Agricultural production on the Mahafaly Plateau in SW-Madagascar has traditionally been based on subsistence rain-fed agriculture, with yields declining as a result of low soil fertility, recurrent droughts, and erratic rainfall. Market-oriented vegetable production in this area may help households improve their nutrition and diversify their income. In field trials between the 2013 and 2016 dry cropping seasons, the feasibility of carrot (Daucus carota L.) and onion (Allium cepa L.) production was assessed by testing effects of manure and charcoal amendments, shading, and seed quality on yields. Due to damage caused by cyclones and strong winds, only data from 2013 and 2016 are reported in this paper. Additionally to the field experiments, effects of salinity on seed germination were also examined under laboratory conditions and in the field. Carrot dry matter (DM) yields were 0.24 to 2.76 t·ha−1 while those of onion were 0.15 to 0.99 t·ha−1 DM. While the combination of manure and charcoal application had only minor effects on crop growth, manure alone increased carrot yield by 26% across years. After one cropping season, manure application reduced soil pH from 9.0 to 8.6 and increased soil Corg from 0.87 to 1.76%, N from 0.08 to 0.14%, and P from 10.6 to 15.1 mg·kg−1. Shading reduced carrot yields from 0.87 to 0.58 t·ha−1 DM in 2013 and from 1.87 to 0.85 t·ha−1 DM in 2016, but increased onion yield in 2013 from 0.24 to 0.62 t·ha−1 DM. Carrot seed procured locally performed better in the field than seed imported from the capital which translated into differences in seedling emergence. Saline irrigation water (electrical conductivity = 7.03 mS·cm−1) reduced seedling emergence rate of carrot from 73 to 20% and for onion from 44 to 28% and unprimed seeds performed better than primed ones. Using shading during the dry season is not advisable for carrot and onion production, but improving seed quality and targeted use of soil amendments (time of manure application, manure quality) may enhance vegetable yields.

Grass pea (Lathyrus sativus L.) has a Mediterranean origin and was spread to Western Europe, Africa and South Asia. Over time, this grain legume crop has become important in South Asia, where it is often affected by waterlogging at germination. Therefore, varieties with waterlogging tolerance of seeds at germination are needed. This study evaluated waterlogging tolerance in a grass pea diversity panel. First, morpho-agronomic traits of 53 grass pea genotypes from 7 diverse countries (Afghanistan, Australia, Bangladesh, Cyprus, Ethiopia, Greece and Pakistan) were measured in a glasshouse. Seeds of the collection were then sown into waterlogged soil for 6 days and is subsequently drained for 8 days. Finally, representative genotypes from each country of origin of the three survival patterns (described below) were then tested to identify the effect of seed priming on germination and seedling growth in waterlogged soil. Canonical analysis of six traits (seed weight, pod length, pod width, flowering time, time to maturity and seedling survival) showed that genotypes from Bangladesh and Ethiopia were similar. There was a significant variation amongst genotypes in waterlogging tolerance. Genotypes from Bangladesh and Ethiopia showed the highest percent seedling survival (54% and 47%), with an ability to germinate under waterlogging and then maintain growth from the first day of draining to the final sampling (Pattern 1). In contrast, genotypes from other origins either germinated during waterlogging, but did not survive during drainage (Pattern 2) or failed to germinate and had low seedling survival during waterlogging and drainage (Pattern 3). Priming seeds reduced seedling survival in grass pea. Despite Mediterranean origin, specific ecotypes of grass pea with greater waterlogging tolerance under warm wet conditions have been favoured in Bangladesh and Ethiopia where adaptation to extreme precipitation events at germination and seedling survival upon soil drainage is critical for successful crops.

This research communication addresses the hypothesis that, during the summer in the subtropics, natural tree shade helps to improve milk functional characteristics such as stability and acidity. Sixteen Holstein lactating cows were enrolled. The study consisted of three periods (pre-stress, heat stress and post-stress) based on allocating grazing cows into two treatments (with and without access to shade during the Heat Stress period). Overall THI during the trial was (mean ± se) 76.0 ± 3.4. Access to shade prevented the heat stress-related decrease in milk stability both in the ethanol and in the coagulation time test, as well as maintained milk acidity within an acceptable range (14 to 18°D).

Field studies using area-of-influence techniques were conducted in 1987 and 1988 to evaluate soybean growth and yield, and to predict soybean yield losses from photographs of jimsonweed and common cocklebur canopies. Differences in weed competitiveness within the 100-cm area of influence were induced by dates of soybean planting, locations, weed species, and years. Soybean yield losses within the first 20-cm interval from weeds correlated well with yield of all soybean plants within 100 cm of weeds (r2 = 0.86). Soybean growth responses as a function of distance from weeds were best described by complex polynomials, but simple linear functions, based on a data point from soybean plants nearest a weed and from the average of plants 60 to 100 cm from a weed, closely approximately actual yield losses (r2 = 0.96). Soybean yield losses were highly correlated (r2 = 0.84) with leaf area of weeds as viewed from directly above the weed-crop canopy. Weed canopy diameter, measured from overhead photographs 8 weeks after soybean emergence, also correlated well with soybean yield losses (r2= 0.82), but correlation with actual weed leaf area was not significant (r2 = 0.31).

The effect of soil moisture, temperature, and light intensity on the spray deposition of fenoxaprop and imazamethabenz applied to wild oat plants was examined by using fluorescent tracer dye. Based on either biomass or total leaf area, the apparent deposition of the two herbicides diminished in the following order: shading > low temperature ≥ drought ≥ “optimum” > high temperature. The enhanced phytotoxicity of both herbicides under shading could be associated with increased spray deposition; and reduced fenoxaprop phytotoxicity under high temperature stress could be related to reduced deposition. Changes in spray deposition were attributed mainly to differences in herbicide interception due to altered plant morphology. Reduced retention for both herbicides was exhibited only in the plants grown at high temperature. Under “optimum” conditions, fenoxaprop phytotoxicity was directly associated with leaf orientation and thus with the proportion of projected leaf area at the time of herbicide spraying. Given similar application conditions, spray deposition of fenoxaprop and imazamethabenz on wild oat could be estimated by determining the ratio of the projected leaf area, as measured by an image analyzer, to the total leaf area.

Greenhouse studies were carried out to determine the effects of different shading levels on biomass accumulation of purple and yellow nutsedge. Artificial shading levels provided were 20, 40, 60, and 80% of incident sunlight in addition to the full sunlight control (0% shading). Yellow nutsedge shoot and tuber number, plant height, and shoot and tuber dry weight were less affected by 20% shading than were these variables for purple nutsedge. Shoot and tuber dry biomass for both species responded linearly to shading level. In yellow nutsedge, 80% shading reduced dry matter partitioning to the tubers and increased partitioning into the shoots. In contrast, biomass partitioning to purple nutsedge tubers was decreased under high shade conditions without increases in partitioning to the shoots. The light compensation point was lower for yellow nutsedge than for purple nutsedge. This could possibly explain the wide distribution of yellow nutsedge in relatively low light intensity environments, in contrast with purple nutsedge, which generally occurs in tropical areas where higher light intensities are the norm.

The nitrogen (N) response of competing plants may be affected by photosynthetically active radiation (PAR) availability and maximum potential growth rate, which determine N requirements. The responses of two crop (corn and soybean) and six weed species (common lambsquarters, common waterhemp, giant foxtail, velvetleaf, wild mustard, and woolly cupgrass) in low and high (150 and 450 μmol m−2 s−1) PAR levels to daily fertilization with either low or high (0.2 or 7.5 mM) NH4NO3 levels were studied. Leaf area of all species responded positively to N by 8 d after emergence (DAE) when grown in high PAR; in low PAR, most species did not respond until 11 DAE. Dry weight and leaf area of all species at 18 DAE were greater with high than with low N. These responses to high N were also greater in high than in low PAR for all species. Dry weights with high N were up to 100% greater in low PAR and up to 700% greater in high PAR than dry weights with low N. These responses suggest that low PAR reduced the benefit of N to the plants. The regression of relative growth rate (RGR) with high N to RGR with low N had a slope that was less than unity (β = 0.79), indicating that species with a higher RGR with high N experienced greater decreases in RGR with low N. Similarly, the sensitivity (change in RGR) of plants grown with high and low N was positively related to RGR with high N. RGR differences among crop and weed species may be related to differences in N requirement that could be exploited for weed management. RGR and seed size were negatively correlated, which may explain previous observations that small-seeded weeds were more sensitive to environmental stress.

Corn and soybean were planted in narrow- and wide-row spacings to study the effects of glyphosate application timing and row spacing on light interception and subsequent weed growth. Corn planted in narrow rows (38 cm) had greater light interception than corn planted in wide rows (76 cm) from 35 to 55 d after crop emergence. Soybean planted in narrow rows (both 19 and 38 cm) had greater light interception throughout the growing season than soybean in 76-cm rows. At maximum canopy closure, narrow-row soybean (both 19 and 38 cm) intercepted more light than narrow-row corn. Biomass of weeds emerging after glyphosate application was greater when soybean was planted in 76-cm than in 19- or 38-cm rows. However, weed biomass was generally similar in both row spacings of corn. Sequential glyphosate applications reduced weed biomass in corn each year compared with a single glyphosate application at the 5-cm weed height. Sequential glyphosate applications that followed initial glyphosate application to 10- or 15-cm-tall weeds did not reduce weed biomass compared with a single application.

Pitted morningglory seed were collected in the fall of 2003 from Blackville, SC, and 2004 from Pendleton, SC, to assess the effect of After-Ripening and burial on light and temperature requirements for germination. Pitted morningglory germination was evaluated over a 12-mo period after maturation. Germination was neither stimulated by red light or inhibited by far-red light, nor was it reversible by red or far-red light. Light was not essential for germination of buried seed. Direct exposure to sunlight prevented germination of recently mature seed, but not once seed had sufficiently after-ripened. Pitted morningglory was capable of germination in darkness over a wide range of constant and fluctuating temperatures immediately after maturation. Germination in response to temperature varied with time of year after maturation, with the population from Pendleton having increased germination in May. Thermal fluctuations increased germination of both populations at suboptimal temperatures. Thermal amplitude regulation of germination varied over time and appeared to play a more important role in germination of after-ripened seed than recently mature ones. The ecological significance of changes in germination requirements with After-Ripening is discussed.

Experiments were conducted in 2002 and 2003 to determine the influence of soil thermal amplitude on common cocklebur emergence. Additionally, common cocklebur achenes were collected in fall of 2003 and of 2004 to assess changes in light and temperature requirements for germination over a 12-mo period under field conditions. Common cocklebur germination in response to the light environment and to constant and fluctuating temperatures were evaluated under controlled conditions following achene retrieval from the field. There was a linear inverse relationship between shade intensity and soil thermal amplitude, which explained 77% of the variability in emergence in the field over 2 yr. Emergence decreased as soil thermal amplitude declined, with 95% shading resulting in a 72 to 88% reduction in emergence. Neither red nor far-red light had much effect on germination, and burial did not induce a light requirement. Germination of achenes retrieved from the soil surface or buried in soil generally was not affected by red or far-red light, and the achenes did not acquire a red-light requirement following burial. Daily exposure to natural greenhouse light at 24 to 30 C was essential for germination immediately following achene maturation, whereas no germination occurred in darkness. A thermal fluctuation of 15 C increased germination percentages over those at constant temperatures regardless of time after maturation or retrieval-depth of achenes. The mean fluctuating temperature over all sample dates that was generally optimal for germination was 25 C (17.5/32.5 C low/high temperatures; 15 C daily fluctuation) in April or May and July or August in both years. Germination was generally optimum at constant temperatures of 35 or 40 C. The higher mean temperature requirement for germination at constant temperatures than at fluctuating temperatures likely contributes to reduced emergence in spring and summer months, when earlier emerging weed species or crops have already become established, and the thermal fluctuation requirement for germination reduces the likelihood of emergence in an environment where light availability is diminished.

Neotropical bracken fern invades disturbed forests and burned and abandoned pastures in Latin America, inhibiting the growth of associated vegetation and altering community structure. Cutting of all aboveground vegetation every 6 to 12 mo has proven to be inefficient as a control method. We studied the impact of selective cutting of bracken every 2 mo, shading, and a combination of cutting + shading during 14 mo in a bracken-dominated, abandoned pasture in Veracruz, Mexico. At the end of the experiment, cutting with or without shading drastically reduced bracken cover from >90% to less than 1%, decreased leaf number from 18 to fewer than two leaves per m2, and depleted bracken leaf biomass. The significant reduction of bracken was correlated with a significant 3.9- to 5.7-fold increase in richness of other plant species. Cutting without shading was the only treatment that significantly reduced rhizome biomass to less than 62% of control plots, whereas cutting + shading was the only treatment to promote a significant increase in both cover and shoot biomass of successional plant species. Selective cutting of P. arachnoideum repeated every 2 mo was more successful than nonselective cuttings repeated at longer intervals, because it removed newly emerging leaves before their complete expansion and supported the recovery and reestablishment of other plant species, which may help to control bracken. Although costs for the first year of selective cutting were twice as much as for nonselective cutting, it may prove less expensive and more efficient than nonselective cutting in the long term.

Introduction. Ricinodendron heudelotii (Euphorbiaceae), en voie de domestication au Cameroun, est un arbre fruitier sauvage aux amandes oléagineuses comestibles. En milieu naturel ou en pépinière, les plantules sont détruites par Diclidophlebia xuani (Hemiptera : Psyllidae). Matériel et méthodes. L’incidence des dégâts causés par ce ravageur dans les conditions naturelles a été évaluée sur des plantules âgées de moins de 3 mois, en milieu ombragé et en milieu sans ombrage. Les données ont été collectées dans deux sites des environs de Yaoundé entre avril et mai 2000. Résultats et discussion. L’analyse des résultats a montré que les indices de dégâts du psylle ont été plus élevés à Nkolondom qu’à Nkozoa, probablement à cause du nombre plus élevé de plantules dans le premier site que dans le deuxième ; quel que soit le site, les dégâts ont été plus spectaculaires en milieu sans ombrage qu’en milieu ombragé ; les dégâts ont également augmenté avec le développement de la plantule jusqu’à ce qu’elle soit complètement détruite avant d’atteindre quatre mois. Conclusion. En définitive, les plantules de R. heudelotii sont plus sensibles aux déprédations du psylle lorsqu’elles se développent en milieu sans ombrage.

The photosynthetic and respiratory activities of the leaves of a tropical tree, cacao, Theobroma cacao L., grown under shading, were determined in relation to leaf age and light conditions within the canopy, in order to gain a deeper insight into characteristics of the leaf population composing a canopy.

The specific leaf weight and leaf water content varied with the height of leaves from the ground and/or the irradiance. The net photosynthetic rate also varied markedly depending on leaf age and irradiance. The leaves in full or nearly full irradiance (<70% full daylight) attained the maximum rate c. 60 d after the leaves emerged, and the rate decreased to nearly zero at a leaf age of c. 270 d.

The nocturnal leaf respiratory activity was proportional to the photosynthetic activity during the day, but the proportional ratio was not constant throughout the survival period of leaves. Within the closed canopy, the upper leaves, which much higher ratios of respiratory to photosynthetic activity, under full or nearly full irradiance, tended to have much shorter mean longevities (c. 160 d) than the lower leaves under a lower irradiance (c. 310 d).

To gain detailed information on the structure and dynamics of the foliage within a canopy, the longevity of leaves of cacao trees (Theobroma cacao L.) growing under normal commercial planting shade in Bahia State, Brazil, was determined relative to their position within the canopy and the time of leaf emergence.

In the experimental stand, the relative light intensity above the cacao canopy ranged between 30 and 100% of full daylight, and 4–10% at ground level. The mean leaf area index for the canopy, and the extinction coefficient of the foliage were 3·9 and 0·61, respectively.

The longevity of leaves of adult trees of cacao with closely packed crowns varied with their position within the canopy, and/or the irradiance received, and the time of emergence. In particular longevity decreased greatly with the height of the leaf from ground level. The mean longevity for the upper foliage (more than 220 cm above the ground) within the canopy was 181 d; the mean longevity of the lower leaves (0–150 cm above the ground) was about twice that of the upper leaves.

Approximately 23% of emergent leaves fell within 60 d of emergence, following infection (about 14% of loss) or as a result of wind damage (about 5% of loss). Thereafter, in mature and senescent leaves, leaf fall followed normal physiological changes.