Defoliation Height Research Articles

Tailoring defoliation and nitrogen management for large canopy radiation use and biomass production of perennial systems destined for biorefinery

Perennial leafy grasses and legumes are promising for extraction of proteins with a green biorefinery amid increasing demand for local production. However, which defoliation strategy increases radiation-use efficiency and biomass production still needs to be determined. A multi-year field experiment started in 2019 in Denmark with fertilized grasses (perennial ryegrass, tall fescue), unfertilized legumes (alfalfa, red clover) and their fertilized mixture (grass-legume), each defoliated at 2-, 4- or 8- weeks interval, at either 7-9 or 12-14 cm defoliation height. The main aim was to quantify effects of species, defoliation height and frequency, and nitrogen application rate on canopy radiation interception, aboveground biomass and crude protein production, as well as aboveground radiation use efficiency (RUEA).The results showed that accumulated intercepted photosynthetically active radiation (AIpar) increased with increasing defoliation height and decreasing frequency for most systems, with the largest AIpar obtained seasonally by red clover (730-815 MJ m−2) and grass-legume mixture (790-826 MJ m−2) defoliated at medium to low frequency. Tall fescue defoliated at medium to low frequency yielded the highest aboveground biomass (10-14 Mg ha−1) and red clover defoliated at medium to high frequency yielded the most crude protein (2.5-2.9 Mg ha−1) compared to all other systems annually. RUEA decreased with increasing defoliation height and maximum values were achieved at medium frequency, with tall fescue having significantly higher RUEA (1.6-2.1 g MJ−1) than the other systems. Seasonally, RUEA was variable at high defoliation frequency, being consistently higher at the start and the end of the season for ryegrass and the mixture systems.This study pinpoints tall fescue and red clover as perennial crops with high agronomic productivity among tested species for green biorefinery and also concluded that red clover in temperate humid climate maximize productivity and sustainability for biorefining with defoliation at low height and medium frequency.

Effects of conservation versus elimination of growing points on yield, C: N: P stoichiometry, and root morphology of Leymus chinensis

AbstractThe conservation and elimination of the growing point of Leymus chinensis (Trin.) Tzvel. are two common contrasted scenarios during grazing. However, the biomass and nutrient allocation in L. chinensis, as well as their contribution to yield under these conditions are unclear. Therefore, a simulated grazing experiment was conducted using a factorial design that combined two defoliation heights (conservation versus elimination of growing points) and four plant heights (18, 24, 31, and 35 cm) during two growing seasons (2020 and 2021), resulting in eight treatments. Additionally, the experiment also included two identical control treatments with a single mowing in mid‐August. The results demonstrated that conservation treatments for the growing point increased the regeneration time of L. chinensis during the entire growing season in both years compared to elimination treatments for the growing point, due to the alteration in biomass allocation priority and C: N: P stoichiometric ratio between stems and leaves of L. chinensis, as well as root morphological traits. The growth strategy in the treatment with 17 cm defoliation height at 35 cm plant height demonstrated the optimal combination, resulting in stabling the accumulated DM yield of L. chinensis in both years. The findings emphasize the significance of comprehending the correlation between the growing point of L. chinensis and its yield, providing a pioneering approach to guide sustainable grazing practices for L. chinensis grassland.

Dry‐matter production and botanical composition of multispecies and perennial ryegrass swards under varying defoliation management

AbstractMultispecies swards, comprised of different plant functional groups have comparable production potential to high N input L. perenne swards at reduced N when legumes are included. However, information on the appropriate management of multispecies swards is limited. The effect of differing management practices on the herbage dry‐matter (DM) production and botanical composition of different sward types was investigated using a 3 × 2 × 2 factorial design plot experiment. The experiment consisted of three sward types: L. perenne‐only receiving (LP; 250 kg N ha−1 a−1); L. perenne‐Trifolium repens (LP‐TR); multispecies sward containing L. perenne, Phleum pratense, Trifolium repens, Trifolium pratense, Plantago lanceolata and Cichorium intybus (MSS). LP‐TR and MSS received 90 kg N ha−1 a−1. Harvesting of plot herbage took place every 21 or 28 days to a defoliation height of 4 or 6 cm, over two growing seasons (March to November 2020 and 2021 inclusive). Annual herbage produced by both LP and LP‐TR was not significantly affected by defoliation frequency. However, MSS produced 1923 kg DM ha−1 a−1 more herbage when harvested less frequently. Unsown species contributed significantly less to the herbage DM of MSS compared to LP and LP‐TR and remained similar in 2020 and 2021, whereas the contribution of unsown species to herbage DM increased in LP and LP‐TR from 2020 to 2021, with noxious species more associated with LP and LP‐TR than MSS. Results demonstrate the role of multispecies swards in improving the sustainability of grass‐based agricultural systems in an environment of reduced fertilizer inputs.

112 Herbage Mass, Nutritive Value, and Grain Yield of four Wheat Varieties Managed as a Dual-Purpose Crop

Abstract Dual-purpose wheat (Triticum aestivum L.) systems increase farm sustainability by diversifying on-farm income. While these systems are common in the Southern Great Plains of the U.S., they are not often utilized in the Southeast. This study aimed to evaluate pre- and post-grazing herbage mass (HM) of four winter wheat varieties managed under a dual-purpose grazing and grain production system. The wheat varieties evaluated were generic feed-type wheat (unknown variety blend, Feed), seed-type wheat ‘GA Gore’ (Seed) and two forage-type varieties, ‘AGS 2024’ (AGS) and ‘Pioneer 26R41’ (Pioneer). The experiment was a randomized complete block design (n = 4) conducted during the winter of 2021 and 2022. Three grazing frequencies were utilized: an ungrazed control (NG), low frequency (LF) and high frequency (HF) grazing schedule. Low frequency plots received monthly grazing in January and February while HF treatments received a third grazing in March. Plots were grazed with 20 cow-calf pairs (Bos taurus) until an even defoliation height of 10 cm was achieved. Herbage mass was determined using three 0.1m2-quadrats per plot and clipped to a 10 cm stubble height before (PreG) and after (PostG) each grazing event. Forage samples were then dried at 45°C for 72 h. Data were analyzed using PROC GLIMMIX of SAS (SAS Inst., Cary, NC) with forage sample date as a repeated measure. Differences were declared at P < 0.05. Final biomass, including stems, chaff, and grain, was greatest for Pioneer but was not different from AGS or Feed (4,112 kg/ha and 4,003 kg/ha; P ≤ 0.94). Before grazing, AGS herbage mass (2,646 kg/ha) was greater (P ≤ 0.03) than all other varieties. There was an interaction (P ≤ 0.01) of variety and grazing frequency for Pre-G herbage mass. Compared with all other varieties, AGS had greater ADF (24.93%; P < 0.01) and least TDN (72.49%: P < 0.01). Forage nitrate-nitrogen was not different (P ≥ 0.49) among all varieties or grazing frequencies (157.73 ppm). Across grazing frequencies, Pioneer had greater final grain yield (3,619.43 kg/ha; P < 0.01) with Seed having the least (1,272.12 kg/ha; P < 0.01). These results indicate that common Southeastern wheat varieties can be successfully utilized in a dual-purpose management system; however, grazing frequency should be monitored to prevent grain yield losses.

Technological Quality of Dual-purpose Wheat Stored

Defoliation may interfere in the sink-source relationship and influence the technological quality of wheat flour. This study aimed to confirm the effects of plant cutting heights and number of cuttings on the technological wheat flour quality of BRS Umbu and BRS Tarumã cultivars after six months of storage. A completely randomized design was used and treatments consisted of a combination of cutting heights (20 and 30 cm) and number of cuttings (no cutting, 1, 2 and 3 cuttings), resulting in the following treatments: 20/1, 20/2, 20/3 30/1, 30/2, 30/3 and controls with no cuttings. Grain moisture, crude protein, hectoliter weight, gluten strength, falling number and wet gluten were determined. It was observed the behavior for both cultivars and number of cuts was similar, and it was found that the defoliation height of 30 cm resulted in greater decreases in PH and W values of 2.5 and 25.5% respectively. The results indicate that defoliation does not lead to the evolution of the stored wheat evaluated technological properties and with storage, properties such as W and WG of both cultivars showed a reduction.

Defoliation heights for palisade grass cv. Marandu in silvopastoral system

ABSTRACT The objective was to test the response of Urochloa brizantha cv. Marandu in monoculture and in silvopastoral system (SPS), at two distances from the trees, and define the best defoliation height for SPS. Four intermittent defoliation heights (25, 35, 45 and 55cm) and two distances from tree lines (2.5 and 5.0m) were evaluated in the SPS with a control defoliated with 25cm in full sun. The experiment was performed in a randomized block design with 3 replicates in a 4 × 2 + 1 split plot scheme. The control had higher forage accumulation (46.9kg/ha. day) than the SPS (31.1kg/ha. day). The bulk density was also higher in the control (0.89mg/cm³) than in SPS (0.48mg/cm³). The percentage of leaves (78.06%) and leaf/stem ratio (6.04) did not differ among the treatments. In the SPS, there was an increase of 31.07% in forage accumulation from 25 to 55cm. The forage accumulation and bulk density of Urochloa brizantha cv. Marandu in monoculture is greater than in the SPS regardless of the management goal and the distance from trees. The goal of 55cm in the SPS presented greater forage accumulation.

Functional Traits, Morphology, and Herbage Production of Vernalised and Non-Vernalised Chicory cv. Choice (Cichorium intybus L.) in Response to Defoliation Frequency and Height.

Chicory (Cichorium intybus L.) used in pastoral systems has the attributes required of a forage species to reduce animal urinary nitrogen loading to soil, increase milk production, and enhance milk fatty acid profile to improve pastoral farm systems for matching increasing global demand for dairy products and environmental standards of livestock systems. Greater adoption of chicory requires confidence in management decisions that can control risks to farm production, namely bolting after vernalisation or a decline in persistence of chicory swards, which have slowed its adoption in pastoral systems. We, therefore, measured functional traits, morphology and herbage production of chicory under irrigated field conditions before and after vernalisation in Canterbury, New Zealand. The experimental site was laid out in a complete randomized block design with four replications where two regrowth intervals and two defoliation heights were applied. Regrowth interval had a stronger influence over functional traits and herbage production than defoliation height, with more pronounced effects after vernalisation. Plants managed under shorter regrowth intervals had narrower roots with lower concentration of sugars than plants under longer intervals, which might compromise their longevity. In addition, plants managed under shorter intervals remained mostly vegetative with heavier and longer leaves, though with reduced photosynthetic capacity than those managed under longer intervals. The thermal time to initiate stem elongation in plants managed under longer intervals was ~274 growing degree-days, with a mean stem elongation rate increasing linearly at 1.4 ± 0.08 mm/growing degree-days. The key outcomes of this research quantify the growing degree-days to initiate stem elongation post vernalisation, which provides management directive for timing of defoliation of chicory in order to maintain feed quality for grazing livestock. Alternating frequent and infrequent defoliation regimes might be used to optimise vegetative growth, root reserves, and pasture persistence.

Defoliation management effects on nutritive value of ‘performer’ switchgrass

AbstractForage species with greater nutritive value have the potential to positively affect animal responses. ‘Performer’ switchgrass (Panicum virgatum L.) was released because of greater digestibility and lower lignin concentrations as compared to ‘Alamo’ and ‘Cave‐in‐Rock.’ However, the relationship between nutritive value, canopy characteristics, and dry matter yield for this species has not yet been established. The goal of this study was to determine in vitro true digestibility (IVTD), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) as a function of a wide range of defoliation management strategies to aim optimize production of nutritious forage. Treatments were the factorial combination (4 × 4) of defoliation height (DH; clipped to 10, 20, 30, and 40 cm) and defoliation frequency (DF; clipped every 3, 6, 9, and 12 wk). The range of digestibility values was greater due to DF (from 590–779 g kg−1 when averaged across DH treatments) than DH treatments (from 675–692 g kg−1 when averaged across DF treatments). In general, frequent defoliation resulted in greater IVTD and CP but lower yields; however, there were interaction effects of DF × DH for all response variables. With the exception of NDF, all response variables had strong correlations with dry matter yield, canopy height, and leaf/stem ratio. Although there are tradeoffs when managing for productivity and nutritive value, there is a wide range of defoliation management options for ‘Performer’ switchgrass that provide flexibility in terms of harvesting schedules to optimize productivity and persistence of nutritious forage.

Management strategies for forage rape (Brassica napus L. cv Goliath): Impact on dry‐matter yield, plant reserves, morphology and nutritive value

AbstractLimited information is available on the grazing management principles of forage rape (Brassica napus L.), particularly in relation to grazing height and intensity and the impact of these on dry‐matter (DM) yield and nutritive value. A glasshouse study was undertaken to investigate the effect of three defoliation heights (plant height at harvest; DH: 40, 70 and 90 cm; L, M and H DH respectively) and three defoliation intensities (height at which plants were cut; DI: 5, 20 and 35 cm of residual height; H, M and L DI respectively) on forage rape (cv Goliath) yield and nutritive value at two harvests (harvest 1, H1 and harvest 2, H2), and the impact of nitrogen (N) and water soluble carbohydrate (WSC) reserves on regrowth. Increasing DH from L to H increased estimated total DM yield (H1 plus H2) from 0.5 to 4.6 t DM/ha but DI did not affect yield. Dry‐matter yield was optimized at 90 cm DH, but greater nutritive value was achieved by harvesting at lower levels of DH. Despite high in vitro DM digestibility (IVDMD; 852–889 g/kg), harvesting at 90 cm DH could not meet the protein requirement of lactating dairy cows and harvesting at lower levels risks nitrate poisoning. Our results indicate the optimum DH may be between 70 and 90 cm DH, and 20 and 35 cm DI, which requires further studies.

PSXI-32 Potential improvements in milk production of mid lactating Holstein cows through changes in the defoliation intensity on a mixed pasture

Abstract An experiment was performed to study the effect of two contrasting defoliation intensities of a fescue based pasture on milk production of 24 mid lactating multiparous cows. The animals were blocked according to parity, body weight (587 ± 42 kg), body condition score (2.77 ± 0.16) and calving date, and were randomly allocated to one of these two treatments: lax treatment (TL) 12 cm and control treatment (TC) 6 cm, with four replications. It was used a second-year pasture of Festuca arundinacea and Lotus corniculatus (2530 ± 180 kgDM/ha), divided into eight plots of 0.3 ha. Each plot was grazed by three cows during as many days as necessary until the defoliation height of each treatment was achieved. This would be determined by daily measures of the pasture height. Animals had one grazing session from 8:00 to 16:00 h. Both treatments received 7.5 kgDM of supplementation (17% Crude Protein; 2.81 Mcal/kgDM) in individual troughs. The cows were milked twice a day (05:00 and 17:00 h). Milk production was registered daily while milk composition was measured at the beginning and at the end of the experiment (samples from two consecutive milking). For milk yield results, a mixed model was used (Glimmix procedure, SAS 9.2, 2010) to analyse with treatment, day and their interaction as fixed effects and block as a random effect. While milk composition was analysed with only treatment as fixed effect. Milk yield was greater for TL than TC, while there was no difference in milk composition between treatments (Table 1). There is a significant effect of the day and an interaction between treatment and day (Figure 1), as difference was greater for TL to the end of the grazing period. This leads to the conclusion that it is possible to improve the milk production through less defoliation intensity.

PSXI-31 How is the ingestive behaviour of mid lactating Holstein cows grazing a fescue based pasture under two different defoliation intensities?

Abstract An experiment was performed to study the effect of two contrasting defoliation intensities of a fescue based pasture on the ingestive behaviour. Treatments were two grazing intensities: lax treatment (TL) 12 cm and control treatment (TC) 6 cm, with four replicants of 0.3 ha each. The starting of the experiment was determined by the three leaf stage. Twenty-four mid lactating Holstein cows were blocked according to parity, body weight, body condition score and calving date. Each plot was grazed by three cows during as many days as necessary until the defoliation height of each treatment was achieved (TL: 6 d; TC: 8 d). The pasture mass was 2530 ± 180 kgDM/ha and animals had access from 8:00 to 16:00. Each cow received 7.4 kgDM of supplementation (17% Crude Protein; 2.81 Mcal/kgDM). After PM milking (17:00 h) animals remained separated in 8 pens, where they received 5.5 kgDM in individual troughs. The remaining supplement was provided in the AM milking (05:00 h). During the access to the pasture, grazing and ruminating times and bites rate (BT; bites/minute) were determined every 5 minutes by visual observation at the beginning, middle and end of the experiment. Daily ruminating (DR) was also logged by electronic recorders in 2h periods (Heatime®HR, SCR Dairy). The PROC GLIMMIX of SAS (SAS 9.2, 2010) with a binomial response distribution and with Logit as a link function, was used to determine the probability of the different events. DR and BR were analysed with a mixed model with block and treatment as fixed effects. The probability of cows grazing was greater for TC than TL and lower for ruminating and DR (Table 1). There was no effect of treatment on BR (55 ± 8.8 bites/min). The changes observed on ingestive behaviour were reflected on productive performance (companion abstract).

Harvest Management Effects on Canopy Height and Light Interception of ‘Performer’ Switchgrass and its Relationship with Weed Infestation

Defoliation management can determine the presence or absence of desirable forage species. Canopy characteristics and light interception are two critical determinants of productivity and can influence weed pressure. The objectives of this study were to determine the effect of the factorial combination of four defoliation heights (clipped to 10, 20, 30, and 40 cm; DH) and four defoliation frequencies (clipped every 3, 6, 9, and 12 wk; DF) on light interception, canopy height, and weed canopy cover and frequency for ‘Performer’ (Panicum virgatum L.) switchgrass and to relate the abovementioned responses to previously reported productivity measurements. The experiment was conducted for 2 yr (2016 and 2017) at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a randomized complete block design replicated four times. Across years, light interception before harvest ranged from ∼45 to 88%, canopy height ranged from 35 to 97 cm, and weed cover and frequency ranged from 0 to 75 and 0 to 95%, respectively. Greater canopy height was associated with greater light interception and lower weed infestation. Weed infestation occurred mainly for treatments harvested every 3 and 6 wk and defoliated to lower stubble heights; however, there was no impact of DH for DF treatments harvested every 9 and 12 wk. Canopy light interception values of at least 70% obtained in our study were associated with defoliation thresholds previously reported in the literature for sustained yields of ‘Performer’ switchgrass. Switchgrass canopy light interception values of at least 70% were achieved with canopy heights before harvest of ∼60 cm tall.

Defoliation Management Affects Productivity, Leaf/Stem Ratio, and Tiller Counts of ‘Performer’ Switchgrass

Core Ideas Defoliation management resulted in a wide range of plant responses that varied by year, with deleterious responses more evident in the second year. Greater leaf/stem ratios occurred with more frequent defoliation treatments. Frequent defoliations such as every 3 wk should maintain a stubble height of at least 40 cm, defoliation frequencies ≥6 wk to 20‐cm stubble height, and ≥9 wk to 10 cm stubble height are warranted to ensure stand persistence. ‘Performer’ switchgrass (Panicum virgatum L.) was released in 2006 by the USDA‐NCSU forage program because of its greater digestibility compared to standard cultivars grown in the southeastern United States. Forages with greater digestibility have potential to positively impact animal responses, however, defoliation management can influence its productivity and persistence. The objectives were to determine the effect of the factorial combination of four defoliation heights (DH) (clipped to 10, 20, 30, and 40‐cm) and four defoliation frequencies (DF) (clipped every 3, 6, 9, and 12 wk) on productivity, leaf/stem ratio, and tiller counts. The experiment was conducted in 2016 and 2017 at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a complete randomized block design replicated four times. In 2016, total dry matter (DM) yield ranged from 4.2 to 13.1 Mg ha−1 being greatest for the 9‐ and 12‐wk DF at 10‐ and 20‐cm DH and lowest for all DH at 3‐wk defoliation frequency. In 2017, the DM yield range was wider ranging from 0.5 to 14.0 Mg ha−1 with lower tiller counts for the 10‐ and 20‐cm DH, 3‐wk DF treatments. Leaf/stem ratio was greater for the more frequently defoliated treatments in both years. ‘Performer’ switchgrass is a productive forage and on the basis of total DM harvested, leaf/stem ratio, and tiller counts, frequent defoliations such as every 3 wk to 40‐cm stubble height, ≥6 wk to 20‐cm stubble height, and ≥ 9 wk to 10 cm stubble height, are warranted to ensure stand persistence.

Defoliation height and potassium fertilization of Mulato II grass

A pot trial in greenhouse conditions was carried out to identify at which defoliation height Mulato II grass (Urochloa hibrida cv. Mulato II) should be managed and to determine whether potassium fertilization is necessary in soil with high potassium content. The experiment was carried out in a greenhouse in a randomized block design with six treatments and five replications. Treatments consisted of a 3 × 2 factorial arrangement, with three defoliation heights (50, 65, and 80 cm) and with or without potassium maintenance fertilization. The production characteristics and chemical composition of the forage plant were evaluated. There was no interaction effect between defoliation height and fertilization with or without potassium on any of the analyzed variables, except for mineral content in Mulato II grass. The tillers and leaves number, shoot dry matter, leaf+sheath, root system, and residue were influenced by defoliation heights and potassium fertilization, except for the leaf blades and root dry matter, leaf blade/stem+sheath ratio, and leaves number, which were not influenced by potassium fertilization. Higher shoot dry matter was observed at the heights of 65 and 80 cm; however, comparing these two heights, leaf + sheath dry matter was lower at 65 cm. Regarding the grass’s chemical composition, there was an increase in neutral and acid detergent fiber and indigestible neutral detergent fiber contents as the defoliation height increased, which resulted in lower production of potentially digestible dry matter, which can compromise the potential use of the forage by animals. Among evaluated treatments, Mulato II grass defoliation is recommended for a maximum height of 65 cm. Potassium fertilization increases the yield and the potentially digestible dry matter content of Mulato II grass, even when cultivated in soil with high potassium content.

Defoliation height and potassium fertilization of Mulato II grass

A pot trial in greenhouse conditions was carried out to identify at which defoliation height Mulato II grass (Urochloa hibrida cv. Mulato II) should be managed and to determine whether potassium fertilization is necessary in soil with high potassium content. The experiment was carried out in a greenhouse in a randomized block design with six treatments and five replications. Treatments consisted of a 3 × 2 factorial arrangement, with three defoliation heights (50, 65, and 80 cm) and with or without potassium maintenance fertilization. The production characteristics and chemical composition of the forage plant were evaluated. There was no interaction effect between defoliation height and fertilization with or without potassium on any of the analyzed variables, except for mineral content in Mulato II grass. The tillers and leaves number, shoot dry matter, leaf+sheath, root system, and residue were influenced by defoliation heights and potassium fertilization, except for the leaf blades and root dry matter, leaf blade/stem+sheath ratio, and leaves number, which were not influenced by potassium fertilization. Higher shoot dry matter was observed at the heights of 65 and 80 cm; however, comparing these two heights, leaf + sheath dry matter was lower at 65 cm. Regarding the grass’s chemical composition, there was an increase in neutral and acid detergent fiber and indigestible neutral detergent fiber contents as the defoliation height increased, which resulted in lower production of potentially digestible dry matter, which can compromise the potential use of the forage by animals. Among evaluated treatments, Mulato II grass defoliation is recommended for a maximum height of 65 cm. Potassium fertilization increases the yield and the potentially digestible dry matter content of Mulato II grass, even when cultivated in soil with high potassium content.

Comparative response of tall fescue and perennial ryegrass swards to variation in defoliation interval and height

ABSTRACTA plot study was undertaken to investigate the interactive effect of three defoliation intervals (one-leaf, two-leaf and three-leaf stage in perennial ryegrass (PR) and one-leaf, two-leaf and four-leaf stage in tall fescue (TF)) and two defoliation height residuals (low, 5 cm and high, 8 cm) on production parameters of TF compared with PR plots. DM yields, botanical composition and tiller densities of both species were all generally greater at the longest defoliation intervals (TF-4 and PR-3). However, this consistently resulted in the poorest herbage quality in the TF-4 treatment. The herbage quality was higher in TF-2 compared with TF-4; however, the DM yield, tiller density and proportion of sown species in the sward were reduced. It is not possible to achieve an adequate compromise between DM yield, botanical composition, tiller survival and herbage quality in TF, throughout the year, when defoliation occurs at the two-leaf and the four-leaf stages.

Effects of degrees of grass competition on spreading of Kura clover

AbstractKura clover (Trifolium ambiguum M. Bieb.) is known to develop an extensive rhizome system when grown in monoculture. However, there is no information about the effects that competition from companion grasses could have on its rhizome development. This study was conducted to determine the difference in rhizome development of kura clover planted in grass, grass plus nitrogen (grass + N) fertilizer, or killed‐grass plots, and to evaluate the effect of defoliation height on kura clover rhizome development. Using 1‐year‐old smooth bromegrass (Bromus inermis Leyss) and Kentucky bluegrass (Poa pratensis L.) swards, experiment 1 and 2 commenced in August 1991 and May 1992, respectively, at the University of Wisconsin Arlington Agricultural Research Station. Ten kura clover entries (populations started from seeds or from rhizomes started from clones) were transplanted into each sub‐plot. Two cutting height sub‐plots were superimposed on each of the three grass sward types. In each Exp., two plants from the same seed or rhizome source represented the experimental unit. Individual plants spread up to 1 m in diameter over a 2‐year period after transplanting when there was no grass competition. For both swards, the mean spread of kura clover by rhizome growth was highest in killed‐grass plots (85 cm diameter), least in the grass + N plots (29 cm diameter) and intermediate (57 cm diameter) in the grass only plots. The defoliation height (4 cm or 10 cm) of the swards did not significantly affect the spread of kura clover regardless of grass status (killed or + or −N) in either smooth bromegrass or Kentucky bluegrass. We conclude that reducing the competition from grasses is a management tool that can be used to maximize the colonizing ability of kura clover.

Quantifying the interactions between defoliation interval, defoliation intensity and nitrogen fertiliser application on the nutritive value of rainfed and irrigated perennial ryegrass

A key goal of temperate pasture management is to optimise nutritive value and production. The influence of individual components such as irrigation, nitrogen (N) fertiliser, and grazing interval and intensity has been well researched, yet conjecture remains regarding practices that optimise pasture nutritive value, largely because interactions between inputs and grazing management have not been quantified. A 2-year, split-split-plot experiment was undertaken to investigate these interactions in a perennial ryegrass (Lolium perenne L.) dominant pasture at Elliott, Tasmania. Irrigation treatments (rainfed or irrigated) were main plots and defoliation intervals (leaf regrowth stage: 1-, 2- or 3-leaf) were subplots. Defoliation intensity (defoliation height: 30, 55 or 80 mm) and N fertiliser (0, 1.5 or 3.0 kg N/ha.day) were crossed within sub-subplots. Herbage samples were collected from each plot four times during the experiment and analysed for concentrations (% dry matter, DM) of neutral detergent fibre (NDF), acid detergent fibre (ADF) and crude protein (CP). Metabolisable energy (ME) concentration (MJ/kg DM) was estimated from these values. ME concentration decreased as defoliation height and interval increased for all time points except during winter. Crude protein concentration increased with increasing N fertiliser applications in the plots defoliated at the 1-leaf stage, but only as N applications increased from 1.5 to 3.0 kg N/ha.day for the plots defoliated at the 2- and 3-leaf stages. As N application rates increased from 0 to 1.5 kg N/ha.day, plots defoliated at the 3-leaf stage had greater increases in NDF concentration than plots defoliated at the 1-leaf stage, except during spring. As defoliation height and interval increased, ADF concentration increased in both spring and summer. Although defoliating at frequent intervals (1-leaf stage) and lower heights (30 mm) produced pasture of marginally higher nutritional value, these benefits are mitigated by the previously established, negative consequences of lower pasture yield and poor pasture persistence. Consequently, grazing management that maximises pasture productivity and persistence (i.e. defoliation between the 2- and 3-leaf regrowth stages to a height of 55 mm) should be applied to perennial ryegrass pastures irrespective of input management.

The effects of defoliating grass in winter or spring on herbage yields and ensilage characteristics

AbstractUnder Irish conditions, the digestibility in May of grass managed for silage production is sometimes lower than expected. In each of two successive years, replicate field plots were established to examine the effects of three defoliation heights (uncut or cut to a stubble height of 10 or 5 cm) applied in winter and/or spring on herbage yields harvested in May and again in July, and on chemical composition and conservation characteristics associated with first‐cut silage. Swards that were not defoliated in December or March had a dry‐matter (DM) yield and in vitro DM digestibility (DMD) in mid‐May of 6597 kg ha−1 and 736 g kg−1, respectively, in Year 1, and corresponding values of 7338 kg ha−1 and 771 g kg−1 in Year 2. Defoliating swards to 5 cm in December reduced (P < 0·001) May DM yields compared to swards that were not defoliated in both December and March, while herbage DMD in May increased (P < 0·001) when defoliated in December or March. There were no clear effects of defoliation height or its timing on herbage ensilability or resultant conservation efficiency characteristics. The effects of defoliation on July yield were the reverse of those observed for May, while the total yield of the December and March defoliations plus the two silage harvests increased as defoliation height was lowered in Year 2 only. It is concluded that defoliation in winter and/or spring can increase herbage digestibility but will likely reduce DM yields in May.

English

Napier grass (Pennisetum purpureum Schumach), the most preferred fodder species for dairy production in East and Central Africa, is under threat from stunt disease caused by Candidatus Phytoplasma oryzae (Ns-phytoplasma). The disease reduces forage yield by 40 to 90%. Two alternative fodder grasses, Guinea grass (Panicum maximum Jacq) and Guatemala grass (Tripsacum laxum Scrib and Merr) and a new stunt disease tolerant Napier cv Ouma 3 were studied to determine their biomass production potential when subjected to three intervals harvest (4, 8, 12 weeks) alongside three basal heights of defoliations (5, 10 and 15 cm). The study was conducted at KARI, Kakamega (high rainfall zone) and KARI, Alupe (low rainfall zone) in Kenya. A split-split plot design with 3×3×3 factorial treatment arrangements was used. A 4-weekly interval of harvesting alongside defoliation heights of 10 and 15 cm significantly increased biomass yield in Napier cv Ouma (38.47 and 33.90 T/ha/year respectively) compared to Guatemala grass and Panicum maximum which yielded 23.3 and 27.4 T/ha/year respectively. There is appositive correlation between yield and morphological parameters with canopy diameter, plant height and number of leaves highly correlating in biomass yield. Key words: Frequency of harvest, alternative species, defoliation height, biomass yield, fodder species.