Semi-arid Tropical Conditions Research Articles

Morphology, yield and quality of ashwagandha (Withania somnifera L. Dunal) roots and its cultivation economics as influenced by tillage depth and plant population density

SummaryAshwagandha (Withania somnifera L. Dunal; Solanaceae) is being cultivated around the world mainly for its root which has rejuvenative properties. Field experiments during 1999–2001 under semi-arid tropical conditions of Hyderabad, India studied the effect of tillage depths (15 and 30 cm) and plant population densities (20, 40, 60 and 80 plants m–2) on root morphology, yield and quality and cultivation economics of ashwagandha. Preparatory tillage to 30 cm depth in combination with a density of 60 plants m–2 gave the highest root yield of 1.2 t ha–1 which was 50% higher than that following 15 cm tillage depth and the same density. This is attributed to the favourable effect of the former treatment leading to 33, 37 and 21% increases in plant height, number of branches per plant and shoot biomass yield, respectively. Further, this treatment produced most (68%) best quality root pieces. Main root length, length of lateral roots and diameter of lateral roots were significantly increased, while the diameter of main root and the number of laterals decreased. Furthermore, increase in plant density from 20–80 plants m–2 increased production of best quality roots from 42% to 59% under shallow tillage and from 53% to 71% of root yield under deep tillage. The implications of change in root morphology are discussed in the light of production of different grades of roots, their market preferences and economics. Deep tillage was equally advantageous for seed production, but plant population density for maximum seed yield (211 kg ha–1) was lower at 40 than at 60 plants m–2 for maximum root yield. Maximum gross and net returns and benefit-cost ratio occurred following the highest root yield.

Comportamento de cultivares de uva sem sementes no submédio São Francisco

Com o objetivo de introduzir, avaliar e selecionar variedades de uva sem sementes, adaptadas às condições tropicais semi-áridas e oferecer novas alternativas aos viticultores do Vale do São Francisco, implantou-se, em 1994, uma coleção com dezenove variedades de uvas sem sementes no Campo Experimental de Bebedouro, da Embrapa Semi-Árido, em Petrolina - PE. Foram avaliadas treze variedades ao longo dos anos de 1997 e 1998, correspondendo a cinco ciclos de produção. As variedades utilizadas foram Vênus, Arizul, Beauty Seedless, Thompson Seedless, Marroo Seedless, Canner, CG 39915, Pasiga, Saturn, Emperatriz, A1581, Paulistinha e Loose Perlette, enxertadas sobre o porta-enxerto IAC 572 ('Campinas'). Foram avaliados aspectos relacionados ao desenvolvimento vegetativo e produtivo das plantas e características e composição química dos frutos. Todas as variedades apresentaram cachos com tamanho pequeno. As variedades Vênus e Marroo Seedless destacaram-se em relação ao diâmetro de bagas, apresentando, respectivamente, 17,83 e 18,26 mm, sem a necessidade de aplicação de reguladores de crescimento. O teor de sólidos solúveis totais foi elevado na maioria das variedades, enquanto a acidez total titulável foi reduzida, resultando em relações SST/ATT satisfatórias. As variedades Vênus e Marroo Seedless foram as mais produtivas, com produtividades anuais de 24 t/ha e 20 t/ha, respectivamente.

Hydrological Land Surface Response in a Tropical Regime and a Midlatitudinal Regime

A statistical‐dynamical study was performed on the role of hydrometeorological interactions in the midlatitudes and the semiarid Tropics. For this, observations from two field experiments, the First International Satellite Land Surface Climatology Project Field Experiment (FIFE) and the Hydrological Atmospheric Pilot Experiment (HAPEX)‐Sahel, representative of the midlatitudes and the semiarid tropical conditions, and simulated results from a land surface model, Simplified Simple Biosphere (SSiB) model were statistically analyzed for direct and interaction effects. The study objectives were to test the hypothesis that there are significant differences in the land surface processes in the semiarid tropical and midlatitudinal regimes and to identify the nature of the differences in the evapotranspiration exchanges for the two biogeographical domains. Results suggest there are similarities in the direct responses but the interactions or the indirect feedback pathways could be very different. The arid tropical regimes are dominated through vegetative pathways (via variables such leaf area index, stomatal resistance, and vegetal cover); the midlatitudes show soil wetness (moisture)‐related feedback. In addition, for the midlatitudinal case, the vegetation and the soil surface acted in unison, leading to more interactive exchanges between the vegetation and the soil surface. The water-stressed semiarid tropical surface, on the other hand, showed response either directly between the vegetation and the atmosphere or between the soil and the atmosphere with very little interaction between the vegetation and the soil variables. Thus, the semiarid Tropics would require explicit bare ground and vegetation fluxes consideration, whereas the effective (combined vegetation and soil fluxes) surface representation used in various models may be more valid for the midlatitudinal case. This result also implied that with higher resource (water) availability the surface invested more in the surrounding environment. On the other hand, with poor resource availability (such as water stress in the tropical site), the surface components retain individual resources without sharing.

Influence of irrigation and nitrogen on herbage and oil yield of palmarosa ( Cymbopogon martinii) under semi-arid tropical conditions

Influence of irrigation and nitrogen on herbage and oil yield of palmarosa ( Cymbopogon martinii) under semi-arid tropical conditions

Long-term studies on yield, quality and soil fertility of lemongrass (Cymbopogon fiexuosus) in relation to nitrogen application

SummaryA field experiment was conducted over five years (1992–97) at Bangalore (13.58N, 77.558E, 930.m above mean sea level) to study the effect of nitrogen application (0, 50, 100 and 150.kg N ha–1 year–1) on yield, oil quality and soil fertility of lemongrass (Cymbopogon fiexuosus) in the semi-arid tropical conditions of South India. Fresh herbage yield of lemongrass differed significantly between years; the yields increased up to the second year after which they started to decline. During the five years, the response to nitrogen was linear, while still maintaining the same content and quality of essential oil. The oil content and chemical composition of oil did not change as the crop aged. Application of nitrogen and phosphorus maintained the fertility of the soil while potassium depletion was noticed.

The Impact of Wilt Disease on Oil Yield and Quality of Two Cultivars of Rose-Scented Geranium (Pelargonium Species)

The impact of wilt disease caused by Fusarium oxysporum var. redolens (Wollenweb.) Gordon, on plant mortality, yield and quality of oils of two rose-scented geranium (Pelargonium species) cultivars was investigated under semi-arid tropical climatic conditions. Wilt disease resulted in plant mortality of 2.6–72.2% (average 19.3%) in one year old plantation and 0-18.0% (average 4.2%) in three months old plantation. Diseased plants recorded biomass yield reductions of 83.1–88.2% in cultivar I, and 73.6–84.3% in cultivar II and oil yield reductions of 87.1% in cultivar I and 69.1% in cultivar II in comparison to healthy plants. Healthy plants of both the cultivars possessed greater concentrations of linalool and geraniol, while the diseased plants had higher contents of rose oxides, isomenthone, citronellol, citronellyl formate and β-caryophyllene in their oils. Healthy and diseased plants of the two cultivars exhibited trend reversals in respect of components such as geranyl formate, citronellyl acetate, geranyl acetate, 10-epi-γ-eudesmol, citronellyl tiglate and geranyl tiglate.

Volatile constituents of different parts of cornmint (Mentha arvensis L.)

The volatile constituents of the essential oils of different parts (shoot stem, shoot leaf, stolon stem, stolon leaf) of cornmint, Mentha arvensis L., grown under semi-arid tropical climatic conditions were investigated. The shoot leaf gave the highest yield of oil (0.62%), while the stems produced negligible quantities of oil (0.02%). Menthol was the major component of all the oils, with the highest percentage in shoot stem oil (78.16%) and the lowest in stolon (runner) stem oil (43.7%). β-Caryophyllene oxide was present in shoot (stem and leaf) oils, while α-phellandrene and terpinolene were identified in stolon (stem and leaf) oils, which were also richer in limonene, menthone and pulegone than the shoot oils. Significant variations were observed among these oils for other components also. The underground rhizomes of cornmint plants did not yield any essential oil. Copyright © 1999 John Wiley & Sons, Ltd.

Volatile constituents of different parts of cornmint (Mentha arvensis L.)

The volatile constituents of the essential oils of different parts (shoot stem, shoot leaf, stolon stem, stolon leaf) of cornmint, Mentha arvensis L., grown under semi-arid tropical climatic conditions were investigated. The shoot leaf gave the highest yield of oil (0.62%), while the stems produced negligible quantities of oil (0.02%). Menthol was the major component of all the oils, with the highest percentage in shoot stem oil (78.16%) and the lowest in stolon (runner) stem oil (43.7%). β-Caryophyllene oxide was present in shoot (stem and leaf) oils, while α-phellandrene and terpinolene were identified in stolon (stem and leaf) oils, which were also richer in limonene, menthone and pulegone than the shoot oils. Significant variations were observed among these oils for other components also. The underground rhizomes of cornmint plants did not yield any essential oil. Copyright © 1999 John Wiley & Sons, Ltd.

Irrigation and Nitrogen Requirement of Lemongrass [Cymbopogon flexuosus (Steud) Wats] on a Red Sandy Loam Soil under Semiarid Tropical Conditions

A field experiment was conducted with lemongrass [Cymbopogon flexuosus (Steud) Wats] cv. Cauvery at Bangalore, India, during 1993-94 to study the effect of three soil moisture regimes (0.80, 0.53 and 0.40) irrigation water: cumulative panevaporation (IW:CPE) ratio and four levels of nitrogen (0, 50, 100 and 150 kg/ha). Soil moisture regimes maintained at 0.80 IW:CPE ratio significantly increased crop growth, herbage and essential oil yields as compared with those having 0.40 or 0.53 IW:CPE ratio. Application of 100 kg N/ha was found to be the best with respect to the yield of the crop. Quality of the essential oil in terms of its two major constituents, citral and geraniol were not affected by soil moisture regimes or nitrogen application. Oil content was not affected by soil moisture regime or nitrogen application. It was concluded that lemongrass should be irrigated at 0.80 IW:CPE ratio with an application of 100 kg N/ha in the semiarid tropical region of India.

Lamb growth and milk production of hair and wool sheep in a semi-arid tropical environment

St. Croix White hair ( n = 11), Barbados Blackbelly hair ( n = 10) and Florida Native wool ( n = 9) ewes were used to evaluate milk production and lamb growth under semi-arid tropical conditions. Milk production was measured on day 3 after lambing and at weekly intervals beginning on day 7 through weaning on day 63. Milk production decreased over time in St. Croix White and Barbados Blackbelly ewes more rapidly than in Florida Native ewes ( P < 0.01). Total milk yield was not different ( P > 0.1) among Barbados Blackbelly, Florida Native and St. Croix White ewes, or between ewes raising single or twin lambs. Udder volume was largest ( P < 0.08) in St. Croix White ewes, smallest in Florida Native and intermediate in Barbados Blackbelly ewes. All ewes had similar patterns of weight change during the study, but Barbados Blackbelly ewes weighed less than either St. Croix White or Florida Native ewes ( P < 0.05). There was no difference ( P > 0.1) in lamb weaning weight or average daily gain among the three breeds. The results show that Barbados Blackbelly, Florida Native and St. Croix White breeds of sheep produce similar amounts of milk and wean similar size lambs under tropical conditions, even though there are breed differences in body and udder size.

Effect of seasonal climatic changes on biomass yield and terpenoid composition of rose-scented geranium ( Pelargonium species)

Variations in biomass yield, essential oil yield and terpenoid composition in rose-scented geranium ( Pelargonium species) in response to seasonal climatic changes were investigated under semiarid tropical climatic conditions. A large number of essential oil samples were collected during different seasonal months (once a month) and daily during the peak summer season months of May and June. They were analysed for terpenoid composition by GC and GC-MS. The crop yielded the lowest values for biomass yield, essential oil yield and essential oil concentration in the summer months of April to June. Evaluation of terpenoid compositions showed minimum concentrations (% of essential oil) of linalool, geraniol and its esters and maximum concentrations of citronellol and its esters during summer months. The percentages of geraniol and its esters were highest during cool winter season months of December and January followed by rainy and autumn season months. Isomenthone, 10-epi-gamma-eudesmol and other minor terpenoid compounds (present in <1% amounts in the essential oil) did not exhibit any definite seasonal trends. Rainy/monsoon (August and September) and autumn (October and November) season months were characterised by high rainfall, cloudy days and short photoperiods. These favourable environmental conditions encouraged crop growth and produced highest biomass yields, essential oil yields and maximum concentration of essential oil in rose-scented geranium plants.

Decomposition- and nitrogen-mineralization patterns of Leucaena leucocephala and Cassia siamea mulch under tropical semiarid conditions in Kenya

In agroforestry systems, loppings from trees and shrubs are commonly used, often as mulch, as sources of nutrients for interplanted crops. Therefore, it is important to understand the rates of mulch decomposition. This paper reports the results of a study on the decomposition and nitrogen (N)-mineralization patterns of the leaves, small twigs, and mulch (leaves plus twigs) of Leucaena leucocephala and Cassia siamea in a field experiment in an Alfisol in semiarid Kenya. Plant materials contained in 5mm nylon bags were placed below or on the soil surface in an alleycropping system involving the two tree species, with maize (Zea mays L.) as the intercrop. For plant materials of both species (except Leucaena leaves), there were two phases of decompositions: an initial rapid phase and a slower second one; Leucaena leaves had only a single phase. When placed below the soil surface, the decomposition rates of both Leucaena and Cassia mulch were similar (about 12% week-1 in the first phase and 1% week-1 in the second phase). When placed on the soil surface, Leucaena mulch decomposed 1.3 times more rapidly than Cassia mulch in the first phase. The patterns of N release from the mulch of both species were similar to those of mass loss. In general, mulch-decomposition and N-release rates of both species were related more to their C:N ratios than to polyphenol contents; while C:N ratio predicted the rate of first (rapid) phase, the rate of the second (slow) phase appeared to be regulated by lignin and polyphenol contents.

Diversity pattern in Sesamum mutants selected for a semi-arid cropping system

Due to the complex requirements of moisture stress, substantial genetic diversity with a wide array of character combinations and effective simultaneous selection for several variables is necessary for improving the productivity and adaptation of a component crop in order for it to fit into a cropping system under semi-arid tropical conditions. Sesamum indicum L. is grown in Venezuela after rice/sorghum/or maize under such conditions. A mutation breeding program was undertaken using six locally adapted varieties to develop genotypes suitable for the above system. The diversity pattern for nine variables was assessed by multivariate analysis in 301 M4 progenies. Analysis of the characteristic roots and principal components in three methods of selection, i.e., M2 bulks (A), individual plant selection throughout (B), and selection in M3 for single variable (C), revealed differences in the pattern of variation between varieties, selection methods, and varieties x methods interactions. Method B was superior to the others and gave 17 of the 21 best M5 progenies. 'Piritu' and 'CF' varieties yielded the most productive progenies in M5 and M6. Diversity was large and selection was effective for such developmental traits as earliness and synchrony, combined with multiple disease resistance, which could be related to their importance by multivariate analyses. Considerable differences in the variety of character combinations among the high yielding. M5 progenies of 'CF' and 'Piritu' suggested possible further yield improvement. The superior response of 'Piritu' and 'CF' over other varieties in yield and adaptation was due to major changes in plant type and character associations. Multilocation testing of M5 generations revealed that the mutant progenies had a 40%-100% yield superiority over the parents; this was combined with earliness, synchrony, and multiple disease resistance, and was confirmed in the M6 generation grown on a commercial scale. This study showed that multivariate analysis is an effective tool for assessing diversity patterns, choice of appropriate variety, and selection methodology in order to make rapid progress in meeting the complex requirements of semi-arid cropping systems.

Yield and growth responses of kenaf (Hibiscus cannabinus L.) in a semi-arid tropical environment to irrigation regimes based on leaf water potential

The growth response of kenaf (Hibiscus cannabinus L.) to four irrigation schedules based on leaf water potential Χl was evaluated in a semi-arid tropical environment. Total dry matter production was unaffected by regimes in which the mean value of leaf water potential Χl (mean of solar noon and dawn value) did not fall below −1.26 MPa. Stem elongation was more sensitive than dry matter accumulation to plant water stress. — The economic yield for paper pulp production (i. e. total plant dry matter production minus that of the foliage and upper 60 cm of stem) increased with the frequency of irrigation. — Growth recovery by kenaf following a period of water stress was examined. Alleviation of water stress 10 weeks after irrigation, when Χl was −1.60 MPa, produced stem elongation rates that were greater than those of plants previously receiving irrigation. This ability to withstand water stress and partially compensate in growth following alleviation of the stress indicates that the kenaf crop has stress response features suitable for rainfall only production under semi-arid tropical conditions. — Irrigation schedules based on Χl resulted in water applications tailored to crop requirements in that water use increased, and the time interval between irrigation decreased, with increasing canopy development as well as with increasing evaporative demand. However, erratic fluctuations in Χl between irrigations make scheduling by this method difficult and the use of daily mean, dawn or noon values of Χl for scheduling irrigation of kenaf cannot be recommended in environments of high evaporative demand. The factors contributing to these fluctuations in (Χl) are discussed.