Impact of Canopy Destruction from Simulated Hail on Potato Yield and Economic Return

Insurance against hailstorm-inflicted losses to potato crops is crucial for producer risk management. Insurance providers need regionally specific information on which to base estimates of hail damage. The objective of the research reported here was to determine the effects of a range of simulated hail defoliation treatments, low (33%), medium (66%), and high (99%), relative to an untreated control (0%) on yield and grower economic returns from one medium- and one late-maturing potato variety (‘Russet Norkotah TX278’ and ‘Ranger Russet,’ respectively) at three growth stages (tuber initiation, early bulking, and late bulking) in the Columbia Basin of Washington. Plants within the 33% and 66% treatments were defoliated by sweeping a garden rake with 16 solid, curved tines through the canopy of each treatment row several times until plants exhibited the desired defoliation level. Tuber initiation and early bulk plants within the 99% treatment were essentially mowed to ground level. Intensity of defoliation and stage of growth had significant, interacting effects on grower returns. Gross return and yield for both varieties at each growth stage were significantly reduced by 99% defoliation; these effects were mediated by the effects of defoliation on tuber size distribution. Total yield and gross return experienced the largest declines at early bulk compared with tuber initiation and late bulk defoliation in both varieties. When 99% of the early bulk foliage was removed, Russet Norkotah TX278 gross return and yield were reduced to 14% and 38%, respectively, of the values for the non-treated control, and Ranger Russet gross return and yield were reduced to 30% and 51% of control values, respectively. Defoliation of 99% at all growth stages significantly reduced overall market yield compared to controls for both varieties. However, tuber size distribution was most affected by 99% defoliation at early bulk. Severe defoliation (99%) at tuber initiation significantly delayed vine senescence in both varieties. The results of this study suggest that insurance adjusters should take into account the combined influence of growth stage and defoliation level when hail damage occurs.     

Impact of defoliation on yield of group IV soybeans in Mississippi

Field experiments were conducted during 2009 and 2010 to evaluate the effects of defoliation on maturity group IV soybeans, Glycine max (L.) Merr., grown in Mississippi. During each year, two locations were planted with maturity group IV soybeans that were subjected to various levels of defoliation during R3, R5, and R6 growth stages. Soybeans were subjected to various levels of defoliation within the upper 50% of the plant canopy, lower 50% of the plant canopy, and whole-plant canopy. There was greater yield loss from defoliation occurring in the upper plant canopy compared with the lower plant canopy during R3 and R5 stages, but no difference between canopy regions during R6 stage. Yield loss from whole plant defoliation was greater than upper or lower canopy defoliation. Results confirmed that soybeans during R3 and R5 stages are more susceptible to yield loss than during R6. However, yield losses were not significantly different between R 3 and R5 until defoliation exceeded 63%. Dynamic economic injury levels were determined for each growth stage based on yield loss equations, value of the crop, and cost of control and can be used as a basis for developing action thresholds in high-yielding soybean production environments.     

The effect of time of initial defoliation and height of defoliation on the productivity of perennial ryegrass swards

Over a 3-year period the productivity of perennial ryegrass ( Lolium perenne L., cv. S24) swards as influenced by variations in the time of initial defoliation and close (2·5 cm) and lax (8 cm) defoliation was studied. Treatments with initial defoliations in the early vegetative stage, stem elongation and flowering stages of growth gave higher annual yields than treatments in which the initial defoliation was taken at an intermediate stage of growth when the majority of the stem apices had just been elevated above the height of defoliation. Initial defoliation treatments which removed a high proportion of apical meristems while the yield at the initial defoliation was still low produced the lowest annual yield. Consistent lax defoliation reduced yield by 14·5% compared with continual close defoliation. However, taking an initial lax defoliation followed by subsequent close defoliations produced a slight yield advantage of 4·8% over consistent close defoliation. The results are discussed in relation to other research findings and the practical implications commented upon.     

刈割期对多棱饲料大麦饲草及籽粒产量与品质的影响

为探明大麦饲草与籽粒双收的适宜刈割期,以六棱皮大麦皖饲麦2号为材料,设不刈割(T0)及分蘖期(T1)、拔节期(T2)、孕穗期(T3)分别进行一次刈割4个处理,比较了两年度不同刈割期大麦饲草、籽粒产量及品质的差异。结果表明,随刈割期后移,皖饲麦2号饲草产量显著增加;饲草粗蛋白、粗灰分、钙、磷含量显著下降,粗纤维、酸性洗涤纤维、中性洗涤纤维含量显著增加,即饲草品质显著下降。籽粒产量受刈割期影响大,与T0相比,两年度T1期刈割籽粒产量无显著变化,T2、T3期刈割则籽粒产量显著下降;而品质受影响小。说明T1期刈割,可达到饲草与籽粒双收目标,且饲草品质好;在生产中要保障一定的籽粒产量,T2期后应停止刈割。     

Effects of defoliation on whole‐plant maize characteristics as forage and energy crop

Hail affects yield and quality of maize crops, and consequences also depend on the growth stage at which the injury occurred. Whole‐plant maize (WPM) silage is often used within the same farm for cattle feeding and biogas production. The present study aimed to verify the effects of hail damage, simulated by artificial defoliation, on yield and chemical and nutritional features, as well as on biochemical methane potential (BMP) of maize forage. In a randomized block design with three replicates, four defoliation levels (0%, 33%, 66% and 100% of leaf area removal respectively) have been applied at either the V12 (12th leaf), R1 (silking) or R3 (milk) stages for two consecutive years. WPM yield, chemical and nutritional features, and BMP were measured. Dry‐matter (DM) yield per hectare was progressively reduced (p < 0.001) with increasing levels of defoliation and with application at V12 in comparison with R1 or R3 (1.26 vs. 1.39 and 1.46 kg ha^?1 for V12 vs. R1 and R3; p < 0.003). Nutritive value and BMP per unit of product were less altered than dry‐matter yield per hectare by defoliation. Anticipating defoliation reduced net energy for lactation (5.26 vs. 5.46 MJ kg^?1 DM for V12 and R3 respectively; p = 0.02). Total defoliation resulted in an accumulation of nitrates (NO₃) compared to the other treatments (3.98 vs. 1.53 g NO₃ kg^?1 DM; p < 0.001). BMP was mainly reduced by early and complete defoliation. Equations were developed to estimate the effects of defoliation on yield, composition, and nutritive and energetic values of WPM.     

Nitrogen uptake by grasses: changes induced by competing neighbour plants differing in frequency of defoliation

Nitrogen uptake can be modified by both frequency of defoliation and competing neighbour plants. The objective of this study was to investigate nitrogen uptake by Lolium perenne and Festuca rubra subject to weekly or monthly defoliation with five neighbours: either none, L perenne clipped weekly, L. perenne clipped monthly, F. rubra clipped weekly or F. rubra clipped monthly. Plants were grown in sand culture with nutrients supplied as solutions. Nitrogen uptake over a I-week period commencing at the time of a defoliation event was estimated using ^l5N as a tracer. L. perenne had greater dry weight and nitrogen uptake than F. rubra. Neighbours reduced nitrogen uptake per plant. When neighbours were present, clipping them more frequently resulted in greater uptake by sample plants. Over 57% of total plant uptake was partitioned towards the two youngest leaves. In mixtures of L. perenne with F. rubra , the percentages of the total pot dry weight and N content recovered in sample L. perenne plants increased when they were clipped less frequently, compared with when the accompanying F. rubra plants were clipped less frequently.     

Differential red clover germplasm response to defoliation and fungicide application

A primary limitation to the use of red clover ( Trifolium pratense L. ) in the temperate zones is poor persistence. The objective of this research was to evaluate the effects of defoliation and fungicide application on the yield and persistence responses of twelve diverse red clover germplasms. Treatments consisted of reduced defoliation with the application of the systemic fungicide, propiconazole (RDF), reduced defoliation (RD) and a full-season defoliation control. Dry-matter yields were recorded for 3 years and stand density was determined during the third harvest year and again 2 years later. By the third harvest season, stand densities were 52% and 13·5% greater for treatments RDF and RD than the control. After 5 years, stand density on these two treatments was on average 68% greater than the control. RDF plots outyielded RD plots for the second and third harvest years, but both had lower forage yields than the control. Germplasm by treatment interactions were significant for stand density and yield by the third year. RD treatments out-yielded the control by the third year for only two germplasms, the experimental lines FL-MTC and FL6-EF. The treatments affected yield and persistence and enabled the identification of significant differences in germplasm response.     

芝麻不同时期去叶对蒴果发育和产量的影响及保叶增产措施

采用定株观察，以芝麻生长正常单株为对照，研究不同生育时期，不同蒴果发育时期去叶，对芝麻农艺性状和单株产量的影响。结果表明，随着芝麻生育进程，终花期，封顶期，盛花期去叶减产值幅度递增。相同植株同天开花采取不同时期去叶所结蒴果分别与对照相比，去叶时间越早秕籽率越高，千粒重越低。同时还进一步研究出延长芝麻中上部叶片功能期，提高单株产量的技术措施。     

Spring defoliation of white clover seed crops. 2. Potential harvestable seed yield and seed yield components of contrasting white clover cultivars

The effects of different spring defoliation managements on potential harvestable seed yield and seed yield components of three contrasting white clover cultivars were assessed. The small-leaved cv. S184 produced more but smaller inflorescences than the large-leaved cv. Olwen and Menna, a medium-leaved cultivar. Cultivar Olwen, however, produced more ripe and brown (nearly ripe) inflorescences with more florets, seeds per floret and a higher seed yield per ten inflorescences than the other cultivars. Potential harvestable seed yield and individual seed yield components were only influenced by defoliation after bud emergence, as defoliation before bud emergence had no effect on seed yield components. Defoliation after bud emergence had a similar effect on all cultivars: the number of ripe inflorescences was unaffected by defoliation but the number of brown and therefore harvestable (ripe + brown) inflorescences was highest following defoliation three weeks after bud emergence. Florets per inflorescence, seed per floret, 1000 seed weight, seed yield per ten inflorescences and potential harvestable seed yield were not influenced by defoliation after bud emergence. Season had a significant effect on seed yield components and influenced the effect of defoliation treatments, emphasizing the importance of climate in white clover seed production. The results are discussed in relation to the spring defoliation of white clover seed crops, harvesting techniques and the provision of guidelines for optimizing seed yield.     

Effect of simulated hail damage on yield and quality of Russet Burbank potatoes

The yield and quality response of Russet Burbank potatoes to simulated hail damage was dependent upon the amount of damage and on the growth stage at which the damage occurred. Plots of Russet Burbank potato plants were subjected to 0%, 10%, 25%, 50%, 75%, or 100% defoliation at 3, 5, 7, 9, 11, or 14 weeks after emergence. A motorized flail was used to simulate the complex damage that occurs during a natural hail storm. Early season simulated hail damage, when the plants were mainly vegetative, caused yield losses proportional to the degree of damage. Simulated hail damage during the early phases of tuber growth caused minor yield losses (< 5%) at low defoliation levels but severe losses at the higher levels with proportional loss of tuber quality. Defoliation later in the season resulted in progressively less reduction of both yield and quality. At or near maturity, late season simulated hail damage caused insignificant losses unless the stems were damaged enough to prevent nutrition and carbohydrate translocation into the tubers.     

Effect of defoliation frequency and cutting height on growth,dry‐matter yield and nutritive value of Napier grass (Pennisetum purpureum (L.) Schumach)

Growth characteristics, dry‐matter (DM) yield, chemical components and in vitro dry‐matter digestibility (IVDMD) of Napier grass were studied in a randomized complete block design with three replications at Haramaya University, Ethiopia. The treatments were three defoliation frequencies (60, 90 and 120 d after Napier grass establishment) and five cutting heights (5, 10, 15, 20 and 25 cm above ground level). Except for leaf‐to‐stem ratio, all growth characteristics increased with decreasing frequency of defoliation. Similarly, DM yield of Napier grass increased as the frequency of defoliation decreased. Total ash, crude protein (CP), hemicellulose and IVDMD contents of Napier grass increased with increasing frequency of defoliation, whereas DM, acid detergent fibre, acid detergent lignin and cellulose contents increased with a decrease in defoliation frequency. In contrast, cutting heights had no significant effect on most chemical components and IVDMD contents, although total ash and CP decreased as the height of cutting increased. The CP yield per cut and per day was highest at an intermediate defoliation frequency. The results of this study indicated that Napier grass could be categorized under medium‐ to high‐quality herbage if defoliated at 90 d after establishment in the mid and highlands of Ethiopia.     

灌浆后期去叶对夏玉米生长发育及子粒含水率的影响

以郑单1002为材料,设置灌浆中后期(灌浆36 d)不同穗部及穗下不同数量的去叶处理,研究去叶后对玉米群体光合性能、冠层结构、产量以及子粒含水率等的影响。结果表明,穗部叶及穗部以下叶保留3~4片叶,产量不降低;去叶较多情况下表现为减产;不保留穗位叶较对照减产了12.36%,子粒千粒重下降是导致减产的主要原因。去叶后直接导致玉米群体叶面积指数下降,无截取散射略微增加;保留3~4片叶处理,叶片光合性能表现出一定补偿效应,净光合速率高于对照处理,羧化效率略有升高;去叶处理降低灌浆后期子粒含水率,不保留穗位叶片处理较对照处理相比,在灌浆44、52、60 d,子粒含水率分别下降了8.14、8.75、17.84个百分点。     

Effect of defoliation and drought stress on yield components and chlorophyll content of wheat

In order to examine the effects of source restriction and drought stress on yield components, flag leaf chlorophyll content and Relative Water Content (RWC) of wheat cultivars, a greenhouse experiment was carried out at Shiraz University, Shiraz, Iran, during 2009-2010. The wheat cultivars including Shiraz, Bahar, Pishtaz, Sistan and Yavaros were sown in 5 kg plastic pots. The source manipulation treatments including control (C), defoliation of all leaves (D1), defoliation of all leaves except the flag leaf (D2) and defoliation of all leaves except the flag leaf and penultimate leaf (D3), were imposed at anthesis. Results showed that source restriction decreased number of grain per spike significantly in Shiraz cultivar under drought stress condition. Maximum 100-grain weight was observed in C treatment of Yavaros and Shiraz under well-watered condition. Among the defoliation treatments under drought stress condition, D2 in Pishtaz and D1 in Shiraz had the highest (3.66 g) and lowest (2.71 g) 100 grain weight, respectively. In all cultivars drought stress decreased main shoot yield significantly but in Pishtaz and Sistan decreasing rate was less than the other cultivars. RWC in Shiraz decreased sharply from 92.1% in well-watered to 66.7% (27.5% reduction) under drought stress at 10 DAA. After anthesis, Pishtaz and Sistan maintained higher content of flag leaf chlorophyll (from 49.4 to 56.8 SPAD unit) under drought stress condition. Generally, selection and culture of cultivars that had small responses to defoliation might be a useful strategy in yield improvement of wheat in areas where the water availability is low.     

The effect of frequency and height of defoliation on the production and persistence of 'Grasslands Matua' prairie grass

The performance of prairie grass ( Bromus willdenowii Kunth) cv. Grasslands Matua was examined under mowing at five defoliation intervals (10, 20, 30, 40 and 50 d) and two defoliation heights (3 cm and 8 cm). Annual and seasonal production of both the total herbage and of Matua, and the proportion of Matua in the sward, increased with less frequent defoliation. To a lesser extent, increasing the height of defoliation increased dry matter yield. Matua tiller numbers were increased by less frequent defoliation and were greater under the 8 cm than the 3 cm defoliation height. To increase prairie grass production and persistence, rest intervals between grazings of 40 to 50 d are recommended, or alternatively, a management involving silage or hay cutting offers scope.     

芝麻花期叶片光合产物的 运输分配及对产量的影响

在芝麻有效开花结蒴期,对当天见花节位进行不同比例、不同部位剪叶处理,以不剪叶和全剪叶植株为 对照,研究了留叶部位功能叶光合产物的运输分配方向及在不同剪叶部位籽粒中的积累。结果表明:芝麻籽粒产 量全部来源于开花后功能叶的光合产物,剪叶比例越高减产越明显。叶片光合产物的运输分配量的大小顺序为: 向同侧蒴果分配最多,侧向分配次之,横向运输分配极少。     

THE EFFECT OF DEFOLIATION ON THE SEED-PRODUCING CAPACITY OF BRED STRAINS OF GRASSES

Two leafy strains of cocksfoot, S143 and S37 were subjected to winter, spring and winter + spring defoliation; 2 cwt. per acre of nitro-chalk was applied after each defoliation, in addition to the standard manuring for all plots.
Winter grazing of leafy cocksfoot does not appear to depress the yield of seed appreciably when extra nitrogen is applied.
Grazing of cocksfoot in mid-April is likely to depress the seed yield substantially, especially if followed by a very dry summer.
The reaction to hard defoliation by sheep may vary with the growth form of the cocksfoot strain.
Grazing appeared to be more detrimental to seed yield than defoliation by cutting.
During this investigation, prolonged frost which occurred during the early part of the year appeared to have an adverse effect on cocksfoot seed yield.     

The effects of clipping height and frequency on net primary production of Andropogon gerardii (C4 grass) and Bromus inermis (C3 grass) in greenhouse experiments

There are potential agronomic and environmental benefits from incorporating warm‐season (C₄) grasses into temperate pasture systems, usually dominated by cool‐season (C₃) grasses, but there is a lack of information on how frequency and height of defoliation affects C₄ grasses. Three greenhouse experiments were conducted under (i) spring, (ii) summer and (iii) spring + summer clipping regimes. In each experiment, the effects of clipping frequency (weekly and monthly) and clipping height (clipped to 5 and 10 cm) were determined on above‐ and below‐ground net primary production (ANPP and BNPP) and total and seasonal dry matter (DM) yield for Andropogon gerardii Vitman (big bluestem, C₄ grass) and Bromus inermis Leyss (smooth brome, C₃ grass). Six replicates per treatment were used. In all experiments, ANPP and BNPP of smooth brome was greater than that of big bluestem although during late summer months big bluestem had higher DM yields of herbage than smooth brome. There were different effects of frequency and height of clipping for both species on two similar measurements: total annual DM yield and ANPP, indicating that the ability to generalize about the effects of defoliation from ecological and agronomic grassland standpoints is questionable. Clipping effects on ANPP and BNPP were different for summer‐clipped pots than for spring, and spring + summer‐clipped pots, indicating that management could be tailored to meet specific agronomic or conservation goals.     

The influence of defoliation date and harvest interval on the quality of potatoes for french fry production

Summary Trials were carried out in 1984, 1985 and 1986 in which the effect of four dates of defoliation (0, +10, +20, +30 days) and three intervals to harvest (0, +10, +20 days) on yield, tuber size, dry matter, reducing sugar, fry test colour and finish fried sensory quality were examined for two cultivars (Pentland Dell, Maris Piper) on two sites (medium silt, peaty loam). Dry matter content and yield of tubers were influenced by all factors in the trial. Later dates of defoliation gave the lowest reducing sugar levels, palest fry colour, highest yield and dry matter content. Increasing the interval from defoliation to harvest reduced dry matter and raised yield. Significant year effects were obtained for dry matter and reducing sugar content.     

THE RELATIONSHIP BETWEEN COMPETITION AND DEFOLIATION IN PASTURE

Field trials were carried out on a downland permanent pasture at the Grassland Research Institute, Hurley, between 1953 and 1955, to investigate the factors involved in competition in pasture undergoing periodic defoliation. Response to competition was estimated by comparing the yield of species units (either individual plants or close groups of shoots) growing normally in the pasture with the yield of matched units from which the surrounding herbage had been removed. The species studied were cocksfoot, red fescue, creeping bent, plantain, ox-eye daisy and bulbous buttercup. In addition to the estimation of normal competition for environmental resources in pastures of differing height, two special effects upon species due to the presence of surrounding herbage were investigated following unusual results from competition tests in swards under periodic defoliation. First, the influence of surrounding herbage in modifying the growth habit of a species, causing it to grow in a more erect manner, and consequently to suffer more on defoliation at a specific height than in the absence of competition. Secondly, a decreased yield after defoliation, not associated with changes in the growth habit of the species, which was ascribed to an increase in top/root ratio brought about by shading during the preceding period of competitive growth. The effect of selective defoliation of a species in relation to the herbage surrounding it was also studied. Differences in the degree of defoliation of a species and its surrounding herbage had a marked effect upon the degree of competition exerted by the latter upon the former, increasing it when the species was preferentially defoliated and decreasing it when the surrounding herbage was preferentially defoliated. The factors involved in pasture competition under periodic defoliation are listed and discussed.     

Growth, colonization and productivity of two white clover cultivars strip-seeded into an upland Festuca-Agrostis sward

Small plots of a Festuca-Agrostis upland sward on a peaty gley podsol were strip-seeded during late June 1986 with white clover cvs Aberystwyth S184 or Menna at 4 kg ha⁻¹ and defoliated early (20 August) or late (3 September) and then frequently or infrequently (every 2 weeks or 4 weeks) until the end of September. All plots were defoliated in early November, at 3-weekly intervals during the growing season in 1987 and then grazed rotationally during 1988.
Satisfactory seedling establishment, representing 46% emergence, was achieved 5 weeks after sowing. The differential defoliation regimes had no persistent significant effects on clover development. S184 soon produced more leaves per seedling than Menna and a smaller proportion of its leaf number and weight were removed at each defoliation. Following large losses of leaves over the 1986–87 winter, SI84 had significantly more leaves per stolon than Menna; subsequently it also colonized the sward at a quicker rate. During 1987 amounts of herbage harvested (6.1 t ha⁻¹) were similar with the two clover cultivars, with S184 contributing 47% and Menna 44% of this respectively. SI84 made a larger contribution to yield during May and June but Menna was more productive during September and October. During 1988 clover populations were maintained with rotational grazing without additional fertilizer inputs.
The results show that, despite initial soil and climatic contraints, both small and medium-leaved clovers can be strip-seeded into upland swards with large subsequent benefits to yield and herbage quality. However, they also indicate the need for further experiments to determine the influence of sward morphology and defoliation regime on stolon branching rates and accumulation of growing points which, in turn, govern sward colonization.