Narrow Canopy Research Articles

English

This study aimed to determine the effects of plant spacing on some morphological traits and yields of 5 hot pepper lines. The trial was laid out in a 5 × 3 factorial in randomized complete block design with 4 replications. Five pepper lines (ICPN16#3, ICPN16#4, ICPN16#6, ICPN16#7, and ICPN16#9) and 3 plant spacing (70 cm × 30 cm, 70 cm × 40 cm and 70 cm × 50 cm) were used. The results revealed that the closer plant spacing of 70 cm × 30 cm produced tall plants with ICPN16#4 line being the tallest. In addition, line ICPN16#4 produced narrow canopy with more branches, whilst ICPN16#9 (a short line) produced more branches with medium spread canopy. Plant spacing of 70 cm × 50 cm resulted in more spread canopy and number of branches. Closer spacing gave higher fruit yield compared to wider spacing. However, wider spacing gave the largest fruit size.   Key words: Lines, spacing, canopy, plant height, branch, interaction. 

Response of plant spacing on the morphology and yield of five hot pepper lines

This study aimed to determine the effects of plant spacing on some morphological traits and yields of 5 hot pepper lines. The trial was laid out in a 5 × 3 factorial in randomized complete block design with 4 replications. Five pepper lines (ICPN16#3, ICPN16#4, ICPN16#6, ICPN16#7, and ICPN16#9) and 3 plant spacing (70 cm × 30 cm, 70 cm × 40 cm and 70 cm × 50 cm) were used. The results revealed that the closer plant spacing of 70 cm × 30 cm produced tall plants with ICPN16#4 line being the tallest. In addition, line ICPN16#4 produced narrow canopy with more branches, whilst ICPN16#9 (a short line) produced more branches with medium spread canopy. Plant spacing of 70 cm × 50 cm resulted in more spread canopy and number of branches. Closer spacing gave higher fruit yield compared to wider spacing. However, wider spacing gave the largest fruit size. Key words: Lines, spacing, canopy, plant height, branch, interaction.

Cooling effect to mitigate Urban Heat Island by Pterocarpus indicus, Swietenia macrophylla and Samanea saman In Bandung, West Java Indonesia

Urban Heat Island (UHI) has been detected in Bandung since 2001 and it can be mitigated by planting trees such as Pterocarpus indicus (angsana), Swietenia macrophylla (mahogany), and Samanea saman (trembesi). This research was conducted to measure temperature reduction by those road side trees at seven locations. Parameters were tree characteristics including shape and area of canopy, Plant Area Index (PAI), and leaf morphology (shape and arrangement), air temperature, relative air humidity, transmissivity, and surface temperature. Microclimate and edaphic data were measured in sunny day or partly cloudy. Data were analyzed using One-way ANOVA (Kruskal-Wallis test) to clarify significance differences among parameters in each tree species and measured reduction of discomfort index (dDI%). Air temperature in open area is 33.81±2.32°C, while surface temperature is 37.29±6.63°C. Result shows that trees have varies ability to decrease air and surface temperature. The highest reduction of air (A) and surface (S) temperature is shown by S. saman (A=3.80±1.21°C and S=10.49±2.84°C), then followed by S. macrophylla (A=3.10±1.94°C and S=5.64±5.51°C), and P. indicus (A=2.28±1.73°C and S=5.26±4.30°C). S. saman which has wide canopy with moderate leaf density can reduce air and surface temperature effectively, followed by S. macrophylla with narrow canopy and high leaf density; and P. indicus with narrow canopy with low leaf density. Thus, tree character with broad canopy and dense leaves such as S. saman can be recommended as shading tree to mitigate UHI in urban areas.

Kenaf Morpho-physiological Variations and Response to Weed Pressure in Derived Savanna Agro-ecology of Nigeria

Kenaf response to weed pressure depends on variations in morpho-physiological traits of genotypes. A study was conducted in Ibadan (7°38’ N 3°84’ E) Nigeria in the wet seasons of 2014 and 2015 to determine the response of kenaf genotypes to weed pressure. Twelve kenaf genotypes were planted in a conventionally prepared seedbed at 50 × 20 cm, in 5 x 5 m plot and arranged in an RCBD, replicated thrice. Initial weed flora composition revealed that Panicum maximum, Tithonia diversifolia, Mithracarpus viridis, Commelina spp, Aspilia africana, Tridax procumbens and Pennisetum purpureum were predominant in the experimental site. Kenaf plant height varied significantly and ranged from 30.53 cm to 59.73 cm and 60.67 to 76.80 cm at 6 weeks after sowing (WAS) in 2014 and 2015 respectively. Variation in plant height at 10 WAS did not follow the previous growth patterns in both years of the study. Stem girth at 10 WAS ranged from 1.26 cm (V1-400-2) to 1.47 cm (A-60-282) in 2014. In subsequent year, Tianung had 1.47 cm stem girth as the thinnest, while Cuba 108 had the thickest stem (1.70 cm). Ifeken 400 (56.90 cm) and Cuba 108 (53.57 cm) had the broadest canopy width in 2014 and 2015 respectively, while A2-60-28 (44.85 cm) and V1-400-2 (41.33 cm) had narrowest canopy width in 2014 and 2015 respectively. Genotypes had comparable fibre yield, possibly due to catch-up growth from 8 to 10 WAS. Ifeken 400 (480 kg/ha) and Ifeken DI400 (550 kg/ha) had the highest seed yield in 2014 and 2015 respectively. These were similar with seed yield in other genotypes except V1-400-2 (310 kg/ha) in 2014 and AC-313 (350 kg/ha) in 2015. However, seed yield reduction across genotypes ranged from 55 – 74%, with an average of 68% in both years when compared with the seed yield potentials of genotypes. Evidently, prolonged weed competition might have accounted for the seed yield deficit recorded in the study. Invariably, pre-emergence weed control only may not suffice for weed pressure in kenaf plot when seed production is of interest to the farmers. There was significant weed interference in plots sown to kenaf genotypes with low plant height and narrow canopy width. Consequently, high weed dry weight in V1-400-2 (66.39 g/m2; 89.39 g/m2) might be responsible for seed yield penalty in both years of the study. Whereas, Ifeken DI400 had the least weed dry weight (25.93 g/m2; 26.92 g/m2) and comparable seed yield with the maximum in both years of the study. Genotypic variations in morphological and physiological traits might be responsible for responses to weed interference and crop performance. Early expression of weed suppressive traits evidently influenced genotypes-weed interaction.

Can we manage light interception levels above 70% in apple orchards?

For the last 20 years we have recommended that orchards be designed to intercept a minimum of 70% light interception. Replicated field plantings at Geneva have shown that when tree height is about 90% of the between row spacing light interception is about 75%. This has become our standard recommendation in designing new orchards. However, in recent years three developments have led us to question this rule. First the development of the Tall Spindle planting system and the use of mechanical summer pruning has resulted in very narrow canopy profiles (fruiting walls), which have very good light distribution within the canopy. This could allow taller trees relative to the between row spacing with a height to row spacing ratio of 1:1. A second development has been the use of V-shaped canopies, which are very thin and shoot growth in the middle of the V is controlled with plant growth inhibitors. These V-shaped canopies can intercept more than 75% of available light depending on the open gap at the top of the V. This tree shape allows even the lowest part of the canopy to receive adequate light during the middle of the day with good fruit quality in the bottom of the canopy but also imposes the greatest energy load on the tree and hence transpiration compared to vertical tree shapes. A third trend is the use of reflective films to enhance the light exposure level of the lower part of the canopy. This practice with the use of V-shaped canopies could utilize 80-85% of available light energy resulting in higher yield.

Rainfall interception modelling: Is the wet bulb approach adequate to estimate mean evaporation rate from wet/saturated canopies in all forest types?

The Penman–Monteith equation has been widely used to estimate the maximum evaporation rate (E) from wet/saturated forest canopies, regardless of canopy cover fraction. Forests are then represented as a big leaf and interception loss considered essentially as a one-dimensional process. With increasing forest sparseness the assumptions behind this big leaf approach become questionable. In sparse forests it might be better to model E and interception loss at the tree level assuming that the individual tree crowns behave as wet bulbs (‘‘wet bulb approach”). In this study, and for five different forest types and climate conditions, interception loss measurements were compared to modelled values (Gash’s interception model) based on estimates of E by the Penman–Monteith and the wet bulb approaches. Results show that the wet bulb approach is a good, and less data demanding, alternative to estimate E when the forest canopy is fully ventilated (very sparse forests with a narrow canopy depth). When the canopy is not fully ventilated, the wet bulb approach requires a reduction of leaf area index to the upper, more ventilated parts of the canopy, needing data on the vertical leaf area distribution, which is seldom-available. In such cases, the Penman–Monteith approach seems preferable. Our data also show that canopy cover does not per se allow us to identify if a forest canopy is fully ventilated or not. New methodologies of sensitivity analyses applied to Gash’s model showed that a correct estimate of E is critical for the proper modelling of interception loss.

Street trees in Bangalore: Density, diversity, composition and distribution

Abstract Once renowned as India’s “garden city”, the fast growing southern Indian city of Bangalore is rapidly losing tree cover in public spaces including on roads. This study aims to study the distribution of street trees in Bangalore, to assess differences in tree density, size and species composition across roads of different widths, and to investigate changes in planting practices over time. A spatially stratified approach was used for sampling with 152 transects of 200 m length distributed across wide roads (with a width of 24 m or greater), medium sized roads (12–24 m) and narrow roads (less than 12 m). We find the density of street trees in Bangalore to be lower than many other Asian cities. Species diversity is high, with the most dominant species accounting for less than 10% of the overall population. Narrow roads, usually in congested residential neighborhoods, have fewer trees, smaller sized tree species, and a lower species diversity compared to wide roads. Since wide roads are being felled of trees across the city for road widening, this implies that Bangalore’s street tree population is being selectively denuded of its largest trees. Older trees have a more diverse distribution with several large sized species, while young trees come from a less diverse species set, largely dominated by small statured species with narrow canopies, which have a lower capacity to absorb atmospheric pollutants, mitigate urban heat island effects, stabilize soil, prevent ground water runoff, and sequester carbon. This has serious implications for the city’s environmental and ecological health. These results highlight the need to protect large street trees on wide roads from tree felling, and to select an appropriate and diverse mix of large and small sized tree species for new planting.

Mechanical Thinning of Peach and Apple Trees Reduces Labor Input and Increases Fruit Size

Hand thinning is a necessary but costly management practice in peach (Prunus persica) production. Organic apple (Malus ×domestica) production also may require hand thinning to adjust crop load. Mechanical devices to aid in thinning have been developed, but none has proven highly efficient and capable of completely replacing hand thinning. Narrow canopy training systems and novel peach tree growth habits offer new opportunities to examine mechanical methods for thinning peach and apple trees. Our studies evaluated mechanical thinning devices on peach and organically grown apple trees. In 2005 and 2006, a U.S Department of Agriculture-designed spiked-drum shaker was used to thin pillar (columnar) peach trees at 52 to 55 days after full bloom. The drum shaker, driven at two different speeds in the orchard, reduced crop load an average of 58% and follow-up hand thinning time by 50%, and increased fruit size by 9% at harvest compared with conventional hand-thinned or nonthinned control trees in 2005. In 2006, the shaker was driven at one speed but operated at two different frequencies. At 260 cycles/minute, the drum shaker removed more fruit and reduced crop load to a greater extent than when operated at 180 cycles/minute, however, fruit size at harvest did not differ between the two operating frequencies. The drum shaker reduced follow-up hand thinning time between 54% and 81%. Horticultural and economic evaluations of the drum shaker and/or a German-designed blossom string thinner were conducted in 2007 in four commercial peach orchards trained to a perpendicular V or quad V system and an organic apple block trained to a narrow vertical axis system. Mechanical thinners reduced peach crop load by an average of 36%, decreased follow-up hand thinning time by 20% to 42%, and increased fruit in higher market value size categories by 35%. The net economic impact of mechanical thinning versus hand thinning alone ranged from $175/ha to $1966/ha. Mechanical thinning at 20% full bloom resulted in more fruit in the large size categories (2.75 inches in diameter and larger) than thinning at 80% full bloom. Detailed counts of flowers on branches with different orientations indicated that pruning may be adjusted to improve thinner performance. The string thinner effectively thinned dwarf apple trees trained to a vertical axis system in a certified organic orchard, resulting in a reduction in hand thinning time and an increase in fruit size. Based on our tests, mechanical thinning appears to be a promising technique for supplementing hand thinning in apple and peach trees.

Endogenous hormone concentrations and bud-break response to exogenous benzyl adenine in shoots of apple trees with two growth habits grown on three rootstocks

SummaryScions from two siblings of a ‘Goldspur Delicious’ × ‘Redspur Delicious’ cross were budded to three rootstocks with different levels of vigour [M.9, M.7, and Malus domestica ‘Antanovka’ seedling] and planted in the field in 1997. The scions had two contrasting growth habits: one with narrow crotch angles, numerous short branches and an upright narrow (UN) canopy; and the other with wide crotch angles, few short branches, and a spreading round (SR) canopy. Shoot tips were collected at the time of bud-break in April 2004 and analysed for auxin (AUX), cytokinins (CK), and abscisic acid (ABA) to determine relationships between scion growth habit, size-controlling rootstock, and shoot tip hormone concentrations. Although not statistically different, the UN growth habit had numerically higher AUX, lower ABA, and equivalent CK levels as the SR growth habit. These differences resulted in statistically higher AUX:CK ratios (ACR). It is possible that the higher ACR contributed to the UN growth habit, which had more anti-gravitrophic shoot growth and appeared to have greater apical dominance than the SR growth habit. Either growth habit, grown on seedling rootstock, had nearly twice the ACR than on M.7 or M.9 rootstocks. The synthetic CK, 6-benzyl adenine (BA), was applied to 30 cm shoot explants of both growth habits in a greenhouse in March 2006. An 8.7 mM BA concentration stimulated bud-break in both growth habits, compared with controls, and bud-break was increased more in the UN than the SR growth habit. The results indicate that the ACR may be a factor regulating bud-break and the development of growth habit in apple scions, and that rootstock modified the hormone concentrations in shoot tips.

Harvest Mechanization Progress and Prospects for Fresh Market Quality Deciduous Tree Fruits

Deciduous tree fruit crops such as apple (Malus domestica), peach (Prunus persica), and sweet cherry (Prunus avium) are not mechanically harvested for the fresh market. Attempts to mechanically harvest these fruits by mass removal techniques have not been successful due to excessive fruit damage caused during detachment, fall through the canopy, and collection. Robotic harvesters have not been commercially accepted due to insufficient fruit recovery. A U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) harvesting concept shows promise for harvesting both fresh market quality apples and sweet cherries. Successful mechanical harvesting of fresh market quality deciduous tree fruit will only occur when plant characteristics and machine designs are integrated into a compatible system. Cultivar characteristics that would facilitate machine harvesting are uniform fruit maturity at harvest, firm fruit that are resistant to mechanical damage, and compact growth habit that produces fruit in narrow canopies and on short/stiff limbs. Engineers must develop new detachment principles that minimize the energy input to effect fruit detachment, and develop durable energy-absorbing catching surfaces/conveyors to eliminate damage during collection of the fruit. As technology advances, sorting and sizing systems might be developed that can be operating on the harvester to eliminate culls in the field and deliver only fresh market quality fruit to the packers.

Tropical forest structure: a missing dimension to Pleistocene landscapes

AbstractBy focusing on the horizontal distribution of Pleistocene vegetation types within tropical landscapes, we may be overlooking an equally important feature of palaeovegetation, namely their vertical structure. Tropical forest structure is a critical factor contributing to canopy microclimatology and thus plays a role in defining canopy habitats and species population dynamics. Because of this tight relationship between forest structure and canopy microclimate, flora and fauna with narrow canopy niches may have responded to glacial reductions in forest canopy density in the same manner as if the tropical forest were completely replaced by grassland. This alternative interpretation of palaeo‐forest response to past climate change holds significance for the application of the Pleistocene refugia hypothesis in explaining various biogeographical trends. The role of forest structure in influencing hydrological cycling and the exchange of carbon between the biosphere and atmosphere are highlighted to illustrate how palaeoprecipitation and palaeoproductivity proxy data may be misinterpreted when forest structure is not explicitly considered. This is accomplished through theoretical scenarios using hydrological mass balance equations and simulations using a soil–plant–atmosphere landscape model. Available methodologies to reconstruct tropical palaeovegetation structure are identified, including the use of fully coupled earth system models. Copyright © 2004 John Wiley & Sons, Ltd.

Hedge Pruning Pecan

An ever increasing cost:price squeeze on the profitability of pecan (Carya illinoinensis) farming is driving a search for alternate husbandry approaches. `Wichita' and `Western' trees maintained at relatively high tree population density, by mechanized hedge pruning and topping, produced greater nut yield than an orchard treatment in which tree population density was reduced by tree thinning (144% for `Wichita' and 113% for `Western Schley'). Evaluation of three different hedge pruning strategies, over a 20-year period, identified a discrete canopy hedge pruning and topping strategy using a 2-year cycle, as being superior to that of a discrete canopy hedge pruning and topping strategy using an 8-year cycle, but not as good as a continuous canopy hedge pruning and topping strategy using a 1-year cycle. An evaluation of 21 commercial cultivars indicated that nut yields of essentially all cultivars can be relatively high if properly hedge pruned [annual in-shell nut yields of 2200 to 3626 lb/acre (2465.8 to 4064.1 kg·ha-1), depending on cultivar]. Comparative alternate bearing intensity and nut quality characteristics are reported for 21 cultivars. These evaluations indicate that pecan orchards can be highly productive, with substantially reduced alternate bearing, when managed via a hedge-row-like pruning strategy giving narrow canopies [3403 lb/acre (3814.2 kg·ha-1) for `Wichita' and 3472 lb/acre (3891.5 kg·ha-1) for `Western Schley']. North-south-oriented (N-S) hedgerows produced higher yields that did east-west (E-W) hedgerows (yield for N-S `Wichita' was 158% that of E-W trees and N-S `Western Schley' was 174% that of E-W trees).These data indicate that mechanized hedge pruning and topping offers an attractive alternative to the conventional husbandry paradigm.

Intercropping of Different Secondary Crops in Maize

Intercropping and bicropping are common cultivation systems in many countries. Maize (Zea mays L.) as a main crop combined with a legume as secondary crop is in general use in many countries. These systems may contribute to a higher biodiversity, and reduced import of fertilizer, concentrates and agrochemicals. The objective of this research was to select an appropriate secondary crop that could be grown with maize in an intercropping system to control weeds while maintaining maize yields. Field beans (Vicia faba L.), crimson clover (Trifolium incarnatum L.), phacelia (Phacelia tanacetifolia Benth.) and thyphon [Brassica rapa L. ar. rapa (L.) Thell] were selected as secondary crops. Acceptable yields of dry matter in maize were obtained regardless of secondary crop. Different yield levels were obtained depending on the morphology of the secondary crop. Thyphon, a high, dense secondary crop with large leaves, shaded the lower maize canopy, and thereby reduced the yield of maize. In contrast, field bean, which is tall and has a narrow canopy, did not reduce maize yield. A negative relation was found between the yield of secondary crop plus weeds in August and October and the yield of maize in October. The secondary crops were not sufficiently competitive against weeds in the first part of the growing season. Thyphon competed too much against maize. Field bean and phacelia resulted in a minimum of competition against maize, and a maximum competition against weeds, compared with the other secondary crops.

Growth and architecture of juvenile Carpodetus serratus in closed forest canopy and canopy gap environments

The growth and architecture of juvenile Carpodetus serratus (Escalloniaceae) plants are described, and the habit of plants growing in different light environments compared. Growth was periodic along vertical axes, creating distinct layers of foliage separated by vertical stem sections with no lateral outgrowth. Plants had low foliage density, narrow canopy shape, and the plasticity to adapt to different light conditions. These features suggest that juvenile C. serratus capture light efficiently and follow the persistent multilayer/optimistic growth strategy described by others. In comparison with plants growing in a forest canopy gap, plants growing under a closed canopy had greater foliage density, greater distance between foliage layers, and a less even vertical distribution of leaves within the plant canopy. Closed canopy plants most likely captured diffuse light more efficiently than canopy gap plants.

Vegetative Growth of Coffee Cultivars under Mechanical Pruning Systems

Pruning methods 1.5 × 1.5 m (topping and hedging) and stumping to 0.70 m were used on coffee cultivars Guatemalan, Red Catuai, Yellow Caturra, and Mokka. In the hedged treatment, `Mokka' had the longest laterals, followed by `Guatemalan', with `Red Catuai', and `Yellow Caturra' having similar lengths. `Mokka' had the most nodes/lateral. `Guatemalan' showed the fastest growth (height), followed by `Mokka', with `Red Catuai' and `Yellow Caturra' having similar growth. For 0.70-m pruning, vertical lengths of `Guatemalan' were the longest. `Mokka' had the most vertical nodes. `Guatemalan' had the longest vertical internodes, followed by `Red Catuai' and `Yellow Caturra', with `Mokka' having the shortest. `Yellow Caturra' had the most laterals/vertical, followed by `Red Catuai' and `Guatemalan'. `Mokka' had the fewest. Lateral lengths, nodes/lateral, and internode length were similar for all cultivars. Two-meter pruning height may be best for `Red Catuai' and `Yellow Caturra' because of slow growth, shorter laterals, and fewer nodes/lateral. These two cultivars grew well after being stumped due to faster regrowth and more laterals remaining on new verticals. 1.5-m pruning appears optimum for `Guatemalan', but it grew very well after stumping. It may be better to prune `Mokka' to a 2-m height with a narrow canopy remaining because of its good multiple verticals, fast lateral growth from new verticals in canopy but not in full sun, and more vertical nodes but less laterals regrowing from new verticals on main trunks exposed to full sunlight.

Coupling a spatially-explicit forest gap model with a 3-D solar routine to simulate latitudinal effects

A multi-scaled forest model (ZELIG) which spatially embeds patch-scale processes into a larger landscape was linked with a 3-D insolation routine to simulate the effects of latitudinal variation in solar radiation on the growth and spatial patterns of idealized early successional, shade-intolerant and late successional, shade-tolerant species. At the individual tree level, average tree height increased for the shade-intolerant species with decreasing latitude as steep angled direct-beam radiation more readily penetrated narrow canopy gaps. This yielded an increase in interspecific competition and intraspecific competition among shade-intolerant trees. Consequently, though stem density dropped, basal area of shade-intolerant species increased as growth increased with decreasing latitude. Conversely, basal area for the shade-tolerant species increased with increasing latitude as stem density increased as the proportion of diffuse radiation increased. In terms of spatial pattern, the combined models produced non-random, anisotropic patterns which changed over the course of succession and were different for the shade-intolerant and tolerant species. However, differences in spatial patterns for the tropical, temperate, and boreal solar regimes were inexplicable. Shade-tolerant species consistently exhibited negative autocorrelation on adjacent grid cells (10–20 m away) during early successional stages and later stages after species replacement. Auto-correlation of shade-intolerant species shifted from negative to positive at this scale as its role changed from canopy dominant to gap colonizer. At scales > 20 m, whether or not a specific direction/distance autocorrelation value was positive or negative and significant or not significant was highly variable for both species and was attributed to stochastic properties (i.e., birth and mortality) of the model.

Effects of disturbance and size structure on the regeneration process in a sub‐boreal coniferous forest, northern Japan

AbstractThe stand structure and disturbance history in a sub‐boreal coniferous forest dominated by Picea jezoensis, Picea glehnii and Abies sachalinensis were investigated in four study plots set up in Taisetsuzan National Park, Japan. The effect of stand characteristics on the growth and mortality rates of understory trees was examined. Although all the stands showed inverse J‐shape d.b.h. (diameter at breast height) distributions, the age structure and disturbance history differed amongst the stands. The stands with wide d.b.h. distribution (i.e. large CV and skewness) were more uneven‐aged than those with narrow d.b.h. distribution (i.e. small CV and skewness). The disturbance‐return interval based on the model of Hett and Loucks was 31 to 65 years. The gap ratio in the canopy was also different among the stands. These suggest that the variations in stand structure represent different occurrences of natural disturbances. Furthermore, the structural features such as size structure, canopy gap ratio and density of canopy trees also affected the growth dynamics of understory trees (≥2 m in height and <10 cm in diameter at breast height). The growth and mortality rates of understory trees changed with the canopy gap ratio and canopy tree density. The understory trees of stands with wide canopy d.b.h. distribution had higher growth and canopy recruitment rates than those of stands with narrow canopy d.b.h. distribution, contributing to the maintenance of continuous stand stratification. The understory trees of stands with narrow canopy d.b.h. distribution showed lower growth and higher mortality rates than those of stands with narrow canopy d.b.h. distribution, leading to the formation of a single‐canopy structure. It is suggested that natural disturbance governs the regeneration process in the future by affecting the growth and mortality patterns of understory trees through the stand structure (size and age structure, canopy tree density, canopy gap ratio).

Cassava/legume intercropping with contrasting cassava cultivars. 2. Selection criteria for cassava genotypes in intercropping with two contrasting legume crops

An experiment was conducted to determine selection criteria for cassava genotypes for intercropping with legumes using 18 cassava cultivars which are contrasting in canopy size. Two legume crops were used; one a short-statured, quick-maturing soybean, and the other, a tall, late-maturing pigeonpea. They were sown at 37 days after cassava planting in double rows between cassava rows. Intercropped soybean had little adverse effect on crop growth and tuber yield of cassava, and in some cases it enhanced tuber yield of cassava cultivars with small compact canopies. The effect of cassava on soybean yield was least with short-statured, small cassava cultivars as solar radiation available to the soybean was highest. As the canopy development of cassava was hardly affected by soybean in any cultivars, the selection of cassava genotypes can be made in sole-cropping with selection criteria of high tuber yield and narrow canopy width measured at about 90 days after cassava planting. Intercropped pigeonpea had an adverse effect on canopy development and tuber yield of cassava, particularly of short-statured cultivars. Whilst tall cultivars with spreading canopy were least affected by pigeonpea, they reduced seed yield of pigeonpea to a very low level. It was therefore difficult to determine cassava types suitable for this intercropping. When strongly competitive species, such as pigeonpea, are to be intercropped with cassava, selection can be made initially in sole-cropping with selection criteria of high tuber yield and height which is at least similar to that of the associated crop. The results show that ideal cassava cultivars for intercropping depend on competitive ability of associated species. It is suggested that competitiveness of component crops should be identified using a few cassava cultivars under typical growing conditions before selection is carried out.

HR14 and HR20 common bean germplasm

Two germplasm lines, early maturing HR14 and late maturing HR20, of white (navy/pea) dry edible bean (Phaseolus vulgaris L.) have been released. These lines are semi-determinate and have an upright plant type with high podding nodes and narrow canopy making them suitable for use in developing cultivars for solid seeding and direct combining. The lines are high yielding but lack good cooking quality.Key words: Germplasm, dry edible (navy or pea) bean, erect (upright) plant type, plant architecture

Harowood common bean

Harowood is a late-maturing, high-yielding white (navy) bean (Phaseolus vulgaris L.) cultivar with a semideterminate growth habit. The main advantages of Harowood over other cultivars are its more erect plant type which forms a narrow canopy and its high podding nodes which make the crop suitable for narrow row production and direct combining. Harowood is resistant to the alpha and delta races of anthracnose and to races 1 and 15 of bean common mosaic virus. Key words: Phaseolus vulgaris L., dry edible (navy, pea) bean, upright plant type, cultivar description