrass (

Perennial ryegrass (Lolium perenne L.) is a widely sown pasture species in temperate regions. Under heat and moisture-deficit stress, its production is suppressed and tiller mortality increases, particularly when plants are simultaneously exposed to other stresses such as intense defoliation. We investigated the effects of extended grazing exclusion periods in spring and summer on herbage and soils of rotationally grazed, perennial ryegrass-dominant pastures at a summer-wet site and a summer-dry site in sheep and beef hill country in New Zealand. Treatments comprised ‘grazed’ (conventional rotational grazing), ‘early opening’ (grazing exclusion from mid-spring to mid-summer to allow perennial ryegrass to flower), and ‘deferred grazing’ (grazing exclusion from mid-spring to late summer to allow perennial ryegrass to flower and set seed). At both sites, deferred grazing increased perennial ryegrass tiller density and total vegetation cover, and reduced the abundance of broadleaf species and Pseudopithomyces chartarum spores for up to 15 months after exclusion compared with the grazed control. Herbage production was reduced during the deferred period but there was a growth surge thereafter so that herbage production over the study period was similar in the deferred and grazed treatments. Pasture nutritive values were lower in the deferred than the grazed treatment during the exclusion period but were similar in all treatments by the end of the following winter. In the autumn after deferring, seedlings contributed ~50% of the perennial ryegrass tillers present at the summer-dry site but only ~10% at the summer-wet site, where regrowth tillering of existing plants contributed a high proportion of the perennial ryegrass tillers present. Overall, early opening had few effects on the pasture, whereas deferred grazing had numerous positive effects on the pasture but only short-term effects on soil quality.