Canopy Ground Cover Research Articles

Developing selection protocols for weed competitiveness in aerobic rice

Aerobic rice production systems, wherein rice is dry-sown in non-puddled soil and grown as an upland crop, offer large water savings but are subject to severe weed infestation. Weed-competitive cultivars will be critical to the adoption of aerobic rice production by farmers. Breeding weed-competitive cultivars requires an easily used selection protocol, preferably based on traits that can be measured under weed-free conditions. To develop such an indirect selection index for weed competitiveness, 40 rice cultivars were evaluated in aerobic soil conditions in a weed-free environment in 2003 and in weedy environments over 3 years (2001–2003). Broad-sense heritabilities ( H) of vegetative and harvest traits and their genetic correlation with weed biomass and yield under weed competition were estimated. All the traits measured under weed-free conditions were closely correlated with the same traits measured under weedy conditions. Crop vigor ratings at 2, 4, and 6 weeks after sowing (WAS), canopy ground cover at 6 WAS, height at 3 and 4 WAS, tillers per plant at 4 and 8 WAS, vegetative crop biomass at 4 and 9 WAS and plant erectness at 3 WAS under weed-free conditions in 2003 were all positively correlated with means for yield under weed competition and negatively with means for weed biomass across three years. In general, traits associated with rapid seedling biomass accumulation were also strongly associated with weed suppression and yield under weed competition. Regression analysis revealed that yield and early vigor under weed-free conditions in a single three-replicate trial could be used together in an indirect selection index, explaining 89% and 48% of variation for yield under weed competition and weed biomass, respectively. The predicted indirect selection efficiencies of weed-free yield and vigor ratings as selection criteria for yield under weed competition and weed biomass were high. Visual vigor rating at 4 WAS is the best vegetative trait as an indirect selection criterion for use together with weed-free yield, but it could be replaced by plant height at 4 WAS without loss in selection effectiveness.

Actual Performance versus Theoretical Advantages of Polyacrylamide Hydrogel throughout Bedding Plant Production

An appropriate blend of growing media components increases water holding capacity and reduces irrigation frequency. Synthetic commercial materials, referred to as hydrogels, have remarkable hydrating properties, but can add significantly (about 15%) to the cost of growing media. The literature generally states that the physical characteristics of hydrogels, such as polyacrylamide (PAM), are altered by the presence of divalent cations (Ca2+ and Mg2+). Few studies, however, have simultaneously investigated plant growth and development and media characteristics on a daily basis throughout plant production. Thus, the mechanisms explaining the reported beneficial and/or detrimental effects from PAM incorporation remain hidden. In this study, canopy ground cover of two species [pansy (Viola ×wittrockiana Gams) and new guinea impatiens (Impatiens hawkeri Bull)] was measured daily, from transplanting to marketable size, using digital imaging to determine growth differences of plants grown in media containing different amounts of PAM. Media water content was determined with time-domain reflectance probes every 10 minutes in media treatments. Total number of irrigation events, time between irrigation events, root development after 4 and 8 weeks of growth, flower number, flower longevity, and dry masses of the shoot were also measured. Scanning electron microscopy revealed significant structural differences in hydrated PAM depending on water quality. The pansy canopy coverage was significantly greater with hydrogels, and root growth early in production was enhanced with PAM. No such effect was observed for new guinea impatiens. Total flower numbers and flower longevity of new guinea impatiens decreased with increasing amount of PAM (16.7% or higher) in the media. PAM incorporation reduced the need for irrigation early in production for both species, but by the end of production, those new guinea impatiens plants were smaller (less shoot dry mass) and required irrigation as often as plants grown without PAM. This effect coincided with reduced media volume, air capacity, and total porosity in PAM-containing media. Theoretical analysis of the potential benefits from hydrogels confirms the potential benefit early in production with little to no benefit later in production and in post-production. These data will assist growers in determining if the benefits derived from the use of PAM justify the added cost of medium.

On-farm assessment of regional and seasonal variation in sunflower yield in Argentina

Using an on-farm approach, we investigated constraints to actual yield of sunflower in six agroecological zones within the Argentine Pampas during three growing seasons. In 249 large, grower-managed paddocks, we quantified a series of variables related to: (1) crop phenology, growth, and yield; (2) the physical and biological environment; and (3) management practices. Variation in yield among zones and seasons was analysed on the basis of four biologically-founded assumptions: (1) grain number accounts for a large proportion of the variation in yield; (2) grain number is associated with a photothermal coefficient, Q= R ( T- T b) −1, where R and T are average solar radiation and air temperature respectively, during the 50-day period bracketing anthesis; and T b is a base temperature; (3) crop growth and yield are proportional to light interception, and therefore proportional to canopy ground cover; and (4) yield is proportional to the fraction of seasonal rainfall that occurs after anthesis. Average yield ranged from 1.1 to 2.7 t ha −1, grain number from 2400 to 5400 m −2, individual grain mass between 40 and 69 mg and grain oil concentration between 42 and 52%. Grain number accounted for 43% of the variation in average yield while Q accounted for 23% of the variation in grain number. Low yield was associated with deficient ground cover in 25% of the crops; part of the remaining variation in yield was accounted for by sets of measured variables particular to each zone, including soil shallowness, low available P, low initial water content, weeds and diseases — chiefly Verticillium wilt ( Verticillium dahliae) and Sclerotinia head rot ( Sclerotinia sclerotiorum). Across zones and seasons, the proportion of seasonal rainfall occurring after anthesis accounted for 28% of the variation in crop yield. A trade-off is highlighted whereby beneficial effects of rainfall that favours growth and yield may be offset by the detrimental effect of abundant moisture that favours major fungal diseases. We emphasised the value of combining experimental studies — which provide biological background in the form of working hypotheses — with on-farm research that realistically quantifies yield response to key factors.

Linear Mixture Modeling Approach for Estimating Cotton Canopy Ground Cover using Satellite Multispectral Imagery

Researchers have sought techniques for estimating plant canopy characteristics from remote sensing data that are not site-specific. In this study, a procedure for estimating cotton ( Gossypium spp.) canopy ground cover based on a linear mixture modeling approach was tested using Landsat multispectral imagery. Ground cover estimated from scene reflectance in the red and near-infrared wavebands was compared with corresponding field measurements. Statistical analysis of the results suggest that the procedure produced accurate, unbiased estimates of cotton canopy ground cover. The procedure appeared to implicitly compensate for the effects of shadows in the scene. These results agree with the findings of earlier studies and support the proposition that this procedure should be more universally applicable than commonly used empirical curve-fit techniques.

Utilization of Fodder Trees and Shrubs in the Arid and Semiarid Zones of West Asia and North Africa

Utilization of fodder trees and shrubs (FTS) in the Mediterranean arid and semi-arid zones was initiated after World War I and expanded between 1950 and 1970. A similarly slow expansion has taken place in other arid zones in the USA, South Africa, South America, and Australia. Currently in West Asian and North African (WANA) countries, the area planted with native or exotic species is about 10 6 ha. Mainly they include three categories of plant species: cacti, saltbushes, and wattles. At this time there is an expansion of hectareage and a diversi-cation of genetic material. The relative success of FTS has a number of reasons. They are tolerant to drought and have the ability to accumulate green fodder over several seasons, providing fodder reserves for times of dearth and thus permitting a switch from transhumance to sedentary husbandry. Deep rooting enables them to reach water resources unavailable to herbaceous species. Their Rain Use Efficiency (RUE) and Water Use Efficiency (WUE) rates provide productivities three to five times higher than rangelands. FTS have a positive impact on soil fertility due to their organic matter production, hence they increase microbial activity, rates of geobiogenic element cycling, and soil structure stabilization. Their above ground biomass, canopy ground cover, provides a microclimatic buffer role for wind, temperature and evapotranspiration, and their landscape roughness factor makes them efficient for erosion and desertification control. Other positive aspects include: the use on non farming land; general suitability for runo farming systems; production of valuable goods, such as food, shade, and firewood; providing wildlife shelter; and other benefits. FTS plantations are subjected, however, to constraints that limit their expansion. Their main shortcomings include the cost of establishment, often not affordable by a small farmer; required long-term planning may not be feasible, as a secure land tenure system often is nonexistent. Appropriate methods of cultivation are not being applied, management, and utilization are lacking, and availability of plant material is limited. Discipline of utilization, allowing regeneration of stands after defoliation is a problem. Identification of constraints indicates needs for research and extension activities. These include reduced-cost of establishment and improved management methods, such as ensuring availability of low-cost seeds and selection of high grade cultivars, and introduction of new high quality exotic species. Additionally, integration into economically feasible and socially acceptable production systems, including joint cultivation with cereal farming and combination with runo farming techniques, should be developed. Legal, regulatory, and administrative incentives are also needed.

Estimating Cotton Canopy Ground Cover from Remotely Sensed Scene Reflectance

AbstractMany agricultural applications require spatially distributed information on growth‐related crop characteristics that could be supplied through aircraft or satellite remote sensing. A study was conducted to develop and test a methodology for estimating plant canopy ground cover for cotton (Gossypium hirsutum L.) from scene reflectance. Previous studies indicated that a relatively simple relationship between ground cover and scene reflectance could be developed based on linear mixture modeling. Theoretical analysis indicated that the effects of shadows in the scene could be compensated for by averaging the results obtained using scene reflectance in the red and near‐infrared wavelengths. The methodology was tested using field data collected over several years from cotton test plots in Texas and California. Results of the study appear to verify the utility of this approach. Since the methodology relies on information that can be obtained solely through remote sensing, it would be particularly useful in applications where other field information, such as plant size, row spacing, and row orientation, is unavailable.

CASSAVA VARIETAL RESPONSE TO FERTILIZATION: GROWTH DYNAMICS AND IMPLICATIONS FOR CROPPING SUSTAINABILITY

Four contrasting varieties of cassava (Manihot esculenta Crantz) were grown for ten months over two consecutive seasons in hillside Colombia with or without nitrogen, phosphorus and potassium fertilization. Sequential harvests were every two months. The two varieties well adapted to acid soils (CM 489-1 and CM 523-7) had higher yields and exhibited the strongest response to fertilization, highest solar radiation use efficiency, earlier canopy ground cover and higher leaf litter accumulation. The export of potassium, however, was no higher than in the other genotypes, mainly as a consequence of higher potassium use efficiency in the adapted varieties. Significant amounts of total calcium, magnesium and nitrogen accumulated in the whole plant were recycled in the leaf litter during growth. High-yielding varieties adapted to acid soils did not exacerbate soil fertility problems of cassava crops; rather, they were beneficial. Certain growth parameters could be used to select for varieties with low impact on soil fertility.

Dry matter accumulation in potato clones under seasonal high temperature conditions in Pakistan

The effects of seasonal high temperatures on potatoes were investigated under field conditions near Peshawar, Pakistan. Five potato clones (A79196-1, Desiree, DTO-28, LT-1, Russet Burbank) were grown during the spring season at two locations. Canopy development, vine dry weight and tuber dry weight were determined at 13-day intervals, starting 68 days after planting (DAP). Tuber yield was higher in heat tolerant clones compared to heat susceptible clones. Location significantly affected tuber dry weights. Tuber dry weights of Russet Burbank were consistently lower than those of DTO-28. Ground canopy cover of DTO-28 occurred earlier and reached maximum at 75 DAP, compared to 90 DAP for Desiree. DTO-28, because of its high tuber yield under cool as well as hot temperatures, and its relatively early bulking, should be a promising clone for a short duration crop in hotter regions.

Multiple Incidence Angle SIR-B Experiment Over Argentina: Mapping of Forest Units

Multiple incidence angle SIR-B data of the Cordon la Grasa region of the Chubut Province of Argentina are used to discriminate nate various forest types by their relative brightness versus incidence angle signatures. The region consists of several species of Nothofagas which change in canopy structure with elevation, slope, and exposure. In general, the factors that appear to impact the radar response most are canopy structure, density, and ground cover (presence or absence of dead trunks and branches in particular). The results of this work indicate that 1) different forest species, and structures of a singlee-species, may be discriminated using multiple incidence angle radar-imagery and 2) it is essential to consider the variation in backscatter due to incidence angle when analyzing and comparing data collected at varying frequencies and polarizations.

Seasonal Micro-Habitat Relationships of Ruffed Grouse in Southeastern Idaho

We summarized characteristics of micro-habitats selected by ruffed grouse (Bonasa umbellus) in southeastern Idaho for all seasons. Ruffed grouse preferred stands dominated by quaking aspen (Populus tremuloides). Drumming sites selected by males were typified by high vegetation density. Brood hens selected relatively open areas with high cover of herbaceous vegetation. Drumming sites differed (P 2,130 m): quaking aspen, aspen/conifer mixed, dense conifer, and open conifer. A description of each of the vegetation types is in Stauffer and Peterson (1985). Size of stands in each cover type ranged from 23 cm dbh/ha 35 (17) 86 (31) 12 (8) 73 (38) Maple/ha 300 (82) 0 (-) 94 (76) 9 (9) a Sample size. b Standard error. >200 ha. Cover types generally were well interspersed throughout the study area. We spent 1,593 hours (spring, 322 hours; summer, 543 hours; autumn, 296 hours; winter, 432 hours) searching for grouse from May 1979 through May 1981. At these times, an area comprising one or a few vegetation types was selected and thoroughly searched. Searching effort was distributed among each vegetation type in approximate proportion to the type's occurrence on the study area. Locations of grouse flushes were used as the center of a 0.01-ha circular plot for which we recorded (Noon 1981): percent of area within 40 m of the plot center that was comprised of coniferous or deciduous cover or open; percent tree canopy and ground canopy cover; canopy height and average height of herbaceous vegetation; number of woody stems 69 cm); slope; aspect; and vegetation type. Counts of woody stems and trees were converted to number per ha. Additional data recorded at drumming sites included drumming log diameter and length and an ocular estimate of the percent of five strata (0-0.5 m, 0.51-1.5 m, 1.51-3.0 m, 3.01-6.0 m, >6.0 m) with vegetation. Means for data recorded in the 0.01-ha plots at grouse locations were calculated for various combinations of vegetation type and season to describe the characteristics of sites selected. We used Hotelling's T2 and multivariate analysis of variance (MANOVA, Morrison 1976) to test hypotheses of no difference in habitat use by groups of grouse as described in the objectives. We established 150 random plots to sample habitat characteristics assumed available to grouse in aspen and aspen/conifer stands, which were preferred vegetation types (Stauffer and Peterson 1985). Random plot data were subjected to a principal components analysis (Morrison 1976) to reduce the set of correlated variables to independent components that represented habitat gradients occurring within aspen and aspen/conifer stands. We then assigned observations of ruffed grouse in aspen and aspen/conifer vegetation scores on each of the habitat gradients to compare characteristics of microhabitats where we observed ruffed grouse to what was available. Appropriate transformations (log, square-root, or arc-sine) were applied to non-normal variables. RESULTS AND DISCUSSION Ruffed grouse exhibited a preference for sites dominated by aspen (Stauffer and Peterson 1985), thus only data from grouse observations in aspen and aspen/conifer stands (N = 207) are presented here.